texts:
If one looks up the meaning of shear strain, most sources talk about this situation:

That is, a force acts along a surface of an element at it is elongated, turning a rectangle into a rhombus. Apparently this is called "simple shear".

But then I found out there is something called "pure shear", which is illustrated in this picture:

So pure shear, on the other hand, is a "flattening" of a body; the element is squeezed flatter on one axis and elongated on another. There is no change in angle between the lines, as there was in the simple shear case.

My question is: Why are these two things both called "shear strains"? What do they have in common, besides that neither change the area of the element? What is "pure" about "pure shear" and "simple" about "simple shear"?

Simple shear is caused when the force is acting along the surface of the element, without normal forces. But what about pure shear? It involves squeezing in one axis and elongating on other, so it must be caused by normal forces, right? But if this is right, then it wouldn't make sense to put this in the same category ("shear") as simple shear, as one would be caused by normal forces that act directly on the surfaces of the element, and the other by forces along the surfaces of the element.


texts: How strong is the adhesion between UHMWPE Fiber and Epoxy Resin?

texts: How strong is the adhesion between Ultra High Molecular Weight Polyethylene(UHMWPE) Fiber and Epoxy Resin normally? If we take the UHMWPE fiber sheet as it is without subjecting it to any chemical or plasma treatment (for improved surface bonding between UHMWPE fiber and Epoxy resin), can a laminate be formed through compression molding? Will there be any issues or  loss of mechanical properties like impact resistance for UHMWPE?


texts:
Looking at the teeth of a chain saw, I believe the chain moves from right to left while cutting.

It has two wedges A and B.

I've never owned a chain saw, so I've been trying to visualize how these two wedges work.

And I feel stuck because the wedge A seems unnecessary. Also it doesn't look that sharp and it seems to block the sharper wedge B. I'm dying to know the purpose of wedge A here. Appreciate any help. Thanks!


texts: Distinguish between dead center and live center in a center lathe tool when this terms are used in the context of work holding in a lathe


texts: Simulation of temperature in insulated box

texts:
I have a box outside that I want to insulate such that the temperature inside the box doesn't drop below 10°C given outside temperatures of (in the most extreme case - at night) -10°C.  Inside the box I have a "heater" of 5 W.  The box is in direct sunlight during the day (only if the sun shines, though).

I want to simulate the temperature in the box in order to help me decide on isolation material / thickness.  I'm unsure which factors I need to account for.  So far I have:

heat loss due to heat transfer through box walls
heat "gain" due to the 5 W "heater".
heat "gain" due to the sun shining on the box at day.
heat capacity due to the box (isolation material as well as air volume)

Are there other things to consider? Any thing which I'm modelling too simple?

Heat loss due to heat transfer through box walls:

lambda = (Q * l) / (A * deltaT)
thus =>

Q = A * lambda * deltaT * (1/l)

where
  Q = heat transfer
  lambda = thermal conductivity of material
  deltaT = temperature difference
  l = thickness of isolating material
  A = surface area of box

Heat capacity of box:

Once for the air and once for the isolation material.

E = c_v * V * T

 where
   E = "heat energy" in box
   c_v = (volume) specific heat capacity
   V = volume
   T = temperature (in K)

Heat gain due to the sun:

The most tricky I guess.  Assuming (https://en.wikipedia.org/wiki/Sunlight) I probably get about 120 W / m^2 due to sunlight and just (for simplicity) the top side of the box (A_top) I guess I still need a "efficiency" factor?  This is on the outside, though, so I guess the maximal heat transfer to the box (heating) is limited by the isolating material?

Simulation:

I'd start with the box (air and isolation material) being at outside temperature.  Then adding all heat gains (heater and due to sunlight during day) and (using the now higher temperature in the box and thus a temperature difference) subtract the heat lost due to heat transfer through the walls. And all that for each second.

1. E' = E_n + (P_heater + P_sun) * 1s
2. use E' to calculate T_box and thus delta_T
3. use delta_T to calculate Q
4. E_(n+1) = E' - Q


texts: Maximising the trace of the observability Gramian

texts:
Suppose I have a matrix W. This matrix has an observability Gramian Q. Is there a way to see which changes in the matrix W will maximise the trace of Q? Is there a natural way to express maximising Q as a function of the entries of W?

Thanks!!


texts: Does a column produce horizontal thrust?

texts:
For a single 4x4 wood column loaded with say 300lbs of weight is there any horizontal thrust being generated in any direction? Columns don't seem to be referenced in this manual.

Engineering Wiki - Civil Engineering


texts: Is there a linkage or other mechanism which can simulate a pivot, without extending that far?

texts:
I have a bar which I want to move as if it was pivoted on a point beyond its end.

e.g.

--------    *

         /
        /
       /
      /

Is there a linkage, or other mechanism, which can let a bar move as if it were pivoted at a point beyond its end (the asterisk), yet not extend as far as the (virtual) pivot point?

The mechanism can extend to the left, above and below the bar, but cannot extend towards the (virtual) pivot point.

(I have already thought of using two arcs to constrain the ends of the bar, but that seems prone to jamming.)


texts: In NOx sensors there are oxygen pumps that pump the oxygen out of the chamber. My question is, the oxygen is obviously pumped through the Zirconia zeolite, but how does it get released from at other side? Does it go through the electrode?


texts: Fan blower with less airflow in the center

texts:
I'm building a ducted fan and I would like it to:

have a uniform airflow at the output
have good static pressure
have a square section output (see figure: air enters the circular edge and exits from the square edge)

In my application the output section will be covered by a breathable membrane.
While doing some tests I noticed that the airflow in the center was much weaker than at the sides, with this blade design (counter-clockwise rotation):

How can I get more uniform airflow?

Here are some thoughts on how to improve the design, but since I don't know virtually anything about fan design and fluid dynamics I'm asking more competent folks here to judge whether these ideas could work:

adding more blades
make the blades flatter
make the blades wider
reducing the radius of the mounting cyclinder of the blades
make the output section smaller than the input section

Do you know if any of these would work? Do you have better suggestions?


texts: Why is Rocket Nozzle CFD done in 2D instead of 3D?

texts:
Why do I see rocket nozzle CFD like the one here in this SpaceX video done in 2D?

Real Fluid flow is three dimensional and involves an x, y and z axis. Is fluid flow done in 2D only because computers are not powerful enough to run 3d fluid flow simulation? Or is CFD done in 2D because that gives an accurate enough real world approximation? Or is it a bit of both.

Freshman majoring in Aerospace engineering.


texts: Why can't energy be entirely recovered from a moving car's rotating wheels?

texts:
I have a friend who isn't properly visualizing energy loss in a moving car.

His idea: Cars that can run forever without being recharged  - - > while the engine rotates the front wheels the move the car forward, there is a device at the back wheels using the back wheels' rotation to generate and store power. The engine draws this restored power to move the car forward and the cycle continues. Now, this is a "perfect" scenario where there's zero energy loss through friction, heat, sound, etc.

I first told him that something similar was already being done: regenerative braking. He said his idea was to generate energy **while*  the car was moving.

My counter to why that was rubbish:
I reminded him the amount of energy in a given system remains constant. Nothing created or destroyed, just transferred form one form to another. Thus he could not "recover" energy that was being spent to move the car forward. He moved on to elaborate that there would be two engines, one rotating the front wheels with an attached dynamo to recover energy, and another rotating the back wheels. I tried to explain he had added another energy consumer, with no way to recover this extra energy being spent...and that's how it would go. You add an extra engine to overcome the dynamo's resistance and move the car, you are spending more than you are recovering, and will eventually have to charge up. To help him visualize, I made a sketch, trying to be more realistic:  (please ignore my use of battery capacity, it's only there for the concept, not to be realistic)

I also mentioned to him that this scenario was even ignoring the other loads of problems and dangers that present themselves with having wheels rotating at different speeds. Plus the wear on the slower rotating ties which are effectively being dragged against the road. For some never-to-be-discovered reason, he simply could not  understand that to get the slower (front) tires to NOT be a problem, you have to increase the front engine power output for to match the wheel rotation speed of the rear wheels. Again, only recovering a fraction of that energy (where did the rest of it go? He can't understand and I can't figure out how to explain it to him). To counter my logic, he proceeded to mention that trucks don't have an engine attached to all their wheels. Hence, some energy can be captured from those "free-spinning" wheels. Oh my God.
Newton's first law of motion applies here: A car with the engine rotating the wheels towards a given direction goes nowhere if say, a dynamo is offering equivalent or greater resistance in the opposite direction to capture that energy (again, assuming a "perfect" scenario with no energy loss). I tried to elaborate that to move the vehicle, you first exert a force (engine power output) great enough to move the vehicle from its static position (resistance? gravity? I don't understand physics enough to know what to call this), and anything like a dynamo (friction, resistance) serves to make that more difficult, so you can't simultaneously "recover" energy you are spending. I proceeded to explain that regenerative braking worked because the generated energy was being recovered from the moving vehicle's momentum through offering resistance, hence why the car slows down and why you can't sustain-ably use it while the car is in motion.

This guy is super stubborn to being corrected once a very dim bulb lights up in his mind and he believes it a genius idea and can't be dis-proven. I am horrendous at teaching constructively, and would appreciate someone breaking down why his idea is a victim of basic laws of physics.

I even stated if that were possible, it would already have popular applications in industry like electric vehicles.


texts: Effectiveness of positive pressure in highrise buildings?

texts:
The common knowledge these days seems to be that positive air pressure pumped into the common hallways of highrise buildings will allow smokers and non-smokers to live in the same highrise.  Good seals between units is still needed, but the positive pressure prevents smoke from going into the hallway, and then into neighbouring units.

During the summer, many people open their windows.  In fact, I like to put a fan in front of the window.  Often, this blows cigarette smoke from neighbouring units into my unit.  There is simply not enough ventilation to mitigate the heating up of the unit without a fan.  Otherwise, it might possible that the positive pressure alone would ensure that smoke doesn't come in from the outside (assuming that the air from the corridor is bearably cool, which it often isn't).  For the time being, I try to choose a window that is as far from the smoking apartment as possible, and place the fan in front of that window.

In the spring and fall, however, it might be possible to do without a fan in front of the window, and let the apartment be ventilated by the positive pressure.  I don't know where the intake for the positive pressure is, however, and the air quality smells really "non-ideal".

Another complication is that the windward side of the building will experience a high pressure outside, and I wonder it is enough to counteract the positive pressure from the inside.

There seem to be so many variables that can upset the conditions for positive pressure to work.  I wonder how well understood is the benefit of positive pressure?  Or is it just one of those things that sound reasonable, but difficult to study empirically based on actual highrises?

I eventually want to move, but in the mean time, I am trying various coping mechanisms based on whatever I can understand about positive pressure.  A complicating factor seems be the eddies on the leeward side of the building, making it hard to gauge whether to open the windows or which windows to open.


texts:
In the latest StarTalk NDT says that without friction space crafts would not be able to slow down when reentering orbit. The friction against the air slows it down from 17,000 miles per hour down.
There have been animals that have been found to create something close to zero disturbance as they move through the water. Is this friction reduction? I can't find the article now but I think it was sharks or alligators. And some beetles have shell structure that water rolls off of.
Are there any frictionless objects or is it possible to create frictionless objects?
https://www.youtube.com/watch?v=XJcFWR9LrBU
Super conductors
https://youtu.be/wlvHD6N5Gkk


texts: Truss analysis of internal forces in members

texts:
I am trying to calculate the internal forces and their nature in this truss, however, I cannot seem to do so as both the method of joint and the method of section do not work. I think this is because there are not enough conditions of equilibrium that can be used. Is there any way to actually calculate the forces in the members even if this is the case?

For example, at joint A, there are 3 unknown members, and all the members acting through it are only concurrent at that specific point, making it impossible for me to use the equilibrium condition of the sum of moments being 0.

It would be extremely appreciated if someone could inform me about how to calculate the forces in the members of this truss. Thank you.


texts: Alternative to silicone that is non insulating

texts:
we are developing a product and would like to use silicone, as it has good texture and durability, however it is an insulator. We would like heat to be able to pass through the silicone rapidly. Does anyone know of any alternatives to silicone that can conduct heat and is widely available?

Thanks


texts:
We have steel hollow tubes of 80 mm length and 0.5 mm cross section, that we need to cut in smaller pieces of 10.1 and 10.5 mm length. We have been using utility knifes with very poor results.

I am looking for a tool that can do the job. Something like scissors or pliers, to be handled manually.

Every answer or suggestions is welcomed.


texts: Transferring heat using a pipe at temperatures below the boiling point of water

texts:
I'm trying to find the canonical method for transferring heat from a 70–80 °C source to heat up some air in a box to 45–50 °C. My understanding of heat pipes is that the liquid inside has to evaporate in order for heat transfer to occur. Many heat pipes use water, but water doesn't boil at 50 °C.

What is the canonical/best way for transferring heat at 70 °C?

Here's a simple sketch:

where the black rod is the proposed heat pipe insulated with some rubber (green).


texts: How to estimate power consumption for an oven given volume?

texts:
Is there a good way to estimate the power consumption of an oven/heating device given the volume of the oven? I'm trying to do really, really dirty/quick math - I know that the average oven uses probably between 2-4000 Watts, but I'd be looking for a similar estimate with a volume of about 1.3 cubic inches, so it would be far, far less than a normal oven.

I'm under the assumptions that heating up and insulating a smaller space would be significantly easier (better than just the linear ratio in size) than a regular oven. Is there a way to figure out how much power input would be needed to heat up that much volume in ~20 minutes (or any time)? I'm not sure of all of the factors that would need to come into play (I'm sure insulation/heat retention is important, but I don't know a typical number for that). I'm not sure if convection or conduction would be better, but presumably the one that would use less power? The maximum temperature would be ~400F.

This is for a project I just thought of, which is why everything is somewhat vague. I'm basically just looking for the worst case ceiling, and the best case ideal to have something to start from. Thank you!


texts: Joining the negative PV wires of 3 solar arrays for 3 MPPT controllers in an inverter?

texts:
My Inverter has 3 MPPT inputs. For some design simplifications (Involving ATS), i would like the three arrays to have separate PV+ but join the PV- wires together at a bus-bar and take the Inverter negative DC input from there.

Will this have an effect on the performance of MPPT operating independently? or should i keep the PV- wires separate?


texts: How do I size metal plates to get the correct dimensions after folding?

texts:
I am designing a metal plate that will be laser-cut (or machine-cut) and then folded. I want to know how to size the pre-folded plate in order to get the right dimensions after folding.

My actual part is not exactly like this (I simplified it for ease of drawing) but it shows what I want to achieve. In this case it's a 2mm aluminium plate, the red arrows show the inner dimensions after folding that I want to specify and achieve. The holes must also line up and the window should be correctly placed.

Intuitively I would expect some compression along the inner part of the folds and stretching on the outer parts - ideally along the centre of the plate - but I don't know if this is what will happen.

Assuming the red arrows are 100mm each, should the plate be 300mm? I'm guessing not, so how do I calculate the radius of curvature that will be achieved and if I need to add (or remove) material at the folds in order to achieve my required dimensions?


texts: How can I increase the rotational speed of a stepper motor by creating an assembly program on a PIC16f84a?

texts:
For the hardware I am using a 10MHz Xtal Oscillator, two 22pf, and Step Motor 28BYJ-48 5V DC
Below is the code that I have done so far. How can I increase the rotational speed of the step motor? I tried putting a low value (0Ah) to COUNT1 however, it did not rotate instead it only caused the step motor to vibrate. Please help me solve this tiny problem of mine.
; CONFIG
; __config 0xFFF1
 __CONFIG _FOSC_XT & _WDTE_OFF & _PWRTE_ON & _CP_OFF

RES_VECT  CODE    0x0000        ; processor reset vector
    GOTO    BEGIN           ; go to beginning of program

;Constants

STATUS  EQU 03h
TRISB   EQU 86h
PORTB   EQU 06h
COUNT1  EQU 08h

MAIN_PROG CODE              ; let linker place main program

BEGIN
bsf STATUS,5        ; go to bank 1
    movlw   00h             ; put 0000 to w register
    movwf   TRISB           ; make all pins as output
    bcf STATUS,5            ; goto bank 0

PROCESS
    movlw   b'10000000'
    movwf   PORTB
    CALL    DELAY

    movlw   b'01000000'
    movwf   PORTB
    CALL    DELAY

    movlw   b'00100000'
    movwf   PORTB
    CALL    DELAY

    movlw   b'00010000'
    movwf   PORTB
    CALL    DELAY

GOTO    PROCESS             ; loop forever

DELAY
 LOOP
    DECFSZ COUNT1,1         ; subtract 1 to the total COUNT1 value
    GOTO LOOP              ; until reaches zero
   RETURN                  ; return to PROCESS

END


texts: What is this large steel structure used in excavation?

texts:
I keep seeing these large rectangular structures on job sites they put in the ground.

I'm guessing something for strengthening the surface structures?


texts: Can I weaken a coil spring consisting of spring steel?

texts:
I have a steel coil spring that is used by compression. It is too strong, and I would like to reduce its strength by some fraction, ideally keeping its length.

Reducing it to roughly half would be nice. Uncontrolled heating and cooling in air would make it very unelastic, I think, and shorter after the first compression.

It can be manually handled. (The dimensions are: cylindrical with diameter 3.5 mm, length 60 mm, and round wire wire diameter 0.5 mm.)

I would be interested in the theory, even if it's something that I can not do, like precisely controlled heat treatment. I have only two of them, it can be very slow.


texts:
I have an idea for a sports equipment innovation "a new product" that a track and field athlete can use to practice and train his sport. The technology involves a laser beam. I'm wondering if my idea is feasible and/or if it has already been done because we think the idea is good.

The idea is that when training pole vault or height jump, the athlete uses a laser beam instead of a bar, and the laser beam measures if the athlete succeeds. Has it already been done or is it not feasible?


texts: What practically is constant volume heat addition in SI piston engine?

texts: Isochoric means constant volume (In SI engine: piston should not move when the spark is ignited). In reality piston always keeps displacing up and down means volume changes. So, how does this make it a Isochoric Heat Addition in power stroke.


texts: air resistor decreasing resistance over fixed time

texts:
Imagine I'm breathing through a wide straw/tube in my mouth. At the far end of the straw is a resistance mechanism. I want it to be that as I exhale there is no resistance, but as soon as I start to inhale I'm met with strong resistance so that little or no air can pass. But over the course of a few seconds, I want that resistance to drop to zero (either to drop smoothly or to "pop" to little or no resistance after a couple seconds). Furthermore, I want the timing of that resistance fall off or "pop" to be independent of how hard I am inhaling -- either a strong or a light inhale will produce the same result: strong resistance dropping (or popping) to little or no resistance over a couple seconds.

I'm trying to think of a way to do this purely mechanically.

Three mechanical timing mechanisms come to mind:

the balance wheel of a mechanical watch (which causes ticking at a constant rate regardless of how tightly the watch's mainspring is wound)
an hourglass (the concept here is that an inhale of any strength would flip the hourglass, and the number of grains fallen would represent the decreasing air resistance)
a hydraulic door-closing mechanism (where the door closes at roughly the same speed regardless of the pressure applied)

All of those are just "inspirations" in the sense that they seem like they can be used as the basis for a mechanical timing mechanism, but I don't know how to turn any of them into a concrete design for this purpose. Any suggestions welcome.


texts: How to slide 2 small pieces of metal into each other

texts:
I'm trying to build a keyboard addon for my smartphone (https://gitlab.com/xengi/mkbd65). The last challenge I'm facing is how the two pieces, namely the smartphone and the keyboard should slide back and forth.
I know I need some kind of linear slider.

Something like that: http://en.smoothgroup.cc/goods/detail/58.htm

How would I construct or implement something like that? Is there a better way to do it? What do I need to consider which I maybe haven't thought about?

I don't think I'm able to do something like that: http://phonesdata.com/files/models/Nokia-N950-482.jpg

So my goal is to build something like that: http://phonesdata.com/files/models/Nokia-N900-684.jpg

Any help appreciated!


texts:
I have been asked to provide some of our technical docs in both metric and US units.  For the most part, that is easy enough:

approx 1cm → approx 1/2"
500μm → 0.02"

But then I start getting stuck:

50μm → 0.002" or 2 thou or 2 mils? Is there a common symbol for thou/mills?
20nm → ???

I imagine that people who care about nanometers have mostly gone metric now anyway, but it would still be good to provide US measurements for everything. What units are commonly used for lengths smaller than 0.001" in the US, and what symbols are used for them?

If it varies across different fields, the relevant ones would be optics, precision machining and mechanical engineering.


texts: Pressure pumps are used to apply pressure to a system. What would happen if someone attempted to fill, for example, a bicycle tire (with a check valve) to 2 ATM of pressure using a pressure pump that could only supply 1.5 ATM of pressure? As the gas cannot go backwards due to the check valve during filling, could the pressure be expected to rise in the tire to 2 ATM?


texts: What is this 'timber insert' on the construction drawing of a concrete parapet wall?

texts:
A sectional elevation of a concrete roof is shown below (drawing is from the early 70s):

The roof slab is dimensioned as 6" thick with what appears to be 12" parapet wall with a 'Timber Insert'.
What is the purpose of this timber insert? Is it for fixing into?
My assumption is that it does not protrude beyond the face of the concrete i.e. it is not a sheet of timer forming a secondary roof.


texts: Mechanisms to convert linear motion to rotation

texts:
These are the mechanisms I'm aware of:

Crankshaft
Scotch yoke
cam-shaft
wobble drive (a.k.a nutator or Z-crank)
swash-plate

What are other mechanisms to convert linear motion to rotation?


texts: How to compute velocity distribution in the developing boundary layer on the cylinder

texts:
Air flows perpendicular to the axis of a cylinder $a=1$ cm in diameter. Air speed upstream of the cylinder is $U=6.72$ mm/s and its kinematic viscosity is $2.1×10^{-5}$ at 350 K. I want to obtain the velocity distribution in the developing boundary layer on the cylinder by using a numerical method. Which numerical method do you suggest to approach this question?
Moreover, I am curious to know the thermal boundary layer equations in this case.
I would be grateful if you hint me how should I solve this kind of problems or refer me to a relevant reference for these kinds of questions.


texts: How do I build a dc generator at home for my presentaion?

texts: I'm having a presentation about dc generators and I wanted to demonstrate how it works. Anyone have an idea on how to build one. I left my electric motors at home because of Christmas break, now I can't find anything.


texts: methods of propulsion of hydrogen plasma

texts:
What would be the best method of accelerating a continuous flow of hydrogen plasma to 300 000 m/s.

I have thought about a rail gun approach but don't think this would be suitable for these speeds or a continuous flow.

The plasma can be flowing in anything.


texts: Does pressure in a centrifugal compressor increase along the path of the flow?

texts:
Euler turbomachinery equation doesn't include a term for changes in flow area.
But, an centrifugal impeller (not the volute) has increasing flow area along the path of the flow.
Is the pressure actually constant along the path of the flow, and if not, is there an equation that could predict the change in pressure?
(It's non trivial to deduce myself since energy is continuously added to the flow as its area expands)


texts: What bolts should I specify with Weathering Steel?

texts:
When using weathering steel (COR-TEN) on a project, what sort of bolts should I be using?

I have yet to see fixings made of weather steel; presumably because the way it uses a sacrificial layer to form a protective rust coating makes it unsuitable for precision applications (such as bolt threads; maintaining the structural area, etc.).

I am also aware that mixing different metals; even various steel alloys, can lead to accelerated corrosion due to anodic/cathodic behaviour.

So what type of bolts should be specified with weathering steel?


texts: Power consumed by a transforming fixture with the light bulb burnt out

texts: Does a metal-halide lamp fixture use power if the bulb is burnt out?  If so, how many Watts would a  277 V, 1,000 W fixture draw with the lamp burnt out?  Transformer is in-line between the 480 V 3-phase supply and the light switch.


texts:
I see that POM gears are often not preferred in high torque settings - but how about 0.4Nm? Is that amount of torque too much for module 1 POM bevel gears? Say they are 16-tooth.

Is 0.4Nm considered moderately high torque?


texts: How can I tell if a gear is pressed or threaded?

texts:
I recently bought my first lathe (A circa 50s PREMO, Australian built with tapered roller bearings) and the spindle has a little bit of wiggle parallel to the axis of the spindle. I decided to pull the spindle out to take a look at 'er, but I ran into a spot of bother with the gear that mates with the reverse tumbler. (And just to be clear, I'm absolutely certain the gear needs to come off before the spindle will come out, it's bigger than the ID of the cone pulley)

This may seem silly, but I can't work out how that thing is supposed to come off. The gear sits on top of a threaded portion of the spindle (And indeed before getting to the gear I had already removed two nuts from that end of the spindle), so that was my first thing to try. Grabbed it with a chain wrench, gave it a fairly good torque, nothing.

Next thing I noticed was that there was a keyway cut in the gear, so I took a look in there. Sure enough, the threads extend under the gear, but curiously there doesn't seem to be a thread cut on the inside of the gear. I would have expected to see the tell-tale profile of the internal thread, but nothing; smooth. My next thought was that it was simple pressed on with a key, but I couldn't see a key, and in fact I'm able to push an allen key down the keyway the full thickness of the gear, there's nothing there. In addition to the lack of a key, there doesn't seem to be a matching keyway on the spindle for the gear to key into.

What troubles me is that if there's a key and I try to unscrew it, I'll break something, and if it's threaded and I try to press it off, I'll break something. Where should I go from here?


texts: Given drive rotation angle, controlling torque, how do I maintain movement speed with varied load?

texts:
I'm working on design of a 3D movement drive (for 3D printers/CNC mills etc) using DC motors and helical drive.

A DC motor drives the leadscrew actuator which supports the working elements (head, table or head bridge).

The current of the motor shaft -> position of the driven element is read with optical encoder. (I can derive speed, acceleration, momentum etc from that.) I can read the current (voltage across a fixed low resistance in series with the motor), and the voltage across the motor terminals, resulting in measurement of the power -> torque.

I can drive the power supplied to the motor through PWM.

For optimal drive, I should maintain movement speed as close as possible to given (right for the used machining parameters), and as I'm machining material, the resistance of the material against the tool will change in more or less unexpected pattern.

This is pretty simple with stepper motors where we just assume the output directly follows the input. In case of DC motor though, the control must be much more reactive, increasing power as torque rises.

What control algorithm would allow me to maintain movement speed closest to preset - meeting the additional condition: restricting or rapidly minimizing exceeding the preset speed; rapidly reduced load as the head exits material could result in speed increase and drive the head into a neighbour element, damaging the work piece.

(please note, this is one of the questions that take long rather than short answers; control algorithms in automatics is a subject of good several semesters of study, and choosing and explaining the control algorithm meeting specified criteria is bound to require some work.)


texts:
I need to identify the seal/gasket shown below so I can order a replacement. I can measure the OD, ID and Height, but I'm not sure what to call it to narrow down my search.

What type of seal is this? What are the parameters I should be searching for?

I don't need an exact match, but something close, as the use is very low-pressure.

It is used in a food-safe context with 100C water at near atmospheric pressure. There is no lubrication and is meant to be washed with food-safe detergents.

The seal has a flat side on the "bottom" that sits against a screw cap. The "top" side of the seal has two small lips that create the seal when the cap is screwed on. The inner diameter is flat and meets the bottom profile at a right angle.

The seal does not sit in a groove or channel in the cap, but just stretches around the OD of the threads and sits on a flat surface.

The seal has an OD of 63mm, an ID of 59mm and a height of 2mm. --These are my best attempt at measuring this as I am unsure how to properly measure a seal like this.

EDIT: Add OD, ID, Height

Top side

Lip Profile of Top Side

Bottom Side

Inner Diameter face


texts:
I want to build a monitor supporting arm for three monitors besides each other. The outer monitors shall be able to swivel forward to reduce size of the whole thing when not in use. My problem's that I have no idea how to design the hinge - the outer monitors should rotate around their inner forward vertical edge, but I cannot put a hinge there, because the monitors have to be as close to each other as possible.

I'm looking for something I can put into the supporting arm behind the monitors that acts like a hinge at the front (outside the arm itself)... how to do this?


texts: What is technology used to seal a gear shaft to metal frame?

texts:
I'm working on paper cut mechanism, I use gears to move blade to cut paper. I would like to get knowledge about the technique of seling gear shafts to a metal frame. It would help me in designing elements in fusion 360, the limitations and sizes that I can use. I found information about gears and bending metal sheet fabrications enough but I failed to find any info about gear shift fixing to metal like it was done in my pictures provided below.

UPD: To due to my poor english my question was not clear enough I had to provide more detailed pictures and edit my initial post.

So I'm making case (frame made from metal sheets, bending fabrication) to hold gears, but some places are narrow and tiny, I'm not sure will be possible to seal pins in those places. If I get more info how the shafts are assembled into a metal cases I could design it in right way.


texts:
In this incident https://www.bbc.com/news/world-us-canada-46274458 an elevator was described as falling 84 floors, but all survived apparently with little or no injury.

It would seem that the car did not actually fall; a "hoist rope" failed, causing it to descend out of control, after which something brought it to a gentle enough stop that none of the occupants came to any notable harm.

My question is about the way in which elevators are designed such that this event unfolded as it did. Mention of a "hoist rope" seems to suggest that there are separate ropes for lifting/lowering the car and for counterbalancing it, and the counterbalance ropes remained intact. But, if it was out-of-balance enough to "fall", what kept it from accelerating, what terminal velocity might it have reached, and what caused it to stop without a significant impact?

Edit:

What I'd like to see is either:

a technical account of what actually happened, or alternatively,
a speculative account of what most likely happened, based on a known facts (or reasonable assumptions) about the elevator in question, and the details of the event as presented in the media.

The point of my question is to cut through the media hype and inevitable distortion of fact to better understand the mishap from a technical perspective.


texts: Orthographic project (section view) dimensioning a counter bore?

texts:
The following question was given in a book as an autocad assignment.
The section depicted in the diagram is not a counter-bore or a spot face hole. But the professor is telling that the hole is a counter bore.

This is the correction suggested by the professor in the blue pen. This is the section view of the front view along of A-A line.
Is the correction correct as I argued that this not true.


texts:
I'm taking a thermodynamics class and had the following question. I was going to ask my professor directly, but it seems like a stupid question with a simple answer, so I thought I'd try my luck here in fear of embarrassment.

When air flows through a pipe, its stagnation enthalpy doesn't change. For a calorically perfect gas, we have that the enthalpy varies linearly with the temperature.

$$h_0 = \text{constant}= h + \frac12u^2$$
$$h = c_pT$$

Let's look at air. Air has a specific heat at constant pressure of $1000\ \mathrm{\frac{J}{kg\cdot K}}$. Room temperature air is about $300 \text{ K}$. Wind speeds are usually below $15\ \mathrm{\frac{m}{s}}$.

Rewriting our equations, we can say:

$$c_p T_0 = c_pT + \frac12u^2$$
$$1000\ \mathrm{\frac{J}{kg \cdot K}} \cdot 300 \text{ K} = 1000\ \mathrm{\frac{J}{kg \cdot K}} \cdot T + \frac12(15\ \mathrm{\frac{m}{s}})^2$$
$$300000 \frac{J}{kg} = 1000T\ \mathrm{\frac{J}{kg}} + 112.5\ \mathrm{\frac{J}{kg}}$$
$$T = 299.9 \text{ K}$$

So, moderate wind speeds don't change the temperature at all. Why, then, does moving air outside feel significantly colder than stagnant air?


texts:
I have a 10mm metal disk that is 1mm thick.  It is easily bent when a force is applied (green arrow) to the unsupported edge.

I need to add a strut, but at what angle?  The part is weight-sensitive, so to keep it simple the strut will be a 1mm wire (single cast part).  A strut with a shallow angle looks like it will buckle, but increasing the angle adds to the overhang.  How do you find the balancing point that gives the most strength?

I


texts:
Problem: how much water (volume ratio) does it take on the exit side to maintain a siphon? Vertical lift 24" from water level to top of an open container? Does it have to exceed the volume on the lift side to begin the process? And how far down the exit line must it remain "solid", filling the tube, before it will start "trickling", not filling the tube? Where does the air start mixing with the water on the low side?

I am not an engineer, so please refrain from equations or physics if you can. I am trying to solve a friends pumping from a 60 gallon container problem. He thought the water may be siphoning past the pump impellers after they had stopped and I felt pretty sure that could not happen then got to thinking about what it takes to siphon. Thank you to anyone who can answer the question in a simple fashion.


texts: Why don't we regularly use fused quartz glass?

texts: Fused quartz glass has an extremely low expansion coefficient. I think I once read on the internet that it can go from 1500°C into water without cracking from thermal shock. Sometimes people drip what's left over into water to put it somewhere but that type of glass probably wouldn't crack. Also, it can get heated to a really high temperature before it starts softening to a noticeable amount. I think it might also be stronger than soda lime glass. It's probably also extremely insoluble in water unlike soda lime glass. It can also be put in an annealer so that it will cool very slowly and be free of stress after it cools. So why isn't that the normal regular type of glass we use?


texts: Minimum base current for transistor amplifier

texts: A transistor, say $NPN$, can be used as an amplifier. It amplifies base current by a factor beta. Is there a minimum base current threshold below which it cannot amplify? Say, are there transistors which can amplify femtoampere?


texts: Mechanism for indicating the direction of a shaft's rotation

texts:
I have a shaft, which will change its direction of rotation somewhat randomly in response to external disturbances, without a ton of speed/torque. I need to figure out a mechanism I can use to actuate something like a pin up/down a short distance depending on the rotation direction of the shaft, or other bi-positional indication of the direction. This will be used to mechanically actuate a clutch elsewhere in the mechanism.
Sprag bearings seem like a nice starting point for this, I can get a disk or gear to rotate/not rotate depending on the direction, with little/no backlash, which is important -- this needs to trigger within a few degrees of the direction shift. However, how would I convert this rotation/non rotation into something I can use as a mechanical on/off indicator like this?
I can also come up with several ideas that involve the mechanism continuously fighting against a friction clutch, but would prefer not to have this source of inefficiency.


texts: Can sensors detect objects 200 metres away?

texts:
I saw in this post on Self driving cars that said the cars developed by Google for the Google Self Driving Car Project, have sensors that can detect objects like humans, plastic bags within a range of two football fields. In my question, I have said "200 metres" which is rough figure because I think a football field would be anywhere between 90 metres to 120 metres.

What kind of sensors are capable of detecting objects in such a long range? If such sensors are available, are they used in any other devices or vehicles today?


texts:
After some research, I found that diesel is my choice of fuel.

Now I need a way to pump it to the engine. My main constraint is price.

So my question is can I use a water pump like one of these, to pump the diesel?


texts: What criteria must apply for torsional effects on this beam to be ignored in calcs?

texts:
I'm interested in how to work out whether torsional effects can be ignored or not, in calculating the adequacy of a given steel beam in the following idealised eccentric scenario.

Or, equivalently, the criteria which must apply, for it to be appropriate to treat the beam and its UDLs as a simple question about vertical plane bending, needing only to consider the actual vs design bending moment, deflection, and bearing support strength.

Description of problem

The problem is idealised and static, so the available parameters are the beam's inherent properties, the UDLs Load 1 and Load 2, and the length (clear span) of the beam.  For simplicity, the beam can be deemed horizontal and both positionally and rotationally fixed at both ends. (It might be the top beam in a moment resisting frame, or both ends concreted into adjoining walls.)

Load 2 is one side of a massive  and stiff horizontal rectangular object, such as a thick steel sheet or precast concrete floor, that's simply resting (unattached) on the bottom flange. (The other side of the sheet is simply resting unattached on a [relatively distant] parallel wall or second beam to the left). There are adequate stiffeners in the flange itself

Question

If Load 2 is small enough, it will be contextually trivial and we can totally ignore the torsional element, and just treat the beam as subject to vertical bending only from Load 1.
If Load 2 is large enough, there will be a torsional dimension to the problem, requiring more complex calculations or numerical methods.

What method, criteria, or formula would be used to determine whether or not the torsional aspects of Load 2 can be ignored, for the purposes of calculating whether the beam is adequately strong for the setup and loads?

Or is it the case that enough stiffeners and the problem can be ignored?


texts: Flow through manifold: convergence issues

texts:
I try to simulate flow through a manifold with multiple inlets & outlets but I'm facing convergence issues.

I know that it may be due to poor quality mesh, but my mesh statistics are:

Minimum Orthogonal Quality =  0.115844
Maximum Ortho Skew =  0.853992
Maximum Aspect Ratio =  31.8148e

which doesn't look that bad to me.

Another point could be due to wrong BCs and I'm not sure wether my BCs are good. For the inlets I calculated mass flow in the domain (since the manifold is a physical part from a measurement system, I know roughly what the flow field looks like and what the flow in and out my domain is) and set it as mass-flow-inlet BC. For the outlets I also calculated mass flow and set it as pressure-outlet with a good guess for the initial gauge pressure and a target-mass-flow.

But as I said, I don't get a converged solution, is it due to these BCs?

I attach some residual plots.
(I wanted to add more but I can only post 2 links...)

If you need more information let me know, I tried to keep it short.


texts: Is there a way by which one could determine the required temperature difference for stirling engine?

texts:
I am trying to make a stirling engine. I did some research work and also reviewed some books but the problem is that a great deal of information on this engine is qualitative, rather than quantitative.
I am just curious to know how can we determine the temperature difference(Tmax and T min) on which the stirling engine should be operated to achieve force (F).
Please suggest some resource for stirling engine if any for beginers.


texts: Is more requested MATLAB or Python in companies (for engineers)?

texts:
My question is not exactly on MATLAB vs Python in terms of features (about which there are plenty of topics yet).
It's a specific question for engineers who have a certain experience with some companies: have you been requested to work more with MATLAB or Python?
I'm referring to use them to write code for math purposes, plotting graphics, fourier transform computations, signal processing etc
How many times have you been requested to work with MATLAB and how many times with Python?


texts: absorption refrigeration with low generator temperature?

texts:
I am IT engineer not a refrigeration expert, pardon my basic question.

Would a NH3 or other absorption cycle work with a generator temperature of say 30C, and condenser temperature of 10C by maintaining correct pressure level.

Most of the technical papers I read on the internet, talk about requirement of 80C+ temperature for generator and 25-30C for condenser. This would make sense if one has access to hot water source like geo thermal, or any other free heat source. But if I have access to low temperature cool water of 10C, and relatively stable heat source of 25C+ (say atmospheric temperature), can a absorption refrigeration system be designed to harvest that energy. One of the main objective is to have very low electrical energy input, so compression system may not work out. The second objective is to have a -3C or lower evaporator temperature to make salty ice and store it, and use it when the cold water source is not available. If at all its possible, what major issues to keep in mind.

I guess even the standard off the shelf absorption systems can be made to use 30C heat, by first passing it through a heat pump to increase that temperature to 80C+. But that additional stage also need lot of electricity.

Any suggestion to effectively harvest this low temperature source would be of great help.


texts:
In my controls class, we're covering phase and gain margins. We're asked to increase the phase margin of a given plant to greater than 45 degrees using a lag compensator. Initially, the phase margin of the open loop is -13 degrees, as shown below:

My understanding is that a lag compensator decreases phase angle around a given frequency. This is the filter, before and after I apply it to the plant:

So, now I have a phase margin of -45.7 degrees. Does this satisfy the original criteria of greater than 45 degrees phase margin?

As far as I know, the phase margin is a measure of safety, because crossing -180 degrees will effectively turn your negative feedback into positive feedback, making the system unstable. This tells me I should use only positive feedback, because the feedback will always be 180 degrees out of phase. But, it's not clear to me whether I was supposed to increase this phase margin somehow using only lag.

For completeness, here are the compensated and uncompensated closed loop systems:

I find it interesting that the maximum amplitudes of either of these functions also roughly correspond to their -270 degree crossings. To calculate these, I'm using MATLAB's feedback(), which uses negative feedback.

Clarification on whatever it is I'm doing would be greatly appreciated.


texts: Finding the momentum source using divergence theorem

texts:
I have the following question:

I understand how to use the divergence theorem but I'm not sure how I would find the momentum source, am I supposed to find the integral of grad U?


texts: Heat loss from the greenhouse to the soil

texts: I need  to find heat loss from the greenhouse. I know how to find heat loss through the walls and roof , but what about soil ? how to find amount heat conductivity loss to the soil ? I would be gratefull for the any reference/method/ article or etc.


texts:
I want to unplug my refrigerator in the winter, and cool it down by taking air from outside. The idea is to lead cool air from the outside through a pipe into the fridge, then let hot air out of the fridge with another pipe to the outside, powered by a small fan.
By looking at the electric power consumption, I estimate that the heat transfer through the walls of the fridge is approx 50 W, when the fridge temp is +5 C and room temp is +20 C.
How can I calculate the needed airflow from outside (L/min) if I want to maintain +5 C when it is -10 C outside?


texts:
A weightless bar is pinned at the top of a triangle with N weight. Both rests at the horizontal plane.
There is a horizontal force F acting on the weightless bar, and a given coefficient of friction μ for both the triangle and the bar with the horizontal plane.
Should a normal and friction force be applied at the base of the weightless bar? Or should the reaction only be at the pinned joint?
Or what other reactions should there be, other than the normal and friction force on the triangle.


texts: ENLIL road-side vertical turbine - creating drag?

texts:
A company called Devecitech has just created what it calls the 'ENLIL' vertical axis wind turbine, that sits at the side of a highway generating electricity from the wind-power created by passing cars

Video here: http://devecitech.com/

My question is: does the presence of this turbine 'steal' energy ('negligible' or otherwise) from passing cars by creating drag where there would otherwise be free space?

If so, will it only ever generate less energy than it 'steals' from the passing cars?

Or is it purely harnessing energy that would otherwise be wasted?


texts: Why is final momentum found by two formulae in case of increasing force not equal?

texts:
So, let us say a body moves with 10 m/s, mass = 10 kg.
At time t=0 a force of 30 N is acting on it. Gradually (linearly) the force increases and finally it becomes 130 N after a period of 2 second .
Now,  we can say that change in force every second = $30+50t.$
Now,  $dp = dt (30+50t)$
Now, integrating and putting limits as t = 0 to t= 2 seconds. We get final momentum = $160\ kg/m s^2$. Now, we cannot say that F=160/2 since value of instantaneous force is not constant.
Part 1: Finding final velocity and momentum:
If I say $130N=10*a $, then a=$13\ m/s^2.$
Final velocity = u+at = 10 + (13)(2) = 36m/s.
Now, Final momentum becomes $m*v =10*36$ = $360\ kgm/s^2.  $
Q1 Now, why is 160 not equal to 360 as the final momentum?
Q2 are final velocity and acceleration correct?


texts: From an engineering standpoint, what is the purpose of the indent in a coffee lid?

texts:
I've see the same lids every day but I never really thought about their construction. There is an indent in a "Solo Travel Lid" for coffee cups that is just above the hole that you drink the coffee from.

You can see the crescent shaped indent in the image. What is it for? Does it somehow increase fluid flow? Is it just a good spot for your upper lip? If so, why is there not a matching one for the nose? I tried googling this but I got no answer.


texts:
I know that heat affects material permeation (increasing it); but I have not been able to find much in the way of data other than biologically, on how it effects materials such as plastics.

Does heat increase permeation exponentially, linearly, etc..?


texts: What is the equivalent of ip rating for mechanical protection?

texts: I'm very clumsy person so I like to buy tools that are just short of bomb proof. I want a pair of digital calipers. So I was wondering is there an equivalent of ip rating for being drop proof to say a 1 or 2 meters.


texts: How to determine the maximum internal stress for a material under compression before brittle failure?

texts:
Let us consider a ceramic material, $\mathrm{Mg_2SiO_4}$ - Forsterite, with a sphere shape.

At room temperature, the ceramic sphere is "trapped" in a matrix which does not expand (null thermal expansion coefficient).

If I raise the temperature of the system (matrix + ceramic), the sphere will not be able to expand and internal stress will grow due to the resulting compression.

How would you estimate the maximum temperature, as well as the maximum internal stress associated before the ceramic sphere fails ?


texts:
I intend to water cool my next PC.  There are three areas of heat production in a PC - the CPU, the GPU and the motherboard itself.  Would it be more effective to treat these three areas separately (with three cooling loops) or as one system?  And by 'effective' I mean best cooling.  My thermodynamics is woefully inadequate, but my hydraulics is pretty fair. (I used to design high pressure sprinkler systems for acft hangers many years ago)
If as a single system would it be better to run the radiators as a common plenum cooling the three heat areas via their own common plenum?  Or, in true series - Heat unit, radiator, heat unit radiator, heat unit radiator, pump...
I use 'three' radiators because in the case I have chosen I can fit three radiators...
--How will you control fluid flow thruogh the three if in parallel? – Solar Mike--
Were I to go the parallel radiator route, I would take pump output and feed that into a common plenum, then have an outlet from the plenum into each radiator.  Getting picky, each outlet from the plenum to the radiators would have to have the same length / restriction to be truly 'balanced'  Taking this idea further, have the three radiators' outputs feed into a common plenum, then have each water block be fed from THAT plenum, and their output go into into a final plenum and from there back into pump.  So, I would have pump out into radiator in plenum, then radiators and on to the radiator out / water block in plenum, then have a water block out / pump in plenum.  From a hydraulic POV, the system is 'balanced' except for the water blocks.   Some wee fiddling and measuring, find out all three water blocks true restrictions then add some to the least / second least and walla!  paralleled and balanced.  But is that the most effective way?
-"What are you doing with your computer that would require all this cooling? Did you modify your CPU to clock faster? – William Hird" -
As a semi-professional animator my PC spends much of its time rendering.  You don't know how annoying fan noise can be until you run most of your threads at 100%  Given that, I also don't skimp on my components.  Two quadros produce a LOT of heat.  I would like to cool them as well to keep the TCO down.


texts: Is stress relieving by stretching necessary when performing a T751 heat treatment after a T651?

texts:
We have a 7075 Al pump housing that has currently undergone a T651 temper but requires a T751 treatment to alleviate stress corrosion cracking.

Is it necessary to re-stretch a 7075 aluminum part to relieve internal stresses after a T751 heat treatment (Solution heat treated and stretched to remove internal stresses then overaged/stabilized) when a T651 (Solution heat treated and stretched to remove internal stresses then artificially aged) heat treatment was performed just previously?

The part will only be held at minimum over-age temperatures to alleviate SCC in order to maintain most of the tensile and yield strength of the material.


texts: Why dig out and then fill in before building a large structure?

texts:
I work in the middle of London, in an area full of large office blocks. Across the road from my office they have started construction of a large building (10 stories plus). Over the last few weeks, diggers have dug a large (and vertical walled) hole. Lorries have taken the resulting dirt and old concrete away, leaving a very neat hole.

In the last day or so, the lorries have returned with new dirt (or the old dirt crushed) and diggers have been putting it back in the hole (and compacting it).

Why put the dirt back? Surely leaving the hole deeper would allow for deeper basement (or digging it shallower would be cheaper)?

I'm not a structural engineer, so this is all lost on me, but I'm fascinated.


texts: Trying to understand how much it costs to run my clothes dryer

texts:
I am trying to calculate the running cost of my clothes dryer and have bought myself an energy meter to check its usage.

I plugged the meter in, reset it, and then turned it over to the aggregate kWh mode and did a single drying session with wet clothes from the washing machine.

After the load had finished the meter read 1.828 kWh and the total time was 1h 13m.

So as I understand it, a single load used 1.828 kWh, and as we are doing about 7 loads per week that would be a total of 665 kWh / year. At the current rate of 33c per kWh the annual running cost is therefore about $219.

Now this to me is a bit strange as just about every website I have seen says that dryers should be costing upwards of $400 per annum for this kind of usage. In addition, my dryer is only a 2 out of 5 stars for energy efficiency.

Can anyone see a problem with my math or logic?


texts: What is the relationship between the type of material(ex: steel, iron etc.), thrust and torque?

texts: If I am drilling through bars of different material(ex: iron, steel etc.) of the same thickness and under the same conditions of drill operations(feed rate and rpm), how will the torque and thrust force measurement change for different materials? For example, let us assume that the materials in question are iron, steel and aluminium.


texts: Maximum error in Encoder when discrete sample interval is 2 ms

texts:
I am using an encoder having 1000 pulse in one revolution in both edges configuration. I used one method in which number of pulse is counted. What is the error in this case?
Another method is alternative approach to Quadrature encoder module where pulse duration is measured. But here we have only 69 pulse per revolution. Here clock cycle frequency is 7.38 MHz. In this case what is the error?


texts: What is the justification for left-hand threads?

texts:
I'm familiar with left hand threads on bicycle pedals. The action of pedaling for that side of the bike would un-thread a right-hand threaded pedal, although some people have hacked a solution.

I have a chain saw that uses a left hand threaded axle to tighten the bar which tensions the chain.

The image below shows the cover over the bar, and also the legend embossed in the plastic.

The right hand "wing nut" is an ordinary thread and serves to secure the cover and the bar, once the tension is set with the left hand knob. Clockwise rotation for the locking nut works as expected. The left hand knob turns a gear in a pinion arrangement, clockwise pushes the bar away from the motor, as per the legend.

The left hand knob has unrestricted rotation (within reason) and has gear teeth as part of the construction. The pinion gear resides under the knob, engaging the teeth and rotating the axle, which resides in the groove shown in the photo. Near the end of the axle, the threads push or pull the rectangular tab (pin) which in turn pushes the chain bar.

As can be seen in this photo, the end of the axle has a severe bend, preventing movement of the tab/pin, removing the saw from service.

Unfortunately, all the sources I've been able to find for the replacement part have indications of "no longer available." Pricing indicates a cost in the US$3.00 range, but that's not helpful without product.

I have a Harbor Freight mini-lathe (toy lathe) that can handle replication of this part, although I'd like to avoid the left-hand thread operation.

I see no practical reason to not use a right hand thread. There are no rotational forces as in the previous pedal example. Once the bar is properly tensioned, the locking nut secures the bar, rendering the axle and pin immobile.

I can easily cut a piece of steel to replace the tab/pin, cut and tap the hole to match the rod which would be cut in the lathe, threaded with an appropriately sized die and mill a flat on the gear drive end.

What technical/engineering aspects would prevent me from making this work?

I do not consider the human aspect of a reversed legend on the knob to be a factor.


texts: Where to start when studying Architectural Engineering by myself?

texts:
I have this idea of creating my own curriculum for studying Architectural Engineering. I aim at talking with actual architectural engineers in my surroundings and ask them for advice on the topics I should study and help me with advancing.

By looking at the programs that universities offer all over the world I got a good idea of the topics to be covered, but since I'm in charge, I would like to personalize my own program. I'd like to cover both the engineering and design part.

If you're an architectural engineer, what topic would you suggest me to start with? What are the topics that you find especially useful and important in your career as an architect/engineer? What would you advise universities to change in their curriculum?

Some context: I'm especially interested in building and repair of houses, combining more classical designs with modern technologies.

Update: I am aware that by studying by myself I won't obtain the necessary license to perform as an engineer.


texts: What wheel setup on a small, solar powered car, would have the least rolling friction?

texts:
We are attempting to design a solar car. The solar panel 4 1/2" x 13".

I like to break these problems into their simplest form, in order to eliminate the least amount of possibilities. So, the goal of the competition, as I understand it, is to transport the (provided) solar panel, and the (provided) electric motor down a 40 foot long track (the car is guided with fishing line as a guide wire).

The texture of the track is similar to the surface of a skateboard, although slightly rougher than that.

Of course there will be many other considerations besides the physical design of the car (gear ratios, lenses and/or mirrors for the panel, guide wire receiver), but right now I am focused on the car itself, and more specifically, the wheel orientation. I am wondering: What is the optimal wheel setup for this car on this track? Some ideas I have found/had are:

Less rotational inertia in wheels will mean more energy being invested into the car itself. Additionally, the car, overall, should remain light weight. So, less wheels, and less massive wheels will be better.
This terrain is relatively rough. As such, wider and larger diameter wheels should be used (the idea that a LEGO car rolls down the driveway extremely bumpily, whereas a bicycle does not). So perhaps large (but light weight) barrel shaped wheels would be most effective.
The height of the fishing line guide wire can be chosen by us. So assuming we have a low friction guide wire receiver (like a lubricated, plastic drinking straw), it seems like we should set the guide wire in such a way to support a significant amount of the weight of the car. (Due to the fact that the car is solar powered, it is extremely unlikely that it would "peel out".) Should this supported weight be changing throughout the course of the track? Perhaps as the car moves along the track, the wire should support more and more weight, as the car will have less torque at those higher speeds, although, on the other hand, the sloped up rope could slow the car down.

What would the most efficient wheel orientation/setup for such a car be?


texts:
I got a question thats been bugging me for a while:

Say that you're given a straight square beam (say one meter long), and you attach three strain gauges on each face. One at 0 degrees, one at 45 degrees and one at 90 degrees. All of these gauges are flat against the beam, so they measure in plane.

My question is: given these strains, could you reconstruct the geometry?

Assumptions:

The material is linear
The deformations are small

I've been trying it for a while, and I can always resolve for the compression and curvature, but the rotation seems to elude me. For simple cases (like pure bending) it  works fine, the sensor at 45 degrees are linearly correlated to the bending. However, when shear is present, these seems not to be the case anymore. As of yet, I can't find a way to correct for this.
Anyone got an idea? This problem has probably already been solved by someone else, but I can't seem to find a good reference to this (for the 3D case).

Any help is greatly appreciated!

Edit: images included

Front view of a small section of beam. The red images indicate strain gauges. As can be seen, only strains in plane can be measured.

Isometric view of a small section of beam, showing two strain gauges as well as the axis. The torsion mentioned would work on the y axis.


texts: Valve first,then heat exchanger OR heat exchanger first then valve

texts:
In my exam, I was given 2 options to design a process. Assuming a saturated liquid coming out from the separator, A) should the stream pass through a valve to reduce pressure, then to heat exchanger to heat it up, or B) should the stream be heat up first, then passes the valve to reduce pressure? Assuming the final temp and pressure in both cases are the same.

What's the justification to that selected option?


texts: Hydrofoil for skeg-hung rudder with forward centre-of-effort

texts:
I am trying to see how much I can reduce the torque on a rudder post by changing the foil shape. I think I need a rudder with a centre-of-effort further ahead than average but I don't know what rudder series to use.

Balancing the rudder (in a spade rudder style) would be much simpler (and more efficient) - however, there is a design requirement for a sharply angled skeg for this particular project. The rudder will be attached/trailing directly behind a skeg.


texts:
I have a balun of rated voltage 20V; however, my transmitted voltage is approximately 1V. Would the balun operate under this condition?

In the data sheet of the balun only the rated voltage and the max voltage (20V and 120V, respectively) are given.


texts: Why is electricity used for powering our device?

texts: Why is electricity used to power most things? Is it because it is the most widely available? Why can't some other form of energy be used?


texts: What is the theoretical grain size in a ideal phase diagram of a metal?

texts:
We suppose thermodynamic equilibrium in a phase diagram, where cooling rates are infinitely long and diffusion in both phases can finish completely. So when we cross the solidus line and we are left with a crystal, will it have a monocrystalline structure?

Now, take for example the iron-carbon phase diagram, when cooling a hypoeutectoid steel below its upper critical temperature, ferrite will start to form around the grain boundaries of the austenite. But if there are no grain boundaries where can the ferrite start to nucleate from?


texts: What is an advantage/disadvantage of difference wheels size in front and rear of a bicycle?

texts:
Suppose there is a vehicle with difference size of wheels in front and in rear. Specifically bicycle, There would be 2 cases that front wheel larger than rear wheel and vice versa

I would like to know what is advantage and disadvantage between each setting. From normal setting to larger front and to smaller front. While rear wheel would be a driven wheel and front wheel would be a control. If control wheel smaller or larger which would become harder? Or which setting would be less efficient?


texts:
Does anyone know what these three symbols are? I am working to identify them but they do not seem to appear in the site: https://www.edrawsoft.com/pid-legend.php

Does anyone know a better reference for P&ID diagram symbols?


texts: Is it possible to create a compressed/freezed air energy storage solution that also purifies the air of pollutants?

texts: Basically can engineers design a machine where , while we are freezing and compressing the air for energy storage, we can also purify it of pollutants?


texts: How to get the bending moment for tie member?  For the tie member, there is no uniformly distributed load and concentrated load, right? How to get the bending moment? The tension force was found to be 18.2kN btw.


texts: I need to build an air tight system that can hold gas (Argon Gas). I see that most pipes use steel. Is steel tight enough to hold that gas? Argon is very dense, so I think it should have no problem.


texts: Why is tensorial shear strain half of engineering shear strain?

texts:
Small deformation shear strain $\gamma$ in engineering can be expressed as

$$\gamma_{xy}=\alpha +\beta ={\frac {\partial u_{y}}{\partial x}}+{\frac {\partial u_{x}}{\partial y}}$$

where $u$ represents the displacement of the edges of the infinetesimal element. But in the strain tensor we have defined

$$\epsilon_{xy} = 1/2 \gamma_{xy}$$

The shear strain represents the change in the angle between the lines of the infinitesimal element. So why do we define the tensorial component as half of this angle? Why not just use the angle itself?


texts: What temperature could be achieved when nitrogen is used as a refrigerant in the heatpump?

texts:
Well we all are familiar that nitrogen is used to achieve low temperature.
I was just wondering how can one determine the temprature that could be achieved when phase change of nitrogen is done from gas to liquid state.


texts: Communicating losses and imprecision in liquid measurement by analogy

texts:
I'm writing a presentation for people and I need an analogy to convey the following problem:

  Person A wants to sell a liquid, so he fills a tank, measures volume
  and sends to Person B. Now Person B receives the liquid and wants to
  know if he received the volume he bought from Person A, so since this
  liquid is now stored in his tank, Person B measures the liquid volume.
  Person B measures won't match exactly Person A measures - due to
  losses and imprecisions in both measures.

These are oil tanks and I need to explain this to really varied audience that contains people unskilled in metrology. Also, Person A and B can be the same person in different places - which is actually the case that I'm studying.

I think an analogy for the tanks would be good, but I can't think anything! How can I explain this problem in a way that a lay audience will understand?


texts:
I'm working on a balancing robot. I'm familiar with the simple PID control loop but i can't understand this PID control loop.

Is this actually a cascade control loop? The programming states that the angle control PD loop is executed every 5ms, the speed control PI loop is executed every 40ms and the steering PD loop every 20ms. From my understanding, based on the loop/function execution timing, the innermost loop is the angle control loop, then the steering loop and the outermost loop is the speed control loop. Correct?
Why is this complex control loop better than a classic control loop with P, I and D in one single controller?
How many control loops can be nested within each other? I have only seen one inner loop and one outer loop. Is it possible to have 2 inner loops and one outer loop? Or 3 loops, each nested within the other?


texts: Statically determinate structure by adding moment

texts:
I'm considering the problem below.
It's a setup with a roller joint and a pinned joint with a hinge between the two rigid links.
Since there are now 3 unknowns for 3 equations and a zero moment at the hinge the system is  onefold statically underdeterminate. If I would add an external moment over the hinge would that make the structure statically determinate?


texts: How should one clean the blades of a turbomolecular pump

texts:
I have a turbomolecular pump from Osaka vacuum that is quite dirty, and I'd like to clean the blades off to improve balance.
I'm not quite sure how to approach this, I've tried carbon cleaner for turbochargers for cars to no success, and my next thought is to walnut blast the blades, but I'm worried about bending them.
What method should I use to clean these unknown deposits off the blades of this pump?


texts:
I am trying to implement a simple LQR controller in MATLAB for a purely deterministic system. The code is shown below:

%% Continuous Time
clear all; close all; clc;
% Parameters
n = 2;
m = 1;
A = [1 1; 0 1];
B = [0.5; 1];
C = [1 0];
Q = eye(2);
QT = Q;
R = 10;
x0 = [1; 0];
T = 10;
N = 50;

% Backwards recursion for P(t), t = T -> 0
P0 = QT;
[tout,Pvecout] = ode45(@(t,Pvec) mRiccati(t,Pvec,A,B,Q,R,n),[0 T], P0(:));
Pvecout = flip(Pvecout);

% Flip (and interpolate) to get P(t), t = 0 -> T
t = linspace(0,T,N);
deltat = t(end) - t(end-1);
P = [];
for i = 1:N
    Pvecoutk = interp1(tout,Pvecout,t(i));
    P(:,:,i) = reshape(Pvecoutk,n,n);
end

% Simulate dynamics with (time-varying) LQR controller
x = x0;
xk = x0;
u = [];
% Linearized dynamics (!)
Ak = eye(2) + deltat * A;
Bk = deltat * B;
for i = 1:N-1
    Kk = inv(R) * B' * P(:,:,i);
    uk = -Kk * xk;
    xk = Ak * xk + Bk * uk;
    x = [x, xk];
    u = [u, uk];
end

% Plot results
figure; hold on; grid on;
plot(t,x(1,:)); plot(t,x(2,:));
figure; hold on; grid on;
plot(t(1:end-1),u);

%% Useful Functions
function dPdtvec = mRiccati(t,Pvec,A,B,Q,R,n)
    P = reshape(Pvec,n,n);
    Pdot = (P * A + A' * P - P * B * inv(R) * B' * P + Q);
    dPdtvec = Pdot(:);
end

Instead of solving the discrete time Riccati Equation (which I have already implemented), I am trying to do everything in continuous time to get the solution. Thus, as you can see at the bottom, I have a function that computes the matrix Riccati ODE, and this gets fed into MATLAB's od45 solver, with the usual initial condition $P(T) = Q_N$, where $Q_N$ is the terminal cost matrix. This gives me $P(t)$, which checks out well. The problem is that when I go and simulate the dynamics, they diverge for some reason. I am not sure why.

Interestingly enough, if I use the the constant, steady-state gain $K_{\infty} = R^{-1}B^\intercal P(0)$, then everything works out nicely, but if I use time-varying gains (which are more accurate!), the solution doesn't work out. I think it may be due to some kind of discretization errors when simulating the dynamics, but I really don't know. Feel free to copy and past the script; any thoughts would be appreciated!


texts: I have been doing research into artificial Intelligence applications for protection relays. I have read a lot about theory and the possibility of them being used, but have failed to find evidence of it ever being implemented. Can anyone point me to some information on actual implementations and statistics on its usage.


texts:
Here is a typical definition of air pressure:

Air pressure is caused by the weight of the air molecules above. Even tiny air molecules have some weight, and the huge numbers of air molecules that make up the layers of our atmosphere collectively have a great deal of weight, which presses down on whatever is below.

And yet, all sources I've seen state that air pressure is equal in all directions.

1 & 2 seem contradictory.

Related question:

Why does air pressure from above not crush us? The answer I see consistently given is that an equal air pressure from below balances it out. But if a car were resting on me from above and crushing me, then another car pressing against me from below would not relieve that pressure -- it would only increase the pressure I would feel! If I were in an enclosed closet, and one of the walls were to press in against me, and then the opposite wall would also press in against me, the second wall would not "balance" things out, but rather only increase the pressure I would feel!


texts:
I have a linear actuator that I'm using two relays (Wired as a h-bridge) to control the movement of my actuator.  Is it ok to leave power to it all the time, or do I need to cut the power once it reaches its travel limit?
Thanks!
-Brennan


texts: Why are spur gear ratios not always whole numbers in practice?

texts:
Defined the Gear Ratio ($i$) as the ratio between the number of teeth on the pinion (driving gear) ($N_{1}$) and the number of teeth on the gear (driven gear) ($N_{2}$).

Why is this better, if better at all, having non-integer values of $i$? Could anyone please illustrate using arguments exploring the fabrication and performance points of view?


texts: Why is hydrotest pressure more than MAWP as per ASME Sec VIII Div 1

texts:
My understanding of MAWP in ASME BPVC Sec VIII Div 1 code is that it is the maximum pressure a pressure vessel should be subjected to. If that is the case, then why should the hydrotest pressure  be kept at 1.3 times MAWP . Would'nt it damage the vessel, since it is exceeding MAWP.
Can anybody please clarify on the same.


texts: Is there an analytical solution for the Navier Stokes equation for flow through a flattened tube ( flat plate in the center and semicircular lobes at the end).


texts: I'm trying to use a 1500 RPM-rated electric motor to accelerate a (light, 25kg) shaft up to 50 000 RPM. At these speeds I figure using a belt system or roller chains is out of the question due to wear and friction; are these kinds of speeds possible to achieve reliably with a mechanical transmission or do I need to turn to hydraulic transmission? Or what is an efficient way of achieving this?


texts: Is this dropout design as bad as I think?

texts:
I bought a 1990's steel mountain bike a few weeks ago and I have some concerns about the design of the rear dropout, pictured here:

It seems to me that an ideal dropout design would redirect upward force from the wheel axle toward the ends of the seat and chain stays. The axle mount should be positioned closer toward the center of the bike, and below the chain stays so as to distribute upward force between them. Here's a diagram showing how I expect force to be transferred to the frame by the wheel axle when the bike lands from a jump:

For maximum load-bearing capacity, I would expect the dropout to redirect the force of impact perpendicularly to the tip of the seat stay. However, here the angle is about half that, so half the force is applied to the seat stay as torsion force instead of compression force. This isn't ideal because the soldered joint isn't as strong as regular steel, so it becomes a stress point when torque is applied. While that's still the case when compression force is applied, the joint is less vulnerable to compression force due to technical reasons I can't explain.
Almost every other dropout design I've came across at least tries to redirect the force so that it meets the seat stay directly. Here is an image with some examples of other rear dropouts:

In these examples, upward force is always directed toward the base of the seat stay, whereas the chain stay of my bike extends in a way that pushes the axle mount further to the rear, off center from the truss that connects the chain stay, seat stay, and axle. I think this means that most of the force is transferred perpendicularly to the upper truss member, which connects to the seat stay at an angle and exerts perpendicular force that's not balanced out by opposing force from the lower truss member.
In the examples, while some axle mounts are positioned further away from the stays than others, the dropouts in those cases are long and flexible enough to provide structural support that can absorb some force of impact. In my bike, the dropout is both off center and not long enough to provide structural support by itself, so I think most of the force is transferred directly to the seat stay at an angle.
I don't think the chain stay handles much load either because it sits slightly below the axle mount point and so doesn't receive much compression force.
Finally, the dropout functions to securely join the seat stay with the chain stay, but the lower truss member doesn't form a very smooth curve between the stays, creating a stress point at the chain stay.
Is my analysis correct? Does any of this have a significant impact on the stability and strength of the bicycle?


texts: How to solve this Question regarding compound accelerations

texts:
So , I was trying to solve it. Then , I notice that acc of 2kg mass has 2effects. One acc from the force to left and one from the Question , it says acceleration to be up. Then , the 2kg mass would go diagonally and not straight .
I am not getting how to solve this Question further . Is it possible to solve this Question from inertial frame.


texts: What is this mechanical device and what does it measure?

texts: I’m thinking some kind of torque measuring device but I can’t find confirmation.


texts: Deflection of 2" steel tubing with braces across 15' unsupported span?

texts:
I'm making metal frame to support a wooden deck.
The yellow object is the concrete base where there is a 2" trough where my metal frame needs to support a 300-500lbs deck load.
The span between the unsupported trough is 15'. The length of the cross brace is 22"
The red frame is 2" welded steel tubing. Wall thickness 1/8".
I understand 2" will have huge deflection at 15' unsupported span but will adding cross beam like this reduce this deflection to be acceptable to support a ground-level deck?


texts: How do you use an insulation jacket's R-value for calculating heat transfer from a hot water tank?

texts:
I know how to use thermal resistance circuits to calculate heat transfer in Cartesian and cylindrical coordinates, but I don't know how to deal with real-world insulation values, and I was not able to find much about this online.

For example, I have this hot water tank that has an insulation jacket with 2" R-12.5 insulation. For simplicity, let's assume the insulation is the only thing that separates the hot water from cold outside air (no heat transfer from bottom of tank, top of tank, etc. Just through the insulation jacket). Assume water tank thickness aside from the 2" insulation jacket is negligible.

So it goes hot water -> insulation -> cold air outside. I can look up a free convection coefficient for the tank's hot water and can look up a convection coefficient for air as well. That allows me to use the formula
$$
R=1/(h*2*pi*r*heightofinsulationjacket)
$$
twice (once for water and once for air).

So the problem is how to deal with the insulation jacket. How do I interpret 2" R-12.5 insulation? How do I factor in the thickness of the insulation? The surface area is taken care of in the heat transfer equation.

$$
Q''=(Tf-Ti)/R
$$
or
$$
Q=(Tf-Ti)/R*A
$$

Updated: How do I use an R-value in cylindrical coordinates?

e.g.
$$
R/A=1/(hW*2*pi*r1)+Rins/(whatAreaHere)+1/(hA*2*pi*r2)
$$

I am missing the area for my R-value insulation


texts: How to find the entropy for a given temperature using P-H chart for a refrigerant?

texts: How do I find the entropies for T1 = -10 deg C and T2 = 30 deg C, respectively using the R-134a refrigerant chart (SI):


texts:
I need to figure out what type of steering does this 1:10 Himoto Buggy Zmoto Z-3 RC car have in order to be able to calculate the steering angle from servo position for a robotics project. Is it the same mechanism as Rack-And-Pinion steering?

I guess the steering angle change will not be constant (steering won't be linear) from servo since the rotational movement of servo is translated in the steering mechanism? I mean, whether one degree from 0 to +1 on servo will translate to the same steering angle change as for example step from +45 to +46 on servo. If not, what is the non-linear relationship there?

Here are pictures of the steering mechanism (more at the link above):


texts: Why do solar cells need to be square-shaped?

texts:
There were circular solar cells 30 years ago. Why do we have square-shaped solar cells now? Why square?
Furthermore,
Why do monocrystalline solar cells have rounded/cropped edges?


texts: How to determine minimum aluminum t-slot profile type for frame?

texts:
For a frame with dimensions 1000x1000x400, I am determining which T-slot extrusion type will be strong enough.
I am considering both 30-6060 (30 series I-type, metric) and 20-4040 (20 series I-type, metric).
The extrusions will be joined by fairly small corner brackets, which will only be mounted on the inner T-slot of each extrusion. On the outer T-slot, I will be inserting a polymer panel using a rubber seal/profile to ensure the panel seals properly.
For simplicity's sake I am not planning to add anny additional structural supports, ideally the extrusions themselves should be strong enough.
Whether the frame is sturdy enough depends of course entirely on the requirements. I will be using this frame to mount a sliding mechanism, sort of like a drawer, except it will be motorized. The total weight of the "drawer" (the moving part of the drawer + anything mounted on it) will be around 5-6KG. Apart from this drawer mechanism, not much else will be mounted into the frame.
I am planning the add two additional horizontal extrusions, mounted with the same brackets. On to these extrusions I will be mounting the linear guides for the "drawer" mechanism.
Any input is greatly appreciated.


texts:
A certain product (link: Metro, somewhat safe for work) is currently trending on social media, that allows men to convert the kinetic energy of their more vigorous personal activities into electrical energy to recharge their phone.

I've had kinetic watches before, which re-charge by the day-to-day movement through wear; all of which have needed a few extra shakes periodically to keep them going- so it seems dubious to me that the band could really generate enough energy to charge my phone, which must require substantially more power...

Would/does the W*nkBand (product site: nsfw) work?


texts: How can I measure if water is flowing through a copper pipe?

texts: Is there a non intrusive way to measure if water is flowing through a copper pipe or just standing still in it? The copper pipe belongs to my heating system and is always under pressure with water, flowing or not.


texts: Modeling Rotation and Translation of surface B.C. in Abaqus

texts:
I am trying to model a test which has grips that can translate in X and Y directions, as well as rotate. I have been trying to model this using constraints and a reference point but have not been able to model a situation where the coupon is rotated and translated, using the top surface of the coupon as the surface being moved, the rotation is about the Z axis.

Any help would be appreciated!


texts: Mechanical properties of tin base alloys

texts:
I am trying to find information about the details of mechanical properties of tin-base alloys, such as ~8% antimony Brittanica. But probably since tin is use primarily in decorative applications or as solder, I have failed to find detailed material properties like you would easily find for more common engineering materials.

Specifically, I am interested in fatigue limits as function of the number of cycles, and the effect of casting temperature and cooling rates on material properties.

All I have been able to find is that Brittanica has around a 100MPa yield strength. Does anyone have a more extensive reference?


texts: We are working on a mounted screen design that will have microphones at the bottom of the screen housing. The screen housing will be sitting at a 10.5 degree angle. So we are worried about water sitting in the microphone hole and not giving us good microphone quality. I have included an image below showing the design. I am stumped and cant think of another way to fix the water not being able to drain out of the hole because of the angle. Any suggestions or help would be greatly appreciated. Thanks


texts: Where the Water Have Gone from Engine from a Combustion Process (C8H18+12.5O2==>8CO2+9H2O)?

texts:
During studying engine's exhaust as I asked here, I have to go far. The thing I though is quite simple, the fact is complicated. Thence I knew that there is water produced in combustion process. The combustion formula is: $C_8H_{18}+12.5O_2\rightarrow8CO_2+9H_2O$. Mean, every 1 of 4 strokes of 4-strokes engine will produce water (cyclic process: intake-compress-power-exhaust). This is the answer for me why the muffler always tear-dropping water especially in the morning or when the weather is cold.

But, that happened if the car is still good enough.  Before my current car, my old car seems didn't have that kind of tear-drop water from the muffler. Not sure what had happened to the engine. The muffler was dry and clean, no smoke. So my question is, where the water have gone? Which one is better, a car with water tear-dropping from the muffler? Or a car without that water? My question is for the same ca or closed in it piston's displacement and its power.


texts: why do we consider the external pressure when calculating the boundary work

texts:
Suppose that there is a piston cylinder device . It contains a gas with pressure P. The external pressure is Pext . In order for the gas to expand , I think that P must be greater than P ext , and it will expand until the pressure of the gas is equal to the external pressure.
The thing that I cannot understand is that when we calculate the boundary work we multiply the external pressure by the change in volume. Since the gas is expanding , then the gas is DOING the work ON the surrounding , then I expect that when calculating the boundary work is to consider the gas pressure. What is wrong with that ?


texts: I am doing research into lunar regolith's hardness in relation to abrasion of lunar tools and need to choose a hardness scale (either Mohs, or Rockwell A, B, or C). Is either of these metrics more legitimate/accurate than the other?


texts: Create a mate that allows a part to move within a specified distance from another part

texts:
Can I create a mate in solidworks that allows for a part to move up and down but stop at a certain distance from another part?
I have an L-bracket mated to an aluminum rod (black). If it is possible I would like the whole black rod and L-bracket combo to move up but not exceed a certain distance from that horizontal rod below the L-bracket. This mate should be defined from one of edges of the horizontal rod and the bottom side of the L-bracket.
Is this possible?


texts:
For a nonlinear system,
$$
\begin{align}
&{\boldsymbol x}(k+1)={\boldsymbol f}({\boldsymbol x}(k),{\boldsymbol u}(k),{\boldsymbol w}(k)) \\
&{\boldsymbol y}(k)={\boldsymbol h}({\boldsymbol x}(k),{\boldsymbol v}(k))
\end{align}
$$

I would like to find the Extended Kalman Filter (EKF), having a look at wikipedia, I have reached

$$
\begin{align}
& \hat {\boldsymbol x}(k+1|k)={\boldsymbol f}(\hat {\boldsymbol x}(k|k),{\boldsymbol u}(k|k)) \\
& {\boldsymbol P}(k+1|k)={\boldsymbol F}(k){\boldsymbol P}(k|k){\boldsymbol F}^T(k)+{\boldsymbol L}(k) {\boldsymbol Q}(k) {\boldsymbol L}^T(k)
\end{align}
$$

and

$$
\begin{align}
&{\boldsymbol S}(k+1)={\boldsymbol H}(k+1){\boldsymbol P}(k+1|k){\boldsymbol H}^T(k+1)+{\boldsymbol M}(k+1){\boldsymbol R}(k+1){\boldsymbol M}^T(k+1) \\
& {\boldsymbol K}(k+1)={\boldsymbol P}(k+1|k) {\boldsymbol H}^T (k+1){\boldsymbol S}^{-1}(k+1) \\
& \hat{\boldsymbol x}(k+1|k+1)=\hat{\boldsymbol x}(k+1|k)+{\boldsymbol K}(k+1)[y(k+1)-{\boldsymbol h}(\hat {\boldsymbol x}(k+1|k))] \\
& {\boldsymbol P}(k+1|k+1)k=[{\boldsymbol I}-{\boldsymbol K}(k+1){\boldsymbol H}(k+1)]{\boldsymbol P}(k+1|k)
\end{align}
$$

where

$$
\begin{align}
& {\boldsymbol F}(k)=\frac{\partial \boldsymbol f}{\partial \boldsymbol x}|_{\hat {\boldsymbol x}(k|k),{\boldsymbol u}(k)} \\
& {\boldsymbol H}(k+1)=\frac{\partial \boldsymbol h}{\partial \boldsymbol x}|_{\hat {\boldsymbol x}(k+1|k)}\\
&{\boldsymbol L}(k)=\frac{\partial\boldsymbol f}{\partial\boldsymbol w}|_{\hat {\boldsymbol x}(k|k),{\boldsymbol u}(k)}\\
&{\boldsymbol M}(k+1)=\frac{\partial\boldsymbol h}{\partial\boldsymbol v}|_{\hat {\boldsymbol x}(k+1|{\color{red}{k+1}})}
\end{align}
$$

Is this obtained formulation correct?

My main concerns are about the whole timing indexes especially the last one.


texts: What type of supports exists for ballscrews or leadscews?

texts:
For Linear actuators, a common mechanism is to use ballscrews with ballnuts.

The ballscrew is supported at the two sides by a set of bearings which permit the rotation of the screw while keeping the axial reaction force to the ballnut movement.

Looking for those ballscrew supports, I found there are several categories:

Floating (identified by F)
Fixed (Identified by K)

An other letter indicate several types/shapes of supports: E, B, F, etc.

Those pieces are usually sold in a set of one fixed and one floating support:

  e.g.

  BK + BF

  EK + EF

  FK + FF

....

I could not find understandable information about this.

What types of ballscrew/leadscrew supports exits?
What is the difference between them?


texts: Where to find springed pegs with screws for a CNC mill?

texts:
I need to hold small pieces of wood in place to be drilled by a mini computer-numerical control (CNC) mill. I have a book stand (no affiliation) that has two "springed pegs" fastened with screws:

  Springed pegs allow very thick book

I think these would do very well and I could not find such springed pegs separately. Are they available under a different name?

Update: My current solution prevents the pieces from shifting horizontally by slotting them in a pocket with their exact size with 5 mm of depth. I have been holding the pieces in place with double-sided tape and it works. A milling job takes about a minute and I have hundreds of pieces, so I am looking for a quicker solution. The machine uses a downcutter that presses the wood into the bed, so I think light tension would be enough.


texts: Why does AN-94 have higher burst fire than its cyclic rate?

texts:
AN-94 is an assault rifle of Russian design chambered in 5.45 caliber. It is claimed to be state-of-art in Russian small arms development.

The most important design differences (relative to common designs like AKM) include:

Internal receiver, chamber, bolt, bolt carrier, barrel and gas tube/piston are all integrated into one independent assembly - called firing unit.
Stock, external receiver form what is called "Effect Envelope" and firing unit can move along the barrel axis relative to this envelope - which is supposed to increase accuracy by delaying recoil until the second round is fired.
The firing unit includes a rammer connected to the bolt carrier by a cable and pulley system. The rammer is moving forward as the bolt moves backwards, to accomodate for pre-feeding sequence, by stripping the next round from the magazine and moving it just in behind the chamber, where it's being subsequently fed by returning bolt.

The gun specification claims that when firing full-auto the first two rounds are being fired at 1800 rpm speed, but all subsequent ones at 600 rpm. Why is the time between the first two shots shorter? I can't find anything that would differentiate between the first two and all the subsequent rounds? I would understand if the gun was either keeping the same cyclic rate or rather shoot in a continuous stream of two-round bursts with mean rate of 600rpm but neither is the case. Can someone explain this to me please?


texts: Securing aluminum angle to steel tubing without through-bolts

texts:
Overview
I'm planning a rack for solar panels on the roof of a cargo trailer. I will mount the panels to a pair of 15 series 80/20 aluminum extrusion rails. I will mount the rails to the roof of the trailer using aluminum angles. Here's a view from a Sketchup model giving a rough idea:

Specifics
My question revolves around mounting the set of aluminum angles to the trailer's steel roof beams. Here is a rough model showing the relevant parts:

The aluminum angle is 1/4" 6061-T6 with 2" legs cut to 2" wide. The steel beam in the trailer roof is 1" wide, 1-1/4" tall, and about 1/8" thick. Between the angle and the beam is the thin aluminum skin of the trailer.
The interior of the trailer is finished and prevents any access to the beams from the interior so I can't use through-bolts to attach the angle to the beam.
So my current plan is to drill and tap, from the outside, the top of the beam. Then I can attach the angle to the beam using two bolts that screw into the top of the beam. I plan to use 1/4"-28 bolts. I also plan to use VHB tape between the aluminum angle and the aluminum roof skin.
Question
Finally, the actual question. Since the steel beam is only 1/8" thick, is the choice of using 1/4"-28 bolts strong enough? Or would 1/4"-20 be better? My thought is finer threads gives me a better grip over courser threads.
Side question (that may be off-topic) - is there a better, stronger way to attach the aluminum angle to the steel roof beams than screwing in bolts given that the steel is only 1/8" thick but I can't use through-bolts?


texts: Elevator standby + moving passanger , electricity consumption changes

texts:
I'm interested specific on electricity consumption changes on 2 different situations inside an elevator.

When the elevator is stopped and people enters the elevator, does it change in any way the electricity consumption? Simple logic tells as that the elevator in this state is stopped by brakes, and brakes pressure is not affected by the amount of people being inside the elevator, so there should be no difference on electricity consumption on this case.
If elevator is going up/down, and a passenger is walking, jumping inside the elevator does this makes any difference on power consumption of the elevator? or regarding the external motor we can see all the cabinet as a unit and the forces that interact inside the cabinet doesn't change anything regarding the external force that is trying to make all the cabinet move ? If it's true how is called this principle?