texts: What method can I use to make a pivot point in an aluminum linkage?

texts:
I recently had a project where I made an aluminum linkage (similar to a scissor lift) operated by linear actuators. Aluminum pieces were fabricated from 6061 "standard" aluminum stock, 6mm (0.25 inch) thick. The bars are at most 750x75mm (30x3"). The application was mostly cosmetic (for a special effect) rather than lifting or exerting much force.

I used shoulder bolts with a nylon washer between the aluminum pieces to reduce friction, and standard zinc-plated steel washers on the exterior sides.

The problem I encountered was tightening the bolt too much would result in too much friction, whereas too loose would result in one of the aluminum pieces coming slightly off the shoulder of the bolt, skewing, and causing similar problems.

What would be a better way to create a reliable pivot point that doesn't require constant adjustment?

I put together this illustration as an example:


texts: I want to test non woven fabrics to see if they are polypropylene, the lining material of N95 masks

texts:
A group of us are sewing face masks to prevent the spread of sputum. I've learned that the lining of an N95 mask is made of polypropylene.  Polypropylene is also a common interfacing product for sewing.  I want to identify polypropylene in non woven breathable "fabric" products that I have on hand around the house, for example: some "plastic" grocery bags are breathable and, I suspect, made of polypropylene.

Is there a simple test?  The burn test?


texts: Was our wireless home telephone in the 1990s encrypted or completely insecure? And how did it work so far from home?

texts:
In the mid-1990s, our family got a cheap (I assume, since we weren't rich) but at least brand new telephone which either had two wireless "units", or one (my memory is a bit foggy on this detail), but the point is that, you could take the unit(s) with you outdoors, for example sitting in the garden, even going as far as into a nearby store (150 meters away), and it would still work to talk into, somehow communicating with the base unit in our house.

It also allowed you to press a "local call" button which would skip the telephone network and just ring the other unit (or the base unit; I'm unclear on this) directly, then working as two-way walkie-talkie. This was extremely cool to avoid having to shout that dinner is ready all the time. Mum would just press the "local call" button on the base unit next to the kitchen, and we'd get a signal. (Really, we didn't even need to pick up the phone -- the signal itself was enough to know that we were supposed to come in or come upstairs.)

I find this concept very fascinating, but I'm confused about how it technically worked:

How was it able to work so far away from the house? What if others also had the same model/make phone? Would we not get each others' signals then?
Was this encrypted in any way, or was it just blasting out all of our "private" conversations all over the place whenever we were talking into its units? I don't remember it coming with any warning note saying something like: "Please note that anyone can listen to your conversations with a radio receiver!"
Was the "local call" feature different in any way from the normal wireless mode between the unit(s) and the base unit (which of course was connected to the telephone network by wire)?

I cannot remember which brand or model, unfortunately, but I suspect it's as it usually is: it was not some unique invention but rather one of countless clones of some original invention that numerous companies created with "cookie cutter" blueprints.


texts: The direction of the internal axial force of a tapered bar

texts:
https://classes.mst.edu/civeng2210/concepts/05/elongation/index.html
If the bar is separated in to segment AC and segment CB, to maintain its  equilibrium, Shouldn't the N(x)s be directed in opposite?
In Static, I learned that if we apply two equal, opposite forces at the ends of a member and cut it at the middle, there should be internal forces equal and opposite to each forces at the ends of the segments like this.

PS:I should've been clearer. What I'm asking is why all the forces(P and N(x))of the portion AC in the first pic are pointing right, whereas F and F' of the portion AC in the second pic are in different directions. Why is that? I'm totally confused.


texts: Is there a step by step guide to adding dimensions to a floorplan?

texts: I'm learning AutoCAD and decided to make a floorplan as my first project. I know how to insert dimensions in AutoCAD but I don't know where to actually put them. E.g. in this image do I put the distance between the outeredge of the wall and the door or the inner edge of the wall and the door? Can I put the written dimensions on the inside of the building instead of the outside? These questions might not be very clear but basically what I'm asking is: is there a step by step guide for putting dimensions in a floor plan. I've looked at some images of floorplans and they're really not helping me much


texts: comparing backlash of different mechanisms

texts:
I have a cylinder with a shaft in its center that I need to rotate at 120 RPM on 180°, for costing reasons, I would like, if possible, to reuse the same DC motor that I already use for another system. That motor has a speed of 6000 RPM so I need a reduction ratio of 1:50.

I don't have a lot of space under the cylinder, so I decided to move that motor to make it parallel to the cylinder (and then to the cylinder shaft), this also means that I won't be able to direct drive the cylinder shaft and I will need to use at least a pair of pulleys (with belt :)) or gears.

So what would be the best way to reduce the speed of the motor adding the least backlash ?

Currently I see these 5 solutions on which I would like to get external reviews on them :

Only pulleys: since I'm using GT pulleys and the maximum reduction ratio with 2 pulley is 1:4, I need at least 3 pairs of pulleys to get 1:50.
Planetary gearbox with 1:50 ratio + a pair of pulleys or gears having the same teeth count (just because the shaft are parallels)
Planetary gearbox with a ratio smaller than needed + a pair of pulley or gears that reduce again the speed appropriatelly to get the 1:50 at the end.
A pair of gears giving me the 1:50 ratio directly (if I find a gear with enough teeth..)
Replacing the motor by a servo which I do not know why are larger but shorter than the motors I found, and so it could fit under the cylinder.


texts:
I have cylinder model that I control with 4/3 directional valve. When 4/3DV control input is 10V, cylinder moves forward and when valves control input is -10V, then cylinder moves backward. I can get any data from cylinder(position, speed, acceleration,force).

Now I want to make control system for this. I would like to make control system that I can set target position and target speed for system. I could use PID controller, but what parameter to control?

Just asking what is the best way to make this kind of control system, be fore I start to make it.


texts:
I have a tube with a circular cross-section, this tube protrudes from the ground vertically for a section, then arcs over to one side. At the end of the tube, a flat plate is mounted to the end of it. The arc is of a constant radius but is not necessarily a 90 degree bend. (i.e. the angle of the flat plate to the ground plane is not necessarily 90 degrees). How would you go about calculating, by hand,  how much load the flat plate could hold before the tube bends beyond it's yield point.

Assuming all geometries are known and the material properties are known and constant.

I've been working on a solution using a combination of formulas from Roarks book. But, I'd like to see how others would approach this problem.  "Solve using FEA" is not an answer i'm looking for, but rather a reasonably accurate hand calculation approach.

Edit:
-dimensions and loading direction added

Approximate tube dimensions:

Vertical straight section: 1m

'Bent' section arc radius: 125mm

Flat end, 10 degrees to floor

Tube OD - 25mm

Tube ID - 23mm

Loading direction will be in the negative z-axis i.e. gravitational loading only.


texts:
I try to design a HTD3 pulley, but I don't know, how the teeth exactly should look like. I found the following specification:

But this seems to be wrong, since I found some HTD3 STL files and overlapped them and the teeth form seems different. What is the correct design for a HTD pulley?


texts: I need to build a structure like the one in the picture below. Basically, it is a pendulum that holds a measurement hammer and lets it oscillate without friction. I don't know how to find the two necessary components (the one that holds the hammer and the one that is fixed on the shaft). How are they called?


texts: Why does the AISC handbook only list one figure for Section Modulus for shapes such as Angle(L) steel?  Shouldn't there be two? The steel is asymmetric.  Is the figure given just the Delta to the bottom or something; figuring a design only needs to be concerned with Tension?


texts: What are the factors considered in the development of the video game controllers over the years?

texts: What are the ergonomics taken into account in evolution of video game controller over the years.


texts:
Before to present my question, I have to say that I'm not a hydraulic expert.

I'm working on a water valve design and I found this model which work with a diaphragm and a spring. I want to consider all the variables acting in this mechanism in order to understand how it works.

This is how I think it works:

The water flow pushes the diaphragm to let the water flow pass through the valve, the dynamic pressure in the pipe is about 14 PSI. When the water tank starts to fill, buoyancy force acts against the float closing a little hole which acts like a water leak.

The water inside the diaphragm chamber generates a force that pushes the diaphragm up, sealing the water intake and cutting the water flow through the water tank.

When the water valve cut the water flow the static pressure in the pipe reach 40 PSI.

According to this, I have some questions:

What is the function of the spring?
The sealing force generates by the diaphragm is higher than the force according to the 40 PSI of static pressure, or they are equal?
The pressure inside the diaphragm chamber rises when the water leak is sealed?


texts:
I have been sent a clip of a drawing with the following annotations on it, but I've never seen them before and can't figure out what they mean. Is there a standard interpretation of these callouts?

Initially I thought that they might be some metric notation for I beams with the height shown in mm, but weld callouts on the drawing use fractional inches and american electrode designations. Furthermore the members they refer to are rectangular and square tubes, not I shapes.

There is some ambiguity if the material in question is steel or aluminum (an email said aluminum but the electrodes for welding are steel.)

I will obviously also contact the person who provided the drawing, but they got it third hand so it may take a long time to get to the source.


texts: Does a roadway bridge experience more load when vehicles are parked or when they are moving?

texts:
Bridges are designed for the loads that come from the vehicles that are expected to cross them.  This includes the weight the vehicle and any dynamic loads that may be introduced from movement of the vehicle. Dynamic loads may be from "bouncing" or from hitting a joint or pothole.

Initially it would seem obvious that more load is applied to a bridge while the vehicles are in motion (weight of vehicle plus dynamic load). The dynamic loads are proportional to the travelling speed of the vehicles, but as vehicles go faster, they typically are spaced farther apart.

When vehicles are stopped, they typically are much more closely spaced than when they are moving.

Can there be a situation where more load is on a bridge because of closely spaced parked vehicles than from moving vehicles that are farther apart?
Are these two situations covered in bridge design?


texts: Make something that turns yet locked in place

texts:
I imagine this is an easy concept but I do not know much about mechanical engineering design.

I am trying to make a "knob" like a control knob in solidworks that turns and is locked in place after twisting.  I am thinking of a twisting knob in a labyrinth game or something like a foosball table knob that is locked in place after turning, or just a general control knob on an oven.  I want to figure out how to design the "interface" that lets the knob turn yet stay in place after turning but do not know enough vocabulary to point myself in the right direction.  Does the "interface" I am looking for have a name? How does one go about making it?


texts: Finding Supply/Nominal voltage for Torque Motor BLDC

texts:
I'm a bit confused by torque motors datasheets as it never mentions any nominal voltage. I would like to run a torque motor on a 24 V battery.

The required max torque is 150 Nm (=21000 oz-in) and max speed 15 RPM. (=1.57 rad/s). I have found a motor that shows max torque, max current at this torque but I don't find any nominal voltage.

If I multiply $K_e$ (V/rad.s^-1) by max speed and add the voltage drop in the resistor ($R*I_{max}$), I can find 132 V.

Why does the torque motor not have a nominal voltage? (compared to the classical BLDC motors)
Are the supply voltage calculations (132 V) correct?
In this case, should I choose a boost converter (24 VDC -> +132 VDC?) followed by a motor drive that can handle this voltage?

You can find the motor datasheet below.


texts:
What is the definition of anti-windup? How does it impose the constraints?

What are the advantages of MPC and anti-windup over each other?

Does anti-windup guarantee the constraints or does it just try respecting them?


texts: Wall functions and separation in turbine blade simulation

texts:
I am simulating a turbine and I have some question about standard wall function in FLUENT.

Standard wall function requires $y^+$ value between 30 to 60 on the blade. but the following quote states:

  When using wall function models, the $y^+$ value should ideally be above
  15 to avoid erroneous modelling in the buffer layer and the laminar
  sub-layer [Source]

Why $y^+$ value should ideally be above 15 by using wall functions?
Can massive separation be modeled with $y^+$ value between 30 to 60 on the blade? because it is mentioned according to FLUENT help:

  Traditionally, there are two approaches to modeling the near-wall
  region. In one approach, the viscosity-affected inner region (viscous
  sublayer and buffer layer) is not resolved. Instead, semi-empirical
  formulas called "wall functions'' are used to bridge the
  viscosity-affected region between the wall and the fully-turbulent
  region. The use of wall functions obviates the need to modify the
  turbulence models to account for the presence of the wall.

In other words, I think that there is a velocity profile in viscosity-affected inner region as a wall function that it can almost model boundary layer and massive separation. For example, wall functions with 30

I studied this article but I don't understand the following sentences:

  The logarithmic law for mean velocity is known to be valid for . In
  FLUENT, the log-law is employed when . It should be noted that, in
  FLUENT, the laws-of-the-wall for mean velocity and temperature are
  based on the wall unit, $y^*$ , rather than $y^+$. These quantities are
  approximately equal in equilibrium turbulent boundary layers.

What is difference between $y^*$ and $y^+$? What is the exact meaning of "equilibrium turbulent boundary layers"?

Generally, my question is that when wall function approach is used, viscosity-affected inner region (viscous sublayer and buffer layer) is computed by using semi-empirical formulas with good accuracy. Is this statement correct?


texts: How to model a humidity control system inside a box?

texts:
I am a computer engineering student and currently having my undergraduate thesis. My thesis is about a chicken egg incubator and i need to control the humidity inside the incubator.

Right now, i dont know how to calculate the transfer function of the humidity control system. Please someone point me to the right direction.

Is it possible to get the transfer function if i can give a step input (turn on the humidifier) and then get the s-domain of the output, then divide the output over the input because transfer function = output/input? or is this method difficult considering im only an undergraduate computer engineering student?


texts: Is it possible to apply different boundary conditions on the same model for different load cases?

texts:
Instead of creating multiple bridge models with different boundary conditions for differential settlement, and combining the forces output manually in Excel, is it possible to specify different boundary conditions within the same model, using different load cases?

I am using both MIDAS and SAP v18 software and I would like to know if there is any way to do this in any bridge structural modelling software. Or is there any software that doesn't require you to add a restrain to a node for which you are applying a movement?

This limitation on the software introduces significant additional effort on the part of the Engineer. Has anyone thought of some way to overcome this issue when dealing with differential settlement or other soil movements?


texts: Are British Universal Beams and Columns cut according to imperial or SI measurements?

texts:
In product catalogues, beams like UB 152x89x16 have dimensions written in mm to the nearest one decimal place. Are these beams cut and measured using an SI ruler or an imperial ruler. I am asking this question because I have trouble matching some of the section properties given in the table for some of the beams. So I presume that the dimensions given are rounded off dimensions and the actual dimension could be given in exact fractions of an inch.

Am I correct?


texts: By approximately what ratio does power steering (on a car) amplify the torque applied?

texts: Power steering on a car is a form of torque amplifier: the driver applies X Nm (or ftLb) of torque, and the power steering adds Y torque -  but maintaining the same angle of turn.  But what's the approximate ratio of Y:X for the power steering on a typical domestic car? Is it e.g 10:1 ?


texts: Ineffective purging of a flame monitor lens

texts:
There is a wall-opposed flame monitor detecting coal, oil and gas combustion in the burners, attached to the furnace walls in a coal-fired power plant.

I'm looking for suggestions to clear the dust or particulates from the lens, as it is affecting the signal and leads to tripping.

Right now, it is cleaned by supplying purged air from the core air fan. However, this has been found to not be effective as the contaminants still exist.

What would be the cause of such an ineffective system? Could the purge air system be improved by using higher pressure air from other components?

Much appreciated


texts: Are Loop Closure Equations and Holonomic Constraints the same thing?

texts: I'm reading a book on robotics, and it has a different section on each term. The way both concepts are worded and phrased mathematically make them seem like they both constrain the configuration space of a closed loop mechanism in more or less the same way. I'm not sure if I'm missing something, but they seem like the same thing.


texts:
What is the highest sampling time ever applied in Model Predictive Control (MPC)?

For an HAVC (Heat, Air Ventilation, and Cooling) it can go to hours.

But, I am looking for a sampling interval in the range of months or years.

Does any one know any practical application?


texts: ZARN bearings vs thrust tapered bearing pairs

texts:
Does anyone know how needle assemblies like this stack up against having a pair of thrust tapered bearings back to back in terms of radial and axial load? That is, a bearing like this:

as opposed to this:


texts: Is twisted belt configuration a good practice?

texts:
Internet is full of twisted belt examples (30, 60, 90 degrees), however, the allowed misalignment tolerances claimed by the manufacturers are less than several degrees.

The very term misalignment seems to impose the two pulleys are out of single plane.

So, would it be correct stating that?:

180 / 360 degree twist is ok
any other twist is a misalignment and therefore is a bad practice

Apart from timing belts, are there other belt types which would enable me driving i.e. 30kW load at 30 degree belt twist?


texts: Grad student needing help with a fluid mechanics issue in project

texts:
BROUGHT OVER FROM PHYSICS STACK EXCHANGE

As the subject states I have hit a wall in a fluid mechanics associated problem in designing an experiment for my grad project.

Long story short, I'm an engineering undergrad who got a broad education in formal engineering topics (thermo, heat and mass, classical mechanics, systems, circuits, etc. etc.), but literally only did 1 fluid mechanics course. I am now a Masters student doing more biologic focused research. I am working with stem cells and I need to perform a flow experiment in which I run continuous fluid over my cells in a flow chamber at a specified flow rate.

My problem is that I have been using a syringe pump as it was what the facility provided and it's less than optimal. Only 30 mL at a time and at my specified flow rate I end up having to change it a lot and therefore flow is discontinuous and not really up to the rigor of my experiment. I get ok results, but I think it can be better.

What I'd like to do, and my problem is, that I'd like to run a circulating system with a continuous pump. I just don't know how to figure out what pump to use. I have some support and money from the lab, and I'd prefer to be able to tweak the flow rate if possible.

To set up the problem:

I am using an Ibidi mu VI 0.4 chamber slide. Full literature available here:

https://ibidi.com/channel-slides/57--slide-vi-04.html

Quick and dirty dimensions:

Outer dimensions (w x l) 75.5 x 25.5 mm² Adapters Female Luer Number of channels 6 Channel volume 30 µl Channel height 0.4 mm Channel length 17 mm Channel width 3.8 mm Volume per reservoir 60 µl

Using their literature provided I have already calculated that I need to provide a flow rate of:

4.73 mL/min

which corresponds to a shear stress of: 6 dyne/cm^2 (0.6 Pa)

my tubing dimensions are:

L = 20 cm inner d = 1.6 mm

I have a reservoir of cell media of maximum 50 mL which needs to sit beside the microscope in a heater to provide the maximum "comfort" and conditions that my cells like (37 degrees C)

Now, for the life of me I can't figure out how to determine an appropriate set up/pump to make this into a continuous flow, needed to pump/circulate for 2 hours

Can anybody at least put me on the right path to designing this?? I don't have the time to relearn all my fluids, but I don't mind brushing up on topical required reading to solve.

I can also attempt to make a diagram if you need a better visual representation. I hope I explained my problem thoroughly though.

Thank you,

A frustrated grad student


texts: Convert translational stiffness to rotational stiffness of a screw

texts:
I have the formula for the translational stiffness which is :

However, what I would like to find is the rotational stiffness. Is there any formulas to convert from one to an other knowing the pitch of the screw and the diameter ?


texts: What will be the the width of the column strip in the case of 2 different spans in the same direction?

texts: Say we have a plan of a building as follows and it is required to be designed using DDM (Direct Design Method). since the moment needs to distributed laterally into a column and middle strips and according to ACI 8.4.1.5 "A column strip is a design strip with a width on each side of a column centerline equal to the lesser of 0.25ℓ2 and 0.25ℓ1." but in this case, both L1 and L2 have different spans and i dont know what to choose.


texts: What's the difference between impeller and rotor in centrifugal pump?

texts: The two terms seem interchangeable and I can't find a strict definition for both, so what's the difference between them if there is any?


texts:
I have an infrared thermometer that supposedly goes up to 1200F (https://www.amazon.com/gp/product/B00IT0ODPQ/ref=oh_aui_search_detailpage?ie=UTF8&psc=1).

However, I used this on my electric stove when turned to max. The coils are cherry red which is normally 1500F. Nichrome is usually rated to go up to 1400F.

Nevertheless, the thermometer never showed more than 900F.

What is the problem? Are these types of thermometers just unreliable?


texts: Is it possible to get the hardening exponent and coefficient (n, k) if I just know the yield point, the ultimate stress, and the failure strain?

texts:
For a certain steel I have the following data:

Yield stress and strain (engineering)
Ultimate tensile strength (engineering), I don't have the strain at this point
Strain at failure (engineering), I don't have the stress at this point.

I want to recreate the true stress-strain curve, maybe using the hardening exponent and coefficient.
Is this data enough? Or will I need more?


texts: What factors are needed to be taken into account when building a vending machine?

texts:
I'm a software engineer whose main concentration has been data science with some minor electrical engineering on the side.

I want to delve into some mechanical engineering by building a proper mini vending machine but am having trouble knowing which materials to use as a consequence of not knowing where to find good documentation.

Is corrosion resistance important for a vending machine? Do I use aluminum or steel? What factors would I need to take into account if it were a 2 meters tall, 1 meter deep machine, for example? Or another size?

Apologies if this is mistagged.

Thank you.


texts: Software: Is it okay to charge client for project refactoring?

texts:
Refactoring is a daily thing in engineers life, and I wondered if it's common practice to charge client for refactoring.

Let me know (all) your thoughts on this,
Thanks!


texts: Which component of vehicle tailpipe emissions has the greatest social cost?

texts:
Emissions

Emissions from vehicles have an associated social cost for everyone. We hear a lot about CO2, but CO2 is not the only thing that comes out of a tailpipe. From Wikipedia, emissions components of petrol and diesel engines are:

Nitrogen
Carbon dioxide
Water vapor
Oxygen
Nitrogen oxides
Carbon monoxide
Particulate matter
Hydrocarbons
Sulfur dioxide

My impression is that CO2 gets the most attention because climate change is a hot topic. This doesn't mean that it is the emission component that has the highest cost to society though.

  Do any of the components above have higher costs to society than CO2 per same unit of measure (e.g. gram, kilogram, or ton)?
  If they have higher costs per unit of measure, do they have a higher cost than CO2 based on their component percentage in typical emissions? The component may be very costly per ton but it makes up a very small amount of typical emissions.

I know that cost is kind of hard to define in these cases. It does seem possible though, because in reports on greenhouse gas a monetary figure is always given.

Costs

The US EPA (Environmental Protection Agency) has published information on The Social Cost of Carbon. From the SCC Fact Sheet, the cost social cost of a ton of CO2 in 2015 is between \$12 and \$116 depending on the discount rate used.

The Florida Department of Transportation has also produced computer software that estimates the benefits of transit usage. This is the Trip Reduction Impacts for Mobility Management Strategies (TRIMMS) software. As a part of this, a co-benefit of reduced CO2 emissions is estimated at $50/metric ton. (TRIMMS Supplemental Report page 16)

The costs above are for CO2, but I assume that similar studies have been done for other components of emissions.


texts: Design of a hydrogen and corrosion sensor query

texts:
I’m designing a hydrogen and corrosion sensor. A thin film changes resistance based on hydrogen concentration. Then the capacitance between two electrodes will change depending on substrate thickness (corrosion). AC analysis can be used to see a phase change in the impedance, giving capacitance changes. I have designed a basic sensor, here it is with a basic model.

But now I think an interdigitated electrodes might be better to detect the change in corrosion from the steel substrate. I’ve thrown together a basic design. I’m not sure though, has anyone got any thoughts? And what would be the best material for this electrode, I was thinking a copper? Also what would be the best way to go about modelling interdigitated electrodes, assuming lots of parallel capacitors?

Many thanks


texts: How do protective coatings affect the lifetime of bridges?

texts: I'm trying to understand the importance of protective coatings on steel structures like the Golden Gate Bridge. For example, if we stopped maintenance on the Golden Gate Bridge today and left it packed with empty cars, what would be its expected lifetime (until a car falls into the water) and the variance of that lifetime? If we additionally removed all of the paint/coatings on any steel parts, what would be the expected lifetime and variance? I'm hoping for a rough answer from an expert in the field.


texts: What are the advantages of the slide in semi-automatic pistol design?

texts:
A majority of semi-automatic pistols (revolvers excluded) have a spring-loaded component called slide as a part of their firing mechanism. Although historically there are designs without a slide, (notably Mauser C96), those are, if not non-existent, very rare after the World War II.

It probably is safe to conclude that the displacement of other designs are due to some advantages in the slide mechanism. What are those advantages?


texts: Force exerted on wall of a rotating cylinder filled with fluid

texts:
We are given a standard diagram of a rotating cylinder with the parabolic shape in the rotation.

Given:

the distance between the vertex of parabola to the top of the parabola.
the original height of the water.

I have a really general question regarding this problem. From where the vertex of the parabola begins, up to the top, the pressure distribution varies with radius? And from the vertex of the parabola to the bottom of the cylinder, it only varies with height, since radius is fixed?

My question is: can I split the two different areas and integrate $P = \dfrac{\rho\omega^2}{2} -\gamma z$ twice?
Once while holding the radius constant but the height a variable, and another while holding the height constant but integrating with respect to the radius.

I'm planning on using $\text{d}F= P\cdot\text{d}A$ when integrating each one.

A link to an image that looks similar to the one I have : http://demonstrations.wolfram.com/FluidRotatingInACylinder/


texts: Developing a stochastic differential equation model for concrete fibers

texts:
I am working on modeling concrete fibers (metallic fibers) as a mathematical model. My work is for my thesis. I am a PhD student of numerical analysis, but I am working on a real tunnel project.

I have had issues with the distribution of fibers in the concrete. I am trying to find a way to develop a stochastic differential equation for the fibers.

I have the following questions:

Is there any mathematical model for concrete fiber? (not statistical model)
Is there any technical information available for how concrete fibers behave?


texts: I'm attempting to convert a fridge compressor into a vacuum pump, but it got me confused. There should be one inlet and one outlet I believe, but instead I have three, with the third being connected to the second (the white one) through a thin copper tube with the bulky thing at the end of it (see picture). The white tube is the suction, it has a label on it. How would I hook it up, what are the three tubes for? (Sorry if it's in the wrong forum)


texts: How can you sync an electric motor with an IC engine?

texts: Hey guys my first post here. I was planning on building a motorbike that you can also pedal like a bicycle. The idea is that you dont have to have a license if the IC is under 50cc. So the plan is I want to have a hybrid powertrain consisted of a 50cc 2stroke(7kw) IC and a 1kw electric motor. The quetion is will the torque add from the two sources or will one always pull while the other will be getting pulled struggling to keep up? Is it necessary to have the two sources connected to a differential for them to work together?


texts:
According to ASME B31.8-2008 to calculate minimum thickness if a pipe under internal pressure you use:
$$t=\dfrac{PD}{2(SEW+PY)}$$

I have seen this formula re-written in terms of pressure of the fluid within the pipe as follows:

$$p(psig)=\dfrac{2t \cdot S \cdot E}{D-2 \cdot t \cdot Y}$$

Assuming that the reduction factor $W=1$, how do they get to the rest of the formula?


texts: How does the mass flow rate through an annular fin tube affect the heat transfer Q?

texts: I have a fluid flowing through an annular finned tube. The heat transfer (cooling of the fluid in the pipe) is done by natural convection. I am curious about the relationship with how the mass flow rate of the fluid in the pipe affect the amount of heat transfer which can be achieved.


texts: Can the speed of a falling object be regulated using gears?

texts:
I am not an engineering student, but can understand if explained, so excuse me if this is too basic.

For a personal DIY project I envisioned, I need to make an object, attached to a set of gears, fall at a certain speed - 6ft / 24 hours. This object will rotate the first driving gear and the resultant driven gear at 3000-5000 RPM. I estimate the ratio to be 1:100000.

So basically my question is whether the speed at which the object falls (from gravity) be regulated? The weight of the object doesn't matter, since I can set it to whatever is required for my rate of descent.

The setup will be similar to: http://s.hswstatic.com/gif/clock-weight-train.gif


texts:
I did some calculations to find out the moment of inertia and physical qualities of some metal.

I am using typical medium carbon steel.

I'll use a density of 7.8 g/m^3 until I get better numbers.
There's a solid circular shaft that's 1000mm long
The diameter of this shaft is 40mm

This gives me: Polar moment of area 251327 mm^4

The next part is the motor.

This will be a shaft connected to a 15HP 1200RPM motor but I'll be adding a gearbox to bring the RPM down to about 85RPM this will give me about 1256 newtons/meter of force.

I am a bit lost at this junction.

Do I need to convert the newtons to MPa or the Polar moment to some other units?

How do I compare the 1256 newtons to the amount of force this cylinder can withstand 251327 mm^4

would this pipe bend or break under the max torque load?

How can I relate 1256N.m to 251327mm^4 to see if the pipe would break?


texts: Is surgical and medical mask based on static electricity? By static electricity I mean like 3M N95 mask with at least two different layers of positive and negative static electrical layer. I googled and find that someone says medical mask filters only by physical fiber to trap particles physically, while some others say it also attract particles by fibers with static electricity to increase breath flow rate. However, it seems not true because medical mask seems like have only three layers, outer, inner, and middle, which is seemly impossible to form a static electricity mask. Unlike 3M N95 mask has 5 layers, outer, positive charged, separator, negative charged, inner, which is more trust worthy. BTW, surgical and medical masks are basically the same beside outer layer. Surgical is blood-proof, and medical is not. And, I ask because of corona virus. If without static electricity, then it is possible to reuse only if I do not damage it physically, to protect myself from potential public risk.


texts: How do I measure vibration of a moving object?

texts:
I want to measure the vibration of a roller coaster cart while it is riding down the tracks. Handheld data loggers with a pin on them won't work. I'd need something I can attach or place inside of the roller coaster track. I am worried that conventional data loggers won't be well suited for this because the acceleration of the cart influences the vibration readings when using an accelerometer. I have found exactly 0 results on Google for "measuring vibration of moving objects"-like queries. I want to measure 3-axis G-force.

Is there anything you could recommend me to use?


texts:
I have to build a box to extend the length of a projector bracket:

The projector bracket weighs 7kg and has an arm of about 500mm. The projector weighs another 5kg.

The box has a depth of 140mm. That is the length by which I need to extend the length of the projector arm because the wall on which the bracket is mounted is recessed by 140mm behind the image surface.

Does one of the following two ways of joining offer a stronger structure?

I don't have tools to make complex joints. I can only screw ½" plywood at right angles.


texts: Why do hydroelectric plants use turbines instead of an efficient 'water wheel' configuration?

texts:
I have been thinking about hydroelectric plants and I have been wondering why they are built the way they are.  As in understand it, a stream of water is sprayed at a turbine, located at the bottom of a dam (Pelton Turbine.)  This does not seem to be a very effective way to convert the energy.  What are the factors that make this method effective?

Another method would be to place the water into buckets, then connect these buckets to a belt system and use the belt to power the generator.  This method is similar to how  water wheel works.  What are the draw backs to this method that make it less effective than the turbine.


texts: How to join 2 mm stainless steel welding rods without a TIG welder

texts:
I have to build an egg tray. The material used for such trays is 2 mm stainless steel welding rods.

When I queried nearby workshops they said a TIG welder is needed to weld such material and it is very difficult to weld such thin rods: they bend or lose temper. I don't have a TIG welder. Is there a cost-effective and simple way to do this?

I also found an article about soldering stainless steel. I have a soldering iron. Can stainless steel be soldered with the soldering iron used for circuit soldering? What type of flux and lead would I need? Will it produce an effective and permanent bond?


texts: Why don't we use feather like structures for hang gliding?

texts: I'm not entirely sure if this is the right site for this question, but I recently went on a Greek Myth Binge and came across Daedalus again, and his famous first hanglider, made from feathers. Now, obviously this wouldn't work, even if we ignore using wax as a glue and the heavy structure and short wingspan, the feathers of normal birds are likely to small for human sized wings, and too fragile. And today, we of course have hangliders, but they're made from fabric or similar things, and I was just wondering why we don't use modern technologies to imitate feathers, of course optimized for human use. Would these hangliders be less effective than our ones? Or too expensive/complicated to build and maintain? Is it even possible to build a feather based hanglider? Why or why not?


texts: What is the best way to find solved problems similar to the one at hand?

texts:
This is a general question, so sorry if it breaks the rules. However, I think it is very important as more often than not someone else has already solved a similar problem that can be applied to solve the problem at hand or at least give clues on how to proceed.

For example, I was trying to figure out a way to distribute fluid flow evenly across several openings in a channel. Luckily a short google search revealed an article ”Flow distribution in manifolds” which was precisely what I was looking for.

What do you think is the most efficient method of finding similar problems that have already been solved?


texts:
I made a mathematical model (transfer function) of a rlc circuit. I simulated it in matlab simulink with step input and square wave input and observed the result. I can also calculate this system with step input since its transfer function is simple 1/s. But i do not know how to calculated square wave transfer function. Is there a way to find square wave transfer function or just i have to break the signal in to high or low form.
THanks


texts:
Hey I was wondering what kind of chassis, wheels, gears are for a robot with a lot of torque. Please help. I have decided on a trapezoidal chassis, and I know that the servo connects to the small gear and the wheel connects to the bigger gear. But I do not know what the optimal gear ratio should be and size of the wheel. Also should I have 4 wheels (two in the back and 2 small ones in the front.

The competition is to see if you can pull the other robot in a tug of war. It is going to be happening on a typical gym floor at a school. We are provided with only two servos, and we can make any design that can move and work for the tug of war.

The robot has to be 8" x 8" x 8" and should not exceed 2 lbs.
There is no budget, and I am building this for real, not fiction. I'm planning to laser cut the chassis but I don't know how long and wide it should be. We also can laser cut wheels (I don't know if I should use 4 wheels or 3). If I am going to do the tracks (like on a tank), how would I do that? Does it require 4 servos and 4 different gear boxes?
Also, for the type of gears, which one would be the best?


texts:
I need to cool 3 galons of water from 77 to 32°F to form an ice bank that I will use to cool beer (it is a noble effort, you see).

I figured I need to install a cooling capacity of 0.34 kw to lower the temperature and form the ice in four hours.

I think I should use R134a as my refrigerant, and think I need a 1/2 hp compressor (0.34 kw plus 20%).

I want to use a single 42 feet,  5/16" copper pipe as my evaporator (26°F), and a similarly sized condenser (86°F) hopefully without forced air (ambiente temperature is 68°F), but are most uncertain about these calcs.

Guidance would be very much appreciated...


texts: Is there a mushroom head bolt standard for sizes smaller than M4?

texts:
Is there a standard similar to DIN 603 / ISO 8678 (metric mushroom head square neck bolts) for sizes smaller than M4. DIN 603 only goes down to M5 (please correct me if I'm wrong).

I did see similar mushroom head bolts used in piano actions (which is what I want them for as well) but I can't find any more info than that.
Basically what I'm trying to find is something like M4 screw/bolt with a smooth mushroom cap and without any driving features (no slot). Like a DIN 660 rivet but with threads. Or a small DIN 603 bolt.


texts: I want to build power meter for wifi signals. One way to do it is to use a diode to rectify AC signal and amplify that before measuring. But are there diodes which work at such high frequency? Also, are there other methods?


texts: Would some manufacturing processes be more efficient if driven differentially by a single motor, up to ~150 kW, than multiple lower-rated motors?

texts: I'm writing a discussion paper on the potential energy efficiency benefits of integrating different manufacturing processes by co-location on the same site. One possible field for integration is in the coupling of motors to loads. Motors are not my field, but I know that motor efficiency (within a range of speeds) increases up to about 150 kW. Would it be more efficient for some processes (loads) to be driven by one powerful motor, operating at low torque but differentially connected to loads via efficient transmissions, than using multiple lower rated (and therefore less efficient) motors?  Obviously the efficiency gains would need to be greater than total transmission losses!


texts: How can I make an uncalibrated flow meter for water flows of a few liters per hour

texts:
Or alternately what is the name of the device I'm looking for?

My first thought is to make a narrow V shaped chamber by gluing 1/4" acrylic together with 2 face plates and a mid plate with a triangular hole removed.  The liquid comes in at the bottom and lifts a slightly heavier than water bead.  Faster flow has to get further into the V chamber before it spreads far enough to match the net gravitational down on the bead.

At 10 liters per hour, flow through a 1/4" pipe is about 9 cm/s.

This seems like such a simple way to do it, I'm sure there are off the shelf ones available for a few bucks.  But often searching depends on knowing what it's called.

This is one that I found on ebay, but intended for gasses, not liquids.

this sort of design with 2-4" plumbing is used for pneumatic seed sorters.  However in those, you are indifferent to turbulence.  For this application to have something reasonably repeatable, I think I need non-turbulent divergence.

Purpose:  I'm trying to make a fertilizer injector with minimal pressure drop.  Overall the notion is to put a slight constriction in a 3/4" pipe creating a small (few oz) pressure drop.  Two small diameter hoses connect to the bottom and top of a chunk of PVC pipe with the fertilizer inside it.  Since the pipe is pressurized to the line pressure, the differential across the constriction will move water through the device.

A small valve on the 1/4" line can be used to adjust the flow to put the bead at about the same place each time.

Another thought would be to use something like the IV drip chamber.  This is a comparable flow rate.  For long duration, I don't know if you could maintain air in the chamber.

Are there other effects I could use?


texts: What's the difference between pulsed lasers and frequency combs?

texts: Can you please explain the difference between high-energy pulsed lasers and frequency combs?


texts:
I am struggling to solve this problem and my available time conflicts with my professors available time. Could any of you offer me some help, perhaps describe the method I would use to solve such a problem in a way that I can learn from it?

Thank you. (Problem follows):

The circuit designer wants to change the values of R_1 and R_2 so that the design output voltage v_o = 5 V is achieved when the load resistance is R_L = 200 kΩ rather than at no-load. The actual output voltage must not drop below 4.5 V when R_L = 100 kΩ . What is the smallest resistor value that can be used for R_1?

(R_1 and R_2 are unknown quantities.)


texts: Do LiDAR sensors generate point cloud data from a single collection or build them up over multiple collections?

texts:
I am currently writing a background section on lidar sensing for part of my dissertation. I have either confused myself or not thought on the topic enough and I am attempting to gain a clearer understanding of how, and the form of, data from a lidar camera is produced.
At surface level or in terse summaries of lidar sensing you may frequently see something akin to "lidar sensors produce point cloud data". Though through my research I don't necessarily directly see how this is achieved. For example, in Paul McManamon's work "Field Guide to Lidar" he provides a high level categorical description of lidar sensors

Range-only lidar, or 1D lidar, measures only one dimension: range. 2D
lidar is similar to passive imaging in that it measures both azimuth
and elevation but does not measure range. A common type of lidar is
the 3D lidar, measuring angle/angle/range. A 3D image can be only 3D,
with no grayscale, or can measure grayscale. Polarization and
color(wavelength) are other dimensions that can be measured.

Based on my experience, and McManamon's description of 3D lidar, I have seen two distinct forms of lidar imagery. The first is a point cloud, a set/bag of points in 3D space with no regular structure, grid, or ordering. The second may be described as a "2D depth image". Here the $X, Y$ values fall on a regular grid or structure and have some ordering (almost directly analogous to an RGB image $X, Y$ values) and the $Z$ values are naturally understood and viewed as greyscale pixel values where the grey intensity relates to depth or range from the viewing location.
Thus from my understanding lidar cameras do not directly capture and produce point cloud data, they capture "2D depth images". These images are then translated to some global coordinate space and co-registered. After this process the regular structure, grid, or ordering disappears as the single collections, specifically pixels, are mixed into a true point cloud.
Is this the correct understanding of how lidar sensors produce point cloud data, or is there some form of sensor which natively produces a point cloud from a single image collection?

Hopefully this is a good forum for this question, other sister sites such as Digital Signal Processing and Electrical Engineering seem to specific for this question.


texts: Terminology: Flexible protrusion for a latch

texts: What is the name for a protrusion of material that's built to be flexible in order to act as a latching mechanism? These show up in all kinds of products, but one of the most recognizable is in a snap-fit buckle (below). Is there a name for this component?


texts: Exiting air temperature in direct evaporative cooler vs cooling tower

texts:
In a direct evaporative cooler, dry air is passed by a water reservoir to evaporate water into the air, causing the latent heat of vaporization to be absorbed from both the air and the water; this results in the air leaving the cooler at a lower temperature, as desired. An image for this process is below:

In the type of recirculating cooling tower typically connected to the condenser of a thermoelectric power plant (image below), dry air is passed by hot water coming from the power plant's condenser. This causes water to evaporate into the  air, absorbing the latent heat of evaporation from the water and the air, resulting in a lower water temperature, as desired.

The thing that is confusing me is the fact that evaporation of water into air in the direct evaporative cooler (first image) causes the air to leave the cooler at a lower temperature, but in the recirculating cooling tower, the air leaves at a higher temperature than it came in at. My questions are as follows:

1) What is the main reason for the difference in air temperature leaving each of the respective cooling systems?

2) Is the higher temperature of the air leaving the cooling tower due to sensible heat transfer (from warm water to cooler air) in excess of absorption of latent heat from the air?


texts:
I am checking to see if this is done correctly, the slot is a little confusing for me.

B is a pin in a slot, solve for the spring constant (k) so the 50 lb force applied does not move pin B

Solving for the moment about A I get

50lbs*2" - sin45(N)*3"

N = 47.1 lbs

Then solving for forces in the Y direction I get

k*.125" - sin45(N) ==> k = 33.2lbs/(.125") = 266 lbs/in


texts: Calculate numerical directional derivative on triangular element

texts:
Given a triangle with nodes 0, 1, and 2 where each node is located at $r_i = x_i,y_i,z_i$ for $i = 0:2$ and has an associated scalar value $\phi_i$ at the node, how would I evaluate the directional derivative $\nabla_u \phi$ at the centroid of the triangle at the centroid of the triangular element given the direction $u$.

I've figured out how to evaluate $\nabla_u \phi$ on each edge separately but not sure how to get the value at the centroid.


texts: How much water do steam turbines consume per kWh of electricity generated?

texts:
I know this depends on some factors, and I can only think of these: the inlet steam's temperature and pressure. If there are more factors then please do tell me.
What is the maximum figure in liters for water that is needed per kWh of electricity generated by solar CSP? Figures on the internet go from a mere 4 liters to 70 liters for every kWh generated? What's right and what's wrong?
Note: I am only considering water for steam, NOT for cooling.


texts: Constructing small Kretschmann Surface plasmon set up

texts:
I am trying to build a SPR setup at home which is based off this diagram:

I wanted to try to miniaturize it and had some concerns about my strategy.
So I was thinking I could buy a big prism and maybe use a glass cutter tool from amazon to slice it cross-section wise to make it smaller. Although I am uncertain of this strategy or if there is a better method. As for the laser, I can find small lasers on amazon, but I was wondering which manufacturers could build me a laser smaller than the size of something like a finger nail or even smaller?


texts: Determining compatibility of pressure gauge with sulphur hexaflouride (SF6)

texts:
I have a type of pressure gauge (material in contact with medium: 1.4542 (17-4 PH / 630)²) that I would like to use for sulphur hexaflouride (SF6) at room temperature and pressures of typically 6 bar.

Unfortunately, the manufacturer is not really interested to support me with information if this sensor is compatible with SF6, either they tell me to find out myself or just not to use it.

So I wonder - how would you approach this issue, what limiting factors other than the material in contact with the medium and the max pressure could there be?


texts: Plastic deformation due to the motion of dislocations

texts:
In this picture do we speak of (microscopic) plastic deformation if the edge dislocation has moved all the way to the right and emerges out of the surface? Or if you apply shear stress and stop when the edge dislocation has moved from A to B is it then plastically deformed aswell?

How about with this situation? Is it only plastically deformed when the dislocation line has moved all the way to the left and thus the screw dislocation emerging from the crystal?

Ow and one last small question:
'before and after the movement of a dislocation through some particular region of the crystal, the atomic arrangement is ordered and perfect; it is only during the passage of the extra half plane that the lattice structure is disrupted'

This particular region is that the region B to D, when the dislocation starts at A and moves untill emerges? And if the dislocation motion stops while the edge dislocation is at position B or C then this region isn't ordered and perfect? Because there is a linear defect in it?


texts: Did a RTC solar tracker need any photosensor?

texts: I planned to do a solar tracker for my project and I am going to make a RTC solar tracker(actually still considering). So, do I still need photosensor like LDR for tracking the sun?


texts: Calculate Rolling Resistance Experimentally

texts:
I am trying to calculate the exact rolling resistance ($F_{rr}$) of my car. The approach I am going with is a coastdown test at a low speed so no drag slows down the car. From there I am going to measure the speed of the car several times and find the acceleration and therefore $F_{rr}$. With the help of an online polynomial regression, I am going to find the function of $F_{rr}$.

However, I am not sure if my approach is correct and if the function that I am going to find is indeed capable to give me the $F_{rr}$ at higher speeds.


texts: How was the trajectory of the V2 ballistic missile (during boost phase) calculated?

texts:
I'm well aware of Helmut Hoeltzer's "Mischgerat" analog computer, and I read that it not only served as a kind of "fly by wire" computer on board of the missile, but also as a simulator on the ground that calculated V2 trajectories.

But, I didn't find any clue about how it did it -  how Hoeltzer calculated optimal trajectory to hit the target (cities). I think the trajectory had to calculated accurately because only by following an accurate trajectory a ballistic missile could hit a city sized target.


texts: What is diffusion in the context of compressor?

texts: When studying about the axial compressor, I came across the term 'diffusion' being used to explain the conversion of kinetic energy to pressure, also terms like 'diffusion factor'. What is being diffused in the compressor?


texts: How do I find the closed loop pole at A?

texts:
This is the question

What is the damping ratio associated with the pole at A'? Using the values
of a and b from (a) above, determine the closed loop poles atA' and the
corresponding value of K for this pole. Do not read the value of `A' from the
gure.

The above is the answer provided by the lecturer. I understand most of it except that I dont understand how did he get the expression highlighted in red. Could anyone explain to me how he did that?


texts: Mirror-like reflective liquid crystal display panel

texts:
I can't find any information about this on Google, so I thought I'd ask it here.

I am looking for a LCD Screen-like panel which uses a mirror-like liquid crystal so that I can make a pane of glass into a mirror electronically.

The "pixels" do not have to be as small as a normal LCD display,
in my case I want "bands" of pixels that have a dimension of 30x2 centimeter.

So it's not really a display, it's more like a dynamic mirror.

Does this technology exist? I remember seeing something like this a couple of years ago but I can't remember where.

For my prototype I'd have a big glass panel resembling a window, and using for example an Arduino I'd like to switch some segments of the panel on or off, and those segment will reflect light with a mirror-grade finish.


texts: How to calculate Reynolds in rectangular pipe

texts:
I work in a lab and i was given the mission of identifing the reynolds in a square pipe, in different flow rates
I have the dimentions of the rectangle - 5cm X 6cm, and I have the flow rate. the fluid is air (so I also have the charecteristics of the fluid)
what is the characteristic length here? and can i assume the speed of the air is the same in all the cross section? (we are talking about q between 30-100 m^3 per hour)

thank you.


texts: Normalization and Non-Dimensionalization of a mass balance equation

texts:
I would like to ask what is the difference (if any) between normalization and non-dimensionalization. I will try to explain what I have done until now with an equation that I would like to work with and you can make your comments on this specific example. The mass balance is given by:
$$\frac{\partial C_{i}}{\partial t}=-u_s\frac{\partial C_{i}}{\partial z}+\rho_b \sum_{k=1}^{N_{reac}} \nu_{j,k} R_{i,k}$$
If we choose as characteristic values the:
$$L_o, F_o, T_o, P_o, m_o$$
$$u_o = \frac{F_o Rg T_o}{P_o L_o^2}$$
$$C_o = \frac{P_o}{Rg T_o}$$
length, molar flowrate, temperature, pressure, mass accordingly, and by substituting then we get:
$$\frac{u_o C_o}{L_o}\frac{\partial C^*_{i}}{\partial t^*}=-\frac{u_o C_o}{L_o}u_s^*\frac{\partial C^*_{i}}{\partial z^*}+\frac{m_o}{L_o^3}\rho_b^* \frac{F_o}{m_o}\sum_{k=1}^{N_{reac}} \nu_{j,k} R^*_{i,k}$$
where $^*$ denotes the dimensionless (?normalized?) variables. After some more calculations we get:
$$\frac{\partial C^*_{i}}{\partial t^*}=-u_s^*\frac{\partial C^*_{i}}{\partial z^*}+\frac{F_o}{L_o^2 u_o C_o}\rho_b^* \sum_{k=1}^{N_{reac}} \nu_{j,k} R^*_{i,k}$$
BUT
$$\frac{F_o}{L_o^2 u_o C_o}=\frac{F_o}{L_o^2 \frac{F_o Rg T_o}{P_o L_o^2} \frac{P_o}{Rg T_o}}=1$$
So is this equation normalized? or non-dimensinalized? Shouldnt there be some Peclet / Reynolds etc number to work with? If for example I try to change the inlet conditions then this number ($\frac{F_o}{L_o^2 u_o C_o}$) will still be equal to 1. Can anyone point out a book or a site where I could read and understand more about this subject?

Thanks in advance!


texts: How to calculate airflow in m3/min on a gas turbine outlet?

texts:
I'm currently trying to figure out the airflow of a gas turbine in m3/min.

I thought that i would be able to measure the windspeed over a known cross section on the intakte of the turbine and then air in would be the same as air out.

I was then told that this is not true for gas turbines due to compression of some sort.
If air mass in is not equal to air mass out, how do i then calculate/measure the airflow.
For further info i have the following specs on the turbine:

Thrust in N
EGT in °C
Massflow in kg/s
Exhaust gas velocity in km/h
Power output in kW
Fuel consumption in ml/min


texts: Angled Nozzle on Pressure Vessel - Weld Preperation

texts:
I wonder if anyone can help!
I'm trying to model 3D geometry of nozzle to shell weld. I am having issues ascertaining correct bevel angle at a given point.
Surely the bevel angle would change due to the relative angle between the nozzle and shell around the nozzle?
UW-16 doesn't seem to define?


texts: Control Partitioning in presence of external disturbance force

texts:
I am simulating the dynamics of a control system that has been designed using the control partitioning technique (model-based control + servo control).
I am having a query for the case when an external disturbance is present in the control system.
So there are a couple of configurations that are possible:
Number 1:

Number 2:

The only thing which is different between the two architectures is the summation block where the disturbance force is introduced in the control system.
The thing which is confusing me is that all the literature and books I have referred to use the 1st architecture but formulate the closed-loop dynamics according to the second one.
In the presence of disturbances both the systems show tangibly different responses for the same controller properties, a few examples given below:
Impulse force applied on the system at 5 seconds

Continuous Static Disturbance on the system:

Along with the different responses, the actuator efforts will also be different.
This is making me confused as to which architecture will be a truer representation of the actual response of the designed control system in presence of disturbance forces.
I hope my question makes some sense and will provide further elaboration if asked for!
Thanks in advance.


texts: Best way to resume aborted cnc job without endstops by zeroing in on known hole…?

texts:
I have a very simple little T8 CNC without endstops that I use for PCB's. After a failed drill job, the position of the machine is lost and I would like to resume the job.

The machine is running GRBL 0.9 and I'm using UGS for sending the gcode.

So I would like to be able to jog the machine to match a known hole that's already been drilled and then say "hey, you're now at position x, y", but I can't seem to find either a gcode or function in UGS to do this. Is there any such gcode?

My workaround is currently to jog to a known hole, reset to zero, then send gcode to move to the inversion of that known hole and set zero again. Is there any smarter way?


texts: How does a USB plug fit into the receptacle

texts:
I hesitate to ask this on the EE site because it's not really an EE question. I'm more interested in the mechanical forces that keep an USB plug from slipping out of the socket.
I am asking because of the common issue of USB-c plugs becoming loose over time, compared to USB-a plugs which do not seem to have this issue. I wonder what is reason behind this. Is the mechanical structure of a USB-c plug considerably different than a USB-a?
Also, last time I went to have mt phone checked up, I was told that the "sensor" of my phone is misaligned, hence why my plug keeps falling out. I don't understand what the "sensor" being referred to was, nor can I find it on the typical USB-c pin layout. Some explanations on this would be much appreciated.


texts: Ventilation requirements of a closed housing of a video wall

texts:
Our company builds rather large video walls that are driven by computers next to them. In one of our current project the size of the installation is 21 55" displays side by side in portrait mode and 4 computers. The total heat dissipation would be maximum 8000 W, distributed evenly along the housing. This whole setup is in a standalone, about 15 meters long installation. Both the displays and the computers implement forced heating internally.

The interior decoration company that builds the housing asked the question: How big and what kind of ventilation holes should they plan for?

I was searching the net and found certain solutions and online calculators (https://www.engineersedge.com/heat_transfer/convection.htm), also a related question here on Engineering (How to design a cooling chimney for a computer server?) but these are concerned with surfaces being cooled.

In my case the surfaces are irrelevant -I would think- as all devices have forced cooling, therefore I should care about the warm air they produce and push out of their individual chassis.

Please give me a handle, what is the best approach to calculate the venting hole requirements.


texts: Damage to electronics from lightning strike at a distance

texts: Electromagnetic pulse is said to detsroy electronics. Lightning is a type of EMP. As per my understanding lightning is basically a dielectric breakdown, it can be considered as DC current. Can it or any dielectric breakdown damage electronics from a distance, say 1m, 10 m , 100m or 1 km? If yes, how is that possible, because it cannot induce voltage in any wire as it is DC? Even if it is AC of few Hz, the length of any household wire will be very small as compared to the wavelength, then also there will be huge resistance to any volatge induced.


texts: Why isn't von Mises criterion valid when compressive and tensile yield stresses differ?

texts:
For example here, it is mentioned:

The von Mises criterion is NOT a valid yield (failure) criterion for materials with different yield stress values
in tension and compression.

I can't really understand why this is true. I can't really think of a reason why it should not be true either, but I would like some rigorous reasoning behind this statement.
I also have some lecture notes (in my native language, not English) that state that to be able apply von Mises criterion, the compressive limit has to be slightly bigger than the tensile one. So which of these statements are correct and why?


texts: Dimensioning of beam pressed by screw in assembly

texts:
I need help dimensioning a screw-beam system of a press. I built one prototype but the beam is bending too much.

Below is a sketch of my press. In the middle it has a fixing screw which presses downwards on a beam (3D printed plastic) that presses down my Device Under Test (DUT). The problem is that the beam bends too much so it doesn’t apply pressure evenly downwards on the DUT.

(I used plastic instead of a harder material because I have access to a 3D printer but no access to a workshop)

I did some research and found in the book “Mechanics of Materials” of Gere and Timoshenko following formulae for displacement $\delta$:

$$
\delta = \frac{F\cdot L^3}{48 \cdot E \cdot I}
$$
F = Force downward
L = Length of beam
E = Young's Modulus
I = Moment of inertia

And for the moment of inertia:

$$
I = \frac{b \cdot h^3}{12}
$$

So that I have

$$
\delta = \frac{F\cdot L^3}{4 \cdot E \cdot b \cdot h^3}
$$

I believe I can specify a maximum displacement $\delta$ of let’s say 0.1 mm and the compute the necessary beam height $h$ or choose another material with a higher Young’s modulus E

My first question is: How do I compute the force F that the screw is foing downwards? I tried looking in Shigley’s “Mechanical engineering Design” Chapter about screws but couldn’t find anything.
My second question is: Is my dimensioning approach (to specify a maximum bending) correct?

Thanks in advance!


texts: Can someone export file from prt.1 to step?

texts:
I have 2 files in prt, and I need to render this parts but my software can't open this.

Could someone export this files for me to step?

https://www.dropbox.com/s/m9ysajdp6vo89od/pokretlo1.prt.1?dl=0

https://www.dropbox.com/s/nkgqe9scxhjqsw0/pokretlo2.prt.1?dl=0


texts: Is thermal conductivity a property that affects the use of an alloy in high-temperature applications?

texts:
I'm interested in the effect of thermal conductivity on the choice of materials used for high temperature applications such as turbines.
For the particular case of Nickel-Chromium alloys (such as René 41 or Udimet 700), I have found that electrical conductivity is lower than the thermal conductivity of other metallic alloys.
Is this because it is enviable to have a low thermal conductivity in a high temperature application? In this case, why is it enviable?
Is the low thermal conductivity just the result of the alloy's composition and processing but not necessarily wanted?
Thanks!


texts: I have trouble solving part A of the question. I thought the resulting torque would just be 10k * L of the beam.


texts: Will electroplating a ventilated brake rotor with copper improve its cooling capacity and maximum its lifespan?

texts:
Since copper is excellent at dissipating heat and does not rust, I am surprised that brake manufacturers do not electroplate cast iron/steel brake rotors with a thin layer of copper (~.5mm). There are brake manufacturers who offer brake rotors with cadmium or zinc-plated coatings at an additional cost but these coatings usually do not last long especially in areas that use a lot of rock salt.

I think copper plating would be the most ideal coating for ventilated brake rotors since it should keep the cooling vanes from rusting and becoming clogged with rust.  Clogged cooling vanes reduce the rotor's cooling capacity resulting in higher temperatures, faster rotor wear, premature warping, and a shortened lifespan.

Moreover, since copper is very good at dissipating heat, air flowing through copper-plated cooling vanes should draw away more heat from the brake rotor, resulting in a cooler ventilataed brake rotor, maximizing or perhaps even extending its intended lifespan.

Also, since there should be almost no rust on a copper-plated brake rotor, removing an worn out, copper-plated brake rotor should be no problem. Anyone who has worked on brakes knows how time-consuming it is to remove a rusted-on brake rotor or drum.

The brake manufacturer should not electroplate the friction areas (as shown in the picture below) since the high pressure and friction from contact with the brake pads would most likely warp the copper coating, but all the other surfaces would have a copper coating, most importantly the surfaces of the cooling vanes.

Will electroplating a ventilated brake rotor with copper improve its cooling capacity and maximize its lifespan?


texts:
I have an MDOF system with 4 degrees of freedom with forced input at one of the dof (4th dof)(it is a sinusoidal wave with a particular frequency expected to be generated using a shaker); displacement response is measured for this system. I would like to extract mode shapes for this system experimentally, but in order to achieve this objective I took up a theoretical case for understanding various complications and problems in it. So, now my system can be represented as:

  \begin{equation}
G_{YY}=H G_{YX}
\end{equation}
  \begin{Bmatrix}
Y_{1}\\
Y_{2}\\
Y_{3}\\
Y_{4}
\end{Bmatrix}=\begin{bmatrix}
H_{11} & H_{12} & H_{13} & H_{14}\\
H_{21} & H_{22} & H_{23} & H_{24}\\
H_{31} & H_{32} & H_{33} & H_{34}\\
H_{41} & H_{42} & H_{43} & H_{44}&
\end{bmatrix}
  \begin{Bmatrix}
0\\
0\\
0\\
X_{4}
\end{Bmatrix}

Here H is the Frequency Response Function (FRF) and it can be seen that only one column would be needed to obtain the mode shapes of the system. Now, writing a code on matlab give me:

> FRF(i,:)=GYY./GYX
> plot(fr,abs(real(GYY./GYX)))

The amplitudes and shapes could be extracted from the above expressions, but my concern is on obtaining mass normalized mode shapes, i.e.
\begin{equation}
\phi^{T}\left[M_A\right]\phi=I
\end{equation}
If I am not wrong, it should be possible in the case of input + output experimental modal analysis. I know that there would be many complications but at least in the case of a theoretical case it should come right. I generated a code for the above case by using mdof equations of motion for a  4dof MDOF system:

This is what I am supposed to get, as verified with eigen analysis of the mass M and stiffness K matrices:

   -0.1442    0.3651    0.4152   -0.2710
   -0.2710    0.3651   -0.1442    0.4152
   -0.3651   -0.0000   -0.3651   -0.3651
   -0.4152   -0.3651    0.2710    0.1442

But from the frf the the first mode shape is extracted to be:

0.0098
0.0186
0.0254
0.0296

It looks porportional with the actual one but is not scaled to the real values to satisfy mass normalization.
Where am I going wrong?


texts: How can I build propane torch burners that have a custom configuration?

texts:
For doing hard soldering I would like to have a propane burner with a custom configuration. The reason for this is that when soldering there is a region that ideally should be heated slowly, consistently and steadily up to the soldering temperature. Unless the area is small, this is usually not possible with a conventional torch head.
The most usual need is for a linear burner. So, for example, there might be an angle iron that is say 8" long that needs to be attached to a plate. So, in that situation I would want a burner that it is in a linear configuration about 8" long. Also, since the center of the region would get hotter faster, Ideally I would like to adjust the flame in the central orifices of the burner to be lower than the flames on the edges.
How can I build custom burners like this? Is it as simple as tapping an iron pipe and inserting orifices, or are there additional complexities? How do I find out more about the engineering of such burners?


texts: Calculating Z-axis Torque on a 3-D Printer

texts:
I recently built a large CoreXY 3D printer and I am wondering if my 4 z-axis stepper motors combined will have enough torque to accelerate the build plate with a heavy 3d print. During the building to designing process, I noticed the majority of people who build 3d printers, such as myself, do not calculate the required torque needed to accelerate the print bed. Most people just look at existing designs to see what has worked or fail and slow the acceleration in the firmware to a minimum.
I think it would be useful to the 3d printing community if someone could demonstrate methods to calculate the required torque for the CoreXY printer below? The following information may be of use.

Build plate:
635mmx610mm and 6.35mm thickness Mic6 aluminum, mass 6.64kg. Mass of frame
for build plate is ~1kg. Total load on z-axis ~7.35kg.
The 4 z-axis steppers on the bottom make a rectangle that is 543.64mmx789.9mm.
Z-axis spans about 625mm.
Z-axis acceleration: 0.5 m/s2
Z-axis top speed: 10mm/s

Motor torque specs can be found in the pictures below.

Edit adding dimensions of all rotating bodies.  Units are in mm.


texts: I was wondering why carbon nanotubes are not used as artificial muscles yet? I mean they behave similar to real muscles, only that they expand horizontally. What are the current challenges that researchers are facing?


texts: What is the most accurate geometry to represent earth

texts:
Currently software and maps represent earth in many different ways, the latest is Point Clouds as this is the most common surveying tools currently available. For the needs of visualisation, construction etc. this seems to suffice for now. Not sure this is an engineering question but I tried in the philosophy forum and been advised this is applied science.

What is the most accurate representation of earth in a digital format (or mathematical equation):

3D splines
solids and primitives
breaklines/contours
polygonal mesh, TIN
square 3D pixels

?


texts: As I understand from theory that two integrators are required to provide zero velocity lag in a type 2 servo system.  My question is how does 2 integerators help to nullify velocity errors. Less of maths with intuitive  explanation will be useful


texts: Computer engineers -- do computers use varying amounts of power?

texts:
My friends and I are trying to hypothesize how computers use energy. Please settle the debate. Do computers, or any other electrical device of the sort, e.g. 3d printers, use different levels of power from an outlet when completing different tasks? For example, if I keep my charger in the outlet constantly, using it only for, say, emailing, does it use precisely the same amount of power if I were to keep my charger in the outlet constantly, while farming bitcoin, or playing a graphically intensive video game? Can the computer ask the outlet for more power (not more than the outlet is capable of, but in relation to how much it usually uses in menial tasks); or does the computer get the exact same amount of power, keeping it at full throttle, insofar as it is connected to the outlet?

Edit: analogous: for example, assuming my charger stays in the outlet at a constant rate (never being unplugged), will my electric bill increase or stay the same depending on whether or not I email, or if I play graphically intensive video games?


texts: In a device tree for AM335x, how do I know what pinctrl values to use?

texts:
In the Linux kernel's dtsi file (am335x-bone-common.dtsi) for the AM335x processor, there is the am33xx_pinmux tree, with values like this:

    i2c0_pins: pinmux_i2c0_pins {
        pinctrl-single,pins = <
            0x188 (PIN_INPUT_PULLUP | MUX_MODE0)    /* i2c0_sda.i2c0_sda */
            0x18c (PIN_INPUT_PULLUP | MUX_MODE0)    /* i2c0_scl.i2c0_scl */
        >;
    };

How do I know what values to use for the pinctrl-single,pins entry?


texts: How to repair stripped, leaky pneumatic fitting?

texts:
I have a pneumatic cylinder with a stripped fitting, which causes a slow leak. I took it to a machine shop and he tried to re-thread it but there wasn't enough good metal left to get a good thread. He told me there wasn't enough room for an oversize fitting and suggested I try liquid thread sealant.

Unfortunately, this hasn't worked. There is still a slow leak.

This is for a DIY RV loft type bed that uses 4 pneumatic cylinders to lift the bed up toward the ceiling, which will never need to support more than about 25 LBS or so - just the weight of the bed.

I'm thinking I should maybe try Blue Block or epoxy, but hoping to get some advice first.

Much thanks...Jon


texts: Kinematics Mechanics Find the length of the belt and the speed of the rack

texts:
For A. I know that the formula for belt is simply
$L=\frac{Pi(D_a+D_b)}{2}+2C+\frac{(D_b-D_a)^2}{4C}$

Which gives me $L= 116.99"$ since C is equal to $50$

For B. However I'm stuck and can't get the speed of the rack, I think it moves to right based on my inspection.

So I got stuck after solving rpm of Pulley B which is $40$rpm from from velocity ratio of $3:1$ from $(N_aD_a)=(N_bD_b)$ now i know that shaft C is turned 3 times for every 2 times of B. My problem is I need to get the diameter of gear B to relate it to Gear C that drives the same as gear 2.

Please include your formulas and show your solution.


texts: What is the difference between hydraulic and ABS brakes?

texts: Recently I read an article about ABS brakes. In that, they repeated several times the term that traditional hydraulic brake replaced with ABS brakes. Why it so? The reason for choosing ABS is mentioned in that article. Is anybody knows about it?


texts:
I'm trying to figure out how to construct a CNC XY table, ala this instructable:

https://www.instructables.com/id/Low-Cost-Hobby-Servo-XY-Table/#discuss

I'm a noob with mechanical design/mechanical parts, so I don't understand a lot of what this guy is saying. One of those things though, is that you can use (paraphrasing here, with limited understanding) a 10 turn potentiometer with a servo to ... make a motor?

What I'd like to know is, what is a 10-turn potentiometer? Is that somehow different from regular potentiometers? How do you modify a servo with a potentiometer, and how does that allow you to turn something more than the 180 or 90 degrees that a servo allows?


texts: How to make sure the material is titanium?

texts:
I am looking for non-destructible way which can be performed in home conditions to tell if the material is titanium (in my case it is a mug). Advices like "grind it" or "use electronic microscope" could be useful but I cannot apply them as stated above. I am targeting primarily aluminium and steel alloy because of their competitive prices and availability. In pure form detection would be easy (weight) but what about the alloy?

I am also asking for non-expert level ways -- I can weight something, boil water, measure temperature or resistance, those kinds of stuff. I am not a chemist for sure.


texts: What is the Gear Transmission Error and How would a Signal Analysis look?

texts: I understand the Transmission Error is the displacement error of the gear shafts, but if measured how would the signal over time show and why? if its a sinusoid would that mean that only a few times per cycle the displacement occurs or is it always present?


texts: Can i switch negative feedback to positive feedback in PID control?

texts:
I am learning Control Theory and i have a confusion about whether the following PID controllers are interchangeable or similar.

Are they equivalent? Why?
Is there any difference in how i would implement both of them in code? I have to program this in Arduino.

Here is the first control loop which is the normal definition of a PID controller:

And here is the changed one with the negative feedback changed to positive and the setpoint changed from positive to negative.


texts: What kind of materials are plastic syringes made from?

texts:
I'm trying to figure out what kind of materials my disposable plastic syringe is made from. I have a Medefil MIS-1130 syringe and when I visited the company website I couldn't find any information on what the disposable syringes were made from (although they did tell me a lot on what's NOT in them).

I'm trying to find a regulation or something that could help me identify what kind of plastic and rubber are used to make the shill, plunger and seal that make up the disposable syringe. Can anyone on here please give me some guidance?


texts:
I got this stand from a friend of mine years ago. Its unbranded. I want to use it to hold a 55 gallon fish tank which can weigh about 456 pounds to 622.5 pounds.

How can i calculate a estimate of how much weight this stand will hold ?

The wood is 61 in by 17 in and about 3/4 in thick. The metal underneath it is 2 inches. The metal legs are 28 inches high and 1 inch on each side.

If not, then is there any way i can easily modify the stand for more support? Perhaps stick some 2x4s or cinderblocks under it?


texts: Computing error dynamics from state space deadbeat observer

texts:
I'm trying to solve this problem:

  Given the transfer function:

  $$ G(z) = \frac{z^{2}+2z+1}{z^{3}-z^{2}-5z+1} $$

  Design a deadbeat observer for this transfer function and compute the
  error dynamics $e(0)=e$.

I know that to design a deadbeat observer, you should first convert the transfer function to an observable canonical form, then design your observer to place the poles of the transfer function at 0.

I know that $e(k+1)=(A-LC)e(k)$, which I'm guessing I have to use. I can find the matrix $(A-LC)$ but not any of the other matrices. This is where I'm stuck; how do I compute the error dynamics?


texts: grey cast iron from freezing point to room temperature (cooling process)

texts: Do grey cast iron expand from freezing point to room temperature (cooling process)?


texts: How do I interpret a fillet indication on a technical drawing

texts:
I'm reproducing in Fusion 360 an object based on a technical drawing, but I have trouble understanding what this means:

When I read the Wikipedia article on Engineering drawing, abbreviations and symbols, it states:

Radius of an arc or circle. Flats and reversals (falling within the dimensional tolerance zone) are tolerated unless "CR" (controlled radius) is explicitly specified.

But I still don't understand how this radius is being measured and therefore how to reproduce it.


texts: Trying to visualize the resulting interaction between two pulleys

texts:
I'm trying to get an answer for something potentially quite simple, but I can't visualize it (nor do I have the parts yet to build it). It's for a little hobby project, but I'm slightly concerned I have made an assumption about what will happen, which may not be correct. I've drawn the problem below.

In essence you have two pulleys connected by a timing belt.

Pulley A = 80 Teeth
Pulley B = 120 Teeth

Pulley A is static, it does not rotate at all. Pulley B is free to spin around its own axis. It also then rotates around the axis of A, keeping the timing belt taught.

In one revolution of pulley B around the axis of A (dotted line), how many times would pulley B have rotated?

My assumption would be that it would be 2/3 rotations of pulley B for every time it does an entire revolution around pulley A.


texts:
Updated with comments/answers from community to make more complete
I'm trying to understand why gears are designed in some specific way instead of another. So far my understanding is that:

energy is preserved (- some loss due to friction)
if the speed of rotation is changed
then the force/torque is inversely & proportionally changed

Criteria I'm aware of are:

speed: how much to increase/decrease
force/torque: how much to decrease/increase
backlash: lost motion due to gap between gear teeth which can cause precision issues
robustness of gears: strong enough to handle increased torque?
angle of rotation: eg change 90 with worm gears
direction of rotation: whether we want input/output rotate in same direction
wear and tear: due to contact/force applied by gears on each other
space available: to fit the gears

And some business criteria such as cost & availability of the parts.

QUESTIONS:
-Other than those listed above, are there any other considerations when designing gears?
More specifically, if space,cost,availability weren't concerns, would there be any reason why someone would favor a design with fewer gears (eg A) rather than more (eg B)?
A: 8:1 ratio with 2 gears (64 teeth -> 8 teeth):

B: Same 8:1 ratio with 4 gears (2:1 ratio on the 3 driven gears, taken from here)


texts: What is the simplest spring system that could produce recoil absorption comparable to that exhibited by the AA-12 assault shotgun?

texts:
In this video, the video emphasises the very low recoil level of the AA-12 fully automatic shotgun. In particular, at this point in the video the presenter uses one hand to relatively lightly grip the gun while firing 300 rounds per minute. Note that the presenter does not brace the shotgun against his shoulder.

The image below is a frame from the video at 5m:03 - it shows the gun in"mid burst" - two cartridge cases can be seen in the air, one having just been ejected and the other is closer to the camera. The users 'stance' appears to be intended to show the effortlessness of holding the gun while firing. If he is in fact using typical 12 gauge shells (which he implies that he is), holding a "normal" shotgun like this when firing would result in it being torn from his hands.

In the video the presenter claims that the shotgun exhibits, for all intents and purposes, zero recoil. He remarks that there is a spring system in the buttstock that counters the momentum of the recoil.

I can think of two ways that the spring system could work:

The first recoil (or something else) compresses the spring, and then the spring extends upon the generation of the second recoil.
Each recoil compresses a stiff spring that extends more slowly than the recoils compress it. Assuming a sufficiently quick firing rate over a sufficiently protracted period, complete compression of the springs would obtain; consequently, the user would need to abstain from firing the shotgun until the springs extended, lest s/he absorb the recoil herself.

However, it seems to me that those systems would work only if the user braced the shotgun against something (i.e. his/her shoulder).

What is the simplest spring system that could produce recoil absorption comparable to that exhibited in the video?


texts:
As far as I know, propane with oxygen will burn at 2800 °C and steel will melt at ~1500 °C. Brass is even less.

What I am trying to do is a rocket nozzle.

Is there a way I can built this with steel or is it simply too hot? And for the burning temperature of propane, 2800 °C, is it the temperature IN the nozzle, OUT of it, or IN the combustion chamber?


texts:
For the sum of forces about x axis = 0  , how do we know there is a 1.73kN force and also the 0.81kN force ? Where are they coming from ? Can someone explain about it ?

Secondly , where are the fixed moments of 100kNm come from ?


texts: What changes can be made to a whistle to change these variables?

texts:
I have read that the longer the whistle the lower the pitch and the shorter the whistle the higher the pitch.

But there are other factors. Pressure, size of the inlet, size of the outlet, diameter of the whistle... what changes occur to the whistle when these variables are changed?

More importantly, is there a way to change the threshold of when the whistle starts making noise?

For example: I want a whistle that only makes noise between 1 and 2 pounds per sqft of pressure. Outside that range it is quiet. Is it possible?

The source of the 20 mph airflow is after the whistle and increases in pressure over time, 30+ days, so when the pressure goes beyond a specific point, I'd like a whistle so I can hear it. What variables need to be considered when designing a whistle that can do this? And how would you do this?


texts: I am always fascinated to watch construction on field as it  helps me to build my knowledge deeper. The answer to a question what I am looking upto is HOW is the brick size decided ? Like in India we have standarized size of 19×9×9 cm But actually how only this size became standard?


texts: Looking for feedback on a lift bed power lift mechanism

texts:
I built a king size lift bed.  I want to add a powered lift mechanism to raise and lower it to access the storage area under it.  In order to get the height I want when the bed is raised, I'll need about 20° of lift, which will raise the foot of the bed up to about 46".
I have a pair of linear actuators I would like to use to do the lifting.  Each has 12" of travel and is rated for 200 pounds.  Currently, it requires about 85 pounds of lift to raise the bed.  The base of the bed is 14" high, and the lift needs to be inside the bed, so it cannot be higher than 14" when the bed is lowered.  Those are my only real constraints.  The bed frame itself is made from 1x2" 14ga steel tube, and the frame supporting the mattress is 3/16 2"x3" steel angle.
My plan is to have a pair of scissor type lifts, one on each side.  The lower part of the lift would be connected to the base via a pivoting rod, and the upper part of the lift would be similarly connected to the bed frame.  The actuator would press on the joint on the lifts to raise and lower the bed.  The actuator would be aligned so it is even with the center of the lift when the lift is down.  This will allow the most direct force from the actuators when the mechanical advantage of the lift is lowest.
If the legs on the mechanism are 13.75" between pivot centers, it would be 12" high when closed, and have a vertex angle of 64°.  When the actuator fully extends, it should raise to 27.5".  By placing these lifts about 45" from the head of the bed, it should have the desired result.
So, are my numbers correct and am I on the correct path, or is there an easier way to accomplish my goal?  See image below for a visual on what I am thinking.

I have or have access to a fairly complete welding and machine shop, so I can do a reasonable amount of fabrication.


texts: I want to determine the point where the maximum stress is located. Also, I want to know how this kind of questions is answered.


texts: How to draw the velocity and acceleration diagrams if there is no connecting rod between the pins?

texts:
From the previous examples I've seen, there is a connection rod, for example, between a and c and then another rod from c to one of the pins. However, in this case, the rod ac is directly connected to another pin? I assume there is no relative velocity in this case. Is this assumption correct?

EDIT: By pins, I was referring to O2 and O8. I've just realised that C is a slider. I thought it was a rigid 'pin' like O2 and O8. Sorry for the confusion.

So I think I know how to approach this problem now. Va is perpendicular to OA. Vc is a horizantal line from O2. Vc/a is perpendicular to the rod AC starting from Va.Then I need to intersect Vc and Vc/a to find the magnitude of Vc. Is this approach correct?

EDIT 2: I'm running out of time. I quickly sketched this to check if I'm on the right track.


texts:
The question says, "Perform RM scheduling for the following task set: T1=(2, 0.5, 4), T2=(3, 1, 10), T3=(5, 1, 10) and T4=(7, 0.45, 15)".

Here the standard notation (Period, execution time, relative deadline) is used.

I understand that the priority will be as follows: T1, T2, T3, T4

In this case, job T1 is released consuming time 0 to 0.5 and then job T2 is released consuming time 0.5 to 1.5. At 2, job 1 needs to be released again and hence I cannot release job T3 from 1.5 to 2.5. Can I skip priorities and release job T4 from 1.5 to 1.95?


texts: Rotational bending in Timoshenko beam theory

texts:
The Wikipedia article on Timoshenko beam theory says:

  The model takes into account shear deformation and rotational bending effects,

I am familiar with shear deformation, but what is meant by "rotational bending"? Google search yields no good explanations of the term, so what do we mean by that? What kind of rotational bending does the Timoshenko model account for that the Euler beam model does not?


texts: Compute compressive forces necessary for thread rolling

texts:
Is there a mathematical method or reference source/handbook for computing the compressive forces necessary for thread rolling? I realize I could use FEM, but that is a lot of work, so I am hoping to avoid it if at all possible.

I am designing a frame that will hold two parallel radial rolls and gearing to drive the rolls into the workpiece while rotating and I need to know the approximate forces involved so I can (1) dimension the frame to be strong and rigid enough, and (2) accommodate appropriate gearing.

The variables are the material being rolled (typically annealed alloy steel or stainless steel), the diameter of the material (expected to be between 1/4" and 3/4") and the thread pitch. The type of thread is Acme.

I am not asking for an answer that computes the compressive force. I am looking for an answer that tells me how to do the computation myself, or at least explains the theory.

I know I can go to LMT Fette and they can just tell me off the bat, but I would rather not be going hat-in-hand to vendors every time I need to solve a problem.


texts: ASCE 7-10, Fluid load factor for basic combinations for strength and allowable stress design

texts:
In ASCE 7-10, with regards to strength design,for fluid load, it mentions that where fluid loads are present, they shall be included with the same load factor as dead load D in combination 1 through 5 and 7. How about for load combination 6?

Load combination 6 is as follows:

0.9D + 1.0W,

which I expected to be

0.9D + 0.9F + 1.0W

However due to the statement in ASCE 7-10, I do not know what factor to assume for fluid load as fluid load will be present in  my situation. The same applies to Allowable stress design load combination albeit with different combination.


texts: What is a PD pump that I can use as an immersion pump for a slurry?

texts:
I need to pump a thick slurry from a tank. The slurry can be pumped, but won't flow well enough that I can use a suction pump from outside the tank. Normally, I'd use a centrifugal immersion pump that can be drawn from the tank for service. But with the thick slurry I need to use a PD pump.

One option that I'm looking at is a monopump housed in a long pipe, so the rotor/stator packet is submerged and operated by a long shaft in the pipe. But this will probably get expensive and I'm open for other options. Another consideration is ease of service, the immersion pump linked above would have to be lifted with a crane out of the tank for service.

The application is agricultural / bio-energy; tank depth is 4m.

So I'm looking for a PD pump that is ...

capable of pumping thick slurries
can be put into my sump pump and retrieved for service with low effort (which probably rules out long driveshafts)

I'm mostly hunting for ideas, no need for a concrete product recommendation.


texts: How to find who occupies pin X in Device Tree?

texts:
I've already learned how to find which pins can be assigned to a functionality I just open the [arch]-pinfunc.h file and find the entries after __ for given functionality and then find the pin that provides it, left of the __ in the entry. Then I just write the right entry in .dts/.dtsi referencing the pin identity in a way specific to that entry.

But the worse problem is if the pin is already assigned - conflicting with my purpose - and I don't know what to. Not such a big problem if it's a default described in the datasheets, worse if it's an obscure helper functionality left over from development, and not even routed to the board so I won't find it in the schematics. The device tree for modern processors is extensive and long and normally I'd need to check every single entry (out of a couple hundred) to see if any uses the pin I want.

Is there any easier/simpler way to find what functionality is currently assigned to given pin in .dts?


texts: How might a clockwork mechanism be built, to behave in a pseudo-random or chaotic way?

texts:
My brother asked me how I might build a functioning alethiometer, which is a fictional device superficially resembling an analog pocket watch, but with essentially random movements. I told him I would use electronics rather than clockwork ("clockwork" is colloquially synonymous with predictable mechanical motion, after all). But that didn't stop me from wondering how it might be done in a purely mechanical way.
A larger, immobile device might combine a pendulum clock with a chaotic double pendulum system, for example. What other mechanical randomness source might work for a smaller, portable device?