texts:
Novice engineer here (primarily IT guy - I consider myself a jack of all trades, but go easy on me - I don't profess to be at the level of most of you.)
I recently adopted a rescue dog, who is a real sweetheart. My only regret is/was not realizing how much hair she sheds. I've never owned a dog that shed a ton, so this is new for me. It gets EVERYWHERE. Vacuums, sticky rolls, the works - barely dents the amount. I can blow off or wipe off my desk and keyboard and within 30 seconds have more hair there.
I'd like to take a stab at building (since I can't seem to find anything close commercially available) an "electric dog hair wand" of some kind. I saw this post - Need electrostatic material to attract pet hair
which is what got me started in this forum. I'd like to try building something in a portable "magnet" wand like device first; and then go from there once I got a grasp of how well it works / shortcomings etc possibly building other "traps" such as mats, etc to help keep the hair contained.
The last post from William Hird in the article I quoted has basically what I am looking/trying to do.

high voltage charging circuit like the ones designed to charge up electrostatic loudspeaker diaphragms, just a low power high voltage power supply that feeds the conductive layer through a high value resistor, somewhere in the range of 5 megohms or so. This is the way to safely generate a strong electric field without the chance of getting a bad shock.

It sounds like the main difference is that I would be hooking it up to a metal wand/rod as the "conductive layer" and then adding a light coating of non-conductive (insulating) paint or epoxy to prevent shocking myself.
Assuming I'm halfway in the right direction here, I was hoping someone could elaborate a bit more on the "high voltage charging circuit like the ones designed to charge up electrostatic loudspeaker diaphragms". I am vaguely familiar with what a loudspeaker diaphragm is (although I did not know it needed a high voltage charging circuit), but I don't know if the same would be recommended for a smaller and portable unit, nor how exactly I would hook it up to a metal wand / rod.
Sorry for the long post and detail, but I figure its better to be thorough all at once. All advice and feedback is much appreciated!


texts:
How is the bore diameter of a flange Type 21 - acc. EN 1092-1 determinated?

In the standard:

  NOTE 5 The bore diameters of flanges type 21 are not specified in this standard, the effective bore diameters are usually
  given in the relevant component standard(s).

What are the relevant component standard(s)?


texts: Adjusting root locus to get a stable system from unstable system

texts:
Most of the books that I referred to, used compensators to improve transient performances of a stable system using root locus and compensator design. I got a system which is actually unstable for all values of K (one pole is almost on imaginary axis). How can I change the stability of this by adding some poles or zeroes? For e.g., I can move the breakaway point on origin to left by adding some complex zeroes (trial and error). This way there will be some finite range of gain for which system is stable. Can someone point me to a good resource to learn this?
The TF whose root locus is plotted is:
$$\frac{-95.17 s^3 - 8130 s^2 - 187.6 s - 7695}{0.1 s^5 + 1.292 s^4 + 3.138 s^3 + 2.179 s^2 + 0.016 s + 0.01}$$

(There is one more finite zero far left which I couldn't fir in the screenshot and if it helps, this is a model related to some aircraft). Thanks for the help!


texts: Maximum allowable crack in Post Tension concrete

texts:
What is the maximum allowable crack size dimension in a post-tension concrete slab before it is considered a "structural" crack, in Arizona, USA? Is there a certain standard for this. I have tried looking for it in my state's ROC rules but they have nothing for what is considered to be a "structural" crack in a post-tension concrete slab. It's hard to give warranties without having specific measurements and standards to abide by.

Edit: This is for a on-ground slab with an ABC foundation


texts: Creating a rotating unit with the extended arms varying the trajectory in accordance to ODE's

texts:
I plan to mimic binary stars and their orbital decay due to gravitational wave radiation. I want to make a rotating shaft with extended arms, each being able to hold cast iron balls of specific weight, hence mimicking a binary with a circular orbit, when rotated.

This I can construct, my problem however is that I need the extended arms to vary in length such that they trace an ellipse with a specific semi-major axis and eccentricity. The arm must continue to vary in both of these parameters according to the ODE's which explain the time dependency as follows:

  $$\frac{de}{dt}=-\frac{304}{15}\frac{G^{3}m_{1}m_{2}(m_{1}+m_{2})}{c^{5}a^{4}(1-e^{2})^{\frac{5}{2}}}\left[1+\frac{121}{304}e^{2}\right]$$
  $$\frac{da}{dt}=-\frac{64}{5}\frac{G^{3}m_{1}m_{2}(m_{1}+m_{2})}{c^{5}a^{4}(1-e^{2})^{2}}\left[1+\frac{73}{24}e^{2}+\frac{37}{96}e^{4}\right]$$
  Note: The value of 'c' and 'G' I would be taking are  1 and 2.226e-19, to simplify the calculations.

I would then measure the time taken via a sensor, this would be the life time of the binary.

How do I build such a device? Is there any specific tech available that I can use for this specific issue that I have highlighted? Or can anyone provide some idea how to go ahead. Any help is appreciated.


texts: Practical examples of LTI transfer function

texts: My question is pretty simple. The transfer function of an LTI system seems rather limited in use since the initial conditions must be zero. What are some practical engineering uses of it, and examples? I understand it's mathematical use, but fail to see where it's utility would really come in handy except in very simple mathematical models.


texts: I want to know what is the meaning of dσ/du in this solution?


texts: What is the difference between I3C and F4C microprocessor crystals?

texts:
Background: We are in the process of developing a sensing application. We are currently using an Evaluation board from a vendor for initial development work that has a MSP430 microcontroller.

The first version (000) of the board had 240 ABMM I3C Ceramic surface mount microprocessor crystal from Abracon on the board. This evaluation board with custom software works fine.

The second version (001) of the board has a 240 ABMM F4C crystal. The second board with the custom software doesn’t work at all. Although the crystal is from the same vendor the crystals appear to be slightly different.

Picture of Crystal from the working EVM board

Click on image for a larger version of the image.

Picture of Crystal from the defective EVM board

Click on image for a larger version of the image.

Below is the schematic for the crystal

Question: What is the difference between the two crystals? (I3C vs F4C)

Note: I'm wondering if one of the components is not a genuine part and is a knockoff.

References:

Datasheet for Ceramic surface mount microprocessor CRYSTAL 240 ABMM


texts: Why the design of continuous beam is always more economical than beam with supports?

texts:
Assuming that I have a beam that spans across a few supports. I can design the beam as a continuous beam (a beam that is loaded and has more than two supports), or individual beams that each encompass between two supports.

From what I know, the design of continuous beam is always more economical than beam with supports. Why this is the case? I understand that this is because the forces and moment in continuous beam are less than in beams with multiple supports. But I am looking for a deeper, more physical explanation on why the forces are smaller in continuous beam.


texts: How to calculate properties of a thread?

texts:
I have a simple thread joint between two objects:

and want to find a size of those threads so that after rotating male part it stands at the specific angle. For those who is curious I made it in Fusion 360 and added joints to these parts, also specified limits of sliding upward and downward. The problem is when it totally rotates till the end, the upper part stands in the wrong direction. I am going to 3d print it, so I need it to be as precise as possible.


texts: How to analytically estimate the pressure loss through an liquid injector?

texts:
The simple orifice and a pipe have well-documented pressure loss calculation.

But when an injector has complicated flow patterns, is it possible to break it down into simpler sections by which the pressure loss can be calculated?

Or are there procedures to estimate the injector pressure loss?

Or is empirical the only way to measure the pressure loss?


texts:
From ASME-Y14.5, a regular feature of size is defined as "one cylindrical surface, a spherical surface, a circular element, or a set of two opposed parallel line elements or opposed parallel surfaces associated with a single directly toleranced dimension". Is the following a regular feature of size?

Does this qualify as a "circular element" thus making it a regular feature of size?


texts: What methods are used to extract energy from low energy heat sources?

texts: Most of what I was able to find pointed towards thermoelectric generators which are very inefficient, stirling engines which have a low torque output at low temperatures, or generators that use the organic rankine cycle. What are other methods of getting power from a low temperature heat source? And are any of them currently viable or potentially viable in the near future?


texts: When backup cooling fails in reactors without passive safety, what is the risk of radioactive contamination?

texts:
Most/all nuclear fission reactors require cooling.  Due to radioactive decay heat, this is true even when the reactor is switched off.  Hence, there are requirements for nuclear plants to have power at all times: for example, in the United States, they must  have backup battery power for 4–8 hours (example source), with the assumption that power is subsequently restored.

If, power is not quickly restored to a nuclear reactor and there is a prolonged loss of cooling event, what is the risk of large-scale radioactive contamination of the environment?

For the purpose of this question, assume nuclear reactor models that are currently common in the United States or western Europe.


texts: Will a short brick wall help shield against bass or will it go around?

texts:
I have a noisy neighbor (unreasonable and hostile) generating low frequencies that are disturbing. I'm at the point where I realize I need to just build some kind of barrier, and also buy better windows and doors.
So I am thinking of building a short wall (maybe 7 ft tall) to absorb or redirect the low frequencies (40-80Hz). Building material will be double brick, high density. The impact on my house is worst in the section directly facing the brown wall, hence why the wall is short.

The horizontal brown line shown above is meant to be the wall.
Before I start, I am concerned that the barrier will maybe allow the sound to pass around (or above). I suppose some sound is to be expected, but I want to eliminate most of it.
I just want to find out if my approach makes sense, or whether I should also be looking at some kind of DIY "bass trap" shape of this wall to absorb even more.


texts:
This is slightly similar to a question I previously asked but now I decided to simplify the question and model it similar to a design I have in mind.

I sketched out a slightly simplified model. It is a cantilever rod with two supporting rods of slightly larger diameter, connected by a plate. (Ignore the weight of the individual parts. For illustration purposes, I draw this to resemble a cantilever beam from the side view but in actual design, this drawing is actually the top view.)

My aim is to calculate the deflection/bending in the rods (more importantly, the two side/supporting rods) due to the force applied. The plate can be considered rigid.

I'll break down the question into two parts, so that I can understand the concept better:

If the three rods were of the same length (the middle rod is not extended and force is applied at the end of the three rods), how do I calculate the forces acting on each rod and then the deflection?
With the middle rod being longer than the supporting two rods. How should I approach calculating the deflection in each of the rods?


texts:
I need to make PTFE caps on my test tubes. Why PTFE? The test tubes contain industrial solvent mixtures & the rubber caps that came with the test tubes are very, very slowly being dissolved.

I need about a dozen caps. If I were to make it out of solid PTFE, turned on a lathe creating the cap, then it would be expensive. So I'm thinking of having thick cups of PTFE. Then it would be filled by a soft elastomer, creating the cap. Seeing that most PTFE pieces are created by taking PTFE powder & thermoforming it in molds, the production method is expensive even if the cups are lightweight. So I'm thinking "what about vacuum forming?", so I'm here. Can Vacuum forming be used on PTFE?


texts: what goes on in this 6 acre water sewage plant?

texts:
This water sewer plant is about 1/4 mile from vacant rural lot I own. With no particular weekly pattern I occasional hear what sounds like a large generator or pump faintly in the distance.
From this image, can somebody explain what they might be doing there? Does it appear that any waste or sludge is being reintroduced back into soil in those two dry ponds?
I have not tested the water yet, planning to , but how safe for contact with human skin (not drinking) can I expect a shallow well to be a 1/4 mile away from this plant?
It's in central Florida, please do not ask me for detail on the location.

update: here's another picture:


texts: Quantifying and measuring friction under extreme conditions

texts:
I want to quantify friction between a bullet and barrel to test different friction-proofing coatings and treatments.

Is there a controlled test I could do at low speeds in a lab between samples of treated copper and steel that would be theoretically applicable at velocities up to 1000 m/s?  I.e., is the dynamic coefficient of friction considered constant between two materials like copper and steel up to speeds of 1000 m/s, or is there a known relationship between speed and friction that would allow extrapolation from lab-measured coefficients?  And what lab tests would be suited to measuring that coefficient to high precision?

(I realize that the most obvious way to approach this problem would be empirically: i.e., just shoot the different projectiles and compare the resulting velocities.  I have tried that and gotten confusing results that appear to be attributable to the sources of error in internal ballistics: in particular to the fact that different coatings are probably altering the diameter of the projectiles at the micron level, and dimensional changes can overwhelm the changes in friction, which render A-B comparisons invalid.)


texts: What is the theory behind imaging a precision pinhole?

texts:
In my efforts to characterise a 0.67 NA microscope objective (working distance of about 15mm, effective focal length of 25mm), I have placed a 20 micron precision pinhole at the focal plane of the objective, and back illuminated the pinhole with a 767nm laser. The light coming out of the objective is focused onto the imaging plane (camera plane) with a F=1 metre lens.

By my understanding, the image field $U_i$ should be a convolution of the Point Spread Function (PSF) $h$ and the object field $U_o$, i.e.

$$
U_i(x_i,y_i) \propto \int_{-\infty}^\infty\int_{-\infty}^\infty h(x_i-\xi, y_i-\eta) U_o(\xi,\eta)\, d\xi d\eta\, ,
$$

where the proportional sign is for good measure as there are some coefficients in front, but that does not affect the profile. The image intensity profile is given by

$$
I_i(x_i, y_i) = |U_i(x_i, y_i)|^2\,.
$$

In my case the microscope objective has a circular aperture, and that means that the PSF $h$ is given by the airy function, i.e.,

$$
h(x,y) = \frac{J_1 \left( \frac{2\pi}{\lambda} NA \sqrt{x^2 + y^2}\right)}{\sqrt{x^2 + y^2}} \, ,
$$

where $J_1$ is the Bessel function of the first kind, order one.

I have plotted out the intensity profile (gauss quad integral) that I expect for the current pinhole and wavelength, taking into account the magnification of the system, and I got the following plot.

However, this differs from my measurements taken in experiment:

The size of the image is approximately 20 microns (pixel size = 3.75/40 microns).
The number of peaks somewhat represent what is shown from the plot above. What concerns me more is how the intensity profiles goes to zero between peaks, unlike what the theory predicted.

Is my understanding of the current theory incorrect?


texts: What is the difference between using separate lathe and mill or a combination machine?

texts:
I'm interested in metalworking as a hobby, to make small parts for my numerous other hobbies.  I'm looking at those cheap, typically Chinese import mini-lathes and mini-mills.  I've read about their limitations as compared to larger machines; this question is not about that.

My question is, what are the pros and cons of a combo mini lathe/mill as opposed to separate machines?


texts: What would happen to a misinstalled globe valve?

texts:
Since globe valves are unidirectional and should be installed in one direction only I encountered a valves supplier that does not mark the globe valve body with flow direction, the valve eventually got welded (socket weld ends, not flanged) in a by-pass branch on a skid.

What might go wrong if the valve is installed incorrectly? Is there any way to check this other than the flow direction on the body (in the as-built situation)?  (the body is symmetrical for both inlet and outlet sides).


texts: Having to build an apparatus, trying to show the concept

texts:
I have to build an electro-mechanical device that has a few sliding and rotating parts controlled by servos and actuators from Phidgets.

I made the prototype with wood; it was crude, imprecise, and looked like it was built from scrap from a junkyard, but it proved the concept.

Now, we are going to need to make the real thing. I spoke with a local company that does CNC work and I tried to explain to them the concept. But I suck at drawing, and the original prototype covers just a part of what we need.

I have several options that I am contemplating:

Building something out of wood again to show them what I need. But it was time consuming and not very good last time
Build something, without the motors, out of legos to demonstrate the moving parts.
Make a proper model in SketchUp, but it won't be able to demonstrate the moving parts. The CNC company told me they'd be happy to see SketchUp/Autocad files, but I'm afraid this won't convey how things move during the operation.
Writing on Stack Exchange to get some fresh ideas :)

What would be the best way to describe a device to people foreign with the concept? They need to understand how it operates, the constraints for the moving parts, etc and eventually come up with the final schematics. So I need to get the point across.

I have never done this before, and this is domain that is foreign to me.


texts: differential drive vehicle in screen coords

texts:
differential drive vehicle in world frame
what would change in the kinematic model of the differential drive vehicle if i  wanted to simulate it
using pygame module in python ( pygame or opencv or any other one )
x_dot = (vl+vr)/2*cos(theta)
y_dot = (vl+vr)/2*sin(theta)
theta_dot = (vr-vl)/w
vr is the velocity of the right wheel
vl is the velocity of the left wheel
theta is the heading angle
it uses a screen coords system which start at the top left corner of the screen insted of the lower left
my initial guess is since only the y axis is inverted then i should invert the sign of the y_dot
i hope i explained my question clearly the picture is in the link above


texts: Non-observable effect of low-pass filter on the Transfer function (of Vibration measured with Laser scanner)

texts:
I have to study the effect of low-pass filters (if any) on the outcome of the experiment. And the experiment here is to measure the vibration of a (metal) specimen by hitting the said specimen with impulse (or "knocking").
Parameters for measurement include:

Average complex (convert from time to frequency domain with FFT)
Hann (or Hanning) window function (this is the next parameter study,
for now, bear with it)
20kHz total bandwidth with 25600 FFT lines (or
25.6kHz sampling rate)

Theoretically speaking, applying the low-pass filter should lead to some differences in the frequency spectrum of the transfer function. Yet, in the image below, there is practically none. Sure, there is a drop of 1~2 dB from 350 to 500 Hz, but my instructor says that this frequency range is mostly noise, and they are not as important as the peaks (where there is no significant change).
Can anyone explain this to me, why there is no difference in the spectrum?
Further check on the components also say that there is only negligible differences in both the input (knocking force) and the output (vibration). My hunch is that for the force, because I only "knock", which means there is no frequency range, and I generate the knocking signal in time domain, so there is no frequency range to block. In other words, because of my setting for the input, the filter has no effect. However, this would not explain the situation with the output and the transfer function.

Edit: Additional graph, with frequency spectrum runs from 0 to 20kHz, comparing with and without 100 Hz filter (with 3 options: No filter (black), Filter on Output only (Yellow), Filter on both input and Output (Blue))
Linear scale for frequency

Logarithmic scale for frequency


texts:
I was wondering how blenders used in the kitchen for the purpose of creating smoothies, soups, etc. operate, particularly, how the rotation of their blade is achieved, i.e. what sort of motor is used for this purpose. I am additionally interested in finding additional Bibliography in the bespoked subject, as well as the industrial methods used to generate each component of blenders (meaning not only the mechanical parts). If anyone has ideas on the Bibliography as well, please let me know.

Thanks!


texts: How to divert solids from a downward vertical pipe

texts:
I am an electronics engineer trying to build one small underwater mechanical device (about 12 cubic cm) as part of a personal automation project. I have figured out the electronics for this, but I am stuck at one mechanical problem.

I want to make a 3D printable CAD model of the device. Please tell me what kind of mechanism I need, and explain its working principles.

Description: Each device will have one inlet and two outlets ($o_A$ and $o_B$). The inlet is at the top and the outlets $o_A$ and $o_B$ are at the bottom. In an underwater installation, these devices would be placed vertically one below other, interconnected with 3/4 inch PVC pipe. Outlet $o_A$ of the above device will be connected with the inlet of the below device with 3/4 inch PVC pipe.  Normally, the solids falling down from the inlet should flow down vertically through the bottom outlet, $o_A$. But occasionally the solids needs to be diverted to the other outlet, $o_B$. How can this be done?

Update
I see from the comments that 'Diverter Valve' is what I was looking for. Please explain its working principles.


texts:
I am trying to derive the isentropic flow equations for a compressible gas by myself and at the end, I have different formulation than the one in the literature. Can you please tell me what am I doing wrong?

So we have a nozzle:

If we do an energy balance and consider that the kinetic energy and the potential energy in point 1 is negligible, one ends up with this relation:
$h_1=h_2+\dfrac{v_2^2}{2}$

By using the ideal gas relation $h = CpT$, and if we then divide the equation by Cp and then by $T_2$, we end up with something like this:

$\dfrac{T_1}{T_2}=1 + \dfrac{v_2^2}{2T_2Cp}$

And finally using $Cp = Cv + R$, denoting $Cp/Cv = k$, using the formula for the mach number $M = v/c$ and the speed of sound in gas $c = \sqrt{(T_2Rk)}$, we end up with this relation:

$\dfrac{T_1}{T_2}=1 + \dfrac{k-1}{2}M^2$

But from the literature one can find that this formula is written like this:

$\dfrac{T_t}{T}=1 + \dfrac{k-1}{2}M^2$

The question is... Is the total temperature $T_t$ in their equation the same as $T_1$ in our case? And if the nozzle discharges to the ambient, is $T$ in their formulation the same as $T_2$ in ours? I'm a bit confused with the symbols and the meanings and I want to learn how this works.

P.S. This is a copy of a question from enter link description here. I have been suggested to try and ask here.


texts: What is the ideal gap between two panes of glass for insulation

texts:
I have two panes of glass, about a 3/8" thick (.95 cm). Space efficiency and aesthetics ignored, how far apart should they be spaced to maximize heat insulation, assuming the gap contains regular air (and not Argon). I read that it's a balancing act between convection and conduction, and that store bought double panes windows are usually in the 1/4" - 1/2" range (0.635 cm - 1.27 cm). Other sources suggest a gap up to 2" (5 cm) is ideal, with the reasoning that a larger gap is always better up until it's wide enough to allow convection. Assuming it's exactly freezing outside and room temperature inside, how to I figure out what gap is best?
Thanks.


texts: Calculating load on planetary gear from driving torque

texts:
I am very new to gears I am fairly confused about planetary gears. I want to know the load on the gears contact point between the sun and the planets and the planets and the ring, assuming the ring not moving. Given I have the solid works file ,the pressure angle, and the gear ratios, I can easily calculate the distances, teeth numbers, etc. I also know the initial driving torque of the sun gear.
So, my question is, utilizing the solid works file and the driving sun gear torque how do I calculate the load on the contact point for each of the gears? Is there a general equation I can use without knowing the power and the rpm?

Thank You


texts: How do I measure the brightness of a light bulb?

texts: I am working on a science fair project. My question is if electricity moves better through a thin wire or a thicker wire. I need to collect data and make charts, and the thing I want to measure is the brightness. The only problem is that I'm not sure how to scientifically measure the brightness of a light bulb. Probably not important to the question but it'll be connected to a single D battery.


texts: Word for the tendency of one metal to rub off on another?

texts: Is there a word for the tendency of some metals to make crayon-like marks on other metals?  For example, a lead bullet makes faint marks on some steels, but not on others with a similar surface finish.


texts: Can wider range (i.e. 600-700 MHz) antenna replace lower range (650-700 MHz) antenna?

texts:
I had an appliance (wireless audio receiver), which has operational range 662-698 mhz (and had same ranged antenna exactly from factory), like this:

However, that antenna was broken accidentally and I want to replace the antenna, but can't find exactly that model. However, I've found a bit wider ranged antenna:  632-698 mhz

Can that work without problems? may i replace with that?

EDIT: exact model is: shure ULXP4 (662-698 mhz): Sophisticated, scalable
wireless solutions (also here specs: ULX Wireless System Specification Sheet)  and replacement antenna I want is: http://bit.do/fgergsadf


texts: Does it make sense to have a pressure and flow controller on a single closed line?

texts:
I have seen P&IDs in which a single line has both a pressure and flow control valve. Based on my understanding of Bernoulli's equation however this doesn't make sense to me - because ultimately flow velocity and pressure are dependent on one another, by controlling one you are affecting the other (due to conservation of energy).
See for instance the image below:

Does anyone have any idea how this could work in practise?
Best wishes and thanks!


texts:
If I take a large thin plate and I uniformly drill a very large number of holes (diameter "d") very close together (minimum spacing "s"), what will be the stiffness of this new plate? When I say "stiffness" I mean the derivative of average macroscopic displacement with respect to stress. With no holes it would be Young's modulus.

Here is a way to visualize how the drills are to positioned, i.e. close packed circles with space in between.

This is the question I want to answer. Of course, the stiffness will depend on which direction the stress is applied - for example, if I am pulling along the "grain" it will be stiffer than if I turn the plate 45 degrees and pull.

I thought about doing some sort of analytic model (found a few papers but they are hard to understand). Or a finite element model. However, I am interested in how the parameters "d" and "s" (see above) change the stiffness for each type of circle packing pattern. I am stuck now, what would you recommend as the best way to approach this problem?

Also, if this problem has already been solved (wouldn't be surprised) and someone could point me to a reference that would work too.


texts: How to tune the radial mode vibration of a PZT disc transducer?

texts: I am trying to create a set-up where I can radially vibrate a 1x1 cm sample using a piezoelectric disc transducer. I know that at the $f_{min}$ of a PZT transducer, for the disc geometry, there is a radial vibration. How can I tune this vibration if I want to vibrate my sample radially at different frequencies?


texts: Analog PID controller - settings wrt $V_{err}$ - setpoint always higher than room temp

texts:
I designed from scratch an analog PID controller to mantain a temperature selected in the range of 60 to 80ºC with a room temp say = 20ºC.  The "plant" is a simple 4R7 5 W resistor heated by a PWM-controlled current (100% to 0% range).

For any given setpoint, say 67ºC, I know that room temp is lower, so, if heat is not supplied, the cold source (room) will be pulling the temperature continuously down.

My question: where should I "center" my PWM duty cycle excursion?

If $V_{err}$ = 0, DC = 50%? I heat the resistor with more or less current, pivoting on $V_{err}$ =0
For $V_{err}$ =0, DC = 0% (minimum or null current)?  I heat the resistor with a varying current only if Verr is positive

Option 2) seems somewhat reasonable to me, but, at the same time, I see that I am just controlling the heating side of this. Do I leave the room alone doing the cooling with no current supplied by me?


texts: Is there any way to simulate belt transsmition with non-circular cog?

texts:
I want to do a simulation of a transmission with toothed belt and elliptical gear. I've tried in Autodesk inventor by modeling wheels separately and then adding a belt with the "synchronous belt tool" but the software doesn't recognize elliptical cog as a cog. I'm thinking about doing an accurate model of the belt, but is there some kind of constraint/link I can apply in the assembly process that would make the belt move realistically when I simulate the rotation of the cogs?

I'd really like to see your point of view.


texts: Control System Question - spectra and their degrees of excitation

texts: What is the difference between impulse, step and sum of sinusoids signals in terms of their spectra and their degrees of excitation ?


texts: How can I determine horizontal force reactions in a fixed on both ends beam like this one?


texts:
I was playing with a spring, and realized that I've never wondered why a spring gets harder and harder to compress the more you try to compress it.

It seems easy at first though. What is the scientific explanation behind this?

thanks,


texts: Is the fill factor of a photo-voltaic cell constant?

texts:
An important factor in specifying the efficiency of photo-voltaic (PV) cells is called the fill factor (FF). It is defined as the ratio of the maximum power of the cell to the product of the open-circuit voltage $V_{oc}$ to the short-circuit current $I_{sc}$.
$$
P_{max} = V_{oc} * I_{sc} * FF
$$

Is $FF$ constant in this equation?  I've found online that
$$
FF = \frac{V_{mp}*I_{mp}}{V_{oc}*I_{sc}}.
$$
But it wasn't specified if those values are under STC or not.  If they aren't, then how would I get $V_{mp}$ and $I_{mp}$?


texts:
Consider a control problem of the form:

$\frac{d \vec{x}}{dt} = F(\vec{x}, \vec{u})$

where $\vec{u}$ is the control inputs and $\vec{x}$ is the state variables, and all we want to do is drive the system from $\vec{x}_0$ to $\vec{x}_1$ in some given amount of time $T$.

I have two questions:

What is known about how many solutions for $\vec{u}$ exist for such a problem?
How do engineers address/interpret the existence of multiple solutions?


texts:
so I am very interested in flying.  I don't have any formal education in the topic so take my questions for what they are.

I was thinking about VTOL aircraft and the current state of such machines.  A thought crossed my mind as I was pondering the topic.  Would it be possible to produce a solid structure VTOL hybrid airship/airplane that is only slightly heavier than the air around it?  It seems like this type of craft would provide for very long flights and "futuristic" landings.  I understand this is no spaceship but the implications of building such a device seem like the "henry ford" moment of our generation.  An interesting hybrid called the solarship was recently developed by some private company.  That craft uses two different methods for generating lift (lifting gas and a wing).  There is another method that we use to generate lift on helicopters.  Could all three be combined with a craft slightly heavier than air?  The mechanical motion required for lifting such devices is very low (little RPM required).  The solarship is extremely small.  I don't suspect we will develop personal airships.  I was thinking more like larger commercial craft though both would be cool.  I understand the craft would need to be made up of something very light, maybe a metal microlattice or a carbon body or even 3D printed plastic.  It seems like such devices could benefit from hollow wings filled with lifting gas as well.  Additional concerns would deal with punctures to the hull.  Maybe a balloon inside the hull?  There are solid structure airships already but those craft are easily damaged by wind and other extreme weather.

An additional question I have relates to the design of airships.  Some recently built craft have deviated from the traditional blimp design.  Why are there no vertical airships?  I assume this is because of buoyancy or just the fact nobody has thought to build one.  With airships the heaviest part will always be on the bottom.  Even if we put the hull on top it would just flip over right?  It seems like we could build some pretty cool designs with these considerations in mind.

Now don't get me wrong, I understand there are some major challenges associated with such an undertaking.  Hydrogen is dangerous, helium is in short supply and hot air probably won't provide the necessary lift.  Perhaps this will be more appealing once nuclear fusion is available.  Though I think people will be more concerned with creating new thrust devices once fusion is a reality.

Thanks in advance for any helpful information.  I do apologize if the question sounds stupid.  Again, I am not formally educated in aeronautical engineering.


texts:
Let's suppose I have a water jet as source, and this jet goes through a tube and is equally divided into 4 tubes. Is there a way to control the flow/pressure at each of those tubes separately by adding a different nozzle at the end of each tube or controllable valves at the beginning of each tube? Or is it only possible to get relative pressures at each tube.

And how can something like this be implemented?

An application would be having only one horizontal tube (source of water) connected to 4 vertical tubes used as fountaines and where I want to control the height of the water output of each fountain.


texts: Do generators run slower if the load is lower?

texts:
When I see electrical generators specified, they usually give the fuel consumption as at "rated load". So,for example, a 5 kilowatt generator might consume 0.6 gallons per hour.

However, what happens if the load is less than 5 kilowatts? Does the generator still run at the fixed rate and any excess electricity is just shorted to ground?

Or does the engine run slower and just generator less energy? How does it know what rate to run at? Does it have to manually adjusted?

If the engine is run at less than its maximum load, what would be a typical loss of efficiency? Can someone provide an example curve that shows how a generator loses efficiency at sub-optimal loads?


texts: How many units of HB are used for steel bridges?

texts:
Bridges in the UK can be assessed (to standard BA34/90) using an HB vehicle (to standard BD37/01). The HB vehicle is 16 wheel loads, each of 2.5kN times "units".

For concrete bridges the number of units is normally defined as 45 units at Ultimate Limit State (ULS) and 0 units at Serviceability Limit State (SLS); although the number of units for SLS is 30 if the bridge spans transversely. Reference: BS5400-4:1990 Clause 4.2.2 as modified by BD24/92.

For steel bridges there doesn't seem to be an equivalent clause. So how many units should be used at ULS, and how many at SLS?


texts: How can i calculate drag on an Angled area?

texts: I want to calculate drag force at special angle on a sphere . There are some grooves on the sphere and these groove have a special angle on the sphere. In other words, I want to calculate drag force on the these grooves. How can I do it in Fluent?


texts:
When I read about stress analysis and specifically in the context of strain gauge, I often see the phrase resistance per unit strain or voltage per unit strain.  I understand the electronics and how some of the equations are derived or come about. I have a basic understanding of what stress and strain are, but I don't get what per unit strain is and why we're using it.
Take the simplest example - a strain gauge connected in series with a constant current source, where $ E $ is the voltage drop across a strain gauge, $ R_g $ is the resistance of the strain gauge, $ G_F $ the gage factor, and $ \epsilon $ the strain:
$$ E + \Delta E = I(R_g + \Delta R_g) $$
$$ \Delta E = I \Delta R_g = I R_g {\Delta R_g \over R_g} = I R_g G_F \epsilon$$
Everything makes sense until the equation is rearranged and call it the potential drop per unit of strain:
$$ {\Delta E \over \epsilon} = I R_g G_F $$
One unit is a measure of unity. One unit of strain therefore is $ \epsilon = \Delta L / L_0 = unity = 1 $. That implies $ \Delta L = L_0 $, or the change in length equates its initial length. If the object is under tensile stress, $ \Delta L = L $ is a 100% elongation. So the term potential drop per unit of strain would logically mean the voltage drop per each 100% elongation! Most strain being measured in the elastic region is well below a few percent.  100% elongation (or my take on per unit strain) feels .... out of context here.


texts:
Currently, I am thinking that since electromagnetic waves loose energy over distance, you might be able to figure out the relative distance to each of three radio "beacons" and use this information to triangulate the position of a robot with a radio sensor on-board.

What information each radio signal could I use to measure the distance to correlating beacon? Amplitude, perhaps? The entire system would be running indoors in a relatively small area, so it needs to be relatively precise.

Is this even a reasonable idea, or are there better methods I could use?

Note: I asked a similar question about radio triangulation on the Robotics SE, where someone asked me to look into the Engineering SE instead.


texts: Why aren't counterweights used more for garage doors?

texts:
One of my garage door torsion springs broke again.  It makes me wonder why some sort of counterweight system isn't used instead.  Torsion springs seem to have a 90 day warranty generally and are "rated" for up to 15,000 cycles.  It seems like there is a lot less stress on a system that uses counterweights, this company has a counterweight system for high use places (condo buildings or businesses with large garages or car washes) with warranties for 100,000-500,000 cycles.

Is it initial cost?  Space required?  Just to keep repairmen in business?


texts: How do you make a 3D print with an accurately aligned bore hole?

texts: I am printing a wheel with a 2.5mm hole in the middle to accept a shaft of a motor with a set screw. The problem I am having is that the wheel is always wobbly when spinning (sometimes more, sometimes less without changing any parameters). Is there anything I can do to make this print as perfect as possible and prevent the wheel from wobbling?


texts: How to mount a load-bearing gear shaft through a wooden plate

texts:
I don't have experience in mechanical engineering so I came here to ask for help. Here is sketch of one simple construction I want to realize:

Here we have 5 cm thick wooden plate, 50 cm long and 35 cm wide. I will drill a hole through the plate for 40–50 cm long shaft, which will carry a fixed gear driven by a DC motor to rotate the shaft. The shaft must be able to carry a load of at least 30 kg.

My question is, how can I "fix" this gear shaft to carry a load without falling down? Here is one shaft I found; I don't see way to use it in this situation. How would I mount a gear on this shaft?


texts:
I have a carbon fiber composite component that is often and repeatedly subjected to stress. When it was brand new, everything looked normal. After a week of use, there are what seem to be bubbles developing under the clear coat.

1) Why would there be bubbles developing under the clear coat? Wouldn't the manufacturing process of heating and vacuuming bagging have eliminated most of the air within the composite?

2) Does the presence of these bubbles indicate a manufacturing defect?

My suspicions are that these bubbles are merely a cosmetic defect as I can see them, which indicates that they are not in between the layers of unidirection fiber which actually gives the structure its strength. On the other hand, the presence of the bubble does make me wonder - are there possibly large voids within the structure? From what I understand voids weaken carbon fiber composites, correct?


texts: What is difference between lift and elevator and hoist?

texts:
I am very confused by the three terms:lift and elevator and hoist

Are they all technically same thing or different??


texts: Hermetic Cable Seal With Space Limitations

texts:
I have an application wherein I need a hermetic seal at cable exit points from a plastic housing. The cables are not removable. I'd like to achieve this seal using the plastic housing itself by creating a friction fit between the hole and PVC cable jacket (since there's only about 5mm of vertical space to work with). A couple questions:

Is this possible? How can one prevent the seal from breaking as the cable is moved into different positions?
What are the best practices for such designs?

Thanks for your help!


texts: Dynamics of a rigid body in a system of two linear drives

texts:
I've been trying to solve the dynamics of this system for quite a while, but cannot seem to get the right answer. I've tried solving it with Lagrangian method but I am not so confident with the equations I'm getting.

Firstly, looking at the picture below,

there are three components in the system where 1 is the link between 2 and 3. 3 moves linearly along the y axis and is driven by a linear drive. 1 is actually a linear drive that moves 2 up and down, but because there is a surface when x=0, the friction between the surface and 2 cause 1 and 2 to rotate just as in the picture.

I've been trying to solve the dynamics of this system in terms of x,y,theta, and velocity and acceleration (dot(x),dot(y),dot(theta),twodot(x), etc) from the lagrangian method. But my initial attempt had l to be constant when it actually moves due to ux. I also did not consider the surface to be deformable; the surface in which the linear drive 1 exerts a force of ux deforms as it is not a rigid body. For simplicity's sake, I considered the reaction force from the surface to be f and tried to solve the dynamics again, but got totally confused as I couldn't figure out how much work was being done by f and as there were new variable of l ldot l two dot.

Basically, it would be really helpful if anyone could define the work done by the external force, (the u's and friction and f)as well as kinetic and potential energy of each parts so that I could use them in the lagrangian method.

Also, if you think that there are other methods other than lagrangian to solve for the acceleration and velocity of x y and theta of this particular system, that would also be great.

Thank you in advance.

Edit:

Basically, the problem to solve is the acceleration of x y and theta at point (x,y) when the linear drives on m3 and m2 are given a force of uy and ux, respectively. I am trying to solve the accelerations in terms of uy ux Ffr theta and f (the springy reaction force of the surface at x=0). m's are all masses, s is the thickness of 2 r is the vector of (x,y) with respect to the the point of rotation.

My initial attempt at this problem doesn't consider l to be changing (but it changes since its a linear drive that gives a force of ux).

i first found the acceleration of x y relative to the point of rotation.

then i used the lagrangian work theorem to derive the following equation:

using the equation above i found theta two dot which i plugged into the acceleration equation of x and y.

This is basically how I attempted to solve the problem and it would be great if anyone could also following this logic to derive a correct answer as opposed to my worthless one.


texts: Whats the difference between leading edge and slat?

texts:
According to this figure whats the difference between leading edge flap and slat and why the slat come with plain wing and TE flap come alone?
thanks.


texts: Calculation of power for a pipeline crawler

texts:
I am an engineering student. I am working on a project where we need to use something called a vertical pipeline crawler. It is just a device that travels inside pipelines for inspection.

I found a crawler online, and I wanted to calculate the amount of power it uses. In specifications (there is more specs than below):
Speeds up to 10 m/min
Mass: 10 kg
Maximum pull: 27 kg
Power: 600 W 115 / 230 VAC

Initially what I did was to multiply the weight it can carry by the speed:
mgv = 27*9.81*(10/60) = 44.145 Watts
But it also says 600 W for power in specs. So how much power does this device need? Is the input 600 and output 44.145, isn't that very inefficient for an electrical device? Is my thought process wrong, what should use?

(I didn't want to share the link for the product thinking it might be against the website rules, however its pretty easy to find online)


texts:
We have a plate capacitor:

The picture shows this plate capacitor where the space between the electrodes is filled with a dielectric plate with dielectric constant $E_r = 8$:

Determine the length of $h$ to which should extract dielectric plate,
in order to reduce the capacity of capacitor by 4 times
What will be the percentage decrease in capacitance if we pull the plate to a length of $a/5$?


texts:
From wikipedia, there's this animated GIF of a linkage.

Question: How does it calculate log? All I see there are trig functions and circles. log doesn't show up in geometric maths, does it?

My friend thinks it's just a (lucky) approximation.


texts: Are Green strain calculations apt for volumetric strains?

texts:
I am trying to calculate large volumetric strains but I am somewhat confused whether Green strain is the right thing to be using or whether I should use good old-fashioned engineering strain.

The work I am doing is looking at strain of a deformable pipe. I am measuring longitudinal ($L_s$), circumferential ($C_s$) and volumetric ($V_s$) strain. As the strains are large and I want to avoid errors due to rotations, I have opted to use the Green-Lagrange strain tensor for the $L_s$ and $C_s$ in the form

\begin{equation}
 \frac{d\mathbf{x}^2-d\mathbf{X}^2}{2d\mathbf{X}^2}
\end{equation}

Where $X$ represents the undeformed configuration and $x$ the deformed configuration.

I'm pretty sure that I should be using normal engineering strain for the volume but I just want some clarification.


texts: Why do bikes have different sized tires?

texts:
I see figures claiming that the front brakes provides 75% of the stopping power for a bike. So why is the front tire not as wide as the rear, especially since the engine and rider are closer to the front?

The front tire has bigger demands on grip and supporting weight, but is given less.


texts: How can I turn home gas (LPG) from liquid to gas?

texts:
"LPG" is the term used here for a mixture of Propane & Butane sold for public use. The exact ratio varies depending on where you buy it and I think also with the season and is not known to me.

I am working on a personal project, I have a gas tank (Liquefied petroleum gas) with a pressure of 4-5 bar (about 50 to 80 psi). Gas in it is a combination of liquid and gas (you can hear the liquid inside if you shake it).

I need some kind of a device/filter that would convert it to gas at the output (instead of liquid) with a small pressure so I can burn it cleanly.

I tried using an industrial vaporizer that is designed to produce gas from LPG, but it gave me something stronger than I need, and when it burns it seems that it is "not clean". (Maybe the industrial gas that is used with the vaporiser is a different mix of gases than domestic LPG?)

Basically, what I need is to build something that works like a large version of  a cigarette lighter, like this :

As you can see, in a lighter like in the photo there is liquid and gas, and a wick that turns produce "clean" fire, without all the side effects that the vaporizer creates.

Now, I am missing a lot of knowledge here, and I would like to know if someone can guide me to how should I do this, what are the names and definitions for the stuff I need etc,
Any knowledge regarding to what I should do, or how, or where can I find it will be mostly appreciated.

EDIT:

When I used the phrase "home gas" which is common in my state, I meant Liquefied petroleum gas (LPG).

Here is the vaporizer I used now (it belongs to someone who knows what he is doing, I do not plan on killing myself :)

So, I'll try to re-describe my problem,

I want to get "clean slow flame" such as is produced by a cigarette lighter.
Instead, what I am getting, regardless of the vaporizer pressure setting, burns  like it's not clean - it acts as if some of the gas is not really burning or properly vaporising when it comes out.


texts: why not put the compressor right next to the evaporator?

texts: the cold line from evaporator to compressor will gain tons of heat on a super hot day even with insulation. if they put the compressor right outside the evaporator, both of the long lines will be hot and there will be a bit of free cooling. why don't they do something so obvious? there must be a very good reason right?


texts: Column Buckling Boundary Conditions -- Welded Tubing Practical Application?

texts:
I'm trying to do some calculations for a personal project.  I'm trying to understand column strength / buckling.  My questions relate to Effective Length Constant, which is based on Boundary Conditions (how the ends of the column are restrained) The four choices there are:  Free, Fixed, Guided or Pinned:

Here's a sampling...

And different end conditions affect the Effective Length Constant, used in buckling calculations:

(edit.. ref: source for the above Length Constants)

But my dilemma is I'm intending welded metal tubing without corner gussets.  I think with a gusset (and / or with cross bracing straps), I'd use Fixed-Fixed calculations, but simple butt welds that's not so clear.

Does anyone have testing data or other experience on how to address end conditions for buckling calculations with a simple welded butt joint at the ends of a column under load?  <---- Here is my question for this posting...

And just for reference, the kind of thing I'm investigating is a drive on vehicle ramp.  Obviously lighter is better for handling and storage... And yes I'm thinking astronomically large safety margins, but I'd like to know the real load capability numbers.

Note: related reference.

Again, how does one address end conditions for welded in place column materials?


texts: Should lithium batteries be recharged after every use , or when they are exhausted?

texts: For a small unit like a drill: Is it better to charge after any use or wait until the lithium battery is exhausted ?


texts:
I am currently building a mini boat-like robot to clean the water from floating trash. I used two servo motors to move the loader that I have installed in front of the boat, and two 3 V DC motors installed in the back to allow the boat to move across the water. I also used Arduino to program my servos and motors. When I tried to test my robot in water, the two DC motors did not push the boat forward. Why didn't the air push my boat?
Here are the materials that I used to build my robot:

Two 1 L water bottles
A small plastic box to hold the electric circuits.
Another small plastic box to serve as a trash collector.
Two plastic propellers (taken from a mini fan).
A toy loader.

The total weight of the boat is around 700 g. The picture below is the robot I am working on:


texts: PSCAD question regarding how to use graphs

texts:
so this question is to do with coursework, but I just need some guidance as I am not exactly sure where I'm going wrong. I missed my 2 weeks of practical classes due to my roommate having covid-19, so was forced to teach myself the programme. The only part I'm struggling with is how I make the graphs work, I'd assume that I am missing something obvious that needs to be added. I will also add the only piece of work ive been given to go off by my lecturer so that it does show what I am aiming to complete.

Edit: I hadn't tested the programme when I added graphs for the current loads. But have seen the errors but is something id fix once I knew how to make a working graph.
Edit: Updated with correct graphs, got some work to do.

Edit: Circuit now with loads A, B and C having the current measured.


texts: How small can you get a stream of molten steel to be at low pressure?

texts:
I'm designing a crucible / extruder, and right now it has a .6mm hole to extrude from. Will this work? A chart with various metals listed would be nice.

Pictures:
Click to expand


texts: Feedback control of two-link planar manipulator

texts:
TL;DR: how can I calculate the disturbance at each joint due to coupling forces in a two-link planar robot manipulator actuated by two independent DC motors?

I'm studying control theory and trying to work through a simple example using a two-link planar robot manipulator:

My goal is to simulate PID control of the planar two-link manipulator, where each joint is actuated by an independent DC motor. The input is two continuous signals $$\theta_1(t), \theta_2(t)$$

which represent the desired angle for each joint at time t.

Following this paper: Modeling a Controller for an Articulated Robotic Arm, I can obtain an expression for the voltage I need to apply to each motor to achieve a desired angle. The paper also describes the PID controller necessary to maintain the desired angle given an error signal $$e(t) = \theta_{desired}(t)-\theta_{actual}(t)$$

Since each motor is controlled independently, coupling effects among joints due to varying configurations during motion are treated as disturbance inputs. My question is: how can I model this coupling effect in order to "simulate" the error signal e(t) for system under ideal conditions? By ideal conditions I mean that the disturbance due to coupling among joints accounts for 100% of the error signal.

My current thought is to use an expression for the dynamics of the two-link planar manipulator, as per the following book: A Mathematical Introduction to Robotic Manipulation

This way, at time t, we determine the voltage to achieve the desired angles for each independent motor, then plug that into our DC motor model to obtain the generated torques: $$\tau_1, \tau_2$$

We then plug these torques into the dynamics to get the actual angles, taking into account the coupling forces, and then use the actual angles compared to the desired angles in order to generate the error signal that feeds into the PID control loop.

Does this approach make sense? If not, where have I gone wrong and how can I simulate the error signal due to coupling forces?

Edit: one commenter points out PID control may not be optimal for this problem. If this is the case, what alternative control strategies should I use?


texts: How to measure velocity of hot gas ( temperature range: 100 - 450 ºC)?

texts: I want to measure the velocity of hot gas coming out from an incinerator. The temperature can easily shoot upto 400-500ºC. I've checked online for hot-wire anemometers, even they claim to work in the range of 0-50 ºC or 0-70ºC. Moreover they are dearly expensive. Can someone suggest a good and reliable solution?


texts: How to detach/unrelate one part from another in Solidworks?

texts:
I have created second part on the basis of first one. Why not? Now I can't neither delete nor suppress initial part without deleting or suppresing my new one.

Why? And how to "detach" (or whatever you call it) new part from old one and retain only new one in the file?

Here you see "new" part in yellow. Gray one is old and unneded. How to remove it?


texts: How does the locking mechanism of a secure bicycle dock work?

texts:
I am trying to understand the physical locking mechanism used in bicycle docks, as in the image below, to secure the bike to the dock.

I want an in-depth understanding of the mechanism for a design project I am doing on bike sharing systems. I most interested in the type of docks Citi Bike uses.


texts: Can magnetic stripes be read wirelessly with lasers or other technologies?

texts:
I know that magnetic stripes used in credit cards and audio tapes are typically read by a magnetic reader head. But is it theoretically possible for the stripe to be read by a laser in a similar fashion to a barcode scanner?

I also heard of technologies like magnetic secure transmission by Samsung that emulate the magnetic stripe within 3 inches of a card reader. I'm guessing the smartphone or device that does the MSE is using more power to ensure the magnetic field reaches the card reader's reader head from a distance of 3 inches.

I'm curious about the opposite. Could a magnetic reader head theoretically read a magnetic stripe with a gap distance (even a very small gap say 0.01mm) or without physically touching the magnetic stripe? Or is the magnetic field generated by the magnetic reader head too weak to handle any gap between the reader head and the magnetic stripe?


texts: Resultant force coordinate for parallel 3d forces acting on a slab

texts:
Apologies if I have done something wrong, first time posting on a stack exchange website.

Four forces act perpendicular to the surface of a circular slab (assume mass of slab is 0 and middle of slab is at 0,0,0)(all forces in -y direction)

Force 1 is located at 5,0,0 and has a magnitude of 77.4kN

Force 2 is located at 0,0,5 and has a magnitude of 48.6kN

Force 3 is located at 0,0,-5 and has a magnitude of 24.4kN

Force 4 is located at -5,0,0 and has a magnitude of 97.6kN

What is the coordinates of the resulting force (x,y,z) to two decimal places?

My working currently and my initial answer

The given answer is (0.49,0,-0.41) and I don't know where I went wrong.

After talking to my lecturer, she said the question was supposed to be determining the z coordinate only, which is why it would say the answer was correct when 0.49 was put first, meaning that the answers I calculated were correct.


texts: What is the difference between both of these terms? Especially in configuration and application?


texts: Does same stress always produce same strain?

texts:
I am reading pure bending from Beer Johnston's mechanics of materials.There,a
prismatic member having a plane of symmetry was subjected to equal and opposite couples M and M'acting in that plane.It was said about this member that since the bending moment M is same in any cross section,the member will bend uniformly.I could no understand this.Is it because that stress will be same on each cross section and therefore since same stresses cause same defoemation,it will bend uniformly?


texts: Poisson relationship between area and length of electric wire

texts:
I was given the following formula to relate the change of area against the change of length of an electric wire with a Poisson ratio:
$ {\Delta A \over A} = -2 \nu {\Delta L \over L} $
where $ \Delta A \over A $ represents the change in cross-sectional area of the wire due to the transverse strain as the wire gets pulled longitudinally stretching length $ L $ to $ L+\Delta L$.
I don't get how this equation is derived. The Poisson ratio is defined by $ \nu = -{\epsilon_{lateral} \over {\epsilon_{longitudinal}} }  = - {{\Delta d / d} \over {\Delta L / L}} $ where $ d $ is the diameter of the cross section. Then the ratio of the area:
$ {\Delta A \over A} = {{0.25\pi(d+\Delta d)^2 - 0.25\pi d^2} \over {0.25\pi d^2}} = {{2d \Delta d} \over d^2} + {{\Delta d^2} \over {d^2}} = -2 \nu { \Delta L \over L} + \big( \nu {\Delta L \over L} \big)^2 \neq -2 \nu {\Delta L \over L} $


texts: Shock loading stresses due to falling: what strength to use for acceptance criteria?

texts:
We are evaluating a design in which a fall-arresting safeguard would be subject to a shock load in the event of a catastrophic failure of a different component, which is required to meet compliance with our design standard. We believe that the equation below (found in Machinery's Handbook, p.279 of the 29th Ed.) is appropriate for approximating the stresses due to this type of loading:
$$
p = p_s\left(1+\sqrt{1+\frac{2h}{y}}\right)
$$
Where:

$p$ = stress (psi) due to shock caused by impact of a moving load
$p_s$ = stress (psi) resulting when moving load is applied statically
$h$ = distance (in) that load falls before striking member
$y$ = deflection (in) resulting from static load

Our problem is that in sample calculations of real-world scenarios, we are finding that the resultant stress is far higher than the ultimate tensile strength of the material. My intuition is telling me that the transient nature of the loading means that tensile strength alone is not an appropriate constraint but I'm unable to find any literature to back up that hypothesis. Additionally, our design standards (CMAA 70 and 74) don't seem to indicate any special allowed stress specifically for shock loading.
To be clear, since this is a safe-guard in case of catastrophic failure, we are not concerned with investigating fatigue rupture. If this safeguard is ever activated once, the product is rendered unable to function and replacement of the entire assembly is necessary.
So my question is, what strength is appropriate to use (if not ultimate tensile) as a measure of acceptable dynamic stresses due to shock load as a result of falling and what reputable sources are there to cite this information? Otherwise, are we incorrect to be using the above formula to estimate stresses due to shock load as a result of falling?
Here is a sample calculation:
Inputs:

$p_s = \frac{Wl}{Z} = \frac{1102.5lbf\times1in}{\frac{4in\times(0.375in)^{2}}{6}} = 11760 psi$
$h = 0.5 in$
$y = \frac{Wl^3}{3EI} = \frac{1102.5lbf\times(1in)^3}{3\times(2.90\times10^7psi)\times\frac{4in\times(0.375in)^{3}}{12}} \approx 7.21x10^{-4} in$

Result: $p \approx 4.50x10^5 psi$. Without any special factor on strength, comparing this to $UTS=65000psi$ for the steel we are using, this would lead one to believe that this shock would cause this safe-guard to fail (to put it lightly).
Here is a loading diagram (rounding 0.375 to 0.38) to help illustrate the loading scenario which would produce the numbers above:


texts:
I have a machine that has power output of 2750 watt, which is blasted to a insulator foam with thermal resistance of 2.1 m2 kelvin/watt where the insulator is 5 cm thick and it drives the heat into ventilation and out of the roof.

I want to make sure that the insulator can withstand the heat blast from the machine. So if I know that 2750 watt can output 9383 btu/hr where 1 watt outputs 3.412 btu/hr, how can I be sure that the insulator can withstand the heat without it getting spread out? regards

Edited additional info: exhaust temp is 40 degree Celsius, room temp is 25 degree Celsius, and outside temp is 32 degree Celsius.

Flammability limit:
lower limit for hydrocarbon gas (part of the foam) 1.8% by volume
upper limit for hydrocarbon gas: 8.5 % by volume
flash point of hydrocarbon gas: -84 degree Celsius

Volume of the exhaust = 50x 60 x 200 cm cube = 600,000cm cube


texts: How to solve for moment with uniform distributed load

texts:
How do we get the moment when there's a distributed load?

For example, the picture below has 9[(60)(18)]. I get that 60 is the distributed load and 18 is the total length of the load, my question is how did it get the 9?


texts: Finding initial length of a bended plastic sheet (Bend Allowance)

texts: I have a 1.5 mm thick plastic sheet part which hast to be bent at a joint 0.3 mm thick by ~ 10 Deg. I know (found from design drawing) compressed and stretched lengths of the joint. How can I find the length of the joint in non-bent (flat) position so that when it is bent the compressed and stretched joint lengths have the initial known lengths ?


texts:
The formula for newtons to pascals is below.

$$1\text{ Pa} = 1\text{ N/m}^2 = 9.81\text{ kg/m/s}^2$$

I am trying to solve this problem but the units are a bit confusing. I want to get the shear stress (tau) based on these input variables.

General stress = Force/Area

The force is 1255Nm the area is length 20mm and height 10mm.

$tau = 1.255\ x\ 10^6\ Nmm\ /\ 200\ mm^2$

with straight division,

$1,255,000/200 = 6275$

but I am unsure about the units;

How do I mathematically devise the units?

[Edit 2]
I think I've narrowed down the question and would like to see if I am on the right track.

The formula: Tau=Tr/J
since I know the Maximum torque, the polar moment of inertia for a solid shaft, I should use the Modulus of rigidity from the material properties sheet for Tau then solve for the radius to get the diameter of the shaft.

Is that correct?


texts: Constructing a structure with given constraints

texts:
I have a problem where I have a few points in 3D space with given constraints (forces, moments) and I have to create one connected structure which satisfies these constraints. Are there any pre-existing algorithms to do this? Can someone guide me where to look?
Note: I actually want to write an algorithm to construct a wire-frame model with given vertices. I also want that this model can actually be constructed IRL, and with some function other than being a paper-weight, like probably a truss/support structure for something else.


texts: Question about a particular statement on plastic deformation of single crystals

texts:
"...the wider the dislocation, the lower is the elastic energy of the crystal because the atomic spacing in the slip direction  is closer to its equilibrium spacing."
What has elastic energy to do with the atomic spacing in the slip direction?


texts: Force necessary to resist motion due to torque on a drum brake

texts:
A drum is subjected to a counterclockwise torque of 16 in-lb. What horizontal force is necessary to resist motion?
Coefficient of friction = 0.40
Weight is neglected.

I'm having a hard time on this one. I've tried to separate the torque into a normal and tangential force and do a summation of moments at B and even at A. No luck. Though I doubt that's how it should be tackled.
Edit (my trials/errors):
I've read a pdf on brakes and learned that there are so many types and equations to accommodate each one. The closest I've seen to the one above was that of a single block brake; with 3 variations on the position of the line of action (the tangential force), $f$, passing through, above, or below the fulcrum.
![An example of a brake system, with the tangential force below the fulcrum]
(https://i.stack.imgur.com/xtKAl.jpg)
It doesn't look the same, but the proof in this was the one I used. That being:
$$T_b \text{ (Braking torque)} = f \text{ (tangential force)} \times r \text{ (radius of wheel/drum)}$$
And the old
$$f = \mu \text{ (coefficient of friction)} \times N \text{ (normal force)}$$
I think my mistake was that I used the 16 in-lb torque as the braking torque ($T_b$) and went on from there.
$$\begin{align}
T_b &= fr \\
\therefore f &= \dfrac{T_b}{r} \\
f &= 16\text{ in-lb} / 8\text{ in} \\
f &= 2\text{ lb downward} \\
N &= \dfrac{f}{\mu} \\
N &= \dfrac{2}{0.40} \\
N &= 5\text{ lb leftward}
\end{align}$$
And then a summation of moments at point B (counterclockwise positive), giving:
$$\begin{align}
\sum M_B &= P(9) - N(9) + f(2) = 0 \\
\therefore 9P &= 5(9) - 2(2) \\
P &= 4.5556lb
\end{align}$$
I also considered the pinned support reaction at A, which gave off another incorrect answer.
The correct answer is given: $P = 3.43\text{ lb}$


texts: Isn't this explanation of speed regulation in a DC shunt motor wrong?

texts:
This site:(https://www.motioncontroltips.com/faq-what-are-dc-shunt-motors-and-where-are-they-used/ ) explains the speed regulation of DC shunt motor as follows: If the load on the motor is increased, the armature rotation slows and back EMF is reduced, since back EMF is proportional to speed. With less back EMF voltage and a constant supply voltage the net voltage increases. The increase in net voltage results in an increase in armature current. Since torque is proportional to armature current, torque also increases. Finally, this increased torque allows the motor to increase its speed and compensate for the slowdown due to loading. Hence, a DC shunt motor is able to self-regulate its speed, and can be referred to as a constant speed motor.

Considering that torque is inversly related to speed for a DC shunt motor, wouldn't this entire explanation be wrong as the last line mentions increase in speed due to increase in torque ?


texts: Create a thermally homogeneous container

texts:
I want to create a closed container where I will put 12 temperature sensors for a project in my company. I'm a software engineer and I have to deal with this project so I need help because I'm not good at thermal.

This container will look like a pan of 30 cm diameter. There will be one hot point at the bottom of the container to heat the inside of the container. What can I put in the container to have a homogeneous environment without overpressure; water, oil, sand or something else?


texts: Solidworks chain pattern on the outer line of a slot

texts:
I've created a chain pattern to be placed around a slot line, but the problem is that the pattern reside inside the slot instead of outside.
Any ideas on how to change it?


texts: Why the Tensile modulus is always larger than Tensile strength?

texts: I can't figure out this huge difference in values between these two mechanical material properties. When its refer to flexural strength and modulus there's a difference in value (if the material is not isotropic or homogeneous), but not quite significant as the first two.


texts: How to choose an insulating material for a heated metal rod

texts:
I have a rod heater mounted in a brass rod and I need to coat the rod with a solid thermal insulator. I have the following options:

PTFE
Teflon
Polyurethane foam

However, I doubt that the foam would be suitable when it comes to be in direct contact with the brass rod. How can I choose the right insulator for this application?


texts: How to find raw data sets for engineering?

texts:
For one of my courses the teachers asked me to find two samples of 30 or queries of data, and I was thinking on how I could begin to search it?

Most of the scientific articles that i looked for just show the data into graphs or simplified, but that's not really what I'm looking for, any help into how i could begin to start searching for it?


texts:
I am researching a system that appears to have a hydraulic arm with some kind of "handbrake" as pictured below:

System Description:

Table that can raise and lock into place
Locking mechanism triggered by user releasing lever
Locking mechanism released by user pulling lever

I'm new to hydraulics, and I don't know what kind of component this is called. I've searched hydraulic cylinder with handbrake and pneumatic cylinder, but I'm not getting any good information. Can anyone point me in the right direction?

Thanks in advance!


texts: Dimension of the unidirectional mechanical clutch

texts:
This is a problem from the book Engineering Mechanics Statics vol-1 by Meriam Kraige.

The elements of a unidirectional mechanical clutch are shown in the figure.A torque $M$ applied to the outer ring is transmitted to the output shaft through frictional interaction between the outer ring and the balls and between the balls and the inner driven member.If the direction of rotation of the outer ring is reversed,the wedging action of the balls is absent,and no torque can be transmitted to the output shaft.For given values of $r,r_o$ and coefficient of friction $\mu$ which is applicable for both pairs of interacting surfaces,the question is to find the minimum dimension $b$ of inner member which will permit the transmission of torque without slipping.

I couldn't get how to approach this problem.i tried drawing FBD of the balls but could get nothing out of it.Any help shall be highly appreciated.Thanks.


texts: Thermal conductivity relationship with particle size in nanofluids

texts: Is thermal conductivity of nano sized particles and bulk particles the same? If not, what's the difference and is there any relation between thermal conductivity and and particle size?


texts: Separate air from water for water pump in aquarium

texts:
I'm using the following setup to pump water out of a space below the gravel (yellow) in my aquarium:

The tubes displayed as lines are 12/16mm silicone tubes. The pump is a 300l/h electrical water pump.
The problem with this setup is that the biological filtration creates nitrogen compounds. They appear in large bubbles under the gravel which are sucked into the pump. After days the pump starts to run rough because it's not made for handling the gas bubbles in the tube.
I'd like to keep up this setup which is ideal with the exception of gas bubbles reaching the pump. Is there any way to separate the gas from the water before it reaches the pump inlet? A component? A smart arrangement of tube?
The relative height of the pump to the water surface, suction end of the tube or buttom of the aquarium can be modified in order to achieve a solution. I tried to have the pump on the same level as the aquarium as well as a slight elevation which seems to increase the time until the pump starts running rough a little bit.
I'd like to discuss the engineering problem rather than the aspects of running an undergravel filter.


texts: Anomalous oxygen in aluminium sample SEM EDS

texts:
I have a sample of aluminium which I'm interested in finding the rough composition of.

The sample is a part of a large number of samples which I sanded down and polished with a polishing table. I cleaned the samples with acetone, washed and rinsed in ultrapure water. Area spectrum SEM EDS analyses were then ran on all the samples.

Some impurities were left on the surface of the sample as expected. All other samples show oxygen, silicon and carbon impurities assumedly left from the sanding process (silicon carbide paper), the carbon tape for the grounding and possibly carbon impurities in the SEM-chamber. The samples were left to dry overnight so assumedly the amounts of acetone and water on the surface are fairly small.

All the other samples show accuracies and composities that seem sensible to me. However, the aluminium sample that I have shows levels of oxygen much larger than I expect:

So, three measurements of four areal spectrums each. Carbon is left out. And a mean of 17.37-at% of oxygen?

I understand that aluminium has a passive oxide layer and that EDS is a relatively surface active technique. However this paper cites passive layer thicknesses in the order of nanometers, and I understand that the EDS has a penetration thickness in the order of micrometers. A comparable steel sample that I analysed has levels of oxygen that I expected (~~0.1%)

What's going on? Can oxides precipitate inside bulk aluminium during manufacture or aging?


texts: What is "reversal" in mechanical engineering drawing?

texts:
I've come across these terms "reversals allowed" and "reversals not allowed" in a sample drawing while reading a GD&T course.

What exactly are these terms? What do they mean?


texts: Why are FBG sensors recalibrated every 10 years?

texts: So, I am working with FBG sensors and I have read that those sensors need to be re-calibrated every 10 years to get accurate measurements. But no where on the internet (AFAIK) is it explained why every 10 years it has to be re-calibrated and why.


texts: Purpose of special railway transport wagons?

texts: What's the purpose of the special railway transport wagons shown in the photograph?


texts: Adding the effects of two rods to move a single rod

texts:
I have to deal with a situation where I have two parallel and completely independent rods whose motion is dependent only on external inputs, and I want to add up the lengths traveled by each rod.
My first thought was to use two rack-and-pinion mechanisms by which I move two gears, one by each rod, and then couple them to a single rack. But this is not going to work since the rack when moved by one gear, will cause the other to move as well.
This seems to be an easy thing to do on a macro scale but I wish to 3D print this mechanism and they are going to be very small, so I expect to build a very simple mechanism.
Since the description is not so clear, here is a diagram:

When Rod A and Rod B are at A0 and B0 respectively, I want Rod Y to be at Y0
When either Rod A or Rod B is at state 1 and the other at state 0, I want Rod Y to be at Y1
When Rod A and Rod B are at A1 and B1 respectively, I want Rod Y to be at Y1

Rods A and B should be absolutely independent of each other. And the gap between the lower face of Rod A and the upper face of Rod B should be around 35 mm, with all rods being about 3 mm wide. How can this be solved?


texts: Stretch part of object in Autocad or 123D Design

texts:
I'm quite new to using 3D Drawing programs, except a bit of work in Google's Sketchup.
As I'm trying to draw a model that should be 3D printed, and heared that Sketchup is kinda bad practice for this, I started using a different program.

I've started drawing in 123D Design, this was quite working, only now I ran into a problem. I've made a mistake, as the right border is to small, and I need to stretch this. This should be quite easy if the corners weren't rounded. But I cannot find any way to stretch this border with 3mm while the corner is rounded.

The same has to be done for the rear plate.

As I couldn't find out how to do this in 123D Design, I've also tried doing it with Autocad. In here, I found the Stretch command, but this doesn't seem to do what I wish to do.

The selected part in the image is the part i want to stretch by 3mm to the right.

Sorry for the probably little simple question, but I couldn't find how to do this by myself.


texts: Is there an easy way to calculate carrier output of a planetary gear set which has two inputs?

texts: Online I found many guides and videos on how to calculate outputs of a planetary gearset but all of them have only one input. But how can I calculate output speed of carrier if ring and sun gear are moving at different speeds?


texts: Design a worm gear that works with a straight wheel

texts:
Usually, worm gears drive helical wheels. For my application (hand-driven orrery), I am studying a more cost effective approach: using a straight wheel. It is technically possible as you can see with this LEGO model (source):

How can you design this kind of gear train? Specifically, is there a relation linking the thickness of the wheel $b$, its number of teeth $Z_2$, its module $m$, the base diameter of the worm $d$, its number of teeth $Z_1$, and its helix angle $\gamma$?

Consider that the tooth profile as involute and a pressure angle ($\alpha$) of 20°.


texts:
I'm designing a four-wheel velomobile as a small city bike with good weather protection. The top speed in the city is about 25km/h (7m/s).
The total weight of the velomobile is 35-45kg, and I expect the rider with some luggage to be 65kg to 100kg. So the total weight is 100 to 150kg.
The weight distribution is 40/60, where most of the weight is on the back wheels. The velomobile is to be front-drive, and it adds complexity in the design but should not affect the suspension.
The small bumps that make the person bouncing about and make them uncomfortable are 0,5cm to 3cm in the city. It should be a firm but smooth ride on cobble roads and across potholes.
How do I design and calculate the suspension to make it good? The suspension design is double wishbone. Yes, I could (and would like to) make adjustments when changing from a 65kg rider to a 100kg rider, but how do I calculate the proper settings?

I've seen this answer - but I did not quite understand if that also works for very light loads: Car Suspension Force Equations


texts: Calculating the buoyant force of a rising bubble

texts:
I am solving the problem:

  A gas bubble rising from the ocean floor is 1 inch in diameter at a depth of 50 feet. Given that specific gravity of seawater is 1.03, the buoyant force in lbs being exerted on the bubble at this instant is nearest to:

The given answer is 0.020 lbs.

I start from the equation for buoyancy:

$$F_b=(P_{fluid}-P_{bubble})Vg$$

$g=32.2\:\mathrm{ft/s^2}$

$V=(4/3)\pi(1\:\mathrm{in}/2)^3 * (1 \:\mathrm{ft}/12 \:\mathrm{in})^3=3.03*10^{-4}\:\mathrm{ft^3}$

$P_{fluid}=sp.gr(saltwater)*densityH_2O=1.03*62.4=64.272\:\mathrm{lb_m/ft^3}$

P_gas:
Pressure, $P=62.4*50\:\mathrm{ft}=3120\:\mathrm{lb/ft^2}$

$PV=mRT$

$P_{bubble}=m/V=P/RT=3120/53.34*492R (STP)=0.11889\:\mathrm{lb_m/ft^3}$

When I substitute all of the values I only get 0.607 lbs. What am I doing wrong?


texts: For a linear guiding I need to know the concept and understand the jamming limits. See picture. If I choose concept 1 or concept 2, what will be the value of X? How can I calculate this?


texts: Proper designator for a torque guard in a P&ID

texts:
What's the proper first letter designator for a torque guard in a DIN or ISO compliant P&ID? I find fist-letter designators for a few physical values (L for level, S for speed etc.) but none for force or torque. As of now I'd use WS+ (W for weight, mass) as the closest but I'm not entirely happy.

This is either non defined in the codes or nobody bothered to copy the designator to where I can find it.

Note: I'm fine with an answer of the type: "I did X, a dozen people looked at my drawings, no one was confused"


texts: How would adding a wind deflector in front of roof-mounted solar panels affect drag on an RV?

texts:
I am mounting solar panels on top of a recreational vehicle (RV). To reduce drag, I was planning on building a small ramp in front of the panels to deflect wind before it hits the flat panel and mounts. Here is a rough sketch (red is brackets, black is panel, purple is ramp):

Someone told me that there would be MORE drag if I did it this way than if I didn't put the deflector/ramp.  I will do the work even if there will be VERY LITTLE difference between drag avoided by putting in a ramp and not having a ramp at all, but I definitely don't want to do it if it will INCREASE drag.

I think the space under the panel will be minimal.  I am going to try to get them as close as possible to the roof.  The panels are about 2" thick and the space between will be roughly 1/4-1/2 inch.

How would adding a ramp in front of the panel affect drag on the vehicle? Would it increase, decrease or stay the same?


texts:
What is the purpose of the RG10MEG Resistor in this circuit? Why is it there, I can't see any difference in the simulation when it's missing.
PS: U_IN = 3V DC + 1.5V sinusoidal at 1kHz


texts: Eliminating lateral motion in a pair of 4-bar mechanisms

texts:
As my first serious mechanical engineering project, I've built a wall-mounted folding table using of a pair of 4-bar mechanisms (WIP, ignore the wall mounts):

I'm using fisheye bar ends with spherical bearings, like this:

The mechanism behaves more or less the way I'd intended, but the spherical bearings have introduced a lot of lateral motion into the mechanism, which I'd like to minimize.

What is a good way to minimize or eliminate this lateral motion? Should I replace the fisheyes with clevis bar ends?


texts: What is the advantage of using a four-sided crimper vs. pliers?

texts:
I'm trying to crimp some pins onto 20 AWG wire.

I can either use a tool like this:

Or I can just use pliers, which are obviously cheaper and more readily available. Why should I use the more expensive tool?


texts: Rule of thumb maximum flow velocity of water in pipes

texts:
I have come across various values for maximum flow velocity of water in pipes.
At university we were told that 2 m/s is the upper limit where flow becomes turbulent.

In various planning reports I have read recently, 1 m/s is stated as the upper limit. I could calculate the exact velocity at which water in a specific size and type of pipeline will no longer flow in a laminar way, but for infrastructure planning purposes, this exercise is not required. What would a reasonable value for potable water be? Alternatively, what would the value for raw water (river) be?


texts: Calculating typical floor fan efficiency or dP? (Spec sheet too good to be true?)

texts:
I am looking to purchase a fan with high velocity. I am trying to make solid data driven decision based on specs.
I found that most fan's of the 20" diameter variety are around 3000 CFM; however found one that is stated at 6000 CFM  (2.83 m^3/s) with 162 watt and 1450 RPM.
Link to fan:
https://www.homedepot.com/p/Commercial-Electric-20-in-3-Speed-High-Velocity-Floor-Fan-SFC1-500B/302845111
I am using equation efficiency = dP*flow rate/Power and using 50 Pa dP (not sure what is proper value there, but it is giving me reasonable efficiency ratings so I normalized to that) I am coming to an efficiency of 87% for this fan.
It seems like the rest of marketplace is more like 30 to 50% efficiency (again using the assumed dP of 50 Pa).
Can someone help me understand if this is possible efficiency for a floor fan or too good to be true? Am I using correct equations and dP estimate. This is not my area of expertise by any stretch, but from what I have found the efficiency seems implausible.
Many thanks!


texts: Where can I find a lock that can do this?

texts:
I have two pipes, blue & yellow wherein blue is wider than yellow.

I need something (lock) that will prevent the yellow pipe from falling if the lock is tight, and at the same time is able to loosen so that I can adjust the yellow pipe up or down whenever I want.

What I will hang under the yellow pipe is computer speaker, one in my left and right.

Speaker Weight:

Left: 239g (8.4oz), Right: 343g (12.1oz)


texts: How to measure the inertia of an object using a motor

texts:
first time on this board even if I've been lurking for a while.

I'm a tennis racquet technician and, for the sake of saving some money and just for the fun of it, I'm trying to build a machine that could measure the inertial properties of a racquet in a more efficient way than the typical pendulum setup.

Here is a picture of the typical commercially available (and overly expensive) machines:

I figure that an accelerometer ans gyroscope would do ths trick measuring the angular acceleration of the baseline setup (shaft and clamping device) and a motor that could provide data of torque variation due to increased inertia of the added racquet for a given angle should do the trick. Im having trouble finding such a motor or another sensor that could perform thia task.

Any suggestions or pointers here?

Thank you very much!

Claudio


texts:
This might be a stupid question, but I'm new to mechanics, so please bear with me. Suppose I have a compound gearing system defined in the image below (not to scale).

The green gear is the driving gear, and the blue gear is a compound gear.

Suppose I have a driving torque of 10kg.cm, and the ratio is 1:6, this means the output torque is 60kg.cm, correct?

At which point is this torque increase? Is it on the outer edge of the smaller gear (A), or larger gear (B)?


texts: Volumetric efficiency versus pressure ratio for rotary compressor

texts:
I am trying to plot the efficiency graph of a rotary compressor.
I already calculated the volumetric & polytropic efficiencies and the graph versus evaporating temperature is as follows:

Now i would like to find the volumetric efficiency of the compressor versus pressure ratio, but what i see is not the single graph is 4 series of curves.

I have always seen in datasheet they show just one curve as the volumetric efficiency of the compressor.

Would you please tell me what is the approach to calculate the voleumetric efficiency graph of the compressor?


texts: Designing a clamping mechanism for linear sliding stick

texts:
the problem

I'm prototyping for a musical instrument based on sliding sticks (see https://vimeo.com/170450482) but I'm struggling to make a robust, yet smooth clamping mechanism for the sticks. The challenge is to hold the (hard wood) sticks in such a way that they won't fall to the ground, yet are as easy and smooth as possible to move by hand. (And of course it needs to be cheap and easy to produce.) I have thought of and tried a number of solutions, but up until now none seem sufficient.

insufficient solution one

The solution used in the first functional prototype uses flat springs on each side of the board. While it keeps the stick in place, the springs are not easily adjustable, making the stick move not that smooth. Also they were  relatively difficult to manufacture consistently.

insufficient solution two

Trying to find a more adjustable solution, we make clamps with springs for
the second functional prototype. While this allowed for good adjustablilty, this solution had too much wiggle, still didn't feel smooth and was even more intensive to manufacture.

insufficient solution three

Seeing that things needed to get more smooth, we tried to use felt to slide the stick against. This worked yet it proved difficult to make the hole exactly the right size for the sticks plus felt. Above that there were concerns that the felt would get more and more compact over time, as such losing their clamping force.

possible solutions 4?

The ideal solution seems to be in the image below; to use felt, but being able to adjust it's position. Yet I have not been able to find an adjustable mechanism which stays in place and keeps consistent over time.

Are there things I am missing? I am sure there are similar mechanisms out there in the world, but I haven't been able to find anything .

So my question is:

What would be a better mechanism for this problem?


texts: Intuitive understanding of the common normal at the point of contact of 2 gear teeth

texts:
Consider 2 oddly shaped surfaces and pick a point on each of the surfaces. At the point considered we can always draw a normal to the surface. Now if the two surfaces are in contact at this same point will the normal of one surface always be coincident to the normal of the other surface?.

I am asking this because, when studying about gears, there is always talk of the common normal and I am trying to understand if the presence of common normal is due to the design of the gear tooth or there is always a common normal between 2 surfaces in contact.


texts: Compare Genetic Algorithms and Markov Chain Monte Carlo in their statistical properties in parameter estimation task

texts:
I am using GA and MCMC for estimating the parameters of a transfer function. GA returns results that each parameter has one value when minimizing the error function, and MCMC returns the whole chain results for each parameter after the burnin, which gives a statistical distribution of the possible values for that parameter.

My first question is: What is the benefit of using MCMC over GA? Which one is better than other in what aspects?

My second question is: Do I get the mean value of each parameter from the distribution of the chain in order to get the fit for the transfer function? If so, do I do that with mean taking the mean value of the distribution? what if the distribution is skewed?

Thank you in advance

sorry I am new here, I didn't know how to tag this question.


texts: In static equilibrium body, how can an applied moment about an axis contribute to reaction moment to another point away from the axis?

texts:
Determine the resultant internal loadings acting on the cross section at B of
the pipe shown in Fig. 1–7a. End A is subjected to a vertical force of 50 N, a
horizontal force of 30 N, and a couple moment of 70 N m. Neglect the
pipe’s mass.

Well, I can't feel the solution. I would add upward reaction force (70/0.5=140 N) at B due to moment. But I wouldn't add 70 N m to moment equation at point B. can you explain the reason?


texts: Best Fan Positions for Airflow in a Duct w/ Two 90° Angles

texts:
A similar question was answered here. And while that did help me understand airflow, I have an even more specific question with a little different context.

So what I'm dealing with here is pulling fresh air in a vacuum duct through the front passenger door on a 1984 Volkswagen Vanagon. I have 2 sets of 3 vertically stacked 40mm computer fans, making 6 fans in total. You can read more about (and critique(please)) my ventilation system idea here.

As you can see, when the door is closed, air travels through two 90 degree angles. So the question is.... Where is the optimal placement of my fans. Should I put them both just before the first angle to give it the 'OOMPH' it needs? Or should I space them out, one at the beginning of the duct and another just before the angle? Or does it make any difference at all?

I tested it with just a single set of my stacked fans and I was able to feel a little bit of flow coming out of the vents. Can I expect to double that with my other set added?


texts: Arduino Programming IR Sensors and Actuators

texts:
Create the circuit below (Arduino)

You are supposed to use the following code (must download correct library if IDE is too old):
#include <IRemote.h>
int RECV_PIN = 11;
IRrecv irrecv(RECV_PIN);
decode_results results;
void setup()
{
 Serial.begin(9600);
 irrecv.enableIRIn(); // Start the receiver
}
void loop()
{
 if (irrecv.decode(&results))
MECH 303
Page 5 of 6
 {
 Serial.println(results.value, HEX);
 irrecv.resume(); // Receive the next value
 }
}

Now, I am trying to figure how to make different keys. I should be able to
transmit the code received by the IR
remote in your starter kit. I want to write down at least the codes for at least four keys. I need to be able to write the
keys of: forward, backword, 0, and 1.
I am pretty stuck and need help making these keys for all 4 movements
Thank you
Lauren Quinones


texts: Professional threaded insert in plastic?

texts:
I'm getting some plastic parts (made with HDPE) CNC machined. A few of these parts require the addition of threaded inserts. I've printed the parts myself using a 3d printer and when I add the threaded insert, it's impossible to insert it perfectly in the plastic part (perfectly straight in the hole) since I'm using a soldering iron (not very professional) to heat up the insert.
I know threaded inserts are used in professionally manufactured plastic products, so I'm wondering how they make sure the threaded insert is perfectly inserted into the plastic part. Which tool do they use to add the insert? What type of inserts are used?
Thanks everyone for the help.


texts: What is the technical term for a document that contains the results of a final test for a specific product?

texts:
Currently, I have to design a final test for a product. I want to summarize the results in a test report. The report is automatically generated and gives a summary (quantitatively) of which specifications are met and which are not met. If all the specifications are met, the test contains an "OK." Contained are product ID, diagrams, key figures, some explanatory paragraphs, and so on.

Does such a report have a specific technical term in quality engineering? With this term, I may be able to learn about best practices, etc., regarding such reports.


texts: How to calculate maximum rpm for a wheel?

texts: I have a DC motor with a rated rpm of 2750. At max rpm, the rubber wheel that I've attached to it is pulling itself apart (literally, the rubber is being pulled away from the central hub due to the centrifugal force). How can I know before purchasing a new wheel weather it will be able to handle this rpm? Is there a way to estimate this or do I need a spec sheet? I haven't seen any wheels that have a spec sheet.