texts: How do ultrasonic proximity sensors detect motorcycles differently from cars and trucks?

texts:
My car has ultrasonic proximity sensors to help me park. I've noticed that when motorcycles whiz past me the proximity alarm goes off. I originally thought that the motorcycles were just too close, but now I have observed that that isn't the case; cars or other road users at a similar distance and speed do not set off the sensors. It doesn't seem to matter what speed I am traveling.

I am not interested in troubleshooting some aspect of the alarm. I'm just trying to understand why this occurs. What special characteristic of a motorcycle or its movement causes it to be detected by the sensors when other road users are not detected?


texts: Can we build a tool that measure curvature on an arc?

texts:
I know some biologist that are taking curvature measurements on photos with softwares to understand the variation on beak morphology.

I'm wondering if there is a way to build a mechanical tool (or if one exist already) to measure the curvature of a circle's (or ellipse) arc. The arc is not always of the same length, so it would need to be adjustable.

There is a constrain (see the grey line):

I can't fit a big calliper on the bird's head.

I want to know:

the radius of the circle that correspond to the beak curvature
how "steep" is that curvature (probably a lack of vocabulary on my side but see the image down to see what I mean by "steep")

You can see this image as the different birds in the image above. Bird #4 would have a flatter beak than bird #1.

I need to be able to calculate the "steepness" even if the x, y or z are not of the same length.

The idea of bringing a mechanical tool is to calculate rapidly and conveniently a number and add it directly to a dataset. It's much faster than to look at photos and analyse with a software. So if there is a mechanical tool designed for this, it would be super useful.

Again, the image is just a visualization of the problem. I would like to measure the beak of different birds on the field.


texts:
Why are nuts 6-sided?
Why are nuts 6-sided? Why not 4 or 8?


texts: Bearing and Bearing Housing for Said Design

texts:
The system that I'm working on has a rotating cylinder (cleaning head). It needs to rotate vertically between two arms, much like a cleaning brush in a car wash.

Note: I have not considered how the shafts of the cleaning head will be connected to the motor exactly but it would either be directly connected to a coupler or with a right-angled gearbox.

I have added some illustrations just in case.

Specifications of cleaning head:

Weight : 4~5kg

Length : 1.5 m

Rpm    : 100 RPM MAX

I have done a bit of research and I know that the shafts need to be shouldered but how do I make one end of the shaft fixed? Tapered? Have a screw on the end of the shaft and lock the bearing with a washer and a lock nut?

Also, I'm thinking of having the top arm be where the shaft is "fixed" and the bottom be "floating" and connected to the motor. Is this a good decision?

Lastly, what bearings and bearing housings should I use?

Deep groove ball bearings seems to be able to handle the load but since there will be axial and radial loading(the cleaning head will need to tilt about 15 degrees at all times), so roller bearings maybe more suitable. I'm not certain.

There are split plummer (pillow) block housings and flanged housings, which is better for my use?


texts: Limit state design/ LRFD of short steel columns

texts:
Why do we use the yield strength as the limiting strength in short column design when using limit state design.
Why is the full capacity of the material not utilized (as is the case with beams when we compute plastic moments that occur beyond the yield).


texts: Programmable parameter change of Pro/E simulation by using Excel VBA , Matlab, Labview or Pro/E own function

texts:
Now, I've been conducting beam simulation by using Pro/E.

I would like to change payload(force) of beam step by step, and then plot the relation between deflection and payload(load range : 50kg to 500kg, step size : 25kg).

But, this task is too much time consuming, so that I would like to use a programming skill.

At the first time, I checked matlab-Pro/E interface, and I realized I can do something with SimMechanics tool.

But, unfortunately, my computer doesn't have the SimMachanics license.

So, I've been looking for other ways.

My computer has labview and MS-office as a programming language, as well as matlab.

Could I programmably change payload by using these programming languages without additional charged tool like SimMechanics?

If it is possible, Could anyone give me something like source code, documents or helpful site addresses?

If Pro/E provides desired function, it would be great. In that case, I don't need to make a program.


texts: What is the purpose of this dead-end rail junction?

texts:
This rail junction is located on a steep, short, local railroad line from the "mainline" in Reno, NV to the community of Stead.

The track is new/maintained and there is no evidence of an old siding.

As a train travels uphill, the train engineers stop and fiddle with it (I can only assume they are switching the junction), allow the train to pass, and then fiddle with it again before proceeding uphill.

Once the train has passed, it is in the "siding" position (a train traveling towards the photographer would turn off the main rail line into the ditch).

So if the same train then travels downhill and forgets to switch the junction, it would end up in the ditch.

What is the purpose of this junction?

A


texts: Can a retention/detention pond and a parking-lot be constructed in the same site foot-print?

texts:
Retention/Detention Ponds are often added to a site-design to mitigate storm-water runoff. Enhanced Porosity Concrete (EPC), aka Pervious Concrete, can be used as a parking-lot pavement that allows storm-water to flow through it. If a detention-pond was covered with a filter-fabric, and clean-gravel was used to fill the pond on top of the filter-fabric, then EPC could be used to cover the gravel such that a parking-lot would be created on top of the pond, and using the same foot-print as the pond. The gravel would support the pavement loads and the water-storage capacity of the gravel-filled pond would be a function of the amount of void-space in the gravel.

Because parking-lots and detention-ponds both take up a large part of land area of a building-site it would seem that combining the two in the same foot-print would save money and land area for the building-site developer. The pavement would also keep debris out of the pond and create a safer environment.


texts: How can I build a regulated pressurised air supply?

texts:
I need a source of air pressure for an air bearing (3D printed cylinder that expands air upwards like an air hockey table). I would like to be able to control the flow of air. I don't have a lab air supply or advanced equipment, this will basically be a homemade build.

An off the shelf electric pump might be a good supply source. What do I need to regulate the flow?


texts: Most effective heat transfer in a vertical pipe with small top/bottom temperature difference?

texts:
What would be most effective way to transfer heat in the following situation?

Specific conditions: A vertical cylinder or pipe, 30-100cm long, 5-10 cm in diameter, heavily thermally insulated except at the bottom, placed in a solid medium (except at the top, which is in air) whose vertical temperature profile varies on an hourly basis and will change polarity (delta T=T_top - T_bot will change sign), and has a temperature difference of around 2-10ºC.

The bottom of the cylinder is attached to a heat "sink" embedded in the solid surrounding medium. The top has a thin insulation layer between it and the air.

The goal is to tie the top temperature as close to the bottom temperature as possible

My first thought was to use a solid metal cylinder (likely aluminum not copper for cost reasons) since conductive heat transport is agnostic to the top/bottom temperature polarity.

It's tempting to use free convection in a pipe using water etc, which is presumably far more effective at driving heat transport. However, if the top is warmer than the bottom, full-cylinder convection won't happen. Forced convection or pumping is out of the question.

What would be the best strategy here? Would a mix of metal conducting rods in a cylinder otherwise full of liquid be even better?

Update: diagram upload as requested.


texts: ABAQUS Analysis: Difference between assigning Section as Plane stress/strain vs. Element type?

texts:
In ABAQUS, there are multiple ways to specif your part is in plane stress/strain.
1. When assigning the section, one can specify that it is a generalized plane strain section.
2. When assigning the section, one can specify that the section is homogeneous with a plane stress/strain thickness of 1.
3. When meshing the part, elements within the same section can be assigned an element type of generalized plane strain, plane strain, or plane stress.

I have sorted through ABAQUS documentation but have yet to arrive at a satisfactory answer, regarding the effective differences between above options.

It seems that with option 1, there is no thickness specified. Does this mean that abaqus assumes the simulation such that it is infinitely thick in the Z, as is consistent with plane strain? Versus in option 2, the thickness is 1? Meanwhile, how would results be affected if only the elements were plane stress/strain, with a regular solid and homogeneous section?


texts: Could I use thread size M16 for a 15 mm diameter rod?

texts: I am wondering is it possible to have a M16 thread on a 15mm rod? How is this manufactured? Any links to more info or answer would be very helpful.


texts: small relatively inexpensive crack detection apparatus for bike shops

texts: Is there a relatively inexpensive (let's say under $500US) crack-detection device and related mobile app that would be easy enough for a non-engineer/non-metallurgist to use to determine whether a bicycle frame was forming cracks that would be undetectable to the human eye?


texts: Compressing the air thrusted by an aircraft's propeller through a cone like tube

texts:
If I had an aircraft that used propellers for movement and took the air from the front running it through a tube that gets very small towards the end, would it have any impact on the speed?

Would the aircraft get faster because the ejected air would be faster then when it got in, similar to a waterpipe that is half closed?

Would it be slower because the compressed air would act like a barrier for the new air that comes in?

Or would the aircraft have the same speed regardless of whether we run the air thrusted by the propeller through our cone or not?

Here is an image with what I mean:


texts: What material might by used to 'staple' coils down in this stovetop element?

texts:
I have the stovetop element shown in the image below. If you look at the coils, they're fixed down by what look like little staples. I'm wondering what material those staples might be. The surface they're stapled into is a bit spongey, so I assume it (the surface) is an insulator, and that therefore it doesn't really matter what material the 'staples' are.

Element is from a Whirlpool stovetop. Image from this link at repairclinic.com


texts: Rubik cube torque experiment - Correct equations and experiment set up?

texts:
Background
I am attempting to experimentally find out the average torque required to rotate a single face of a Rubik cube. Little to no data is available as it varies from cube to cube. Some people have used a torque wrench but this is not an option currently.
Experiment Set Up
A picture of the setup can be seen below:

The cube is clamped to the table, string is wrapped around one face of the cube and weight is incrementally added to the bag. The mass is then recorded for the cube to rotate >=90 degrees. I constructed the following moment diagram:

Equations
Then I used the following equations to convert the mass of the cube to rotational torque.
F1=m * a = Acting Force
m= Recorded Mass ,a=Gravitational Acceleration
Torque=M1= F1 * X * sin(90)
Question
I did this a set of times to then find the average torque required to rotate the cube face. Are my calculations correct? and is this a viable way to measure the torque of the cube?


texts: What joint can I use for two thin parallel shafts to transmit both rotational and and linear power (in the axis of the shaft)?

texts:
I am here regarding a personal project but I am not a mech engineer. The shaft is a watch stem that is displaced from the crown stem. The two shafts are positioned like in the photo below but are 0.9mm in diameter and about 2mm to 4mm apart (it can vary). The shafts can be threaded too. One of the shafts rotates and drives the other and it also can be pushed and pulled along it's axis a distance of 1mm and the other shaft needs to follow that.
I have considered a universal joint with a third shaft/rod between the two, but they cannot be sourced at this size and are hard to manufacture and I am not not certain that the linear force will transmit well with a steep angle.
The other option is use an ordinary gear on each shaft for the rotation. And then couple the linear motion of the shafts with a metal bracket sitting around both shafts that is allows free rotation of the shafts but secures the linear motion of the shafts.
Another similar option would be to use 4 bevel gears. They would transmit the rotational power between shafts easily and the angled surfaces would restrict both shafts to the same linear movement.
Could someone help confirm this for me, I have no knowledge if this will work.


texts: How does the magnet sheet sliding metal mechanism work?

texts:
I was watching this video - at 10:23 mark where the person was using a hook mechanism for sliding the metal sheets together and noted that sometimes the hook would get caught on a bad angle. To solve this, he used magnets, but I'm not sure how this mechanism works.
If anyone could provide a drawing with explanations where the magnets are placed and how it would affect the sliding mechanism that would be great.


texts: Solidworks: Make a copy of a sketch on a different plane

texts:
I have Sketch 1. It's on Plane 1. There's a different Plane 2, and I want to make Pketch 2 which is simply the entities in Sketch 1 copied to Sketch 2. I don't want to copy-paste, because I want to have their constrains preserved.

Doing "Convert Entities" doesn't help, because the shapes become different, since they are projected to the plane.


texts: Where is the axis of bending for a box lifted by a crane?

texts:
A box is being lifted by a crane. Sometimes the box will be completely full, and sometimes it will only be partially full (indicated by the gray shaded regions).

The question is, where is the axis of bending in both cases? Does it follow the center of mass? Or does it always follow the geometric center?

(Of course I hope the axis of bending will always be in the middle so it could take full advantage of the roof and floor to resist bending.)

Also, if it matters, the crane will actually lift the box at 4 points, not 2. And I moved them inwards from the edges just because I thought that would resist bending more, due to a shorter beam.

Once I know where the axis is, I can calculate the moment of inertia and use the deflection formula

$$\delta = \dfrac{5qL^4}{384 E I}$$

Update

As advised, I did this for a U-shape, but also for the square, for comparison. I had to choose concrete numbers so I picked a 3x3x12 box with wall thickness of 1 cm.

For the square, I found the formula here.

$ I = a^4 - (a - 2t)^4 $

$ I = 3^4 - (3 - 0.02)^4 = 2.13849584$

For the U-shape, I found the much more complex formula here and took it about the y-axis since that diagram was vertical.

$ I =  \frac{2ta^3 + (a - 2t)t^3}{3} - (2ta + (a - 2t)t)\frac{2ta^2 + (a - 2t)t^2}{2a^2 - 2(a - 2t)(a - t)}$

$ I = \frac{2ta^3 + at^3 - 2t^4}{3} - \frac{(2ta + ta - 2t^2)(2ta^2 + at^2 - 2t^3)}{2a^3 - 2(a^2 - 3ta + 2t^2)} $

$ I = \frac{0.54000298}{3} - \frac{(0.0898)(0.180298)}{54 - 2(8.9102)}$

$ I = apprx. 0.179553$

So now I can finally use the deflection formula with both I's. I'm using steel so E = 200 GPa. The distributed load, q, is for a box 1/3rd full of crushed iron ore which has a density of 2,500 kg/m$^3$. q = 72,523 N/m.

$\delta = \dfrac{5qL^4}{384 E I}$

$\delta = \dfrac{5 * 72523 * 12^4}{384 * 200,000,000,000 * I}$

$\delta = \dfrac{7,519,184,640}{76,800,000,000,000 * I}$

$\delta = 0.00004578$ m for the square.

$\delta = 0.0005452766$ m for the U-shape.

...I have to conclude I did something wrong. It is hard to imagine a box of that size, with just 1-cm thick walls, would deflect by less than a millimeter when holding up iron ore, even at 1/3rd full.


texts: How to pull the shooter rod on a pinball game using a servo of some kind

texts:
I want to use a computer to initiate a game on a physical pinball game. (This is to see if I can get the computer to learn to play pinball using machine vision and deep Q networks.) I want to pull the shooter rod out that is used to send the ball into play. You pull back on the shooter rod and release it to send the ball up to the top of the play field. I need to create a hardware solution that can grip and release this so that it strikes the ball under computer control. You can see what it looks like in the image. I can use the computer to run a servo or electromagnet to initiate it somehow but I'm not sure what configuration would be easiest/best to implement. Although it would be nice, its not really important to control how far the shooter rod is pulled.

It seems to me I need a thing that can pull it back and then maybe a solenoid to release the grip suddenly. What kind of hardware solution do you think would work?


texts:
I am currently working on a prototype wire winch. I encountered some difficulties when trying to join the shaft and the cable drum.
Indeed the joint must be a welding, so I presume no keys are needed.

However since I'm not used to welding, I'm just wondering what type of welding would be the best for a Shaft/Drum connection.

I also suppose that welding type would be a "Tee weld" or am I wrong?


texts: Can g(t) be integrated with respect to t? Been stuck on this one for a while

texts:
Trying to work out the closed curve circulation of a velocity profile. The final integral that has been formed is:
$$\int_0^{2\pi}r^3g(t)dt$$

Can somebody help? Not sure whether g(t) can even be integrated?


texts: Could a reciprocating engine be powered by electric arc instead of combustion?

texts:
The heat of a lightning bolt causes the surrounding air to rapidly expand causing thunder in the process.

A reciprocating combustion engine ignites an air fuel mix to use the rapid expansion created in the process to build up pressure and use that to move pistons in order to create rotating motion.

Would a reciprocating engine that uses only air heated by a very high powered electric arc work?

It surely would be very ineffective, hard to supply with enough power without cables and would probably melt the engine block, but could it function in principle?


texts:
Hi all. I am building a machine to deform sheet metal into corrugations. I have attached an image that I got off a presentation from MIT's website. In the example, they provide a formula for the creation of a single indentation.

I edited the image to give you an idea of the shape I am going for. It is essentially a "W" shape after pressing.

I do not know how to apply the formula to my design. Is it the same amount of force that I would require? Double the force or even triple the force. My gut feel is that it should be somewhere between the same and double the force.

Any help would be appreciated.

Kind regards
Stefan


texts: Derivation on torque required to raise load, isn't there a force disapearing?

texts:
I drew a little picture:

Try to use you imagination to view these pictures as profile of bolt threads. In derivation on torque required to raise load, the angle of friction (ro) is calculated like in the left picture. Then it says that due to the angle of the 'tooth', friction-angle is adjusted, like in the right picture.
The problem is, a force F2 should exist, but they just ignore it. Why?
I opend Karl-Heinz Deckers famous Maschinenelemente book, where it shows how to get the formula required to raise load, and also at one point it just ignores the F2 force (at least it acknowledges its existence in one of the earlier steps of the derivation, but then just ignores it).
Can someone explain this?


texts: How do center of gravity varies in submarine between surface and submerged?

texts:
I'm interesting in static* roll stability of submarines. I'm always tempted to compare submerged submarine to blimps and other bigger airships. For airships, roll stability is assured by a pendulum effect, the heavier components being located low into the structure **. I have no idea  of how the masses are spread inside a submarine, but I imagine they are located such that the center of gravity is as low as possible to improve stability.

When submerged, I imagine the center of gravity varies as ballasts can contain a significant quantity of water. Cutaways I found show ballast tank  extend over a significant height of the submarine. Filling them may thus bring the center of gravity closer to the geometrical center of the submarine. This is only an assumption I fail to confirm.

How does the location of the center of gravity change when filling the ballast?

The consequences of this variation on roll stability is out of the scope of this question as the geometry of the immersed part of the hull also change.

* i.e. when the submarine is not moving
** cutaway found on this website give a good overview of where payload was located.


texts: How to calculate the torque of 4 wheeled vehicle before slipping

texts:
I have a 4-wheeled vehicle that is 10 x 10 cm. Each wheel has its own motor. The wheel diameter is 3.1 cm. The total weight of the vehicle is 500 grams. The friction coefficient of the rubber wheels to concrete is 0.6-0.85 (found this online, from the research I did I think it is needed for calculating torque). How much torque is needed on the wheel before the motor becomes too powerful and just cause itself to slip.

If someone share the steps and formulas needed to solve the problem it would be of great help.

So far I only calculated the weight on each wheel (I'm not even sure if this is correct)

$$\begin{align}
W &= \text{wheel}_1 + \text{wheel}_2 + \text{wheel}_3 + \text{wheel}_4 \\
500\text{ g} &= 4\text{wheel} \\
125\text{ g} &= \text{wheel} \\
\end{align}$$

so 125 g per wheel (assuming weight is distributed equally).


texts: Safety factor for pressurized container at 10 ATM

texts: There is no secondary containment to hold any potential shrapnel. How would this change the safety factor that is standard at 2.5? The consequences of this container exploding would be quite extreme as it is under high pressure.


texts: What means the velocity constant of the integration in PI controller formulas?

texts:
I have an equation of a PI controller. What means here the velocity constant "R" exactly?

$$m(t)=K(e(t)+R{\int}e(t)dt)$$

$$R=1sec^{-1}$$


texts: How to find Performance assessment (IAE and ISE) of a PID Controlled system?

texts:
The Integral Absolute value Error (IAE) and the Integral Squared Error (ISE) is to be analysed.

A PID Controller is given as follows:

\begin{gather}
C(s)=K_p+K_i\frac{1}{s}+K_ds
\end{gather}
where $K_p=0.07847$, $K_i=0.03587$ and $K_d=0.04291$.

The transfer function of the controlled system is:
\begin{gather}
G(s) = \frac{1}{s^2+s+1}
\end{gather}

Now as a feedback loop I have following:

Calculating the overall Transfer function $F(s)$ we get:

$$ F(s) = \frac{0.04291s^2+0.07847s+0.03587}{s^3+1.043s^2+1.078s+0.03587} $$

The step response looks like:

Now I wanted to find the Integral Absolute value Error (IAE) and the Integral Squared Error (ISE). By researching google I came to know the principle behind it and I also saw the formulas but how really to mathmetically solve it.

For example to solve for ISE for $W(s)$ as step response in frequency domain:
\begin{gather}
e(s)=w(s)-y(s) \\
\\
e(s) = w(s)-(F(s)w(s)) \\
\\
e(s) = \frac{1}{s} - \left(\frac{F(s)}{s}\right)
\end{gather}

Now I replace $F(s)$ and solve for $e(s)$ ??

After that integrate from $0$ to infinity to the $e(s)^2$??
I don't get it. How am I supposed to get the tuned value for $K_p$, $K_i$ and $K_d$?

Matlab code is here.


texts: How to accumulate torque of multiple independent gears?

texts:
I did not find any answers to this simple problem across the web, maybe seeking help in this forum helps:

As an example, let's assume we have multiple windmills, each of them producing torque, but each of them produces different amounts of torque, because they are not equally exposed to wind.

Now, how could one mechanically build some DIY gears and hacks to accumulate the energies/torques of the windmill-outputs together, without having back-effects to the windmills?

I want ONE output gear, which has the summed-up energy of all input-gears (windmills), and when input-gear-1 would turn the output gear faster than the input-gear-2, input-gear-2 should also be able to add its torque to the output-gear (instead of acting rather as a brake for the output gear).

I can't imagine that such a simple idea/problem has no solution yet in 2019, but I have to add that I am a complete noob in mechanics.

Important: I forgot to mention that I want to build this WITHOUT electricity or the use of any motors.
Think in terms of plastic-garden windmills. Little, wooden or plastic gears. Is it possible to achieve this with plain mechanics? (No electricity or magnetism involved?)


texts: What is the general way for the slab loading be distributed to adjacent beam?

texts:
From what I know, for a nice rectangle slab with 4 edges bounded by beams, one can distribute the slab loading to adjacent beam via the Tributary Area method.

But what if the slab is irregular, or there are arbitrary line loads on the slab, or the slab is not of uniform method, or not all sides of the slabs are covered by beams? How should the slab's dead load and live load, and any load on slab be distributed to beams? Is there a general way?


texts: Can waste heat in specific environments be collected into photons and converted to electricity?

texts:
This question is a repeat of another post on the physics board
Here and here show the possibility to combine photons of lower energy to higher energy. Thinking of an application, it could be used to dissipate heat from a laptop. A liquid cooling device could collect heat from a heat sink, then the device makes infrared photons with the heat and sends photons to an "upconversion" device. This device combines infrared into visible light photons and illuminates a conventional solar cell.
One would think of using a thermoelectric generator which still needs to dissipate heat. However, by imagination could "upconversion" package waste heat collected  and turn it into light? My sentences may appear rudimentary as they are just ideas.


texts:
I'm currently designing a project for a local museum through Purdue University's engineering class. My team has come down to three options:

Trying on a space suit with functioning parts
Looking though a telescope that uses a VR-type experience that displays the Hubble telescope images in a 3D like manner on the end of the telescope,
Or a mars rc rover that uses a QR reader to "scan" various objects on a "martian" surface and displays info to the user.

My team is looking for information on just how reliable QR code readers would be. We would only be using 2-3 simple designs (vertical lines, horizontal lines, and a circle). I could not find much information online other than "best ios QR reader" or "best QR readers!", so if anyone could give some insight to the range of precision that the reader would have (i.e. angle from normal that it would still work, etc) that would be awesome. The reader and code itself would always be at the same height.

Obviously budgets are a factor for this project, and each QR reader differs, but on average how does the QR code reader and software hold up?


texts:
I'm trying to calculate the magnitude and direction of the force exerted on a wheel when encountering a step. The wheel and the steps are non-deformable.
I found two different approaches:

energy approach, from which I can calculate the difference in speeds before and after, but I have no idea how to continue from there.
Vertical component of force for rigid wheel hitting a step

impulse and angular momentum, the procedure described by the user QiLinXue on the bottom of the post bellow roughly makes sense to me, but I have no idea what is the direction of the average force he calculates. I also don't really understand what the velocity change represents.
https://physics.stackexchange.com/questions/515895/what-is-the-term-for-shock-absorbed-by-car-suspension

If anyone has any pointers how to continue from here, it would be much appreciated. I'm trying to calculate the vertical force to select the appropriate spring for the given speed.


texts: Controlling the dynamics of nonlinear systems with an unknown steady state

texts:
On the one hand, the question is simple, on the other hand, I need the help of specialists in control theory.
Let's take a simple gradient dynamical system:
$\frac{dx}{dt}=\frac{df}{dx}$
where $f=e^{-(x-x_*)^2}$ and $x_*$ - constant, that constant defining the position of the maximum.
The transition process in such a system is a transition from state $x(0)$ to state $x_*$.
We assume that we don't know the value $x_*$ in advance, as well as the function $f$ itself. How to make sure that transients in such a system always occur exponentially?
We can do anything: add control signals or add auxiliary variables.


texts: What are the design difference of a steel tank that would withstand 136atm inside and 1atm ambient compared to 1atm inside and 136atm ambient?

texts:
Let'say the steel tank would be submerged deep in the ocean with 136 atm ambient pressure then the other tank with the same material would just be used to contain 136 atm pressure. How would the thickness of the wall differ?

Also, if the tank is designed to be sunk deep in the ocean, would it be cheaper to design a tank that could contain 136 atm pressure then pressurize it at that pressure so that it would have zero forces acting on the tank's walls if the ambient pressure is also 136 atm?


texts: Why scuffed liners or piston rings always have vertical lines?

texts:
This is a picture of a scuffed liner.

What causes the presence of vertical scratches?


texts:
Why are pilot tones repeated so much in OFDM?

I understand the pilot tones are used for synchronization, ensuring the phase of an OFDM signal is correct. It's for fine grained control after using the pre cylicguards to determine the rough start of a signal.

My best guess for repeating pilot tones is redundancy in case there's noise that distorts a pilot tone(s).

I'm not sure what else there would be? As with my understanding, assuming the signal was received perfectly, one pilot tone would work? As you will know the signal is in phase, once the pilot tone amplitude is correct?

Or is it possible to somehow get the phrase for the pilot tone correct but the signal incorrect?

Thanks


texts: Why is the Bush of a motor not replaced with a ball bearing?

texts:
Ball bearing reduces friction to a large extent than sliding friction. Motors use a metal ring called bush which slides against the shaft when the shaft is rotating. If a force is exerted on the shaft in direction perpendicular to the direction of the shaft, the motor stops because of the so much friction present between the shaft and the bush. Here's a photo to be clear :

... Whereas, if a ball bearing is used instead, the force won't be that much effective in that case because of the balls present in the ball bearing as they have to roll and not slide. For those thinking what a bush is, here is a photo:

(Photo taken from Google, edited)

Why is the bush not replaced with a ball bearing?


texts: Calculating leakage in an all steel piston cylinder arrangement

texts:
I wish to calculate air leakage in a piston cylinder arrangement. One side is pressurized and the other is at atmospheric pressure. All steel construction. No piston rings or lubrication. The piston oscillates at about 50 to 80 times per sec, amplitude 5 mm, and is used as an indentation marking tool.

I know the piston diameter, cylinder diameter, piston length, air pressure and roughness. I need to calculate the leakage in liters per minute to determine: If the clearance is increased, how much increase in piston length is required for the same leakage? Less clearance gives more air efficiency, but is difficult to manufacture.


texts: How to find a reference line for " Form Tolerances"?

texts:
In my project I have to choose a form tolerances ( parallelism ) between the handle ( purple part ) and the part that sits inside it ( the grey part ), where the two parts slide on each other.
But I don't know how to choose the right reference line on my technical drawing ( drafting ).


texts: Stall Torque of a DC Motor Less than Theoretical Values

texts:
I have an unknown DC motor with specifications I was testing. I used a Prony Brake setup and scale to evaluate torque, a tachometer for RPM, and multimeters for voltage and current.

I get a linear graph relating torque and RPM. However, when I physically stalled the motor and checked the stall torque, it was much lower than what the linear graph expected! Almost 1/2 the expected value!

Is there a physical reason to explain this? This outlier is pretty consistent through 4 trials. Is it possible it's due to the Prony Brake? Or perhaps something within the motor? Back EMF or something due to friction? I'm at a loss as to why such a data occurred, and not only once but multiple times!

Thank you.


texts: What is the area when calculating the drag coefficient for a race car wing?

texts:
The drag coefficient is given by the following expression

$$C_d = \frac{2F_d}{\rho v^2 A}$$

For a race car wing (which is simply an airplane wing upside down to generate downforce), what should we consider as the area? The cross-sectional area perpendicular to the flow or the wing surface area (parallel to the ground)?


texts: How exactly do noise canceling headphones work?

texts: I purchased a pair of noise canceling headphones today and I was just wondering how exactly they are able to cancel out background noise?


texts: Pade approximations for state space systems

texts:
I am studying the application of Pade approximations on a system with a dead time. In most cases, we consider a transfer function with a dead time and apply the Pade approximation on it.

Now here is my question: can we introduce a delay in state space? If yes, how one can apply the Pade approximation on it? If no, why is it not possible?


texts: Pressure Coefficient with a Minima of 0 on Compressor Airfoils in Cascade

texts:
I am a relatively recent BSME graduate working on reproducing the results of a technical paper to strengthen my ANSYS CFX skills. The paper is "Effect of Section Thickness and Trailing Edge Radius on the Performance of NACA-65 Series Compressor Blades in Cascades at Low Speeds" by Herrig, Emery, and Erwin. My goal is to reproduce pressure coefficient vs axial chord plots for one of the test cases using ANSYS CFX.

Problem Statement/Givens from Paper: The test was performed in a low-speed porous wall wind tunnel with an air average inlet speed of 95 ft/s. The particular airfoil geometry I am examining is an NACA 65-(12)12 (5 inch chord) at an angle of attack of 23.5 degrees with a solidity of 1.5. I made some assumptions not stated in the paper for my CFX model. I applied a free slip wall in place of the porous walls to capture the effect of boundary layer shedding. I also assumed the outlet static pressure was 1 atm and the inlet temperature is 15C. All other solid surfaces are applied as adiabatic walls with a no-slip condition. I am using the default k-epsilon turbulence model, isothermal heat transfer, and neglecting buoyancy effects. The pressure coefficient is to be determined along a mid-span plane on the surface of an airfoil far from the end walls (the third airfoil of the 5 I put in my cascade model).

The Problem: The provided results from the paper have a minimum pressure coefficient of 0. My results, however, have a minimum ~1.05. I noticed all the pressure coefficient figures in the paper have a minimum at 0 and no negative values.

My Attempt at a Solution: I created a polyline at the intersection of the center blade surface and the mid-span plane. I wrote expressions in CFX Post to determine the area-averaged density, inlet velocity (although this is redundant), and static pressure. Then, I created a new variable to calculate the pressure coefficient. The calculation being performed is (P_static_local-P_static_inlet)/(1/2*rho_static_inlet*velocity_inlet^2). I've attached the results from the paper and my produced results. My trend seems to be mostly correct (save the waviness from producing the airfoil profile myself), however, the problem of the y-axis scale still remains.  . To complicate things further, the definition of the pressure coefficient they provide in the paper uses a local total pressure instead of a local static pressure, which changes the shape of the plot completely.

Does anyone know of a standard used to adjust the minimum pressure coefficient to 0? This is the only sort of logical explanation I can conjure at the moment. Of course, if anyone sees any glaring errors in my methodology please comment and let me know.

Thanks for your time


texts: How much air will an engine use per tank of gas?

texts:
Apparently I have a stupid question.

I got curious and crunched some numbers to determine approximately how much air an engine consumes in total to burn a full tank of gas. Something went horribly wrong and I feel stupid.

So theoretically, I can get this number by multiplying the total amount of fuel in the tank, let's say 15 gallons (56.78 liters), by the air part of the air-fuel ratio, which I read is 15:1. So the engine would consume about 225 gallons (851.7 liters) of air per tank of gas?

But that number makes no sense if you take into account the other way to calculate this: engine size. Let's say we have a four cylinder, two liter engine. Since it's four stroke, the air it will consume should be equivalent to its rpm. So at 1,000 rpm it will consume 1,000 liters of air per minute. Right? That's a very long way from a total of 850 liters for the whole tank of gas.

So what did I do wrong?


texts: Developing a model of rate of cooling of steel tube in air

texts:
I am trying to develop an equation to determine the cooling rate of a steel tube in air. I'm using Fourier's Law, Stefan-Boltzman Law, Newton's Law as well as the specific heat capacity equation. The tube transfers heat by radiation and convection to the air and it transfers heat through conduction to the steel cooling bed it is laying on. The equation I have determined from these is $$T_{tube, final} = T_{tube, intial}- \frac{(\dot Q_{radiation} + \dot Q_{convection} + \dot Q_{conduction})\times\Delta t}{\rho VC_{p}}$$ where, $$\dot Q_{radiation}=\epsilon\sigma A(T_{tube, initial}^4-T_{air}^4),$$ $$\dot Q_{convection}=hA(T_{tube, initial}-T_{air}),$$ $$\dot Q_{conduction}=kA\frac{T_{tube, intial}-T_{cooling bed}}{dx}.$$ The thermodynamic properties of the steel are:
$$C_{p}=416\frac{J}{kgK}$$ $$\rho=7667 \frac{kg}{m^3}$$ $$k=24.2 \frac{W}{mK}$$ $$\epsilon=0.86$$ My assumptions making this equation are:

Air temperature and cooling bed temperature is at a constant 300 K.
Temperature dependent properties do not vary much and should be considered constant.
The heat transfer coefficient is 5 tW/(m^2K).
The temperature throughout the tube is consistent

I know the tube starts at about 1300 K and drops to about 1150 K in about 40 seconds, when I use this equation though I get really low final temperatures, sometimes even negative ones. Can you help point me in the right direction? I am not looking to develop a 100% precise equation. Just one that will give me a close estimate with only a few percent error.


texts: Flexible and "Squishable" Tubing for Peristaltic Pump Model in Solidworks

texts:
I have made a rough model in solidworks of a peristaltic pump we purchased in my lab. There are no moving parts. Screenshots shown below. Is it possible to make assemblies with the three sets of tubing (1/4", 5/16", 3/8" ID with 3/32" wall thickness) bent and squashed around the rotor similar to what is shown in 4?
The lengths of tubing are all roughly 4.5 inches long (see 2) and I think they are made of viton. The straight length between the middle of each fitting is 107 mm (4.21 in) so there seems to be only about 0.3 in of tubing left to go over the rotors. The tubing is also compressed by a door which has an inner radius of about 33.3 mm (1.31 in) and is offset from main shaft of the motor by 5.36 mm (0.211 in) when closed. The rotors themselves are 14.5 mm (0.571 in) in diameter, and positioned 17 mm (0.669 in) radially from the center of the main shaft.
Please let me know if this is possible, or if any other information is needed.

Screenshot of Model

I didn't include the tubing here, but that is in the drawing I made below with different views of the pump.

Drawing of Model

I made these measurements myself, so it's not perfectly accurate but I compared the model with the actual pump and it's close enough for my purposes.

Drawings from Amazon

Images from Amazon


texts: Why are tremors of an earthquake felt more on upper floors?

texts: Why are tremors of an earthquake felt most on the upper floors of a building in comparison to lower floors? Does this have something to do with a third class lever?


texts: Device to apply pure normal force over planar surface, without friction-based coplanar forces

texts:
I have to build a device to apply a pure normal force over a force plate. The requirement is that it doesn't apply any shearing (by means of friction) on the surface.

The problem is: for any given device structure, there will always appear some deformation, specially under load, and so I don't want to depend on geometric alignment, I would like to have my indenter to have an appropriate joint with the proper types of degrees of freedom.

I though about a ball bearing roller, but that would only decouple the force along one direction, since it could still transmit force by friction along the other direction.

So my question is:

  What is the recommended way to eliminate coplanar reaction forces, so that only normal force is transmitted and coplanar forces are neutralized?

I think lubricant-based solutions don't fit well, since they are always quantitative in nature. I think a qualitative solution involving mechanical decoupling by a proper joint is better, similar to the ball-bearing one, but with an additional degree of freedom.


texts: I know ceramics are generally considerably less dense than pure metals or alloys but sand is used in barbells for its probably cheapness, user-friendly and easy availability but its a decent density too. rammed sand-  1682 kg/m cubed using Engineering Toolbox compared to 2658 for steel chips.  So if you wanted the most dense for something to have great compressive strength- what would it be?


texts: Arc-welding 2mm thick steel at an angle without burning-through

texts:
I'm learning a bit of stick welding since I keep needing it for certain projects. Total beginner.

The latest thing I decided to make is a table similar to this one:

The material is 2mm thick 40x40mm square tubing - don't know the exact metal type, should be "regular" steel that was a bit corroded from staying in the steel yard.
I tried using 2mm and 1.6mm rutile electrodes.
I tried the 1.6mm at 55~ Amps AC and the 2mm at 60-65 Amps AC. With higher or lower Amps, my electrodes started sticking.
The angle I'm holding the electrode at is similar to this one: https://i.ytimg.com/vi/qTaQf0iPH-g/maxresdefault.jpg

What is happening that on straight flat sections I can spark and keep a straight line and don't burn a hole in metal. The weld is strong and consistent.

When trying to weld the two pieces together, on the outside and inside angles (see red circle) I keep burning through and bigger and bigger gaps keep opening because of this.

On the inner corners I have not had this issue and I have successfully welded thicker metals with 2mm and 2.5mm electrodes without issues.

EDIT: Edited for clarity that I'm not actually welding without melting metal :)


texts: How can I use backcalculated modulus results from FWD testing to represent my existing condition using Pavement ME Design?

texts: We only have one adjusted FWD modulus value for HMA layers, but I can only see input options in the form of a grid of frequency and temperature.


texts: What kind of splines should be used when planning roads?

texts: I would like to plan a small road network for an imaginary city, and I am looking for a way to create curved road segments. I am familiar with cubic Bezier curves, but I am not sure if it's the best fit for this problem, and it's not trivial to offset. Circle arcs are easy to calculate and offset, but they are not as flexible and hard to chain. What kind of splines do enginieers use, when they plan roads?


texts: How to compare two acceleration sensors side-by-side?

texts:
I have a single axis analog capacitive acceleration sensor (from PCB Piezotronics) which is very reliable but expensive. Now I need more axis, unfortunately can not afford buying anymore. So I have ordered a cheaper and "versatile" alternative, digital SPI sensor (Murata) which is easier to interface without additional analog to digital converter, also it has 3 axis.

On the datasheet it looks quite promising, but in reality it is not. I have noticed that the result is floating, even when the sensor is not moving.

I made a FFT and histogram for both new and older sensor, putting them parallel and measuring, Murata looks strange.
Murata SPI:
PCB analog:
Murata also measures a bit higher about 0.58Hz, when PCB is 0.55Hz. Edit: It is because the sample rate is not exactly the same.

What do you think, is my approach is correct? How would you compare two sensors?

Datasheet of Murata SCC2230-E02 sensor - Combined gyroscope and 3-axis accelerometer with digital SPI interface:

Datasheet of PCB sensor: http://www.modalshop.com/filelibrary/3701G3FA3G.pdf


texts: Calculate the Euler buckling load of a column using the finite element method

texts:
I am trying to find the buckling load of following column:

I started from the system of equations $P = (K + K_g(N))U$, where $K$ is the stiffness matrix of a single 2D frame element and $K_g$ is the geometric stiffness matrix of the same element.

The boundary conditions give zero displacements and rotation in the node at the bottom of the column. So I tried to solve the equations for the 2nd part of the column, where the only unknowns are the displacements and the rotation in node 2, with $N = P$. But this gives me the same result as for a standard cantilever beam.

Here's an example on how to calculate the buckling load for a cantilever beam:

I also tried solving the complete system of equations with unknown displacements in node 1 and 2, but without success. And since I need to be able to calculate it by hand, this doesn't seem to be the most efficient way to do it.

I don't know what I'm doing worng. Could someone help me to start in the right  way?


texts: How do I use this " Low-Density, High-Hardness, High-entropy Alloy" to make a good shortsword?

texts:
Given the information on swords here:

  When you need to place a great deal of strength into a thin blade, steel remains the best all around choice. Titanium blades will be simultaneously weaker and softer than similar steel blades.

And the material (LDHEA) described here:

Summarized here from the Applications section of the Wikipedia article on Scandium, as:

  An alloy called Al20Li20Mg10Sc20Ti30 has been shown to be as strong as titanium, light as aluminium, and hard as ceramic.

In combination with other materials, how could LDHEA be used to make a good shortsword?

Perhaps steel for the flat and LDHEA for the edge and point?


texts:
Question in short

The following drawing is a ball-screw with both ends mechanized and a ball-nut on it.

What is the meaning of the indicated notations?

Context

What is clear to me are:

Indications of sizes/distances
Angles
Parameters of precision/error
Diameters

It seem that the little letter (e.g. 2) are related with the values in the box, but I can't understand the meaning. The 1 is completely obscure to me.


texts:
The following scenario:

I am tasked to design a 6.6m high reinforced concrete wall in an industrial building. We have a 10 ton Telehandler (telescopic loader) with 7m maximum reach, loading 1500kg loose material in a scoop.

I need to cater for a "runaway vehicle collision" where:

the vehicle reaches a maximum velocity of 2m/s before it collides with the wall.

I need to find out the worst case collision force on my wall.

Usually I would employ the design methodology for vehicle barriers and parapets in car parks in Eurocode 1 (EN 1991-1-1). But in this case the point of contact is significantly higher than the centroid of the colliding vehicle.

I would assume that the front wheels of the loader leave the ground during the collision, thus there is some sort of energy dissipation there too.

I am pretty sure that the long boom just frightens me and is enough of a distraction to stop me from thinking straight here.

Any help would be greatly appreciated.


texts: Do liquid hydrogen-based cooling devices exist and what are they used for?

texts:
Liquid hydrogen cooling could be some intermediate solution between helium and liquid nitrogen based cooling.  For example, some type of superconductors could be cooled by liquid H2, and this could be much cheaper than the liquid He.

What are their most characteristic applications in the industry?


texts: What's this mystery symbol on a manufactured machine?

texts:
I hope this is the right place to ask this question; if not I'd really appreciate some tips as to where else I can go for answers.

The symbol above (apologies for the blurry quality) is on a Chinese/Taiwanese-manufactured piece of testing equipment. It's located on the manufacturer's sticker. I can find absolutely no trace of it elsewhere on the Internet (I've absolutely, positively searched).

Can anybody shed some light as to what this symbol might mean? E.g. an electrical safety certification, a manufacturing standard...?

Thank you very much!


texts: How does a Y connection in a 3 phase motor create 230V without a neutral/ground

texts:
I know that a 230/400V 3phase motor requires 230V on each coil. No more and no less. So on a 3*230V grid it would be wired in Delta, on a 3*400V it would wired in Y.

I went to evening school to learn about this and my course on the subject has several diagrams on this, most resembling these 2:

We also put this in practice and wired the motors and tested errors etc.

But thinking about it now I noticed that we never grounded the center point of these connections. How can a Y-config at 3*400V produce 230V on the coil?

Is there a mathematical way of calculating this? It's confusing since there's 3 voltages that are all averaged at 400V but measured at any given moment they're 3 very different voltages connected to eachother.

I have however also seen images online of a delta/Y connections that do ground the centerpoint:

And here it totally makes sense that the coil get 230V because we know that L-N voltage is sqrt(3) of L-L voltage.

I feel like I'm missing something here.


texts: How to keep a symmetric-lens-shaped object upright using only wire?

texts:
Given a lens-shaped frame with a single crossbar running parallel to the floor, how could we keep that object upright and stable on one of its endpoints using only wire?

The shape I'm describing is similar to theta: θ

Except it's pointed at the top and bottom. See also Lens (geometry)

You can assume the frame is made from a flexible material, and that the entire frame is one contiguous unit. You can also assume we can freely affix any number of wires to any point on the object and any point on the ground.

As a follow-up, is there an efficient method of positioning the wires so we can keep the amount of wire needed as low as possible?


texts: Are DVD laser diodes single transverse mode?

texts: I am looking for a cheap source of low power single transverse mode laser diode in order to focus them to a very small point. I thought I would get that from a DVD drive but the pattern I see at the focus point isn't a single point at all (2 or more points). I find that strange. Could you confirm that the DVD diodes aren't single transverse mode? (suggestions and reference of suitable diode are welcomed)


texts: Do bottles leaking due to air pressure in an airplane cargo hold?

texts: Is it possible for essential oils to leak from sealed bottles that are being transported by airplane in the cargo hold?


texts:
I need a small air compressor for a robotics application. I currently have one of those 12V tire inflators (200 psi, 1 CFM or so) that is sized well for this purpose (sample image below).

However, in the future I would like to replace this with a lighter compressor with similar specifications (for weight savings). Most of the weight of these compressors is a large DC brushed motor (the whole big silver cylinder in the photo below), while the actual compression module is relatively small. These motors are roughly 350W peak (30A, 12V from spec sheet). Similar DC brushless motors (by wattage) are <150 grams. Certainly they might be at a higher RPM, but even with gears this would still be a lot smaller.

Is there any reason that these huge (3-4 kg) brushed motors couldn't be replaced by tiny brushless motors? If so, why can't I find such devices anywhere? It wouldn't be cost effective for these cheapo inflators (you need more complex controls for brushless), but it seems like there would be enough demand for lightweight compressors for someone to manufacture a few.


texts: Torque computation for different attachment point

texts:
I have a pretty basic question but I would like to be sure of what I think.

I have a setup like the one in the figure. I have two motors which can generate two forces $F_1$ and $F_2$ perpendicular to the plane of the drawing (coming out of the plane of the drawing). The black box is a rigid body of mass $m$ which has the Center of Gravity (CoG) in the middle (the white circle). We can think about two forces coming from two propellers as on a quadrotor UAV or a helicopter.

My question is:
regarding $F_1$, since the corresponding arm is aligned with one of the axes of symmetry of the body (specifically y), if it will be activated it will contribute in torque terms only to a rotation $\phi$ with respect to the x-axis and therefore the acceleration around the x-axis will have this shape:

$I_x\ddot{\phi}=...+L \cdot F_1$

where $I_x$ is the moment of inertia with respect to the $x$ axis.

Instead, if I activate the motor 2, corresponding to the force $F_2$, since it is displaced from the axes of symmetry, but still parallel to one of them, I should have:

$I_x\ddot{\phi}=...+L \cdot F_2 - \underbrace{f(I_y,d_2,a,mg)}_{M_d}$

where $I_y$ is the moment of inertia with respect to the $y$ axis, $m$ the total mass of the rigid body and $g$ the acceleration due to gravity.
The term $M_d$ should take into account the torque coming from the motor and the counter-torque coming from the fact that the point of attachment is not aligned with the $y$ axis.
I would like to know how to write the expression of $f(\cdot)$ which should be quite easy to do.

Thanks for the help!


texts: Is it possible to set up an ultrasonic range-finding system using a separate transmitter and receiver across 30m distance?

texts: I need to set up a system capable of detecting the distance between an object moving further away and an anchor point. This object would be traveling through a slightly curved tunnel (of 1m diameter), making line of sight laser range-finding impossible. The object travels a maximum of ~35m and the object's position should have less than 15cm of error over that distance. From my research, 30m is too long of a distance for typical ultrasonic sensors in which the sensor emits a pulse and then waits for its echo. So instead, if I had a transmitter at my anchor point and a receiver attached to the back of the moving object, could I expect to get accurate distance data based on the time it takes to receive each pulse? Would this data be useable despite the fact that the pulses would likely reflect significantly on the walls of the tunnel? Would this work over such a large distance as well? Thank you.


texts:
I am rebuilding a car engine. With some of the fasteners I am unscrewing, I notice that a lot of torque is required to undo the fastener. It feels like a snap when undoing a fastener, rather than a smooth twist. If I tighten the fastener to a set torque again and loosen it, it requires the same torque as it took to fasten it.

Why would this be? My guess would be something to do with heat cycling.

Note: There is no threadlocker on these bolts.


texts: Water distribution - sizing weir buildings

texts:
I have a building to evenly split a water stream into two: Water flows into central chamber, over two weirs of equal height and length into two chambers and from there into pipelines. I'm looking for rules of the thumb to correctly size the chambers. Weir length is straightforward. But to guarantee even flow over both weirs I need to ensure even flow conditions in the central chamber. So I'm looking on rules of the thumb how wide and high my central chamber has to be, depending on inflow conditions. So far I had no luck with the DWA/ATK (German water and wastewater associaction) guidelines, maybe codes from other countries are helpful here.

Example drawing (top - layout, bottom - cut):


texts: What is the actual stress in a certain point in a body?

texts:
I'm reading my book on strength of materials and it says that the stress in a point depends on the orientation of the section that we are observing, and since there are infinite number of section that can go through a point, there can be infinite different stresses in that point.

So my question is what is the real stress in that point, that we use in out calculations? Is it the largest one?

Because obviously the "real" stress (if there is one) can't depend on the section we decide to look at, so I'm confused.


texts: Safely Measuring Voltage from Solar Panels in an Experimental Research Field

texts:
I'm installing solar panels (not connected to the grid) in units out in a field for research we're doing that looks like this (this is an outdated image, but I can't find the updated one unfortunately):

I have to safely measure power output from each unit, and each unit has 9 panels with the following specs:

Maximum Power: 100W
Maximum System Voltage: 600V DC (UL) Optimum
Operating Voltage (Vmp): 18.6V
Open-Circuit Voltage (Voc): 22.3V
Optimum Operating Current (Imp): 5.38A
Short-Circuit Current (Isc): 5.86A
Operating Temperature:-40°F to 176°F
Output Cables: 14 AWG (2 ft long)
Maximum Series Fuse Rating: 15A

(The panels are coming from Amazon, so I'm not sure how accurate the specs are, and the link to reference them is at the bottom)
These panels are going into an agricultural field, so my primary concerns are: 1) Not electrocuting anyone, 2) not starting a fire, 3) being able to accurately measure the power coming from each unit.
This is my main plan so far, which I'd like feedback on:

Wire all 9 panels in series to minimize amperage
Use 14 AWG wire to take the power out of the field to some sort of resistive load to use the power
The unit will be grounded using grounding rods
On the circuit, there will be a 10A circuit breaker, a manual on/off switch
The resistive load will be connected to a GFCI
Power will be measured using some sort of Arduino based module

Two notes:

I'm not sure what the best, safest (and if possible, cheapest) way to burn the power from the solar panels is. I was thinking using a space heater since each unit is allegedly only putting out a maximum of 900W and commercial space heaters are rated for 1875W. I know I could ground each unit and not have a load and the power will just discharge, but my understanding is I can't measure that.
On the subject of measurements. Are any of the micro controller compatible power meters I find on Amazon going to be sufficient for this task, or do I need to look for something specific?

This has to be done ideally asap, but definitely before the end of May. Although, again, my main concern is doing this safely first and foremost. I am willing to hold off on measuring the power as long as there's as the primary concern is discharging power safely then figuring out how to measure power. I imagine that would involve routing power to a grounding rod, but I'm not sure.
Any advice and feedback is greatly appreciated, and I am happy to answer any questions.
Solar panel link: https://www.amazon.com/Renogy-Monocrystalline-Solar-Compact-Design/dp/B07JXYTFF7/ref=sr_1_1?dchild=1&keywords=Renogy+Solar+Panel+2pcs+100+Watt+12+Volt+Monocrystalline%2C+2-Pack+Compact+Design&qid=1619041063&sr=8-1


texts: How can I measure the flow rate of CO2 gas from two different canisters?

texts: I am looking for some help regarding one topic. I am designing one soda maker and thinking to include a 12g CO2 canister into it as my design only allows that size to incorporate . Now I know including a 14gm canister would be much better(more carbonation) but I am not sure how big the difference can be? So i am planning to do a flow testing to measure how much these two canister differ in case of co2 loading. But I am not sure how to design the testing method. Does anyone have any ideas or any references for a flow measuring test of gases? I will really appreciate the help.


texts: Calculating angle of a 2D vector with positive y-axis

texts:
This has been a burning question that I've been thinking about recently.
In statics problems like the one I've attached here where we are asked to find the angle that the resulting vector has with the positive y-axis, do we take the angle going clockwise or counter-clockwise from the y-axis to the resulting vector?
I remember from class that we calculate the angle between the positive x-axis with a vector going counter-clockwise 'always' however I'm unfamiliar with the rule when it comes to finding the angle with the positive y-axis.
I would appreciate any insight on this topic.

Reference: Engineering Mechanics STATICS, J.L. Meriam, L.G. Kraige, 7th Edition


texts: In FEA, why is the stress at an interior angle (180 deg) it is not?

texts: If you observe the attached figure, I heard some FE analysts say that the stress at the interior corner is always a singularity (but its intensity depends on the value of interior angle) but the stress at an exterior corner is not. I cannot understand why. Some even say that the theoretical value at an exterior angle is supposed to be zero. My question is that is it always the case? Does the exterior angles of a geometry can never result in a singularity, for any type of loading and boundary condition applied to the geometry? Reason being? And if sufficient mesh refinement is provided, so will the stresses at the exterior angles result in values close to zero?


texts:
I have a face mask that I'm planning on making, a cosplay of Wrench from Watchdogs 2. Not satisfied with existing ones, I want to go for a more realistic one.

That being said, this requires that I make the entire part of the mask covering the eyes opaque. I'd also like to be able to look around with my eyes instead of moving my entire head around to view detail. Thid is also critical to the function of the mask. Basically high FOV covering my entire range of vision.

How might I implement this? I've thought about using stripped down VR goggles with a camera, mirrors to bounce light around from another point on the mask, or pinholes in the mask with lenses to allow you to see through them. (If that's possible, I'm not well acquainted with lenses.)


texts: Is there such a thing as a voltage level that is safe for humans in all circumstances?

texts: My question is naive but I'm having a hard time finding a precise yes/no answer when I ask google. The general advice seems to be "it depends", but are there voltage levels where it really does not depend? My intuition is that there are some voltages (eg. 5v) that are so low that it does not matter how many amps the power source can supply because the human body will give enough resistance, even in worst case scenarios, so that current will be limited to safe levels. Is this intuition correct or am I looking at this the wrong way?


texts: Open pipe and relation between pressure and flow rate

texts:
If a pipe (of unknown/arbitrary length) with cross section area $A$ and with a continuous supply of a simple fluid with a known pressure $p$ at the opening to the atmosphere, which has a pressure of $p_a$, what would be the rate of flow out of the pipe?

I have looked but not found an answer anywhere, but apologies if this seems trivial or seems to be a duplicate of another question.


texts: Calculate pneumatic cylinder dimensions from work done

texts: I have a project for which I need a pneumatic cylinder to impart an impact force in such a way that work-done/energy is 4.5 Joules, and the input pressure is 10 bar.  How can I solve this so that I can derive bore & stroke of piston?


texts:
Suppose I have a 5kg framed picture that I want to hang on hooks, each of which can hold 2kg. Is there some arrangement of hooks that will make this safe? How many hooks would I need? I thought that I could arrange the hooks as something like a catenary to distribute the load, but I'm having trouble calculating the force on each hook.

What are the techniques I need to use to solve this problem?


texts:
I have a truck which weighs 190 kg and will travel 100m down a 38° slope.

How I can find the trucks speed at the end of the 100m?


texts:
I need to create a variable 3-7 psi / 0.2-0.5 bar in a low density gas running through some piping. I can calculate the required Cv factor to do this with a valve would be in the 30-200 range. Looking at some valve spec sheets, a typical valve to get to the lower end of that range would have an effective orifice size of about 1".

The trouble is that the gas is supersonic going through that size orifice. Similarly, if I use a 4" valve (such that the velocity would be reasonable in the connecting pipe) the valve needs to be over 90% closed, making the effective orifice size only an inch anyway.

I've thought about just running through a long length of pipe, but its difficult and expensive to make the pressure drop variable. I've also thought about running the gas through a vertical liquid column to create a hydrostatic head on the gas, but if the density is near 1 kg/L, I'd need a 16' column, which would be both expensive and impractical.

Has anyone every solved this problem before? Is there a good way to create substantial pressure drops in gases without creating high velocities?


texts: What is this Y-shaped screwdriver bit, and what is its purpose?

texts: I found this strange looking bit in a bit set of uncommon bits, including Security Torx, hexalobular, tri-wing, spanner head, 12-point flange, Torq-set and others. It's the only one that I could not identify, what is it for?


texts:
I know that on the moon, while the daytime surface temperature can be above 270° F, in the shade but a few feet above the surface temperature can get quite low.  Wondering whether a similar phenomenon can be observed if a vaccum is created around an object which is suspended in he middle of it.

Say for example, a steel ball is suspended in the middle of a  plexiglass cube, by 3 plexiglass threads, and the interior volume of the cube is 1 cubic meter,  and the ball has a diameter of 10cm, the box walls are 5cm thick.  The cube has been evacuated to the practical limit of modern vacuum pumps.   Let's say the steel ball is chilled to a temperature of -20 c (measured at the time the evacuation is complete).   Let's say it's 70° F outside, and the box is sitting on a plexiglass tripod in the shade, shielded from direct sunlight.

What would be the temperature reading of the steel ball, approximately, after say 2 weeks? (i.e. at equilibrium).

(I don't mean to be overly prescriptive, but trying to be sufficiently specific to avoid answers like "it depends on how thick the walls are" and similar)


texts:
I would like to learn to weld (stick welding) for my own purposes (mostly for small repairs and building simple metal constructions). So far I'm trying to educate myself by reading and watching instructional videos, but so far I haven't found an answer to one question which is bothering me (I know it may sound stupid):

Assuming that welding equipment is fully functional (free of any defects and everything is set up properly), is there a risk of electric shock if a welder inadvertently touch part of construction which he is welding?


texts: How much weight can an aluminum tube beam support?

texts: I'm building a set of monkey bars for my kids and want to use aluminum tubing (6061 T6) for the rungs. The tubes will be 3 feet long and 1 inch outside diameter. Supported on both ends with a circular metal pipe bracket. I have a choice of various wall thicknesses, all the way up to a full solid round bar. How do I calculate the minimum wall thickness I need to safely support (without any permanent deformation) something like 200 pounds at the middle point of the rung?


texts:
Most if not all of the off-the-shelf epoxies I've used have generated a fair amount of heat while they are hardening. This seems to indicate to me that these are exothermic reaction, i.e. they generate heat from the reaction.

The common practice at my last company was to apply heat (heatgun or hairdryer) to epoxied joints to get them to cure faster.

As I understand the chemistry though, adding heat to an exothermic reaction should slow the reaction and effectively take longer for the joint to cure.

Was my company's 'standard practice' wrong to be adding heat to epoxy joints and extending the curing time, or is epoxy some type of anomalous material that cures faster when adding heat to the exothermic reaction. OR, is epoxy actually an endothermic reaction and the heat perceived during curing is something else?


texts: How do you determine the apt cutting speed of a hot wire foam cutter?

texts: I am designing an automated hot wire foam cutter for my project, and I am stuck on the computation for the most viable cutting speed of my design. The cutting tool used is a nichrome wire and the medium is a polystyrene board. How do I solve for the best cutting speed of a heated nichrome wire given the melting point of styrofoam boards have a melting point of 240 degrees Celsius, and the Styro board has a thickness of about half an inch.


texts: Why is high stagnation pressure important for propulsion?

texts: In my propulsion notes I always see mention of the importance of minimizing stagnation pressure loss across the inlet shock of a ramjet/turbojet/turbofan. Could anyone explain further why this is the case, possibly with equations to explain certain points in more detail? Thanks very much.


texts: What is the purpose of colour code for telephone wires?

texts:
I'm trying to understand how telephone wires work.
I've stumbled upon this kind of identification method with colours.
I can't manage to understand the reasons why is used and if it's still common to use it.


texts: Calculate attitude quaternion from 2 vector measurements

texts:
I am using a method proposed by R. G. Reynolds to estimate attitude based on two vector measurements, taken from: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990052720.pdf

Suppose we measure 2 unit vectors $b_{1}$ and $b_{2}$ in the body frame, and we know the components in the inertial frame are $r_{1}$ and $r_{2}$. The attitude quaternion can be calculated:

$$ c = |(b_{1} - r_{1}) \times (b_{2} - r_{2})|^2 + ((b_{1} + r_{1})\cdot (b_{2} - r_{2}))^2$$

$$q = \frac{1}{\sqrt{c}} [b_{2} \cdot r_{1} - b_{1} \cdot r_{2}, (b_{1} - r_{1}) \times (b_{2} - r_{2})] $$

Where $c$ is a normalisation factor and $q$ is in the form $[w, \vec{v}]$.

I've been trying this method out and it works half the time, but occasionally all the elements of the quaternion are their negative. Is there a way around this problem?

I know there is also a singularity problem when the two vectors are parallel but I don't think this is the problem?


texts:
I want to buy a "Swiss File #4".

I visited some local stores but noone knew what that was.

I found this nice set of files. Can someone read what it says in the top?
Is some of these file equivalent to "Swiss File #4"?

If yes, i will buy this instead.


texts: Does toe-in in the wheels of a car help with straight-line stability without steering?

texts: For vehicles that cannot steer (built to travel in a straight line) does having the wheels toe inwards help with straight line stability? That is, will it make the vehicle go straighter with slight construction asymmetries and frame warping?


texts: Which power plant will generate more electricity in the below discussed scenario?

texts:
There are two identical power plants(i.e same turbine dimension and same generator configuration). Both have a hot reservoir. Coal is burnt on both power plant to make the temperature of the hot reservoir to be 300 degree Celsius. After setting the temperature no coal is being burnt.
One of the power plant is working on a Rankin cycle and other one on organic Rankin cycle.
With every repetition of the cycle the temperature of the hot reservoir is decreasing in both the power plant.
Will the power plant operating on organic Rankin cycle operate for longer duration since low heat is required for ORC cycle to take place?
I think that power plant with ORC cycle will generate more electricity.
I think that I am able to properly convey my query. Please guide me through my query.


texts: Why does the upper wing skin fail in buckling and lower wing skin does not?

texts:
I am aware of the fact that the buckling is mainly caused in the regions of the specimen which are in compression. But the wing skin doesn't take any axial loads and is used to resist shear, atleast that is what is taught at the Bachelor's level of education in schools. The buckling in the upper skin, according to what I think, happens because of shear. But at the same time, the lower skin also is undergoing shear but the lower skin is not usually seen to experience any buckling failure.
Why is that?


texts:
I have to mount a glass fibre woven mat onto a stainless steel foil and using staples seems to be the only way to do it. The environment is one where a large variety of solvent vapors will be encountered, and as far as I know no adhesive could survive all of them: alkanes, chlorinated hydrocarbons, alcohols, ketones, ethers...

A regular paper stapler works fine, except for the staples which tend to be galvanized steel at best. Stainless steel staples would seem to be an option, but they don't seem to exist.

Can anyone can suggest a better approach?


texts: How the electronic circuit control laser diode?

texts:
I find this scheme here

1 - is data stream come from computer. This 'data' is an electric signal moudulated by the n°2
2 - this is the electronic circuit inside printer that

a) activates the corona wire → b) the corona wire charges up the photoreceptor drum
a) at the same time circuit activates the laser to make it draw the image of the page onto the drum. The laser beam doesn't actually move: it bounces off a moving mirror that scans it over the drum

My question are:

when data stream come from computer to the printer inside the electronic circuit what happens inside this electronic circuits ?
How mechanism 'tranform' this electric signal of data into instruction for laser diode and moving mirror ?
But this step is possible only if you have correct modulation between data stream and instruction laser otherwise printing should be wrong and electronic circuit may break or not work properly.
What modulation technique is used for laser diode ?
which components inside electronic printer is needed to drive and control this ?


texts: Determining the transfer function of a system given the time-domain characteristic equations

texts:
During my time revising for my control engineering module, i've come across this question

The automatic cruise speed control for a vehicle is described by the following equations

$\bigl( 1\bigl)$ $m \frac{dv_0(t)}{dt} + Fv_0(t)=u(t)$

$\bigl( 2\bigl)$ $u(t)=K[v_0(t)-v_r(t)]$

where m is the mass of the car, 1000$kg$, F is the frictional constant 50 $Nm^{-1}s$ and $u(t)$ is the throttle actuator force and K is the proportional gain control for the actuator.
Also $V_0(t)$ is the actual speed while $V_r(t)$ is the desired speed.

There are two parts to this question, and im a bit confused on both of them.

part 1 says to draw a block diagram of the speed control system. In the control engineering module we generally draw the block diagrams as related to s, so i thought i'd get the laplace transform of the function (to get the transfer function) and draw it from the general model of a control system

This coincided with part 2, which wants me to show that the transfer function in terms of K is given by

$\frac{V_0(s)}{V_r(s)} = \frac{K}{1000s+50+K}$

I went about working it out and eventually ended up with this

$\frac{V_0(s)}{V_r(s)} = \frac{-K}{1000s+50-K}$

Can anyone help me figure out where i went wrong?

Also, i attempted making a block diagram in the t domain for this system, however since there are two equations with equal outputs (not summed) i was completely stumped on how i would display that as a model that is accurate, without making assumptions like equating K with the system gain of the other equation


texts: Fluid for mechanical lubrication and hydraulic connection to plastic/rubber parts

texts:
I have a piston made of anodized aluminium and stainless steel with nitrile seals which I need to connect hydraulically to our system which mainly consists of silicone rubber with polycarb and acrylic parts, but I'm having problems finding a fluid which will lubricate the pistons without damaging the seals or any of the materials in the system.

Water

The piston and piston seals (nitrile rubber) are all pretty corrosion resistant but even so the manufacturer doesn't recommend using water in them and can't say what the effects would be, other than washing the existing lubricant out - I don't know how much of an issue water would cause?

As for oils:

Mineral oil attacks the silicone rubber.

Silicone oil apparently 'hydrates' the silicone rubber, so softens and distorts it.

PE-glycol based automotive brake fluid is fine for the silicone and pistons but cracks the acrylic and polycarb.

Vegetable oils are fine for all parts chemically, but I was always taught not to use veg oil as a lubricant and this question seems to answer why - i.e. the veg oil attracts dirt and 'gums up'.

So my questions are:

Would water be suitable as a lubricant for the piston?
If its a closed system and the oil is changed regularly, would vegetable oil (e.g. corn oil) work?
Any suggestions for something to avoid all the above issues?

Many thanks all


texts: What would be the best way to design a sealed computer containing a gas or liquid circulated by a fan/pump to cool the components? ( With a metal case ) Then the computer would not be susceptible to liquids or dust, while avoiding the hassle of heat pipes or complex heat spreaders for all components.


texts: Can a mouse use acceleration to track movement?

texts:
Would it be technologically possible to use mouse momentum measurements to move a cursor on screen instead of the classic laser technology, without losing precision?
This would for example allow elegant wireless rings, that would transfer the motion of finger into the cursor on computer or smart tv display.


texts: Why does the LTE Specification define SC-FDMA as the modulation scheme for the reverse link?

texts:
The LTE specification specifies SC-FDMA as the encoding scheme for the reverse link (mobile to base station) when the forward link uses OFDMA.

What is the reason for the difference?


texts:
A thin walled double pipe counter flow heat exchanger is to be used to cool oil (Cp = 2198 J/kg°K) from 150°C to 40°C at a rate of 2.27kg/s by water (Cp = 4187 J/kg°K) that enters at 21°C at a rate of 1.36 kg/s. The diameter of the tube is 0.127m and its length is 60m. Determine the overall heat transfer coefficient of this heat exchanger using (i) the LMTD method and (ii) the ε-NTU method
My attempt:
Given:
Mass flow rate of oil: $\dot{m}_{o} = 02.27 kg/s$
Mass flow rate of water: $\dot{w}_{o} 1.36 kg/s$
Specific heat of oil: $ C_{p,o} = 2798 J/Kg/.k $
Specific heat of water: $C_{p,w} =4187 J/kg.k $
$$C_o = m_oC_{p,o} = 2.27 \cdot 2198 = 4989.46J/s K$$
$$C_w=m_wC_{p,w} = 1.36 \cdot 4187 = 5694.32 J/s K$$
$$C_o = C{min} = 4989.46 J/Ks$$
$$C_i = C_{max} = 5694.32 J/Ks$$
From heat balance:
Heat released by oil = heat gain by water
$$Co (Ti - To) = Cw (Tco - Tci)$$
$$Ti = 150 Degrees$$
$$To = 40 Degrees$$
$$Tci = 21 Degrees$$
$$ 4989.46 (150-40) = 5694.32 (Tco - 21)$$
$$Tco - 21 = ?$$
I am stuck on calculating $$Tco$$ How do i calculate $$Tco$$
Can anyone help please??


texts: How do maglev trains turn given that they seem to have more than two bogies per car?

texts:
All of the images of maglev trains that I've seen seem to have a continuous drive mechanism along the entire length of each car:

I assume this must be articulated some how, or the train wouldn't be able to go around curved track. How does this function? With two bogies on a traditional train car, the bogies only need to be able to rotate in place, with the train car being a linear line from one bogie to the next over the curved track.

But with however many different articulated sections per car here, how are they attached to the train so that it can turn?


texts: Second Order Transfer Function Question regarding Overshoot Formula

texts:
If I have a closed loop second order transfer function such as:

$$T(s) = \frac{10-s}{0.3s^2+3.1s+(1+24K_{c})}$$

Can I still use this formula for overshoot (when a step input is applied) ?:
$$\frac{A}{B}=e^{\frac{-\pi \zeta}{\sqrt{1-\zeta^2}}}$$
Where $B$ is the step input size

I don't think you can but I'm not sure, can someone confirm?


texts: I have the following system (see picture). When calculating gain and phase margins, should I consider $L=GK$ to be the open loop transfer function? If so, what difference does the transfer function $H$ applied on the reference $r$ make to the gain and phase margins?


texts: What's a control system architecture that can track a ramping reference signal?

texts:
It's well-known that a control system with integral control can track a constant reference signal (command) with zero steady-state error.

What is needed to generate a controller that can track a ramping reference signal (i.e. one that changes at a constant rate) with zero steady-state error?


texts: Flat Fading vs Selective fading, which one is better?

texts: I come from Maths background, but recently I encountered problem where a channel is described as "flat fading channel". I would like to make some conclusions based on that fact.  I suspect that for radio engineers this is self explanatory, but not for me. Do we prefer a channel to be flat fading vs selective fading? Can we even make the distinction here? If no what are the pros and cons of each?


texts: How can we dissipate the heat from a block of 10*10*3 mm with 100 degree Celsius without losing the portability of the block?

texts:
I have a Peltier's device of 10*10*3mm and the material is Bismuth Telluride. The hot side is 100 $^oC$ and I want to dissipate the heat, and at the same time, the device should be portable i.e. it should not be part of the system so that I can't take it with me.

I tried using a vapor chamber and heat pipes. Though I want something lightweight, reliable and effective.


texts: Iris mechanism nomenclature - need help to enable better search results

texts:
I'm researching iris mechanisms with the goal of building a functioning, weather-sealed door. I am learning much as I go along, but am faced with a challenge in nomenclature (I am not an engineer).

I am using Google to search for non-overlapping iris mechanism designs that have the smallest possible distance from the outer edge of the opening to the outer edge of the 'housing' (the word that naturally comes to me to describe that part of the device) - but I am stumped about how to narrow down my search results.

Using the terms "small housing", "narrow housing", "smallest perimeter" etc are not proving to be useful when searching. No meaningful changes in the search results (and there are a gazillion results - I didn't know this mechanism was so popular in the DIY home-cnc world). "Enclosure" and "concealment" do not seem to impact the results much either.

Can anyone advise me on what terms I should use that will enable me to narrow my results? <--- THAT is the question being asked.


texts: Looking for advice on design of some rollers

texts:
I’ve some small U groove rollers I’m having made, 60mm diameter, 60mm wide, 28mm diameter at ceter of U profile.

The rollers need to be silent and have some friction on the rails. Polyurethane seems the most suitable material as it’s the highest load capacity to friction I can find but I’m open to suggestion if anyone can think of something else? I want to maximise how much weight they can take.

I can not harden the polyurethane much as they need to be soft for the friction and to run silent. Also I can’t thicken the diameter of the rollers though I can make the hub smaller to thicken the PU a little.

How do polyurethane wheels fail under pressure? I’m presuming that the PU is displaced and shears of the bonded surface eventually splitting in the centre as in drawing A.

First I though of putting support on ether side as in picture B.

Then I changed the profile of the U groove to have a dip in the centre. The groove should redistribute the pressure away from the centre and into the sides, acting against the side support and on the thickest part of the PU.

I was also looking a whether different shaped larger hubs and thinner PU or smaller hubs and thicker PU would be better under strain?

Finally I was looking at the possibility of support within the PU to increase it’s load capacity and make it less likely to deform, something like a 3D printed Nylon mesh reinforcement. I’m going to talk to the company who makes the wheels tomorrow but I suspect that making a PU mould with a mesh inside will have problems with getting rid of bubbles and cavities.

Is there is anyone out there with any experience or opinion on how PU behaves under stress, any advise how these wheels fail? Are there any other methods of increasing the load capacity of PU that you may know of? Or is there another material that may be more suitable?

Thanks for taking the time Chris, I can’t see a button to answer you apart from the commet one which has a limit to the letters? So I did it here.

The weight capacity is ok but it’s right there on the edge of ok. Unfortunately I can’t add rollers or increase the outside turning diameter.

I need no slippage, so I need some friction and I need a little give so as not to translate tiny imperfections up the shaft and into the mechanism. 85A hardness PU would do the job, maybe 90A, I don’t know, I’m waiting on harder samples to try them out.

The issue of the wedging effect you brought up is something that has been on my mind, I’ll have a look at the conical idea though I’m hoping that by having the PU bonded to the two side supports will go a long way towards mitigating any wedging effect.

PU can move and flex but can it be compressed? I’m unsure but I suspect that it can not or of it can its only by a tiny amount. So the failure point of the roller is down to the displacement only.

By bonding the PU to the hub and also the two side supports I hoped to have the weight acting on the PU where it has the two bonded surfaces to reduce the displacement that can happen.

My natural reaction has been to increase the thickness of the PU to increase it’s load capacity but the more PU there is and the further it is from the bonded surface surely that means the more it can be displaced?

With this in mind I was thinking that it may be better to make the hub the same shape as the roller and have only a thin layer of PU as in the 3rd drawing down. This would increases the diameter of the hub from 16mm to 25mm at the thinnest point. Do you think the thick hub with the thin layer of PU would be better or the thinner hub with as much PU as possible?

Is there another materiality that would be more suitable? I was trying to think of something like layers of leather or rubber or PU coated fabric or something like this but couldn't think of anything.


texts:
So I'm designing an AUV which will have wheels filled with air/helium(*) to ascent to the Antarctica ice shelves from underwater. My goal is retrieve data, images and information about the underwater world of Antarctica.

My question is, what kind of tires and what radius would be ideal to use on this AUV? Note that the wheels will be rolling on ice underwater, so I need a material that will increase the friction.

(*) I have also taken in consideration that the force of the AUV towards the surface (which will be blocked by thick flat ice). For that I was thinking that using helium in the tires and/or other parts(**) of the AUV would increase the buoyant force which would mean greater friction.

(**) Maybe I could add a separate sphere(***) somewhere filled with helium.

(***) Sphere because I can get the most amount of volume possible for the least surface area needed.


texts: Statics - other methods for determining reactions of supported beam

texts:
Question: Because the question regards the statics, I am going to pose it as well.

Are there other methods to solve equilibrium problems other than the method of sections, when dealing with pivots. In the situation, there usually are more equations than unknown variables, hence we split the construction into two and learn about equilibrium at different parts and then solve all equations (splitting the pivot). Method of sections is applicable to constructing the diagrams of the bending moment in the beam.
I have learnt about how to draw 3D diagrams of bending moment in the beam and how to solve the equilibrium problem in 3D for simple cases. However, I would like to ask if anyone has attempted to draw 3D diagrams of the beam (bending moment and shear forces) into different planes (xy, xz and yz planes), in other words, construct it on three screens. No need for that, because it is uncomplicated to draw one in 3D without doing so, but still curious as to whether it is possible. The same questions about statics problem. Would we be able to solve equilibrium 3D probleem by working with three planes (xy, xz and yz), where write equilibrium equations for each plane separately. After that, we put equations together and solve them. My guess is no because the load is connected to the point. Were the answer to be yes, then I would be able to skip the definition of torque about an axis via a point (I cannot realise that), since I can determine the moment of a force (or torque) in 2D system. Despite that, I can definite the torque in 3D about an axis. However, I am still curious!

I study civil engineering and hereby declare having no wish to break the laws of the forum; hence, should the question be not normal or disrespecting the members of the forum, then I would love to be apprised of it. Much obliged!
https://i.stack.imgur.com/AjHWU.jpg


texts: What is the relevant ISO or similar standard to refer to for painted metal corrosion testing?

texts:
We have an electronic display product that will be installed in a street side application. The front part is made from metal and exposed to the elements so it will need to be painted to protect it from corrosion.

Does anyone know what would be a good international standard to refer to when specifying the corrosion resistance of the paint and the final products?


texts:
I would like to create a life size lego Bionicle Aqua axe(gali nuva Type or gali master of water Type). The problem is unlike The trident in this video:
https://m.youtube.com/watch?v=NK6MWt7vpVE&t=641s
I would like it to be able to be used underwater and not rely on co2. I was wondering if there’s a way to charge a piece of brass/pvc pipe To 500+ psi without co2 gas but still have it compact and waterproof. Another bonus would be if it could not have to be charged with a bicycle pump but rather some system built into the staff.


texts: Percent Increase vs. Factor By Which Something Increases

texts:
I would appreciate a quick peer check on the following.

I am currently enrolled in a class where, I think, the professor is repeatedly confusing percent increase and factor by which something increases.

There is a difference isn't there? I'm not going crazy here am I?

As I understand it, to calculate the percent increase I would do:

$$
IV = initial \; value\\
FV = final \; value\\
Assume \; FV > IV\\
\% \, Inc. = \left( \frac{FV - IV}{IV} \right) * 100 = \left( \frac{FV}{IV} - 1 \right) * 100
$$

If I want the factor by which the value increased with respect to the initial value I would take the ratio of the final value to the initial:

$$
Inc. \; Factor = \frac{FV}{IV}
$$

To reiterate, these are not the same things. I just want to make sure I'm not confusing anything before I point it out to him and ask for clarification.


texts: Explicit Dynamic ANSYS - Origami structure

texts:
I am working on a flat-foldable conical structure and I would like to carry out some dynamic tests on it (deployment to get the displacements and accelerations...).

I have designed the folded geometry of this conical structure on Soliworks. This CAD file (geometry) is composed of a significant number of surperimposed surfaces bodies (triangular facets). Obtaining this file is quite complicated and involves a equations and relations.

I tried to use Ansys Workbench and the module Explicit Dynamic, but I have a two issues to figure out and I don't know whether it is possible.
First, when I import the CAD geometry in Ansys Workbench, the MechanicalDesign module recognizes connections between the superimposed surfaces but not between the edges of the facets. I do want any connection between the surfaces so I simply deleted them, but I do know how to create relation between the edges. I do not know if there is a way to fix this.

Does anybody has an idea or better solution to carry out this test ? As a student in Engineering school in another department than Structure and Material, I have only a basic background in the field of Finite Element and simulation.

Secondly, my CAD file approximate (10^-15) the angles and lengths of the surfaces bodies (facets) and I know it can have an impact on the deployment of structure at the initial position...


texts:
I have a seemingly simple structure and I need to perform a hand calculation to check that the stresses in the members are below the allowable values.  In its simplest form, the structure is a rectangular frame made from rectangular tube welded at the corners and suspended from four equal length cables attached at the corners.  The cables meet above the center of the rectangular frame and attach to a hook.

For loading purposes, each member of the frame can be considered to have the same uniformly distributed load along its entire length.

So, it looks something like this:

I have been poring over static, mechanics, structural analysis and other books and resources trying to find the methodology for analyzing this but all of these resources seem to stop at planar structures where the loading is in the plane of the structure.  Either this is a difficult problem, I am overthinking things, or I have been out of practice with respect to statics for too long.

What I have so far is a free body diagram where I have replaced each cable with a spherical moveable support (the 3D equivalent of a roller support).  Each corner is free to rotate in all three directions and to translate in the plane of the frame but not out of it.  So there is a single vertical reaction force at each corner (which is actually the vertical component of the cable tension).  This is an assumption.  Please let me know if I am wrong.

The degree of static indeterminancy is
$(6m + R) - 6j$, where $m$ is the member count, $j$ is the joint count and $R$ is the number of unknown reaction forces.  Plugging in the values leads to an answer of 4.  However, I think I can actually reduce that to 1 since (due to symmetry) the reaction force at each corner is identical.

And this is where I am stuck.  What is the next step? Or is this the point at which people say "let the computer solve it".


texts: How to do a pressure drop or saltation velocity calculation on pneumatically conveyed solids in slug flow?

texts:
If I am pneumatically conveying solids in slug flow, is there a method that works in a general case to determine the pressure drop or saltation velocity? By a general case method, I mean one that is like doing the Bernoulli balance, friction loss term and by extension Reynolds number, etc. for incompressible fluids.

It would be really neat/worthwhile in my mind to know at which point in a piece of piping that the solids would plug due to dipping below the saltation velocity.

Some suspicions of mine: Would the potential relationships involved change significantly for vertical or horizontal piping? Would dilute flow make this problem easier if you assume equal spacing of air between particle-to-particle? Surely you would not be able to consider the air and solids as separate pressure drops, right?


texts:
I have a solution to a problem on the mechanics of materials.
For the last step to find the deflection Vmax I am not sure how equation (15) was simplified to get the answer shown below: