texts: How to make screws stay tight under high vibration?

texts:
I made an electric skateboard (it works great, goes about 25mph) and the motor takes 4 screws to mount it. Motor is mounted to a 1/4 piece of aluminum. The screws go right into the motor and don't come out the other side so bolts are not possible. Over time that crazy vibration (from the road and pebbles and little potholes, from the motor itself being pretty powerful) being makes the screws come loose. Usually happens in less than an hour.

I've tried the strongest loctite but nothing seems to hold the screws in place. The loctite lasts a little longer but still they come loose. I have a Ryobi drill that I tightened it with. Maybe I am using the loctite wrong. I am very new to building stuff that is meant to be used in a more extreme way. In a way where lots of vibration is happening and things are moving very fast. And where you life may depend on it. Plus if loctite is so permanent than how would I be able to fix it if things went wrong? And if I use a less permanent loctite then would it even stay for this type of vibration?

I am well aware that building something this crazy is a good way to get hurt, but I really enjoy learning. I would love to learn how to make something that lasts for years and doesn't come loose. Something that is "skookum".

How do you tighten screws to aluminum that will vibrate a lot and get them to not rattle loose over time.

Motor is here. See BLDC-108.

Here is a diagram of the motor. It does not have the sliding brackets as pictured. It came without those, for some reason.


texts: What does “tempered water” exactly mean and how does it help cool the air?

texts:
It's from Apple's latest Earth Day commerical called “Can a building breathe”.
https://www.youtube.com/watch?v=tNzCrRmrtvE

The commercial is about Apple's new naturally ventilated building called "Apple Park". It says "We run chilled water tubing through that concrete mass, and then we use outside air to be our dominant cooling system, and you're using very little energy to get the tempered water to do this. So it's a breathing building."

I've searched on the internet for the meaning of "tempered water" and some of them say "tempered water" means "Water in the temperature range from 85°F (29°C) to 110°F (43°C)". So it's like mild hot water. Can somebody explain what exactly "tempered water" is and how it helps cool the air?


texts: Does open loop stability guarantee an MPC stability?

texts:
In the following publication

Arce, A., Alejandro, J., Bordons, C., & Ramirez, D. R. (2010).
"Real-time implementation of a constrained MPC for efficient
airflow control in a PEM fuel cell."
IEEE Transactions on Industrial Electronics, 57(6), 1892-1905.

There is a claim that

  In fact, as the fuel cell is open-loop stable and the input signal is bounded, the closed-loop system is stable, at least in the bounded-input–bounded-output sense.

However, I doubt this claim is true for a Model Predictive Control (MPC). But, I do not have a counter example too.

Could anyone please inform if this claim is correct or any counter example exists.


texts: Will natural gas or propane generators also run off of methane?

texts:
I'm looking at building a sustainable energy project that will convert biogas (methane) into electricity. I haven't found any biogas or methane electric generators for sale. It seems that there are some projects that are using generators to convert the methane gas into electricity, however, I can't tell if this is special kind of generator and I just don't know what it's called or if it is a natural gas or propane generator.

So will off the shelf natural gas or propane generators also run off of methane?

Also, how would I go about trying to calculate how much methane it would take to run the generator to produce enough electricity to say charge a cell phone or another small appliance?

Thanks!


texts: Are there design reasons why there aren't pneumatic pistons for chairs with a stroke >= 400 mm?

texts:
In the interest of saving space, I'd like to have a stool that can double as a table. I'd like the height to be adjustable from 16 inches to 32 inches.

But I can't find any pneumatic/spring piston with such a long travel (10" at most). It seems the problem with long travel pistons is that the amount of weight that can be held when fully extended is low due to piston bore volume being so big, allowing the air to be easily compressed. Likewise, an  unreasonably large force will be needed to completely compress the spring when you want to retract the piston all the way. While it would be nice to have an extra tall stool to sit on, most of the time it will only be used as a table when extended that high.

I don't want this to be another shopping list question, so please also discuss any principles and about why this is or isn't practical, or propose alternate solutions


texts: Is there a reason (in terms of the physics involved) why it is better to push start a car in 2nd gear rather than 1st?

texts:
I am struggling to understand why it is recommended to push start a car in 2nd gear rather than 1st - in terms of the physics involved, I fail to see a reason why this would be the case. I have compiled where I am at currently with a for/against list for each option.

Reasons why 1st gear would be better

The engine has a greater mechanical advantage, so an engine that is not firing correctly, is sputtering and not producing as much torque as a normally running engine is less likely to be forced into a stall than in 2nd gear.
For a push speed of X, the engine will be spinning at a higher RPM than in 2nd gear and I assume a higher RPM gives the engine a better chance of starting?

Reasons why 2nd gear would be better

It would give the people pushing the car a greater mechanical advantage than 1st gear, which may make it easier to keep pushing the car while attempting to start it. However, I'm not sure how important this is, as the aim is surely to get the engine running on its own, so continuing to rely on the force provided by the people pushing the car, even after the clutch has been engaged, already suggests the push start has not been successful?
If the push start is unsuccessful and the car comes to a halt, it should do so over a greater distance/time in 2nd gear than 1st, thereby reducing the risk of injury to the people pushing the car, which could happen if the car stops suddenly.

Reasons why gear selection should be irrelevant

Assuming the retarding effect of each engine stroke is a constant and the push speed (and therefore momentum) is the same in both cases, then surely the number of strokes before the car comes to a halt should be the same in both cases. As mentioned above, I assume the likelihood of a successful start is probably related to RPM. However, if it is not and is simply a fixed chance that the engine will start during each stroke, then the likelihood of the engine starting should be directly related to the number of strokes, thereby suggesting there is no difference between the two options? - While the car may stop sooner in 1st than 2nd, the number of rotations of the engine should be the same.
Admittedly, higher RPM is likely to increase engine braking and therefore starting in 1st gear may mean greater retardation per stroke, possibly favouring 2nd gear in terms of increasing the number of strokes before the car stops. Having said that, given the engine does a lower RPM for each MPH in 2nd than 1st, then the car has to slow down more in 1st than 2nd to reach the speed where the RPM will be too low for the engine to run without stalling, which could in fact go in favour of suggesting that 1st gear will in fact have more potentially successful strokes than 2nd. Overall, it seems as though these benefits would approximately counteract the negatives for each gear in this case.

In terms of the physics involved, I fail to see an obvious reason why being in 2nd gear will be beneficial. Have I missed anything? Or is this more of an old wives' tale than actually being something that will impact the likelihood of a successful push start?


texts: Is RotCFD or Ansys Fluent better to capture the wake pattern far downstream of a flow in the case of a rotating blade?

texts:
My main constraint is that the wake pattern to be worked on is far downstream.
Which one will give me more accurate results?
Will these two work well for the far wake at all?


texts: How to inflate or deflate a bouncy ball that lacks a standard valve?

texts:
I found this bouncy ball in my garage. It is too deflated to use and too inflated to store, so I would like to inflate it or deflate it. It doesn't have a standard valve for a bike pump: the only break in the plastic shell is this solid white plug that I was unable to remove.

What is this plug, and can I inflate or deflate the ball?


texts: Want to simulate a mechanism with spring in it for forces acting in different direction (Kinematics). How to do it using solidworks or ANSYS?

texts:
Thought of using motion study in  Solidworks but not able to account for forces at the different axis in it
here is the image to better understand it. There hasn't been any progress with the simulation though, I am still confused about where to start with


texts: What is a definitive discrete PID controller equation?

texts:
I need the equation of a discrete PID controller and I find different answers from different websites. For example, here the answer is:

$$u[k] = u[k-1] + (K_p + K_i \frac{T_s}{2} + \frac{K_d}{T_s}) e[k] + (-K_p + K_i \frac{T_s}{2} - 2 \frac{K_d}{T_s}) e[k-1] + \frac{K_d}{T_s} e[k-2]$$

and that's the equation that is used in this paper, for example. If I write that equation in function of $T_i$ ($T_i = K_p/K_i$) and $T_d$ ($T_d = K_d/K_p)$, I get:

$$u[k] = u[k-1] + K_p \left[ (1+\frac{T_s}{2 T_i} + \frac{T_d}{T_s}) e[k] + (-1 + \frac{T_s}{2 T_i} - 2 \frac{T_d}{T_s}) e[k-1] + \frac{T_d}{T_s} e[k-2]\right]$$

But in wikipedia and in this paper (although they say they're using the written equation above) they use the following equation:

$$u[k] = u[k-1] + (K_p + \frac{K_d}{T_s}) e[k] + (-K_p - 2 \frac{K_d}{T_s}) e[k-1] + \frac{K_d}{T_s} e[k-2]$$

and I think that here they use the same equation.

So, what can I do? Which do I implement? Any demonstration?

Thanks


texts: Are tires symmetrical & are their material properties uniform?

texts:
I've heard that the part of a tire which is towards the inner side of a vehicle has material which is more wear resistant than the part of a tire on the outer side of the vehicle.

In short, I have difficulty with identifying the inner side of a tire. Is there a difference in the material properties of tires from the inner side to the outside?


texts: Percentage area of steel for a retaining wall - standard formula doesn't make sense to me?

texts:
I'm looking at the usual UK/EU standards formula for the reinforcing steel area percentage, in a retaining wall. Essentially in "usual" cases it comes down to 0.13% of the cross-sectional area of Tw (wall thickness) in the upstand of the vertical wall itself, and Tb (base thickness [depth]) for the outer and inner base. If Fy is below a certain amount then the percentage changes but it's still calculated as a simple percentage.

Example scenario

I'm imagining trying to apply this to the retaining wall shown in the diagrams below. In this situation, the retaining wall is built onto one edge of a large and deep foundation. The foundation itself is very deep and very wide compared to the retaining wall built on it. Essentially when the foundation is considered as the base of the retaining wall, it continues on to a distance where the retaining wall is no longer affecting or affected by it.

The kind of dimensions I have in mind are - foundation/base is indefinitely wide (for these purposes), and say 900mm deep. The retaining wall upstand is say 200mm wide and 600mm high, and built at one edge of it. The foundations are deemed not to need reinforcement steel (perhaps because it's basically a large monolithic concrete block or it's on on sufficiently stable ground/rock beneath it). So the only reinforcing steel is the steel required for the retaining wall aspect.

Apparently, the inner and outer steel area is calculated as a percentage of the base's cross-section area. But I'm looking at the three diagrams below, which are roughly to scale.

First (left) diagram - the outer steel is run down to the bottom of the foundations, so essentially the foundations act like a base that's 900mm thick and very wide.
Second diagram - outer steel is only run down to 350mm deep; a more typical depth if it were on a slab not a foundation.
Third diagram -  the 2nd layout is re-visualised as equivalent to two parts - essentially a 400mm base with rebar along the bottom, resting on a non-reinforced 500mm slab.

My confusion

What's puzzling me is why are the steel area requirements, which are based on Tb, different in these three versions? Intuitively, I expected that for any given lateral pressure, the inner/outer steel would reach a sort of limit point where there just wasn't any need to add more, because in the first two cases it's embedded with right angle bends to a point where the limiting failure mode  in the base slab is pullout failure/concrete failure rather than steel elastic limitations (ie not governed by the cross section area of steel), and if the foundation itself is considered structurally adequate, then I'd have thought the second and third would be structurally equivalent and therefore need equal areas of steel too, as they are essentially the same layout.

(Alternatively, the 1st layout seems stronger than the 2nd, as there's even more grip and harder pullout, and the entire foundation slab is engaged rather than just the top half of it, so why does it seem to need more rather than less steel cross-sectional area, to achieve equal wall stability?)

But instead, the standard equation is simply 0.13% of Tb, so if the base is made thicker, which should add not remove strength, then the area of inner/outer steel required seems to have to go up, not down. That feels counter-intuitive.

So I'm left with a mess of confusion: Why does the steel area percentage differ in the three cases shown? Why does adding strength and solidity to the bottom of the base (i.e., as extra depth) cause an increase to the required steel area? Why isn't there some kind of limit based on lateral pressure rather than base dimensions beyond which more isn't needed? Why isn't a further limit reached where it doesn't matter how much deeper the base and the outer steels go, because the extra depth doesn't affect the retaining wall stability? What is the logic behind the cross section area of steel being an unqualified percentage of Tb?

What am I missing, and what should actually happen here?


texts:
When using the finite element method, I have always used either already meshed domains or very simple ones.

From what I've heard, meshing complex geometries is often outsourced to specialized companies (as it is considered not to be an interesting part of the job).

I am wondering how it is done: is it partly automatic, should you have to define the points and connectivities by hand in some cases? What are the most commonly used criteria to ensure the mesh will fulfill the expectation of the customer? What are the trends: should we expect it to be fully automatic in the coming years?

Edit:
I recently found a partial answer to this question: Isogeometric Analysis (IGA). IGA can been seen as an extension of the finite element method in order to solve the problem of mesh generation by creating a mesh directly from the CAD. It uses the CAD spline description of the geometry to automatically build both the mesh and the finite element space.

And one of the reason it has been developped is because the authors noticed that mesh generation is so painful that it takes most of the time to achieve in the industry, and mesh convergence is only rarely checked.

The method seems to be really interesting but not widely used since relatively new (10 years).


texts: AC voltage b/w DC power supply o/p and Ground

texts:
I have various Phoenix Contact Mini DC Power supply units (Pheonix Contact MINI-PS-100-240AC-5DC). It gives the correct DC Voltage across output terminals, as its supposed to. But I also noticed that its also showing an AC Voltage of around 70 - 80 V between the O/P terminals and Ground as well as Neutral.

Is this normal?

I am using this power supply to use in combination with a relay, to serve as a Digital signal (5 VDC) source for monitoring status of certain devices in a system. I am using a National Instruments DAQ+modules and am worried that this AC voltage might damage the DAQ and modules(which are grounded through the DAQ chassis) which are extremely expensive.

Kindly explain if this a fault with my DC Power supply or if its normal.

Thanks in advance.


texts: How to integrate 7 segment display with ULN2003?

texts: I am working on a project. A water level indicator using ULN2003. Now I want to integrate a 7 segment display to indicate the water level. How?


texts:
I have a laser where I can adjust the focal length, however it has a large spot size. I am trying to shrink that down significantly with a microscope objective, how can I go about doing that?

Should I put the laser out of focus, capture the light through the objective, then ensure the objective is at the right height and not out of focus?


texts:
Is there an electric circuit that can multiply the input current? if yes, what is that called, and how to make it?

My input is DC from a small DC motor which I use as a generator.
My input current is 300 milliamps and I need 1200 milliamps as output.
Is there some way to increase the output to 1200 milliamps ?


texts: Effect of overburden pressure on the skin friction pile capacity

texts:
In a given soil, the lateral effect of overburden pressure is constant with depth, as in $p=qk$, where:

$p$: lateral pressure effect,
$q$: overburden pressure
$k$: soil lateral pressure coefficient.

Then, the effect of this overburden pressure on pile skin resistance will be constant or it would vary with depth? I read somewhere that it varies with depth. If the lateral effect is constant as I wrote above, why does its effect on skin friction vary with depth? Or it doesn't?


texts: Up flow vs down flow through a porous fixed bed

texts: How do I analyse for, or what do I need to consider, when comparing gravity-opposed vs gravity assisted flow in a tube containing a porous bed that partially shrinks (through partial mass loss) over a fixed time period?


texts: How to calculate a structure's ultimate load

texts:
Sorry in advance if this question is excessively noobish or seems lazy. I have no engineering background and am unsure where to get started tackling this problem. Links to resources that could put me on the right path would be very much appreciated. I'm not looking for others to do my work for me; I just want to know what sorts of calculations I need to do.

I'm looking to build a cube-shaped structure, roughly 10 ft cubed, for suspending a series of seats (swings, sort of) for people to sit on. I'd planned on building the structure out of 12" aluminum trusses or buying one pre-made. Here's an example of what I might buy or try to build, for visualization.

I'd then loop rope around the horizontal trusses, using the rope to hang "benches"/"swings" from the structure. I'd attach the trusses to plates and use rebar to affix the plates (and the structure) to the underlying ground.

So the question is -- How do I test whether this structure would be sturdy/safe?

If I'm planning on hanging, let's say, five seats from each horizontal segment, how can I calculate if the trusses would support that sort of vertical force?
How about the horizontal force caused by someone potentially swinging on one of the seats?
Horizontal forces caused by wind hitting any tarp (solid or perforated) I use to cover the structure?

If this calculation is too complex/multivariate for an amateur like myself to reliably tackle, is there somewhere I could turn for an engineer's feedback?


texts: How do you create a chamfer in 3D CAD that joins the edges of two different shapes?

texts:
I am trying to make a 3D model.  It consists of a cylinder resting on an extruded ellipse as you can see in the picture below.  I now want to join the top edge of the ellipse with the top edge of the circle.  In a sense, I want there to be a chamfer between the side surface of the ellipse-prism and the top surface of the cylinder.  However, I don't even know what tool to use.  Is it a chamfer?  Is it called something else?  The problem is that the distance from the cylinder to the edge of the ellipse changes depending on whether you are looking at the north/south/east/west sides.

I am using Autodesk's free 123D design software.


texts: How to make factory machine hard disk drive more durable? How much its estimate life span?

texts:
I wonder how can I make hard disk drive more durable? Specifically, I works in a factory environment. And almost every few months, hard disk drive in some of the factory machine are corrupted, and even unrepairable. We already implement several SSD on some of them, but that's not much of help. They're being corrupted too on factory machine with heavy task.

So every time it happened, we always restoring using our backup image. And we already attach all of the hard disk drive with shock absorber to reduce the shake.

Is there any other option or prevention we could use? Perhaps adding any anti magnet material to prevent magnet friction, or something else? And what material we need?

Edit:
Factory machine with heavy task I mention above basically machine to create car metal body and car frame mould.

And when I meant the disk is corrupted, it means unreadable. The whole disk. Not the program files or software related. So it won't boot at all.


texts: Steel : is Damascus steel still relevant compared to modern alloys?

texts:
Damascus steel is a multilayered hand-forged steel used in the past for arabic and japanese weapons and now for kitchen knives and various connoisseur blades. Usually, two alloys are used alternatively to stack layers having different properties and shades.

I wonder if it still has a mechanical superiority over modern carbon steels, especially with "super steels" and tools steels like CPM 3V. By technical superiority, I mean better properties regarding fatigue resistance, impact resistance, tear propagation, edge durability, corrosion resistance, ultimate average tensile strength and so on.

Are there any studies about that ?


texts: Why use a 'dogbone' shape for tensile testing specimens?

texts:
Why is that the shape of the tension test specimen a dogbone-like shape?

I know that it is so that the deformation is confined to the narrow center region and to reduce the likelihood of fracture to occur at the ends of the specimen. But why is this so important? Why can't a cylinder shaped specimen that has a uniform radius all along the specimen be used? Why does it, for example, matter if it fractures near the end (near the region where you clasped the specimen in the machine)?


texts:
In solid state lasers a light source pumps the medium, which is a crystal. A crystal is excited and emits infrared light, until then everything is clear.
What I want to know: after excitement, what controls the flow of those photons emitted to oscillate in the cavity?


texts: Required torque of climbing tracked vehicle

texts:
Currently I'm designing a tracked vehicle for a school project. It has to carry a weight and be able to overcome some obstacles which are about 3/4th the height of the tank. What I'm stuck at, is calculating the required torque for the motors.

This is the basic layout of the tank with some variables. The wheel in the upper right is going to be powered.
Given that there will be enough traction between the tracks and the obstacle, how can I accurately calculate the required torque for the motor of this tracked vehicle to climb the obstacles?

Thanks in advance!


texts: Using a 'D' shaped shaft with a set screw

texts:
Suppose a 'D' shaped shaft with a 4 mm diameter like this type

is fitted inside a module 1 (plastic) gear with a round hole with the same diameter. If the gear has a set screw, will this still be a good fit? Will all the force be transferred to the set screw or will it be distributed onto the plastic surface as well?

Should only round shafts fit inside gears with a round hole? Would connecting D shaft to a round hole gear be less preferable than connecting a D shaft to a D hole - even with a set screw? Yes, there's a set screw, but the flat part of the shaft will have a smaller contact surface, right?


texts:
I've been watching a clip of a robot dragging a heavy load behind it.

I am wondering, in a fairly high level, how does the robot maintain its balance?

For example, I know that with a Segway, there is a gyroscope which senses in which direction the Segway is tilting, to allow the wheels to move accordingly to maintain balance. Is it the same principle with stabilising a robot?

I have also seen that some robots use accelerometers for stabilisation. Do robots need both an accelerometer and a gyroscope?

Would there also be some kind of proportional–integral–derivative (PID) controller, such that when the robot notices that it is tipping backwards, the applied extra forward force does not cause the robot to overshoot?


texts: How to calculate heat loss across a process pipe with perpendicular air flow

texts:
My thermodynamics knowledge is extremely rusty, so I would appreciate some guidance on how to solve this problem.
As illustrated here, I have a process pipe (steel) with a gas flowing through it (blue), with air flowing over the pipe (orange) perpendicular to the process gas flow.
I need to calculate T2 of the process gas, or more specifically (but perhaps more complicated), I need to know if the internal surface of the pipe reaches a certain temperature at any point along its surface. However, T2 of the process gas at the end of the control volume would suffice.
From my research, I know that I need to calculate the Reynold's number of the gas flow inside the pipe, then use the correct Nusselt number correlation for the flow regime and pipe geometry - all well and good. This then gives me my heat flux from the gas to the inner surface of the pipe.
From the other side of the problem, because the ambient air has a velocity, I also need to calculate the Reynolds number of the air moving over the pipe (using the free stream velocity and the pipe outside diameter), I think I would then use something called the Churchill-Bernstein equation to get a Nusselt number for the air flow over the pipe, which similarly gives me the heat flux from the air to the pipe.
However, the temperature of the process gas is >> ambient air temperature, so I would expect a negative heat flux between the gas and the pipe wall.
Now I'm stuck. I'm positive there is an element of conduction through the pipe wall here, but I just don't know how to apply these separate elements of the problem to get the answer.
I am assuming here that the process is steady-state, so I'm not interested in what happens during the process start up. Does that mean I can ignore the effects of conduction through the pipe?


texts: Densities of different phases of steel (austenite, bainite)

texts:
Steel seems to be a very complex material, not least because of the different phases and microstructures. At the moment, I'm especially interested in the bainite formation that happens when austenitic steel is cooled rapidly (but not rapidly enough to drive the martensite formation).

My question: What is the mass density (or range of values, or functions describing the densities in relation to specific conditions) of these two microstructures?


texts: How can I determine a function equation from a graph image?

texts: How can I find out the function equations in a diagram with 5 curves? Measuring by hand is very inaccurate and takes a lot of time. Any other possibilities?


texts: How can I determine the power generated by a regenerative braking system?

texts:
If I have an electric vehicle on an incline (m=17,300 kg) I want to figure out how much energy it would generate by regenerative braking.

I've used $a= g \cdot \sin({\theta}) $ and $f=m\cdot a$.

at 05 deg incline, acceleration is 0.85 m/s/s; this creates a force of 11114.972 N
at 10 deg incline, acceleration is 1.70 m/s/s; this creates a force of 22145.352 N

So bearing these values in mind if I don't want to accelerate and maintain a set speed I will need to create a braking force of 11114.972 N at 5 deg incline - this in turn will keep the machine at the same speed (ignoring friction, bumpy/uneven surface, etc.).

How can I figure out the Watts generated for the regenerative braking force of 11114.972 N?

The DC motor (I think it's 3 phase) is a 105 kW motor rated at 350 V and 300 A, max torque is 190 Nm @ 285 V drawing 285 A. (That's all the information I have for the motor.) Efficiency of the motor would be 0.85 (Assumed).


texts: Stopping force on wire rope from a falling object attached to it

texts:
Okay, bit of a weird one.  Imagine an object of known mass in free fall, tethered by a wire rope to an infinitely stiff sky hook. When that wire rope eventually tightens, what will be the stopping force on said object, i.e. what is the dynamic tension experienced by the wire?
Using linear motion equations we can determine the final velocity of the object.  If the stopping time or distance were known then we could calculate the object's deceleration and therefore the force.
However, how does one determine the deceleration? I thought about using Hooke's law or the wire's strain as a way to determine it's elongation - but one cannot work these out without the force!  Also I can't find any reliable info on a wire's stiffness. Is there a rule of thumb for something like this?
Any help or pointers are gratefully received.


texts: Best method of bouncing laser off series of mirrors

texts:
I'm preparing to add a DIY laser system with the beam bouncing from the module at the top of the stairs and then bouncing off a series of mirrors down the stairs to an LDR.  My question is essentially can anyone give me any guidance as to how best do this and align the laser with the mirrors?  Additionally, I can't find non-commercial information anywhere that explains how to angle a mirror at ~30-40 degrees facing downward and get the beam to still strike them.
Hopefully this is the correct place for this question.  I browsed extensively and couldn't find anything more applicable.  If it matters it's a 500mW 5V red.


texts: How can I arrange my ECO system to enforce the principle of least privilege?

texts:
Right now, changes to BOMs are executed through verbal or email instructions to an employee who serves as BOM gatekeeper. This means paper trails are almost non-existent. Who changed what and why is almost impossible to track down. I'm planning to establish an engineering change order system to correct this.

I have an issue. There are BOM changes that require engineering approval: swapping parts around, changing PCB revisions, etc. But there are BOM changes that don't need engineering approval: wire lengths, lug sizes, pre-approved alternate parts, etc.

Obviously our BOM gatekeeper could just sort the changes into those piles intelligently. But is there a standard automated way to accomplish the same end? To define certain changes that can be made, and others that can't without engineering approval?


texts:
This is a follow-up on my previous question here:
Sizing a motor for a floor jack-like mechanism

The floor jack setup is clearly inefficient when it comes to electric actuators. Something similar to a mobile crane would work better, as I'd benefit from the mechanical advantage of the lever formed between point of rotation and actuator.

My question is: can the actuator be anchored behind the point of rotation of the lifting arm, e.g.

NB: 400 mm is the linear actuator's install length. The stroke is 300mm.

If my understanding is correct, the system should have significant mechanical advantage?

EDIT
Would this setup be similar to what you see on skip trucks? E.g.


texts: How do I say my weight? In which SI units? I see people are using Kg as a unit of denoting weight from my childhood. Answer this question "What's your weight?".


texts: Why are shapes with sharp corners structually weak?

texts:
Please explain my question like I'm 5 too? ELI5: Why do ships have circular windows instead of square ones? : explainlikeimfive

The real answer is that shapes with sharp corners are structurally weak. Arcs and circles are very strong shapes. If port holes were squares, the openings would get damaged and worn out sooner.


texts: Practical low-tech real world method for measuring how much force to close a lid

texts:
I was told I should ask here.  Please note I am not an engineer and I apologize if this isn't an appropriate place, as I suspect this is for engineers to exchange ideas (though I found no "rules" at all).

With no expectation of a high degree of precision, what should I do to mestimate (measure/estimate) the force required to completely close the lid of a large box?  It is hinged and latches, much like the hood of a car, and has gas charged struts holding it open.  It doesn't take much to get it down - I think the struts only slightly offset gravity - but from there it takes considerable force to fully close/engage the latch mechanism (significant friction plus a strong spring).  It is too difficult for the local seniors to get closed, but it is important for theft prevention.

I'd like to put a small motor inside that grabs the latch and pulls it closed that last inch.  I realize I'll have a lot to do to design the "grab" and also to consider things like pinch protection... but for now I just want to see if a suitable motor exists.  What I don't know how to do is calculate the force.

Can I simply stand on a scale and take the delta when it latches, along with the distance the latch traveled?  Intuitively - for my non-engineering brain anyway - I can't really see how the distance matters (if the force is enough to move it an inch isn't it enough to move it a mile?), but the definition for the term "foot pounds" suggests that shorter distance requires less force.  So let's say my scale tells me I weigh 200 lbs and when I press on the hood at the point it latches it says I weigh 100 lbs, and it traveled an inch... does that mean I need a motor rated for 8.33 foot pounds?   Or am I completely off base?

Thank you for your indulgence.


texts: Converting Newton's Second Law Differential Form to Integral Form and Integration Limits

texts:
I am reading a report titled ``Definition of safe separation criteria for external store and pilot escape capsules'' in which the author uses following expressions.

From Newton's second law:
$$ z \left( t\right) = \frac{1}{m} \int \int\limits_{0}^{t}F \left( \tau \right)d\tau dt$$

From Taylor Series,

$$ F \left(\tau \right) = F \left( 0 \right) + \sum\limits_{n=1}^{\infty} \frac{d^{n}F}{d\tau^n} \Bigg\rvert_{\tau = 0} \frac{\tau^{n}}{n!}$$

Substituting the Taylor series expansion in first equation, we get

$$ z \left( t\right) = \frac{1}{m} \left[ \frac{F \left( 0 \right) t^{2}}{2!} + \sum\limits_{n=1}^{\infty} \frac{d^{n}F}{d\tau^n} \Bigg\rvert_{\tau = 0} \frac{\tau^{n+2}}{\left(n + 2 \right)!}\right] + w \left( 0 \right) t + z \left( 0 \right)$$

Questions:

I am familiar with differntial equation form of Newton's Second law,
i.e., $F = m \frac{d^{2}z}{dt^{2}}$ but I don't know how the
author obtained integral form, especially the limits of integration.
Since the integral with respect to $\tau$ is a definite integral, why the author has added constant of integration when integrating with respect to $\tau$.


texts: How to extract solar energy from a wall?

texts:
I have a vertical wall which faces the sun (North in my case as I am in New Zealand) and it gets hot in Summer.I should like to take some of that heat and transfer it into a nearby swimming pool as it seems a shame to waste it.

My plan is to fix 20mm HDPE pipe to the wall on the sunny side and pump water from the pool through it, then back to the pool.Most of the internet based plans have big spirals of exposed black pipe, but this is ugly (though effective) and wastes pipe.It should be possible to apply the pipe to the wall, spaced appropriately then render over the pipe so that the pipe is protected, concealed and also able to extract the energy from the bits of the wall between the pipes. 100% efficiency is not needed but from an engineering perspective the issues are:

The less pipe I can use the better as this will limit costs, reduce flow resistance and of course make it easier to apply the render however the cost of the render is quite high so I need to extract as near as possible all the solar energy from the wall.
I will use electronics to detect when the temperature of the wall is higher than that of the pool so there is no need to plan for winter or not so sunny days - it will just run when it's going to heat the water rather than cool it.
There is no realistic prospect of the pipe freezing - it's a sunny place with gentle winters and the water is salty.
My plan would be to render 25mm deep - the depth of the pipe plus 5mm over the top.  chicken wire over the pipe will hold the pipe and the render in place nicely and should deal with expansion in the pipe well enough.  Fewer pipes will make this less of an issue of course.
If the pipes are placed too far apart, they will not collect all the energy from the sun.

So what is the question?

How far apart should I place the pipes to have most of the solar energy absorbed by the wall enter the pipe, and how should they be configured.

It would be possible to make the render deeper or the pipes narrower.

Two configurations spring to mind also:

a.  A spiral.  This has the advantage of simplicity and low material cost.  No leaks either, but is a very long pipe so resistance is high and airlocking might be a problem.  (not likely as I can just use a more powerful pump of course as there will be no joins)  I favour this option.

b.  A parallel array with large infeed pipe along the bottom of the wall, similar atop it and vertically placed risers between.  Lots of joints in this case but much lower pump force needed and it is easy to bleed any air out.

Will this all just fall apart due to differential expansion in heat?


texts: What is the screen of a microwave made off?

texts: What material is the viewing screen of a microwave made of?  I have been researching and all I find is that the holes on the screen are too small to let the bulky microwave radiation to pass through.


texts: Can air conditioners/dehumidifiers exhaust their waste heat in their exhaust water?

texts:
If I understand correctly, both air conditioners and dehumidifiers conventionally exhaust waste heat through their exhaust air, though both also produce exhaust water. I'd like to know,

Are air conditioners or dehumidifiers currently being produced that exhaust heat through their exhaust water?
If not, are there engineering or physical reasons why this is not feasible?

Use case: I currently live where the weather is regularly both hot and humid, and my current dwelling is configured such that my only feasible options for reducing internal heat and humidity are:

an energy-inefficient external air conditioner (located outside of, but connected to, my dwelling) that also seems inefficient at humidity reduction;
an energy-efficient internal dehumidifier that exhausts

waste heat into the dwelling
waste water into an open reservoir (which I filter for drinking).

What I'd like would be an internal unit like my dehumidifier, but which would instead:

use its wastewater for cooling;
exhaust that warm water into a closed, insulated reservoir;
{sound alarm, shutoff} when the reservoir filled (as it does now) or overheated.

I would then remove and empty the reservoir outside.


texts: steel beam type and size for a clothesline

texts:
I have four posts in a square formation. Posts are also square. I want to bolt a beam between two posts on the left and a beam between two posts on the right, and than run some wire between the beams. Beams will be 2.8m long and distance between them will also be 2.8m. They will be 2m above ground. I was thinking a M10 or M12 bolt at each end of the beam. If the wire is right in the middle of beams and is holding 50kg (number taken from a commercial clothesline) what type of beam will be able to support this?
I was considering an angle 50x50x2mm because I can attach it flat to the square post or a 40x20x2mm SHS beam.
P.S. adding a picture as suggested. Black are posts, blue are beams, red is the wire.


texts: Could electro-osmotic pumping be used to pump 90 ml water at 10 bars in about 25 seconds?

texts:
I am interested in pumping about 90 ml of water at 10 to 12 bars pressure in about 25 seconds.

Can this be done using electroosmotic pump? What is the energy consumption if it can be done..?

Regards


texts: If a driver gear has larger radius than a driven gear, will a larger gear ratio result in more torque supplied to the driven gear?

texts:
Suppose a driver gear has larger radius than a driven gear. For example, we have a pinion with a main disk, where the main disk is larger than the pinion and the pinion is a follower. This is the case in many fishing reels that are "baitcaster" models, such as the following picture diagram,

I am wondering if a larger gear ratio will result in more torque supplied to the driven gear? Specifically, suppose we have two reel models such that the first has a $7$ to $1$ main drive gear to pinion radius, and the second has a $5$ to $1$ ratio. Will the $5$ to $1$ have less torque being supplied to the pinion gear?


texts: Frequency domain analysis of steering system of a car

texts: Can anyone share the equations involved, or some relevant theory material for frquency domain analysis of steering rack and pinion using bode plot?


texts: Heat transfer coefficient of a cylindrical hot water storage tank depending on its size

texts:
I have a simulation model of a cylindrical hot water storage tank. The heat loss is determined by the surface area and the heat transfer coefficient.

A configuration of the storage tank with 900 liters was validated with a real scenario.

Now I would like to test how the scenario changes when the storage tank gets bigger. Thereby my surface becomes bigger, but I don't know if the heat transfer coefficient changes as well.

Does a larger storage tank usually improve the insulation so that the heat transfer coefficient changes?


texts:
I'm attempting to create a suspended shelf. I need to determine the horizontal force at point A to determine whether or not the fasteners will fail. All members are rigid and the supports at A and B are fixed.

I am very rusty on statics and your help would be greatly appreciated! I would attach the work I've attempted, but quite frankly, it's embarrassing.

Thanks for your time.


texts: Would engineering bricks explode if used to build an oven?

texts:
I'm building a pizza oven and, to do so, I bought a whole load of engineering bricks (not these but similar). They've got five holes vertically through them, each hole is 2x6x6.5 cm (80 ml) and the walls, both end and dividing, are 2 cm thick by 6.5 cm high.

When the oven is fired up it will reach ~500 °C. If we use some good solid concrete as masonry for the bricks, which will seal the ends of the holes, I'm worried that as the air heats up, the pressure inside will turn them into a sort of ceramic bomb that will make cooking pizza a rather more exciting experience.

Is that likely to happen? How can I calculate the pressure that will be exerted on the bricks by 80 ml of air at 500 °C?


texts:
How to establish metric specifications for ergonomic suitability of a product? I meant like for a product say electric iron,it has a metric that it provides different temperatures range to iron, which can be measure in terms of temperature.
Similarly I have a question how to measure ergonomic suitability of a product i.e establishing Need matrices and Units.


texts:
I have a 60mm length of wire with diameter of 0.5mm. Meaning it should have a resistance of 0.005 ohm.
I put a constant voltage of 0.3volt through it, but it's only taking  7amp, but according to ohm's law, shouldn't it be able to take 58.5amp?
My power supply has a max output of 10amp, so shouldn't it take at least 10amp? Because I know for a fact the power supply can put out  more, because if I turn up the constant voltage to 0.5volt, it will take  10amp.


texts:
I'm trying to resolve a theoretical problem.
If I have 2 steel boxes made from the same gauge steel (3mm stainless steel) & one is 7 meters by 2 meters by 2 meters & the other is say 30% smaller in length / width / height, which would be the more ridgid?
I would expect the smaller box but just want to confirm with a professional. :)
Thanks for helping!


texts:
I've heard that both of these coupling types introduce a degree of kinematic error in the driven shaft. What does it actually mean in practice? Is it that the driven shaft doesn't turn uniformly even when the input shaft does? But is this error arbitrary or the same amount of error is experienced for every revolution?

In fact, in what sort of application should one be used but not the other?

Any thought appreciated.


texts:
I'm trying to use the mechanical impedance analogy to describe a spring mass damper system as an electrical circuit.

Mechanical Impedances for linear motion are

$$ Z_{lin}(s) = \frac{F(s)}{\dot X(s)} = Ms + B + \frac{K}{s} $$

where M has units of kg, B has units of N-s/m and K has units N/m. The units of mechanical impedance then are N-s/m.

When I translate this to the rotational domain, I start having problems.

Rotational impedance will again be the ratio of an effort (torque) to a flow (rotational velocity).

Similarly, we have

$$ Z_{rot}(s) = \frac{\tau(s)}{\omega(s)} = Js + B_{rot} + \frac{K_{rot}}{s} $$

Based on dividing torque by angular velocity, the units of rotational impedance are [N-m-s/rad], or $\frac{ML^2}{T}$. When I try to verify that the units of rotational impedance are consistent, I get

$$J\cdot s = \frac{kg\cdot m^2\cdot rad}{s} = N\cdot m\cdot s \cdot rad = \frac{ML^2}{T}$$

$$B = N\cdot m\cdot\frac{s}{rad} =\frac{ML^2}{T} $$
and
$$\frac{K}{s} = \frac{N\cdot m\cdot s}{rad^2}=\frac{ML^2}{T}$$

I can't sleep with all those radians being all over the place! It seems awfully inconsistent to have them in different place and I haven't been able to find any sources on the web or in my textbooks that adequately deal with this since mechanical impedance is such a niche topic.   In doing this, I've assumed that the $s$ has units of [rad/s], which some people dislike and just use $s= \frac{1}{T}$ Is there a way for me to make this a little more consistent, possibly by using radians in the units for rotational inertia and the spring constant?

I've also looked at the discussions here:

https://physics.stackexchange.com/questions/36079/unit-of-torque-with-radians
https://physics.stackexchange.com/questions/11500/simple-harmonic-motion-what-are-the-units-for-omega-0
https://physics.stackexchange.com/questions/33542/why-are-radians-more-natural-than-any-other-angle-unit


texts: issues with using variable pattern to control plane angle of feature

texts:
two different problems.  first, I create a feature by creating a sketch for it on a plane that is defined using an angle.  whenever I update some part of the part, it seems, the name I've given to the angle resets.  this is a problem because I'm referencing the name of that angle in the pattern table for a variable pattern.  so it no longer works.  I have realized I should be able to solve this by just leaving the name with it's default values, but it looks like this is a bug.  second, I tried creating a simplified construction to help with this question, creating a part with a feature based off a sketch drawn on a plane whose angle I then tried to change.  and it just didn't work.
edit:  found the following.  maybe it has all my answers???  https://www.design-point.com/resource/blog/winter-challenge-create-snowflake-using-solidworks-patterns/


texts: Volume flow in a non-horizontal Venturi tube

texts:
I'm trying to calculate the volume flow. I've tried setting up Bernoulli and using the hydrostatic pressure and the conservation of mass, as one does to solve a horizontal tube, but I keep hitting up against needing to know the heights z1 and z2, which are not given.

I can't figure out a way to remove it from my equations.

Density is constant.

The system is in equilibrium.

No turbulence.

No friction.

Pressures are constant across the diameters.


texts: How to guess direction of friction in any case

texts:
Here , in case of a death well situation as an example.
Q How is direction of friction going to be opposite to mg or in upwards direction ?
Why not:

In case of like circular turning , direction of friction is toward the centre. Why is it not the same here ?

Online it says that when f=mg , then only net force is  towards the centre. How is that possible ? Normal is pushing the bike. How is it still on the track then if f and mg cancel out.

Friction should be in a direction opposite to motion I.e since the bike is moving forward I,e towards you in picture. Then , friction should be backwards.

Similarly , there are many situation in which it becomes difficult to guess the direction of friction. For example , banking of road , vertical circular motion of a car or bike.
Especially in cases of banked raids, direction of friction changes as magnitude of velocity changes .
Q:What is the way with which I can always and I’m almost every situation , guess the direction of friction or how can you find the direction of friction in an intuitive way.


texts: Why do trains use the same wheels for staying on track and propulsion?

texts:
Trains where originally designed to keep the train on track. At the time trains where pulled by horses and used to transport coal (and such) out of mines. The two functions have very different requirements:
- Keep the train on track
- Push the train forward
How effective would a solution be to push/pull the train forward that pulls on a serrated track?
Or some other surface that provides far more grip/traction?


texts: Low flow hydraulic motor to run high flow pump?

texts: I would like to get some opinions on using a low flow hydraulic MOTOR to drive a high flow pump ? Would the high flow pump be able to create a useable pressure to drive a piece of equipment that requires the greater flow ? Or will the system loss to friction , restriction and mechanical drag make it impossible to realize any useful gains ?


texts: How effective will a cooled mattress be for cooling down a baby?

texts:
I'm trying to make a cooling device to used in hot areas for cooling down newborns. I'm planning to cool down the mattress to a temperature of 37C, how effective will such a system be to keep the body core temp to 37C?
I understand that the baby can not be analysed as a lumped body.
Thanks!


texts: Is a starter relay needed to supply the current to the starter motor solenoid?

texts: Considering the fact that the starter solenoid needs a maximum of 50 Amps initially (in order for the pinion gear to engage to the flywheel through the plunger and lever) and then some 8 Amps during cranking, do we need a relay to supply power to the solenoid? Is this relay of electromechanical type or a solid state one?


texts: What software is used for drawing dynamic & mechanical diagrams?

texts:
I need to sketch some diagrams involving basic symbols like springs and dampers, specifying angles, perpendicularity etc... something like the images below:

Obviously my first option was word, then power point, the visio, in which the latter was a bit more productive, but I haven't found any other software that will let me do the diagrams more productively and have an elegant professional look.


texts: How to calculate the force of a cantilever beam at a given point of deflection?

texts:
I have put together a simple cantilever beam using finite difference modeling according to the following standard wave equation
$$ρAy_{tt} = -EIy_{xxxx}$$
where $ρ$ is density, $A$ is cross sectional area, $E$ is Young's modulus, and $I$ is the moment of inertia.
I have run this simulating a simple deflection where this beam (clamped to horizontal at points 1 & 2) is moving upwards in the positive y-axis until it strikes an immovable object at point 12.
The deflection looks reasonable.

I am now wondering how I would calculate the force exerted by the beam at point 12 based on my finite difference model.
In the finite difference wave equation, local force at any given node would be given by:
$$(ΔxρA)y_{tt} = -ΔxEIy_{xxxx}$$
$$F = -ΔxEIy_{xxxx}$$
Because $F = ma$ and $m = ΔxρA$ and $a = y_{tt}$.
The problem is I think this is just the local force for that node relative to the neighbors. It's not giving a reasonable/useful total force output just by calculating the force at that one point.
This makes sense as the force it calculates is based on the fourth spatial derivative, and at the collision point it's almost perfectly straight so this will be near zero. Most of the restoring beam force is coming from the strong bend closer to nodes 1 and 2.
If I want the total force exerted on the "immovable object" striking the beam at point 12, how would I get that?
I know that in a general approximation, this is given by:
$$F = \frac{6EI(y)}{x^2(3x-a)}$$
Where $y$ is y deflection of a given point, $a$ is the distance to point of collision contact, and $x$ is the position of the point you're assessing. But I actually want to figure this out from my finite difference model so it can account for funnier shapes/motions.
I wonder if this is given by bending moment and stress force:
$$M = -EIy_{xx}$$
$$F = \frac{M (y)}{IA}$$
Where $y$ is the deflection from neutral and $A$ is cross sectional area.
However, I'm getting nothing useful from that. For a simple small plastic lever which should only generate 12 N or so of force from the general estimate equation I'm getting 10s of thousands of newtons using this approach.
Any help? Thanks.


texts: What is the max speed and duty cycle of an air conditioner's magnetic clutch?

texts:
I am considering using an automobile ac compressor to control the resistance of an exercise machine by engaging and disengaging the magnetic clutch to let it slip.
The max torque should be about 500 Nm.
How long does it take to engage once it is turned on  and what sort of duty cycle can I use to drive it?


texts: Polycarbonate as a short-term cryo-tank?

texts:
Can polycarbonate be used to store a cryogenic liquid for a short duration, let's say 15-20 minutes.

I've heard that PVC will be really brittle at low temperatures.

What I'm trying to do is a rocket and I need a tank to store my LOX. I need it to be something like PVC or polycarbonate because they are light and cheap enough for my purposes. Also, they are often sold for tubing, the shape I need.

Any other suggestions of material will be greatly appreciated.


texts: Help understanding performance of a Model Car

texts:
For one of our engineering reports we had to make a model car out of recyclable materials.

One section of the report is we have to discuss some aspects of Physics that will be taken into consideration when making the model car. The model car cannot be powered by electricity or battery and it has to travel at least one metre.

I can only think of inertia(diameter of wheels) and torque that can affect the speed and distance of the car.

Are there any other aspects of Physics that can affect the model car?


texts: Can AC carrying coil be used to destroy electronics?

texts: An air core coil carrying AC current of frequency f will produce an oscillating magnetic field of max amplitude say b inside it.  If an electronic devices or component say transistor  is placed inside it,  will it be destroyed by induced voltage if f= 10 mhz and b= 0.1 T?  Or,  at what combination of f and b electronics devices and components will be destroyed?  How to do such calculations?


texts:
I am designing a pipe strut connected to a UB waler using a 100mm diameter pin through a series of 8 interlocking plates. Each plate is about 40mm thick. To be able to weld the plates to the waler and strut end, I need to leave sufficient space between consecutive plates.

Assuming the plates are 300mm wide and long, what should be the minimum gap between the plates to allow butt welding?

Should there be a maximum gap between each pair of plates if the pin can resist the bending moment induced by the bigger lever arm?


texts: why LP gas tank does not provide fuel when the pressure reaches 10%? And to to resolve the issue?

texts:
I am having this problem that some LPG tanks don't provide fuel and other does..
I was told that the problem is whenever the ambient temperature is low (so is the gas), the pressure drops as well and hencely 2 bar (say it is the 10%) won't feed up..
But is this really the case? I think when the pressure is 10% in hot surrounding, it should have higher mass than when its surrounding is colder with the same pressure (10%-say 2 bar).
So if it is really 10% it should always feed up, the difference is it has lower mass when it is hot.
But if it really 10% and feed up for some tanks but not the other, so the issue is not about the temperature and pressure, maybe the installation.
What do you think?
And how do we get fed by gas after the pressure drops to 10%? do we use pump or heater for example? I was thinking to fill the tank up to 30 bars but it is not allowed to exceed 25 bars..
Another issue;
say we fill the tank in the Winter up to 20 bars, in Summer we also fill it up to 20 bars but surely the mass of the filled gas in Winter is greater than in Summer. So would it last more in Winter -assuming same use?


texts: Efficiency of wireless charging for moving cars

texts:
The UK is about to start trials of wireless charging for moving cars.

What kind of power transfer efficiency is likely to be achievable in such a system, compared to just plugging in the car directly?


texts: Why is fillet weld assumed to be in a state of pure shear stress?

texts:
According to Building codes, when calculating the maximum load a fillet weld can take, one checks only that the stress in pure shear is below the maximum shear strength. We know that shear yielding stress and tensile yield stress are related (using the Von Mises Criterion for the onset of yield):
$$\sigma_s = \frac{\sigma_y}{\sqrt(3)}\approx0.6*\sigma_y$$
where $\sigma_s$ is the yield stress in yield and $\sigma_y$ is the yield stress in tension.
But why do we assume the weld is in a state of pure shear? Why is this a valid assumption?


texts: Where do I get basic mechanical components?

texts: I'm looking for a few basic devices such as converting translational to rotational motion, 20:1 gearbox, etc. Found nothing at Home Depot. Could you suggest where does one buys/orders such components?


texts: How to design a gear escapement like in an old pendulum clock?

texts:
I've already got a gear that has its teets as in the picture:
I want to create the mechanism from the picture, but it's harder than I expected.
I think my gear is not the problem. But I'm not able to create the gray part, the gear anchor.
Is there any way to calculate the shape and/or sizes that matter for the anchor?
I tried a lot of things but I can't find the ideal shape for the anchor points that hook between the teeths of the gear.


texts: I'm looking for a way to keep a wire coiled when it's not being pulled on, and retract when it isn't

texts:
I'm working on an application where a panel rests on a flat plane, and is hinged along one edge with a bit less than 90 degrees of travel. I need to run a wire from the flat plane to the edge of the panel opposite the hinges. What I'd like is to have a small spool of the wire located near where the target edge meets the plane. The spool should let out wire as the panel slowly rises, and as it slowly falls it should pull the wire back in.

What would a product that accomplishes this be called?


texts: Does a gear retain its mechanical advantage in a 1 2 1 ratio?

texts:
For example if the first gear has 32 teeth and the second 64, if the third also has 32 teeth would the output of the third retain the mechanical advantage created by the first 32 tooth gear powering the second?
32:64:32 or 1:2:1
Thanks for your time and help!


texts: Reading stepper motor datasheets to get torque and speed

texts:
I don't understand how to use the information in a stepper motor datasheet to understand how much torque it can generate.  I was going to do a simple board and try to lift a small weight as an example but I realize I need to know how much torque the motor can generate. I'll probably have a little spool out there to hold the string for the weight, which probably also changes how much torque it can deliver.

All I see in this datasheet is "in traction torque" and I'm not sure what that means.   I don't see any graphs or other information that relate how much input voltage/power will give me how much torque.  What happens if I run it at 5 V instead of 12 V, for instance, or if I current-limit it to 1 mA?

I'm just trying to learn what to look for and how to read the datasheet properly.


texts: Solidworks hole table export data format

texts:
I'm trying to help a student with a project. The task is to generate CNC G-Code from a Solidworks hole table export (CSV) using VBA.

The problem is the export format is going to be a difficult to parse. Samples include the following:

TAG,X LOC,Y LOC,SIZE
A1,15,50,<MOD-DIAM> 10 <HOLE-DEPTH> 10
B1,30,80,<MOD-DIAM> 8 THRU ALL

M10 - 6H THRU ALL
C2,134.50,18,<MOD-DIAM> 8.50 THRU ALL

<HOLE-SPOT><MOD-DIAM> 23.79 <HOLE-DEPTH> 7.50
D2,75,24.50,<MOD-DIAM> 13.50 THRU ALL

Each tool size seems to be assigned a letter and a sequence number. That's fair enough and leads to the hope that we could sort by first letter. The problem is that the metric tap sizes follow the same format. I'm sure there are other problems the more we dig.

Are we missing a trick here on the export or has anyone any ideas? I can't find any Solidworks documentation on the matter.

Solution

Based on Jim S's answer below it became clear that complex holes (tapped and counterbore, for example) are split by CR-CR-LF. This is easy enough to filter out in VBA.

Figure 1. A screen grab of the code as displayed by Notepad++ with View | Show Symbol | Show end of line turned on. These three lines should all be one.

Code snippet 1

Private Sub CommandButton1_Click()
    'From http://codevba.com/office/read_text_file_into_string_variable.htm#.XkHkHM77R1I
    Dim strFilename As String: strFilename = Application.ActiveWorkbook.Path & "\HoleTablecsv"
    Dim strFileContent As String
    Dim iFile As Integer: iFile = FreeFile
    Open strFilename For Input As #iFile
       strFileContent = Input(LOF(iFile), iFile)
    Close #iFile
    a = Replace(strFileContent, vbCr & vbCrLf, " ")
    Debug.Print a
End Sub


texts:
I have an intermediate shaft that drives my spindle with pitch (3). On the spindle there is a slide which is moved translationally by the spindle. My intermediate shaft is rubbery and has a very low torsional stiffness. Is it possible to convert this torsional stiffness by the pitch of the spindle to a translational stiffness?
<img src="https://i.stack.imgur.com/Ljgei.png" alt="r/EngineeringStudents - Convert torsional stiffness to translational stiffness
Similar to this picture except that an intermediate shaft is connected to reduce the stiffness of the system" />
I am relatively new to the subject and would appreciate any help.
Many thanks


texts: Calculate required torque for cam design

texts:
Would like to check the following design (snail cam) require how much motor rated torque?
To ease calculation, i have include some assumed factor as below. Two extreme condition (rotation degree) to compare.
What is the motor rated torque required for the design? (is 0.30Nm enough?**)
*please let know if any factor missing or not logic.
*would like to have estimation only, thus to simplify, insignificant and complicated factor can be ignore


texts: installing swing hook before concrete is poured

texts: I want to place a swing hooks in place before the concrete is poured so that , i dont have to drill a hole later. My contractor is not ready to make these bolts with TMT bars itself.. what kind of hooks or bolts should i buy for this purpose and how should it be installed. I expect the swing to handle around 1000lbs of weight.


texts: Is it possible to determine how the steel was made, having its microstructure (for example, to distinguish forging from rolled products)?

texts:
How do you think the steel in these images was made?
Example1
(https://i.stack.imgur.com/oZLRM.jpg)
Example 2
(https://i.stack.imgur.com/jrDE7.jpg)
Example 3
(https://i.stack.imgur.com/fpl2d.jpg)
Example 4
(https://i.stack.imgur.com/U6uhE.jpg)
Example 5
(https://i.stack.imgur.com/cBjaj.jpg)
Example 6
(https://i.stack.imgur.com/P1TcC.jpg)
Example 7
(https://i.stack.imgur.com/x619Q.jpg)
Example 8
(https://i.stack.imgur.com/FUqWa.jpg)
phosphoric iron microstructure:


texts:
When analysing and designing a structure for the serviceability limit state the deflections of each beam must be found. When considering a multistory rigid jointed structure (as below) and applying first-order elastic analysis, what method must be applied in order to find the magnitude of the maximum lateral displacements on each beam (e.g. $\delta$ on the deflected shape)?

Essentially my question is, how do I find the value of $\delta$ on beam BE from the deflected structure.

Am I correct in idealising the beam as the simply supported beam with the correct concentrated moments on either side (acting as fixed support).


texts: Types of state observers/estimators actively used in the industry?

texts:
Most introductory books on control theory usually start their state observation part by introducing the Luenberger observer, and after that they might continue by introducing the Kalman filter. When reading papers from academic journals I have also come across all kinds of fancy nonlinear estimation methods (sliding-mode observers, passive observers, etc...).

However, from my short experience, it seems like there is only one type of state-estimation method used outside academia: the Kalman filter.

Is my observation correct or are other types also being used? If so, why is the Kalman filter so predominantly used over other state observers? Is it because it's fairly easy to implement?


texts: How can Pareto Analysis help solve engineering problems?

texts:
Attach is a Pareto Diagram with Number of Defects in Y-axis vs Causes in X-axis for an engine overheating problem. How can this Pareto diagram help an engineer solve the engine overheating problem?

Reference:

Pareto analysis


texts: Modal Testing and Frequency Response Interpretation

texts:
I'm studying vibrations in a gearhead, for which I have a general dynamic model of 12 degrees of freedom (only translational coordinates) and I have calculated its natural frequencies.

Now I want to try and correlate my model with a physical system. I did some impact testing with a hammer and measured the response with one accelerometer placed on the horizontal direction of the gearheads case.

My theory on mechanical vibrations and modal testing is quite basic and I don't know how to proceed and interpret the results of the readings.

I tried simulating the forced response in order to correlate the model I'm using to the measurements. For example, in one of the experiments, I hit the gearhead horizontally and measured the response on the opposite side of the gearhead with the accelerometer, in the same axis. In the forced response simulation, I applied a unit force on what would be that equivalent degree of freedom.

In the magnitude response of the test, I have a few peaks ranging from　2khz to 24khz (its also the width of my window res). But in my force response simulation I get resonance peaks much higher, from　9khz up to 80khz. The natural frequencies range from 1khz to 16khz.
I have a few questions regarding what I'm trying to do:

Should the natural frequencies I calculated all show in the forced response simulation within a frequency range of up to 20khz, or only those close to the degree of freedom of the applied force in the force vector? In my results so far, none of the peaks in the forced response are close to one of the natural frequencies.
How can I correlate the test measurements with the forced response simulation? none of the peaks in the magnitude response of the tests seem to be close to the simulation.
From the modal test results, I measured some of the peaks and about 3 of them are very close to some of the natural frequencies, does this mean that this frequency were excited in this specific test? or can it be just coincidence? as I explained before, in the forced response simulation I couldn't find any relation.

I should also note that my model is undamped, and my equipment was quite limited (only one sensor and small hammer(22khz)).

I read some theory on varius text books on vibrations and modal testing, they all show how to interpret a general FRF of course, but I can't find practical examples relating a theoretical model and modal testing like I'm doing, not explained in detail at least, most just skip to results, so the general methodology is what I'm lacking.

Thanks.


texts: How fast should I sample with a logic analyzer?

texts:
If I have a 10 MHz digital signal, how fast do I need to sample with a logic analyzer to avoid any bit errors?  Does the minimum sample rate increase if I want to attach a protocol decoder (e.g. SPI)?

I am aware of the Nyquist-Shannon sampling theorem and the fact that a 10 MHz square wave has significant energy at higher harmonics (30 MHz, 50 MHz, etc.).  However, a logic analyzer doesn't need to perfectly sample or reproduce a square wave to know if it is a logic 1 or 0.  I'm looking for what is practically necessary to avoid bit errors or protocol decoding errors.

I am using the Saleae Logic Pro 16.


texts: Applying an adjustable force to a small area

texts: What type of a mechanical device can I use and program to apply a controllable force within the range of what a human can to an area about the size of a fingertip? It is desirable for the applied force to be precise and known.


texts:
I'm hoping for some clarification regarding converting torque to force at point of contact.
I'm tightening some threaded components, the end faces of each are machined and will form a metal-metal seal under compression. I would like an idea of the force being applied at the interface due to a prescribed torque.
Using T = F.r (neglecting friction) the following values apply:
T = 5N.m (setting of torque wrench)
r = 0,0275 m (lever length of torque wrench)
I calculate F = 181,82 N but I think this force is referring to how hard my arm is pushing the wrench to achieve the desired torque.
Can anyone clarify this and suggest how I might go about finding the force at the interface?
Thanks in advance.


texts: Ques: I have a question regarding solid mechanics and plate theory,is 2 layer plate means laminated plate or simply refers to as a plate?


texts: What causes an inflated spherical cap to look more like a mountain?

texts:
I'm working with bulge tests of materials using biaxial loading (applying pressure from one side through a circular aperture).
The materials are clamped on the edges.
The diameter of the aperture is >20 times the thickness of the material.
Based on this, I expect membrane-like behavior, with almost uniform stress throughout the material, and the shape of a spherical cap. The experiments start with a flat sheet and proceed until displacements of the center are around >5-6 times the original thickness. Given this, I figured I could neglect bending and only focus on in-plane stresses.
However, I keep getting a shape that's more like a mountain (upside down version of the below shape):

instead of the actual spherical cap shape.
Why is this happening? I can't figure out why just looking at stress contours that are typically plotted -- usually the expected stress is largest at the center and less at the sides.
I have a theory that perhaps it's because in the center, there are "two directions" for stress to sustain the pressure, but at the clamped edges only one "direction" along the material experiences the stress due to the pressure.
But I don't see anyone else having this issue online so I can't tell if my theory is total bogus/there's another reason this might be happening.
Any insight would be much appreciated. Thank you!


texts: permeation properties of concrete under surface treatment

texts: I wonder which permeation properties are critical in concrete with and without surface treatment (e.g sodium silicates-based solution) , is it air permeability,water permeability or absorption. If u were to measure two of them, what would u choose?


texts: Why does a beam in shear crack at 45 degrees?

texts:
Why does a beam in shear like in this picture crack at 45 degrees instead of vertically? This is called "Punching shear", and requires concrete reinforcement at an angle:

Assuming that the shear force $F$ acts vertically, and that the cross section area of the beam is $A$, the stress at 45 degrees is:
$$\sigma = \frac{F*cos(45)}{\frac{A}{cos(45)}}$$
$$\sigma = \frac{F}{A} * cos^2(45) < \frac{F}{A}$$
So the shear stress vertically should always be higher than at 45 degrees. So why is it normally assumed that the concrete cracks at 45 degrees?


texts: How would you find the amount of 'usable power' in a typical coal mining process

texts:
Suppose you have a typical coal mining process composed of the following steps:
(1) Excavation -> (2) Crushing -> (3) Storage -> (4) Rail -> (5) Power Station
The idea is the coal is excavated out of the ground, crushed and processed, stored, and finally transported by a diesel train to the power station. It is very simplistic and probably missing some steps, but it's just for ease of calculation purposes.
Now I'm interesting in finding the energy loss in each component of this process, scaled down to 1KW.
For example, if I start of with 1KW at the beginning of the process (step 1), how much usable power would be available for me at the end (step 5)?


texts: Transfer function with cancellable zero pole and controllability

texts:
I have a transfer function (From Ogata's Modern Control Engineering)

$$\frac{s+2.5}{(s+2.5)(s-1)}$$

and the theory says the system has a pole zero cancellation and is uncontrollable.

They said that a state space rep of this transfer function has A and B matrix of:

$$ A = \begin{bmatrix} 0 & 1 \\ 2.5 & -1.5 \end{bmatrix} \ \text{and} \ B =  \begin{bmatrix} 1 \\ 1 \end{bmatrix} $$

Using rank(ctrb(A,B)) in MATLAB, the result is not equal to the dimension of the state space so it not controllable.

So I got curious and used tf2ss in MATLAB and got another state space rep:

$$ A = \begin{bmatrix} -1.5 & 2.5 \\ 1 & 0 \end{bmatrix} \ \text{and} \ B =  \begin{bmatrix} 1 \\ 0 \end{bmatrix} $$

Using rank(ctrb(A,B)) in MATLAB, I got a value equal to the dimension of the state space so it is controllable.

What have I misconceived? (and could someone teach me on how to make matrices in Markdown for the above?)


texts: What pressure to take in surface tension question?

texts:
Pressure inside a water droplet is $0.32 N/cm^2$ if surface tension of liquid is $0.095 N/m$. We have to find the radius of the bubble

since it's a water droplet the formula used is $$P_i-P_o=\frac{2T}{R}$$
The $P_i$ is internal pressure wehreas $P_0$ is external pressure so the $P_0$ should be taken in consideration but the solution of the question directly puts $0.32$ in place of pressure difference. where I am doing wrong in the question.


texts: Apologies for the probably daft question, I am thinking of buying a small KURODA ball screw (180 mm overall length, 8mm diameter, 2mm lead). I have a photo from the seller and I noticed a wider area towards one end of the screw. I suspect it is for mounting a pulley (it seems to have a screw flat area). Can you please confirm if my understanding is correct?


texts: What prevents using a toothed blade with a cutoff saw designed for abrasive discs?

texts:
I have an abrasive cutoff saw that I use to cut metal, it runs at 3800RPM. You cannot cut aluminum with these saws, so I bought a carbide blade rated for 3800RPM.

I went to install it, but after looking in the manual I don't think it is such a good idea. It says "No toothed blades". A regular saw runs around 1200RPM.

Why can't I put toothed blades in my cutoff saw? The blade is rated for that speed, would there be a problem?


texts: What is an engineer's liability for code changes that occur after submitting a design?

texts:
What if any liability would an engineer have in the following situation? This is specifically in reference to engineering within the USA.

  An engineer produces a design and plans that meet the standards and codes in effect at that time.  The design is sealed and submitted to the owner for bidding and construction. Because of funding constraints, the project is put on hold. Enough years pass that there have been code changes that would affect the design.  The owner then bids and completes the project as originally designed. This assumes that no engineer was later retained to look at the plans and update them.

What is the engineer's liability for any issues that arise from using the original codes? This assumes that the later codes fix errors or make other needed improvements.
Would it matter if the engineer was aware that the project was being constructed to the original plans after the delay? The engineer is no longer under contract.


texts:
I have here a BLDC motor that is controllable with FOC and I already implemented a position controller. The next step is to implement a velocity controller, but I actually don't see how to control the velocity at very low speeds. The speed is proportional to the reference torque producing current i_d for FOC and so for low speeds, there is only a very low current and so nearly no power. This immediately can be seen, that the motor becomes bumpy for low speeds. The implemented speed controller looks like this and works fine for speeds around 50rpm or higher.

i_q_ref = i_q_ref_old + K_Perr_speed + K_Isum_err_speed

The speed measurement is pretty accurate.

What kind of other control structures can be used to achieve a velocity controller for low speeds with FOC?


texts: How does the parabolic curve help in the integrity of a suspension bridge?

texts:
Why do suspension bridges need to be parabolic? Why can't they connect the towers directly?
Would it not use less material and cost less?


texts: Where can I find technical drawings for computer parts?

texts: I want to 3d print a custom computer case, I have the skillset to do so, however, I do not know where to find the technical drawings required. I need drawings for a 280mm Radiator, an ITX Motherboard, and various other parts.


texts: Aluminium Beam - is it fit for purpose? Can it easily support this load?

texts:
I want to mount two patio heaters on my terrace in front of a window wall.  I cannot attach anything directly to the window wall so I am going to run an aluminium box beam between two brick columns.  The beam will be 5000mm long.  The beam dimensions are 80mm x 40mm with a 4mm thick wall, 13kg in weight.  The heaters weigh 6.5kg each and are 1000mm long.  They will be 1000mm from each end and therefore 1000 from each other.  I need to drill 8 x 8mm holes for mounting brackets (2 brackets per heater, 2 holes per bracket).

I am sure the beam will deflect a little - any serious risk of collapse?


texts:
This is a follow up question to my question here about torque and stepper motors.

There Olin explains:

  Note also that torque isn't the only criterion for a motor. Power is
  another important one. For that you have to decide what's the fastest
  speed you want to be able to pull the mass upwards at. Let's say 2 m/s
  for sake of example. From above, we know the highest upwards force is
  5.8 N.

  (5.8 N)(2 m/s) = 11.6 Nm/s = 11.6 W

  After accounting for some losses due to friction and leaving a little
  margin, the motor should be rated for about 15 W minimum.

I'm unclear about what kind of Watts we're talking about here, is this just Watts in the mechanical sense or in the electrical sense.  In other words should I be thinking about needing to deliver 15W as in 15V @ 1A?

I'm also wondering about controlling the amount of power delivered to the motor.  In steady state I guess it would be Input Voltage divided by motor coil resistance?  But to change the position where the current and voltage are changing the current must be the input voltage / (reactance of the coil plus the coil resistance).  But the reactance changes with frequency... so do I have to look at the rise time of the input voltage to understand the frequency involved and then try to calculate from there.

I'm a little lost on that point, but trying to read more and understand.


texts: How does smartphone VR positioning work?

texts:
I've recently came across Google's cartboard VR headset, which allows you to use your smartphone as a virtual reality device.
The headset basically splits the screen in your left and right eyes, which makes 3D vision possible.
This is a well known cognitive mechanism that I won't discuss here.

Now, what bothers me is actually the sensor side of the question.

Let us use the following frame of reference for the rest of this discussion:

I've been astonished by the precision with which your head's movement is detected.

Sure, the integrated accelerometer (which can detect gravity), can account for rotation around x and y (roll and pitch) since it knows the direction of the ground.

But how do you deal with rotations around z (yaw), which is obviously collinear with the direction of gravity?

My guess is that the system uses the smartphone's magnetometer as a compass (your orientation is then computed relatively to the Earth's magnetic north)

However, many people argue that yaw is detected via the gyrometer. Which doesn't seem right to me, for two reasons:

First, even though it's made to detect a rotation, it will easily get lost in some cases. Indeed, if you rotate you head around z at a constant rate (i.e. without any angular acceleration), the device can not tell whether you're rotating clockwise or anti-clockwise (the tangential acceleration is non-existent). In practice, I agree that this problem could perhaps be fixed by looking at the previous time-steps (if an acceleration has stopped but no subsequent deceleration has been recorded, it means the user is still rotating at constant speed). But would it be precise? Since there is no absolute frame of reference, wouldn't the results diverge quickly?
Second, the very fine precision of the measurement. I've tried to rotate the phone around its vertical axis as slow as I could, and the program was still sensing my moves. Can a smartphone's gyrometer measure such tiny accelerations?

For these reasons, I believe that the magnetometer (i.e. the compass) is the way to go. Even if you turn and shake you phone very aggressively, the virtual reality reference frame doesn't seem to be disturbed. Which lets me think that the device is taking the external world as a reference, rather than relying on it's internal sense of position.

Now, can a magnetometer achieve such a precision of measurement as well? How is the detection of the Earth's magnetic field not disturbed by surrounding sources (I've put a magnet next to my phone, but never managed to mislead the VR program).

Or could the solution lie in a combination of different sensors? (comparing the measurements of the accelerometer, the gyroscope and the magnetometer to cancel most sources of error)


texts: I'm designing a simple gearbox with some fairly strict space constraints. I was wondering if having a belt pulley inside of a custom gearbox is a serious issue for the belt. Would it get worn down from metal shavings or gear lubricant? This screams bad idea to me but I figured I'd get a more experienced opinion. I've attached a picture to demonstrate what I'm talking about.


texts: Pipe-network pressure - mass flow relation

texts:
I have a question regarding a pipe-network:

Pressure A > B
diameters of the outside pipes are bigger than the pipe with the massflow m2,m3

The brown rectangle is a valve (the diameter of the valve is smaller than the pipe-diameter). I know from the continuity equation, that the volume flow rate in a pipe is constant. But how is that relation within a network? Is:

massflow: m2 < m3(through the valve)?
massflow m1 < m2 (smaller diameter)?


texts: Why is the area of upstream face of control volume a stated?

texts: I cannot seem to visualise why the area of the upstream face of control volume is 2pir∂r, can someone pls clarify on why is this the case?


texts: As I was reorganizing my air tool arsenal, a theoretical question popped in my mind I'd like to know the answer to. In designing air flow between an air compressor and a tool (such as a nailer or an impact wrench), when the tool is not taking air from the compressor, is there a mechanism to stop backflow of air from the tool back to the compressor?  Are those mechanisms in the tool, the compressor, or both? Meaning, if the compressor suddenly emptied out, would air leave the tool to fill the compressor or is there a backflow stopper of some sort?


texts:
I'm studying the laser input-output power relation. In particular I'm studying the laser slope efficiency $\eta_s$ ($\eta_s=\frac {dp_{out}} {dp_{in}})$.
However, my textbook tells that $\eta_s$ can be divided in 4 factors: $\eta_s=\eta_p \eta_c \eta_q \eta_t$.
I'm having difficulties in understanding $\eta_c$ that it is called "output coupling efficiency".
On my textbook, principle of lasers by O. Svelto, it is written that it represents the fraction of generated photons coupled out of the cavity, which one can call the output coupling efficiency.
Can you explain me $\eta_c$ in other words? What does it mean "coupled out" in this context?


texts:
In question 3-37,we have
P-p(ATM)=density * g* h and we get h as 8.3 m
But the answer is 1.53 m.How and why?What is wrong in my approach?


texts: Why do petrol engines have lower compression ratio than diesel engine?

texts:
Patrols have higher self-ignition temperature than diesel, but still, petrol engines have lower compression ratios than diesel engines. As the self-ignition temperature of petrol is shouldn't we be able to compress it more. I am not saying compress petrol to the point of auto-ignition which can cause knocking, but just have a higher compression ratio than diesel.

Is it because when the combustion of petrol-air mixture starts the moving flame front starts to compress the remaining air-fuel mixture which could reach a point of self-ignition when using higher CR?


texts: What is API class in subsea torque tools?

texts:
I have been in touch with suppliers of actuators for subsea valves. They have mentioned their solutions are available for no matter the valve size, as long as the interface is API 17D class 2, 4 or 7.

During my search, I could barely find any mention of these classes, even in the API 17D itself.

What are the API classes for torque tools? Do they depend on size? Is there a rule of thumb to "convert" class to valve size?


texts: Rotary Motion to 180 Degrees Reciprocating Mechanism

texts:
Are there any established solutions for truning a gear (or wheel) half-circle in one direction, back in the opposite direction, and repeating? Mechanism must be driven by a motor and continuous rotary motion. Compact and simple mechanisms preferred. Below are two possible solutions I dreamed up. Which one is better and why? Or what should I do instead?

One idea I had was to use a motorized disk (orange) with a slotted shaft(yellow) to create reciprocating motion. Then by extending the shaft and connecting it to a second disk (Red) I could achieve it, I think.

Another Idea I had was to use a full-square Scotch Yoke (Yellow) with gear teeth on the bottom. Properly sizing the connecting gear would allow for 180 degrees reciprocating motion.


texts: How to simulate Ground Penetrating Radar system?

texts:
We have a project which requires Ground Penetrating Radar(GPR). We got a student license of NI AWR software and Ansys HFSS (high frequency structural simulator). Are those the correct software for this types of system simulation.

What we mainly want to achieve is finding a proper ready to use circuit to connect antennas if applicable, determine the system requirements by using the simulation outputs and implementing algorithm to read and analyze data gathered form the circuit in MATLAB.

If those software are OK, can you suggest a reference/source/tutorial or whatever to model the system. As far as I understand, AWR works like a 2D environment which makes me confused how to simulate especially the ground side. HFSS seems more appropriate to model the ground layers, voids or objects with different material properties to find EM characteristics. But I am not sure how to combine this with a antenna system.


texts: Derivation of Bimetallic Strip Stress in Roark's Formulas

texts:
I am trying to understand some analytic expressions given in the handbook Roark's Formulas for Stress and Strain for bimetallic strip stresses. Namely, Roark's Formulas give the formulas

$$\text{Equivalent } EI = {w t_b^3 t_a E_b E_a \over 12(t_a E_a + t_b E_b)}K_1$$

Where
$$K_1 = 4 + 6{t_a \over t_b} + 4\left({t_a \over t_b}\right)^2 + {E_a \over E_b}\left({t_a \over t_b}\right)^3 + {E_b \over E_a}{t_b \over t_a}$$

and stresses of the top and bottom layers of the bi-metal strip as:

$$\begin{alignat}{4}
\sigma &= -&&{(\gamma_b - \gamma_a)\Delta T E_a \over K_1}\left[{3{t_a \over t_b} + 2\left({t_a \over t_b}\right)^2 - {E_b t_b \over E_a t_a}}\right] \\
\sigma &= &&{(\gamma_b - \gamma_a)\Delta T E_b \over K_1}\left[{3{t_a \over t_b} + 2 -{E_a \over E_b}\left({t_a \over t_b}\right)^3}\right]
\end{alignat}$$

where subscripts $a$ and $b$ indicate the two different metal layers, $E$ are the Young's moduli, $t$ are the layer thicknesses, $w$ is the beam width, $\gamma$ is the coefficient of thermal expansion, and $\Delta T$ is the elevation in temperature.

While I understand the Timoshenko bi-metallic strip curvature derivation (S. Timoshenko, "Analysis of Bi-Metal Thermostats," J. Opt. Soc. Am. 11, 233-255 (1925)), which also appears on Wikipedia (https://en.wikipedia.org/wiki/Bimetallic_strip). I cannot understand how the formulas above can be derived from the Timoshenko derivation or what additional assumptions were made.

Roark's Formulas is completely unhelpful in not providing a clear reference in which this derivation is done. If someone could point out a reference I can use to obtain the result shown or can show how the derivation is done, I would be immensely grateful.


texts:
I have two related questions

Why is a thicker tempered glass stronger than thinner?
For example, I have to hit much harder at 3/4”
tempered glass panel surface than I hit 1/4”
panel in order for glass to shatter. My understanding
is that tempering pre stresses and creates a
tension in a surface layer. Why does the
glass thickness matter if the “shield” is about
the same.

Did anybody study possibility of tempering the glass panel
all the way through as opposed to just the surface?


texts: How to scale airfoil coordinates to achieve the required size?

texts: I'm using airfoil data that is generated by a program. The generated airfoil has a chord length of 1 unit. I want to know how to scale up this airfoil to required chord length. My airfoil series number 638xx. NACA five digit series.


texts: Best flow rates of gas and liquid for a specific absorber

texts:
I'm working on a university project about making an absorber function. It's made out of glass and it's very thin (about 6 in diameter). The packing is Berl Saddle made out of ceramic and it's about 0.5 inches. It has a bed height of about 1.406 meters.

My question is, how to determine the best liquid flow for a determined air flow? Since we won't be able to get a supply of NH3-Air mixture in time (nor the time to mix them ourselves),we only need to calculate the best flow rates for the absorber to not flood. We only need to calculate maximum liquid rate so the gas is enough.

I'm new to this, and my calculations were for reducing from X% NH3 to Y% NH3. Any help?


texts: In this case, can I say that $V_E$ correspond to -0.7? if yes, why can this be?


texts: What happens if we operate a positive-displacement pump in parallel with a centrifugal pump?

texts:
I have a system that consists of a centrifugal pump and a positive-displacement piston pump, and both pumps get water from one reservoir and then discharge this water back in the same reservoir.  The two pumps are connected in parallel.

The specs of each pump are as follows:

Centrifugal: $Q_{max} = 33 \frac{m^3}{h}$ , $H_{max} = 9.5m$ , Power= 1.5hp at 3000 rpm
Piston: $Q_{max} = 1.5 \frac{m^3}{h}$ , $H_{max} = 60m$ , Power= 1hp at 1450 rpm

What I need to know what happens if I operated both pumps simultaneously, knowing that both pumps will face the same resistance in the system?


texts: ANSYS - How to extract reaction forces in the critical plan of the weld?

texts: I work on ANSYS WORBENCH and I want to extract the reaction forces in the critical plane of the weld, note that weld is circular.


texts: Zero overshoot criterion from the initial point $x_0$ to the final $x_*$, $x_*$ unknown in advance

texts:
Suppose a system is described by the following ODE:
$$\dot{x} = f(t,x)+u$$
where

$x$ denotes the state of the system
$f(x,t)$ is an unknown nonlinear function which meets the following condition:
$$ f(t,x) = 0 \text{ at steady state} $$
$u$ is the control input

Task: bring $f(x,t)$ to zero (steady state) without overshoot.
Condition: variable $x$ passes from initial state $x_0$ to final state $x_*$, that do not know in advance.
Is it possible to make a transient in such a system without overshooting, knowing only $\dot{x}$,$x$ and $f(t,x)$ ?


texts: Lifting 250 watts of heat using some heat exchanger/heat sink

texts:
I am new to thermal management.

I want to lift about 250 W of heat from hot end of thermoelectric cooler/peltier cooler (TEC).

The temperature of hot side of TEC is 30°C.

I want to use some kind of heat exchanger/chiller to accomplish this task.

I am using equation

$$ P = h S (T_s-T_f) $$
where

$P$ = heat to be removed = 250 W

$h$ = heat transfer coefficient

$S$ = area of contact between hot side of TEC & fluid (air/water) used
for convective heat transfer

$T_s$ = temperature of hot end

$T_f$ = temperature of fluid (air/water)

I do not know how to calculate $h$. If I calculate that, it will give me temperature of fluid.

How do I compute $h$?

And is my approach correct?


texts: Determinating Reactions for the following frame

texts:
According to the frame below, the goal is to determine the reactions of this frame in order to draw after the diagrams N, T and M.

The frame is asymmetric by reference at point C.

All reactions should be determined: at A and E.

I tried to determine reactions by using the equation of moment of the whole frame at one support (at A) and one equation of moment at the hinge for half of the frame.

For each half of the frame, we can also add equations of forces.

I obtained these equations:

Sums of moment for the whole frame seen at A

$$M_A = q \cdot a \cdot a - q \cdot a^2 + \dfrac{q \cdot a^2}{2} - \dfrac{q \cdot a^2}{2} + 3 \cdot q \cdot a^2 - q \cdot a^2 - RVE \cdot 2a = 0$$

Sums of moment for the half frame at point C (Right Half Portion)

$$M_C^+ = -RVE \cdot a + RHE \cdot 1.5a - q \cdot a^2 + 2q \cdot a^2 - \dfrac{q \cdot a^2}{2} = 0$$

Thus, after simplification :
by $M_A$, $RVE = q \cdot a$ and by $M_C$, we obtained $RHE \cdot 1.5 \cdot a - RVE = -\dfrac{q \cdot a}{2}$

Are these equations correct and if yes, how can I obtain all the reactions values? Because in the equation of the whole frame, I am not sure if I need to integrate reactions of the hinge.


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