/r/AskEngineers

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Engineers apply the knowledge of math & science to design and manufacture maintainable systems used to solve specific problems. AskEngineers is a forum for questions about the technologies, standards, and processes used to design & build these systems, as well as for questions about the engineering profession and its many disciplines.

New to AskEngineers? Read our subreddit rules and FAQ page before posting!

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  1. Post titles must be a question about engineering and provide context — be specific. Remember to flair your post. Most general career related questions should be placed in the Monday Career Megathread. Review the wiki prior to posting.

  2. No homework questions.

  3. Avoid questions that can easily be answered by searching on the internet.

  4. Avoid questions that have already be answered by a post in the FAQ section of the wiki.

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  • Mechanical, Electrical, Civil, Chemical, and Computer are reserved for technical questions only.

  • Discussion can be used for general questions that apply to multiple disciplines, including some workplace topics. Note that questions must still be specific to engineering and not a general opinion survey.

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  1. Be respectful to other users. All users are expected to behave with courtesy. Racism, sexism, or any other form of bigotry will not be tolerated.

  2. Don't answer if you aren't knowledgeable. Answers must contain an explanation using engineering logic, and assertions of fact must be supported by links to credible sources.

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/r/AskEngineers

1,729,880 Subscribers

4

Peltier vs Compressor cooler efficiency

I know that conventional Compressor coolers are more efficient than pettier elements, but what I the physical reason? I mean, compressors have an electric motor, bearings, piston, fluids being compressed and moved around, etc. while the peltier element has no moving parts.

5 Comments
2024/07/19
08:29 UTC

5

Potential uses and pitfalls for uses fiberglass sucker rod?

I have an opportunity to pick up about 50 sections of 1" fiberglass sucker rod. Each section is about 40 feet long -- more than the typical 9 meter typical segment.

Rods have been stored outside, and so are shedding glass fibers.

I'm thinking in terms of 5 uses for these:

A: As a frame work for a trampoline shelter, tractor shelter, ... using tarp for the covering.

B: As a green house frame.

C: For spring poles to learn trampoline stunts in slow motion

D: For making jungle gym like structures..

E: For making Tensigrity sculptures.

***

The glass fibers are itchy, and present the same health hazards as working with fiberglass generally. My plan was to sand lightly and paint with a suitable epoxy paint. At this point the one I keep running into is WEST system epoxy.

The poles aren't stiff enough to use like conventional green house frame tubing. When I went to look at th them, I had the seller stand on one end, about 5 feet from the end. I was able to pick up the other end and move it sideways about 15 feet.

An acquaintance attemped to make a half circle hoop with a dingle 40 foot long chunk. It snapped. Have to have some form of ridge pole. This will help with snow shedding.

Conventional greenhouse frames are typically 1.5 to 2" galvanized tubing, cross braced with x's made from what appears to be 3/4" metal EMT tubing I don't think putting a hole in the fiberglass is a good idea.

From previous experience, polyester resin bonds well with polypropylene baling twine. this makes having a few diagonal rodes lashed and resined .

1 Comment
2024/07/19
04:46 UTC

5

Material/Method to diffuse/frost a clear plastic sheet

I have a project that involves vacuum forming polycarbonate as a diffuser for a LED lighting system, my biggest issue is achieving a frosted/diffusing affect, injection molding is certainly out of the question as I don't think I can justify thousands up thousands for such a part. I've tried sand blasting, maybe I didn't use the right media? I think I used #8 glass bead. I've tried acrylic diffusers, didn't really work either. Etching? is that possible?

one of my cars has some aftermarket taillights with solid white plastic diffusers, they are not translucent at all to the eye, but it somehow lights up

2 Comments
2024/07/19
02:22 UTC

5

Why aren’t public asphalt roads seal coated periodically as preventative maintenance

For the roads scholars out there:

Homeowners are advised to seal coat their asphalt driveways every few years to increase longevity.

Why aren’t public asphalt roads seal coated periodically?

The most I is see done from time to time is application of hot tar to fill the cracks that emerge in the surface, but that’s lackadaisical at best

21 Comments
2024/07/19
00:47 UTC

7

How does PWM *really* work?

I am familiar with the basic mechanics of pulse width modulation- for example, take an LED that needs dimming, turn the DC current supplied to it on and off really quickly (maybe at 1 kHz), and change the duration of each pulse to achieve dimming. But, how is the duration of each pulse modulated?

Is each pulse subdivided into computer clock cycles? Or is there maybe some wizardry involving capacitors going on? None of the above?

10 Comments
2024/07/18
23:48 UTC

37

Is there a device that uses electricity to cool things down directly?

I am not talking about anything that can cool things indirectly like a fan. I’m talking about wires that can cool or some sort of cooling element run on pure electricity.

77 Comments
2024/07/18
22:26 UTC

2

What is a good way to transmit ARINC 429 to a distance of 100-150M?

ARINC 429 is designed for cable lengths of under 150ft. I'm looking for a solution to transmit to a distance of 328-492ft (100-150M). Is there as good way to convert it to a format that can get that kind of distance?

9 Comments
2024/07/18
22:02 UTC

3

Single wire DC slip ring

Hi all, I'm electroforming and need to spin an electrified doodad in a vat of acid. I have a power supply that provides low DC current into the bath of acid and the negative end into the central piece. And the center piece needs to be rotating.

The best piece of advice I got while searching the archives was to not DIY a part i can buy, but slip rings are complicated multi wire devices, and since this is near acid, I really need to be able to polish the copper connections (or have some enclosed carbon brush) and clip and alligator clip on and off. I have tried a banana plug, but it doesn't rotate with ease, and I would prefer to use a very small motor to drive the spin.

What I desire most are two solid copper pieces, one that sets in the other and spins freely. Like a central piston that I could rotate and send the electrical current through the stationary copper coupling.

The most simple I have seen is flipping a clock face down to attach the central piece to be electroformed, and looping the electrical current through a wire that just has constant contact.

I'm pretty handy with DIY, but ideally am going to use OnShape to make something I can remake more easy and cut copper washers to have constant contact while the middle spins. And everything else is made of ABS plastic.

But I would just prefer to buy the whole thing and save so much time. Any help or guidance is welcome, THANK YOU

4 Comments
2024/07/18
20:40 UTC

27

What is the purpose of the gaps in the male threads on this plastic cup?

Photo of thread: https://postimg.cc/kVzwLdvv. It's a plastic molded kids cup with a top (not shown). It threads on normally so it's not a quick connection.

I'm guessing either material savings or simplified tooling. I've only dealt with low volume injection molded parts and the purpose of this wasn't clear. I am sure this would be high volume; >100k per year.

10 Comments
2024/07/18
20:37 UTC

9

Does a grade 5 bolt have better shear strength than a grade 8 bolt of equal size?

55 Comments
2024/07/18
19:07 UTC

2

What's a good communication scheme for a modular instrument system?

Hello all - I'm working in a systems engineering capacity on a proposal for a benchtop instrument platform. My vision is to make the system modular with all modules adhering to a common communication protocol. Generally there'd be one "master" module that communicates with a PC (or it may be a PC itself) that operates as the module manager. I have a background in EE but I've never done a modular design. Can anybody recommend a good, easy to use communication standard to adopt for linking together arbitrary numbers (1-10 maybe) of modules? It doesn't need to be screaming high performance - we'd generate <1GB of data per run but as much as possible I'd like to just stick to one standard so that the high level system architecture is straightforward and easily expanded.

Would appreciate insight from anybody who's worked on stuff like this before. And also if there are general modular design resources or handbooks out there that you'd recommend, those would be appreciated too.

5 Comments
2024/07/18
18:59 UTC

3

Roof structural problem, looking for solutions

I am remodeling my 100+ yr old home and have run into a problem where the original roof structure meets an addition done sometime during the 60s. I have not done any work in this area yet.

The original rafters are full 2x4s. Attached across them is a 2x6 ledger (new) that holds the new rafters. This ledge is only attached to the end of the original rafters across the entire back of the house (approx. 33') and has no other connections. I'm not sure if the nails from the ledger into the end of the original rafters is really sufficient for their weight. I don't see and pulling, but several of the new (60s) ceiling joists and rafters are cracking. When I took the ceiling down, you could see where vertical supports had been added at some point, from the joists to the rafters to keep them from sagging.

I'm really not sure, structurally, where to go from here. Obviously, I want this home to be safe and part of the reason I started this remodel was structural issues in another part of the addition. Is there any way to add strength to this without tearing the whole thing off and starting over? Thanks!

9 Comments
2024/07/18
15:19 UTC

2

Keyboard lights blink when turning on the fan

My keyboard which is connected to my CPU blinks when I turn on/off the fan connected to the same extention cord as the CPU. The cpu is off when this happens and remains off. CPU psu is by seasonic 750w gold.

Any idea why this happens? Or why the psu interprets a power surge this way?

Thanks in advance :)

2 Comments
2024/07/18
13:26 UTC

32

Diminishing return or limit of return with speaker cables?

Dear engineers,

Give it to me straight: Is there a limit to return with ordinary, home use, audiophile, bla bla, speaker cable, or is it just diminishing return? What is absolutely necessary (and why), and at what point are we just paying for someone's yacht?

75 Comments
2024/07/18
10:25 UTC

4

Is it RPM or Torque that creates power in a generator/alternator?

If the electricity is generated by magnets spinning against something, it seems to me that RPM would be all that matters because if you can make it spin faster then it will generate more electricity, why would torque matter as well?

57 Comments
2024/07/18
03:16 UTC

30

If AI data centers are using up water should we be building them near polluted water so they can be used to as water distilleries?

Could data centers be built with "steam chambers" to contain the vapors and have the water put back into the ground supply?

Link about AI Data centers using so much water. https://www.newsweek.com/why-ai-so-thirsty-data-centers-use-massive-amounts-water-1882374

40 Comments
2024/07/18
02:29 UTC

2

What coupling method do you guys recommend for tubing?

Working on a tubing system looking for an idea on coupling 3 inch outer diameter tubes together. Preferably something that works underwater, reusable, easy to assemble. If not reusable it would be nice if I could order the part. Could 3d print it as well

edit: the tube will be sturdy. right now it is acrylic

edit 2: sorry title is wrong, it's not tubing it's pipe lol

11 Comments
2024/07/17
23:37 UTC

15

UV cured parts falling apart

Substrate 1: Stainless Substrate 2: clear polycarbonate Adhesive: Loctite quick UV cure

We’ve been making these parts forever. Maybe 1/100, the poly carb just falls right off the steel. Another weird thing, the adhesive turns a white color. We seemingly checked everything. Just looking for anyone with bonding experience that have seen some oddball scenarios like this one and what you did to fix it.

26 Comments
2024/07/17
23:09 UTC

4

Use of an Lead Screw in Place of Gear Rack

Hi everyone,

I'm working on a cost-reduction project where we currently purchase an expensive raw gear rack and have it further machined to fit within a portion of our device. I recently found an ACME lead screw with a similar overall dimensional envelope (length, width, height (diameter)), and it is much cheaper, requiring only minor machining of flats on the ends to fit into the device. Currently, we use a custom component that has a machined spur gear feature to mesh with the rack.

How can I design a custom mating 'gear' feature to mesh with the ACME lead screw? In the device, the rack is fixed while the pinion component is free to move in the +x/-x directions. Since the lead screw uses ACME geometry and the gear is offset (not concentric with the shaft), how do I go about dimensioning the 'teeth' and the angle of the teeth so that they can mesh with the helix of the lead screw?

The device doesnt experience more than 50# of load so I am not so concerned with integrity or power transmission.

Thank you.

12 Comments
2024/07/17
22:59 UTC

0

Will vapor increase turbine performance?

I am thinking of modifying an e-cigarette by applying compressed air to the intake and connecting the outlet to a small turbine.

Would this increase the performance of the turbine compared to just compressed air? In my head the density of air in the turbine is increased with only a moderate drop in velocity, assuming a simple air path through the e-cigarette.

It is for a silly project 🤣

10 Comments
2024/07/17
21:35 UTC

2

Fitting Bearings onto a shaft.

Hello sub,

I have a 6mm shaft that I need to fit 6 bearings with approximately 1mm of space between each https://imgur.com/a/2Zvh9Ph . Additionally, I need the 1st bearing to be a certain distance from the top of the shaft. I'm not really sure how to go about this and was hoping somebody with experience in this area could provide some advice on what tools might be needed or how you would approach this.(P.S. those are female adapters on each end that can be removed)

3 Comments
2024/07/17
21:29 UTC

4

Does a vortex in liquid cause air incorporation into the liquid?

Would causing a strong vortex in a liquid, for example high RPM with a dispersing blade in a properly sized vessel, cause air to become more incorporated into the contents of the mixture than would otherwise mixing it without causing a vortex?

8 Comments
2024/07/17
20:25 UTC

1

How can I control the speed of a single-phase AC motor?

I'm designing a ball mill for my internship and the requirements for the motor are that it's single-phase 120V, 60 Hz, 1/4 hp, and more than 1800 rpm but no more than 3600. I've already found a few models that suit my needs but there is a problem.

I'm being asked to implement some kind of electronic speed control to the motor, which I've seen done before with three-phase motors but never with single-phase, so I'm at a loss as to what the options are and how they'd affect the supply of the motor.

23 Comments
2024/07/17
20:09 UTC

10

What am I missing about spring doorstops?q

There are millions of conical spring doorstops out there, beloved of cats, dogs and children of all ages merrily twanging them.

But every single one I've seen is set up so the door hits it end-on and because the spring is tightly wound there is no energy absorption in that direction.

So what's the point of them? Is everyone using them wrong?

11 Comments
2024/07/17
19:25 UTC

5

Are engineers in North America going to have to start planning for torrential rainstorms in their designs?

The city of Toronto and the surrounding areas (Greater Toronto Area) have suffered massively with massive downpours yesterday.

Take a gander at r/Toronto or r/Mississauga and you will see multiple photos of flooded roads, basements, power outtages and other issues all due lack of drainage or drainage not sufficient for this specific scenario.

It was a hard day yesterday, both as a citizen and an engineer, and I wanted the thoughts of the people on this sub.

With Global Warming and the changing climate patterns, is this a new weakness that has emerged in existing designs, and is it something that will become a new design standard going forward?

28 Comments
2024/07/17
19:16 UTC

0

Could metal exoskeletons make good motorcycle armour?

For a couple of years I’ve been constantly thinking about this idea and wondering if it could actually work. Recently I thought it would interesting to see what actual engineers think about it so I’m making this post.

The idea is to create a metal exoskeleton to make much more affective motorcycle armour. I absolutely love motorcycles, they’re by far one of my favourite things in life but it’s insane how dangerous they can be like the injuries people get can be so bad and happen so easily it’s just crazy, this is why I came up with this idea. But problem is that it’s just an idea and ideas often don’t work exactly how you think they will in real life so I’d love to see what y’all think about it. Like do you think a metal exoskeleton could prevent more serious injuries like all kinds of horrific bone fractures and stuff like that, and could making joints that have limited range of motion also help prevent these horrific injuries? In my head this SHOULD work like it should make your body capable of going through very serious crashes with just minor injuries or no real injuries at all but like I said things often work differently in real life so what do y’all think? Could this work or am I missing something? Or maybe I’m just fkg stupid? I’d appreciate your opinions on this whole thing

33 Comments
2024/07/17
17:06 UTC

0

Which Codesys Software do I need for HMI Development on Engines Using CAN?

In order to be able to develop HMIs/control panels for engines using controller area network communication and the J1939 protocol, which codesys modules will I need to purchase?

0 Comments
2024/07/17
16:07 UTC

5

How does Ultrasonic thickness measurement work?

I understand (I think) the basics of ultrasonic thickness measurement: an ultrasound wave is generated and goes through the material (usually metal) being tested, bouncing off the boundary of the material. The time between emitting the wave and detecting the reflected wave is multiplied by the (known) speed of sound within that material and then divided by 2 to account for the round-trip.

What I am unclear on are the following points:

  1. If the ultrasound wave does not bounce off the material being tested itself but instead goes through, why is it bouncing off whatever is on the other side (e.g. I have a piece of metal resting on a table; how is it that the thickness measured will be that of the metal and not metal + table?)
  2. The ultrasound range starts from 20kHz but apparently some frequencies are preferred for Ultrasonic Thickness measurement. Why is that?
  3. Apparently some couplant is needed between the measuring device and the material being tested; What happens if no couplant is used (and why)?
  4. Unlike piezo electronic transducers, EMAT seem to not need that couplant; what is the difference in the waves emitted by each type of transducers that makes one need a couplant and the other not?

Thanks for helping me understand a little more

8 Comments
2024/07/17
14:53 UTC

20

How do firefighting helicopters stay stable when carrying those buckets full of water?

Recently saw a UH60 pull some water out of a lake to fight forest fires and I was curious as to how engineers account for the sloshing of the water in the fabric bucket.

Are they treating the bucket as a sinplified free hanging weight?

Are there slosh baffles lined in the bucket?

How do they approach issues of stability with and without the water payload?

How do they account for the vibrations running between the tethers of the bucket and the airframe? I imagine it has to be substantial.

12 Comments
2024/07/17
14:33 UTC

3

Drain pipe over the main electrical room in my Condo Building burst twice over two years - Cheating out on maintenance?

Toronto is having some very abnormal rainfall over the last two years and we have had a massive thunderstorm yesterday that resulted in massive flooding all over the city.

I live in a Condo with three towers on the western edge of Toronto. We had a pipe burst over the main electrical room that resulted in the electrical room being flood and no power for the entire day, for my tower only - the other towers in our condo and all the condos around us (16+) were fine. Power was restored after a massive effort by a third party contractor.

The exact same thing happened two years ago. Is the building management doing cheap maintenance? Should this be happening this frequently?

5 Comments
2024/07/17
13:30 UTC

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