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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.

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Career Monday (12 Feb 2024): Have a question about your job, office, or pay? Post it here!

As a reminder, /r/AskEngineers normal restrictions for career related posts are severely relaxed for this thread, so feel free to ask about intra-office politics, salaries, or just about anything else related to your job!

14:01 UTC


How to measure the lumen output of a flashing bike tail light?

I am looking at different bike tail lights and comparing their lumen output in the specs.

My goal is to try to replicate the test results that the manufacturer claims.

Will an under $50 light meter from Amazon do the job? Will it detect the fast flashes?

I googled 'how to measure lumens', 'ansi fl1 test method', and a few other things, but I have not found what I am looking for.

I look forward to hearing what Reddit Engineers have to say. :)

04:49 UTC


SMR code for attaching hardware

Hi all,

Quick questions for the ILS engineers out there (especially the ones with a good LORA understanding): what SMR code do you apply for standard attaching hardware, a part of me trends to say PAOZZ, but I'm in hesitation with XB or XD.

For me the PAxxx are more for the CI's, not really for consumables. However the AP are procured and stocked and can be replaced at LGR.


01:11 UTC


An aquarium rack: cinder blocks, 16' 2X6's, plywood.

I'm looking to build an aquarium rack with cinder blocks on both ends and 16' 2X6's on edge, topped with plywood. Something like this... https://www.youtube.com/watch?v=WAz_uLJj7Hs

The rack would hold 5 40-gallon aquariums, so somewhere around 2000 lbs. If I used 4 2X6's, what would the weight capacity be? What about with 4 2X8's instead?

1 Comment
23:59 UTC


potter's treadle wheel linkage

I intend to build a potter's treadle wheel; there are two variants to consider, the simple leach wheel https://www.simonleachpottery.com/uploads/3/4/1/2/34126045/136038_orig.jpg
and the more obscure 'saviac' wheel -> https://gzandco.blogspot.com/2011/09/saviac-wheel.html which features a linkage that is mounted behind the foot pedal and at a ~20 degree angle.
Is the latter (i.e. the linkage, the other features are almost identical) superior in some way?

22:35 UTC


Measuring fill level of a bin

Lets say I have an ice generator sitting above 1m x 1m x 1m bin. Flake ice falls into the bin and I want to know when the bin gets full so I stop the production of the ice. What is the easies/simplest/cheapest way to determine/measure/approximate how high is the bin filled with ice? Thanks!

20:57 UTC


What material is in Automotive DRL headlights

I'm been developing my own led headlight and the one part I've been stuck on is LED DRLs, I've tested a plethora of acrylic translucent sheets but they all seem to be inadequate. Many OEM manufacturers use clear PC with a very fine pattern in it but that is beyond my manufacturing budget. looking at some cheaper aftermarket headlights with LED DRLs they seem to glow very brightly with only 30W of light.

I provided a picture of a set of aftermarket headlights they use a 4114 bulb for the leds which are only 30W

18:37 UTC


Self-centering mechanism for a large fixture

I'm helping a friend design a large fixture to hold circular pressure vessels with a max OD of 120" and a min OD of 60", similar to a 3 or 4 jaw chuck (doesn't need to spin, just has to sit on the floor and hold the vessel). Because the vessels are circular, the mechanism should be roughly self centering.

I understand how scroll plates work for machining chucks, but given the very large size of the jig, I don't think that's economical. So far the only mechanism I've come up with is a toothed belt drive mechanically linking three screw rods so that they all move in unison. Any other ideas?

18:24 UTC


Best type of anti-seize for fastening dissimilar metals

I will be threading into aluminum using zinc-plated grade 5 steel fasteners in relatively dry conditions. I have decided to use zinc-plated steel fasteners since both zinc and steel are much closer to aluminum in the galvanic series than stainless steel, hence galvanic corrosion will be less likely (although there is a crazy amount of conflicting info out there on this).

My question is what type of anti-sieze compound would be best to further discourage galvanic corrosion? Many sources online seem to recommend copper, graphite, or nickel-based anti-sieze, though this seems odd to me since copper, nickel, and graphite are practically on the opposite end of the galvanic series from zinc, steel, and aluminum. Wouldn't these compounds therefore encourage galvanic corrosion?

18:05 UTC


Innovations, mistakes and discoveries in the field of materials science during WW2?

I recently heard a fascinating story about the routes of commercial ships during WW2.

Supposedly, the ships sailed mostly trough the northern seas and oceans to avoid naval conflict. However, one of the mistakes they made was underestimating the importance of toughness in colder weather. A fair number of ships was constructed using steel with a BCC crystal structure which loses toughness at a drastic rate whilst in a cold environment and becomes brittle. This was ultimately also the reason why an iceberg was able to sink the Titanic.

What similar stories from the WW2 era have you heard?

16:47 UTC


How do they build bridges over large canyons or between two mountains where there is a massive drop underneath?

15:33 UTC


Feasibility of In-Home Nuclear Reactor Furnaces

OMG NOOOO We're all going to grow 4 arms and 7 eyes and die from radiation ahhh panic!!!!

Ok now that we got that out of the way, I've been thinking about this a lot and it really seems like it could work. So first off, the biggest danger is probably bad people "mining" the radioactive material out of their system and using it for nefarious reasons. Lets completely ignore THAT aspect of this. Lets pretend everyone is a good person, but still accidents happen.

I have an oil burning furnace in my house. It heats up water to 180° and moves it through the radiators to heat the home. That also comes with a giant 275 gallon oil tank in my basement. I also have a separate electric hot water heater for hot tap water. In my region, oil furnaces are extremely common. Some people have separate hot water heaters for tap like me, many others get all hot water direct from the furnace.

So I look at this setup and I can't help but think that the whole thing could probably be replaced with a tylenol-sized chunk of uranium! I say probably because I don't even know where to begin doing any math on this.

Now to be clear and specific, I'm not talking about generating power with a reactor in your house. That would be significantly more complicated. What I'm talking about is a system that just creates heat. Heats your house and your hot water.

Is such a system technically possible? I imagine it would be able to run on some pretty low grade stuff. Possibly even the waste material from "real" reactors. It only has to be able to heat water up to about 180°. In-fact, probably a lot less than that if it can do it continuously. A system like this wouldn't be making steam to spin turbines. Burning furnaces operate in sort of a burst-mode but a nuclear furnace could just run continuously but at a lower level. Tap water only needs to be 120°, and the water to heat your house, probably just a few degrees above 70°.

The reactor itself would of course need many fail-safes. I've read about many different kinds of reactors, and some are designed so they can't meltdown. They essentially deactivate themselves in case of a meltdown. It would need to be something like that, with plenty of shielding.

There is a way to create electricity directly from nuclear ratiation, some space robots use that to power themselves. If it's possible, it would have that integrated into it, not to power your house but to power the electronics of the reactor itself.

In this theoretical world, everyone is a good person. But still, housefires happen. We're probably talking about a very tiny amount of radioactive material and it would be deep inside the unit in a non-user-servicable location. But even so, some house fires get crazy hot. Then water gets poured on them and steam billows everywhere.

So to get specific for any nuclear engineers out there, here's the main questions of this post:

• Is it possible to built a nuclear reactor that would have enough energy output to heat a typical home and it's typical hot water use, while fitting in the space of today's typical gas or oil burning furnaces?

• Would a nuclear furnace like this be able to be designed in a safe enough way, with enough safety failsafes, that it would be considered safe for in-home use?

• How much radioactive material would you need for this kind of output? And how long would a device like this be able to run with that fuel? 10 years? 50 years? 100 years?

• Also about the fuel, as the fuel 'ran out', what would be the result? Would the furnace just not be able to create as much heat? So the max temp water it could output would lower over time? So you could essentially keep using it as it got older and older until the fuel was un able to maintain 70° hot water to heat the house, then retire the unit?

• So if the previous bullet pint ^ is how the fuel situation would go, what would the state of that spent fuel be? How much less radioactive would it be compared to when the system was first brought online? I'm wondering if a secondary benefit of a system like this wouldn't only be finding a use for the waste of a bigger nuclear power station, but also that it would be able to 'use up' that fuel and render it significantly less radioactive than it otherwise would be after that amount of time.

• And given the amount of - i assume low grade - radioactive fuel that would be in this device, how dangerous would a catastrophic accident be? Like if all layers of sheilding cracked for some reason. Or if it somehow melted down even though being designed in a way to make that impossible. Would it turn your town into a ghost town? Or your neighborhood? Or just your house? Or would they be able to throw a lead blanket over the reactor, load it on a truck and take it away and the just let your house sit for a while and then everything would be fine after that (except for your disgruntled neighbors).

I assume a system like this, if the numbers actually worked (and again, completely ignoring ALL regulatory hurdles), would integrate a heat exchanger to get the heat from some kind of 'other' fluid inside the unit, to the water itself that you were going to use.

And it would have several layers of shielding, and many independent radiation sensors on it. plus a series of sensors you'd put around it in your house. And then possibly as an extra layer of protection, you could frame it into a closet in your basement (no airflow needed unlike a burner) and maybe use some kind of lead impregnated paint to add an extra shielding buffer.

Imagine having it be 70° in your house, all winter long, for the next 50 years.

If a machine like this were possible, I'm sure it would be very expensive and would require a whole infrastructure to deal with building it, installing it, fueling it, then dealing with the fuel when it was removed or if there was any kind of accident. But compared to the costs of fueling a gas or oil burner, even if a nuclear furnace was very expensive up front, I imagine in its lifetime it would be much cheaper than the alternatives - aside from maybe solar powered heat pumps but you're going to have a tough time keeping your house at 70° when its 5° out and theres only 8 hours of daylight shining on the snow thats burying your solar panels.

14:04 UTC


Is it okay to connect a 6-meter 10A extension cord to a 6-meter 6A extension cord to power a 0.3A cctv camera? (Main outlet + 10A cord + 6A cord + 0.3 cctv)

10:37 UTC


What is the significance of series operation in engineering?

I am not an engineer but my grandfather was in the 50s in Korea. I asked him what was the most important math tool he needed for his work and he drew the sigma symbol.

Is series useful in engineering? Maybe before computers?

1 Comment
06:54 UTC


Please help me. Is the drilled pier foundation suitable for a clay and hydrosol soil type? If the location is in a seacoast/ coastal area?

Help, please. Is the drilled pier foundation suitable for a clay and hydrosol soil type? If the location is in a seacoast/ coastal area? I already researched some information. I just need your insights or opinion about it.

05:54 UTC


HELP solving a complex problem in my backyard? How to rig a system to make TWO 90-degree turns in a drainage pipe underground to remove rocks?

I couldn’t think where else to post this, so here goes …

I have a drainage pipe under the concrete in my backyard that has rocks causing a drainage issue. (We had a flood in our houses last year because of this, it has caused SO many headaches). The pipe goes straight down about a foot, then a 90-degree turn makes the pipe run horizontally. The pipe runs a few feet horizontally, then the pipe makes another 90-degree turn to the left. Just past that turn is a solid clog of rocks and debris.

I have been told by multiple professionals to just rip up the concrete above the blockage to access the rocks and clear it, but this is close enough to our pool equipment to total a many-thousands-of-dollars repair. We have tried “roto-Rooter” type tools that have been unable to make the two 90-degree turns needed to access the blockage. I KNOW there is a way to get these rocks out of the drain, I’m just not smart enough to have a solution!

If anyone here is willing to take a stab at a solution, I’m all ears!

04:48 UTC


Random Mt. Everest Idea to Bring Bodies Home (Although it may just be crazy)

Hello all. Let me start by saying I'm in no way, shape, or form an engineer nor do I have much scientific background beyond random facts I've collected over the years (my area of expertise lies in business management, finance, etc).

I've know for a long time that there are plenty of bodies stuck on Mt. Everest of climbers who never made it back. Just out there, exposed, some right off the path. Retrieving them is too dangerous, either to be carried, dragged, or airlifted off. None of these options are practical.

However, what if a brilliant engineer designed an extremely durable, lightweight, semi-collapsable pod that in which a body could be placed then somewhat suspended inside using various strapping mechanisms? The idea being that this pod could then be sent down the mountain, similar to a sled, but could also absorb a huge impact, such as falling from dropp offs, etc.

Sherpas could plan which direction to release the pod down the mountain with help from topographical maps, and each could be fitted with GPS to track progress down the mountain. May not make it all the way down in one expedition, but if the pods are lightweight enough and sturdy enough, perhaps a few bodies could be progressed down the mountain each expedition and the locations marked for the next one.

Or maybe this is a ridiculous idea and the bodies and pods would just shatter. Or end up in glacial crevasses, lost forever.

Idk, again not my area of expertise. Call it a brainstorming session. Thoughts?

1 Comment
04:25 UTC


Blasting nearby - how to assess potential damage?

Blasting damage

I apologize in advance if this is not the right place to ask this question.

I live in a 2200sqft, two story single family home built in 2017. Crawlspace, hardiboard siding and generally well built based on the independent inspection I had done prior to purchase.

I’m in a gentrifying area of Nashville. In 2020 they began blasting in the immediate area for about 6 months once a day. The blasting came within 50ft of the house. I was concerned about damage and once it was over made a claim with my homeowners. They sent a forensic engineer out and denied the claim saying that the couple of dry wall cracks we had were the result of typical settling.

Now we have a new development behind us, even closer. They just started blasting two weeks ago. The most recent blast this week was within 20ft of my property line. I’ve not seen any obvious damage yet but it’s difficult for me not to believe these two series of blasts aren’t having a negative effect on the house.

What is the right course of action to check for damage? Do I raise a claim with homeowners and risk a premium increase? Or do I hire an independent inspector? I’m not really concerned with cost for inspections so much as I want to address any damage quickly and make sure the builders blast insurance covers any issues. I’m also curious what I should look for? Cracks in foundation? Dry wall cracks? It’s hard to decipher minor, typical settling from damage caused by blasting.

Thank you all in advance for your insight.

03:10 UTC


Smaller Pulley on Electric Motor, Larger Pulley on Tool? Does it matter?

Hi All

I am adding a bandsaw to my shop powered by a separate electric motor via a v-belt. To get the saw to the proper speed I am using a 2" pulley and a 4" pulley.

Is there any sound mechanical reason for me to NOT put the larger pulley on the motor? Most diagrams show the smaller pulley on the motor and the larger on the tool (bandsaw in this instance). Curious what everyone thinks. I haven't found any clarity on the internet.

Thank you!

01:25 UTC


Water tank equalisation time

Just seeing if my thinking is correct here. I have 2x 22kL drinking water tanks right next to each other, connected by a 1 inch pipe both isolatable.

No current way of calculating flow rate between them but would they equalise at close to the same time in any of these cases:

1: tank 1: 100% tank 2: 0% =50% 2: tank 1: 100% tank 2: 25% =62.5% 3: tank 1: 100% tank 2: 50% =75%

Given the increased potential energy of full one in relation to the empty one and the loss of pressure as they meet an equilibrium- if I were to calculate scenario 1 would that be much the same time as any combination of levels?

01:21 UTC


Aircraft design methodology in CAD

1 Comment
01:07 UTC


Gas viscosity and exhaust wrap

Not an engineer but thought this would be the correct place to ask. If gasses increase in viscosity with heat, shouldnt exhaust wrap reduce the efficiency of the scavenging effect in a combustion engine rather than increase?

1 Comment
00:38 UTC


How to determine the torque needed on a DC motor

Hello, non-engineer here trying to build a project for food production.

I’m building a centrifuge to remove the surface water from cooked beans after boiling - basically like a spin cycle on a top loader washing machine.

I’m planning on creating something similar to this diy clothes spinner, but using a larger internal bucket or colander that I can put the cooked beans in a mesh bag inside. https://youtu.be/3jNv6mUmyIY?si=CTJ9RhFL2aYc5XcW

Average weight of cooked beans will be ~2-2.2kg plus water weight after they come out of the pot, so say max 3-3.5kg weight including beans, surface water, and internal bucket/colander.

My question is, what size motor (volts, torque, rpm) would I need to power this? Is there anything else I’m missing? (Unknown unknowns)

I’m in Australia, so metric measurements would be super helpful.

00:20 UTC


What knowledge is needed to build a control system for a TVC solid motor rocket?

My university's rocket team is building a TVC solid motor rocket. The control system sub-team is new and we aren't sure where to start. What resources/knowledge will we need to learn to be able to design the control system in Matlab/Simulink with Monte-Carlo simulations?

23:21 UTC


Hollow blocks used for retaining walls...

Hello, what are the hollow blocks people use to build retaining walls called? They're usually a chipped face, and filled with gravel. What are they called? I'm writing a report and need to address them directly.

They're stacked six feet tall if you were wondering.

22:27 UTC


How come, with all the advanced engineering and billions of dollars invested in aircraft design, manufacturers still struggle to implement a public address (PA) system that's consistently clear and audible for passengers?

From Canada..

20:54 UTC


What's the best way to attach corner braces to reduce lateral racking of a stacked bunk bed?

My daughter's bunk bed is composed of 2 twin beds stacked on top of each other and held in place by a series of infuriatingly-difficult-to-align dowels.

We removed the bottom bunk and front rail to open up the floorspace under the bed. The bed is solid along the shorter dimension, but can wobble a bit more than I'd like along it's length. I'd like to attach a pair of angled braces between the two bunks, but I'm not sure how to arrange them to minimize the sideways racking.

Photo of the bed, with various "Attachment Points" labeled as such;

  • A, B, and C - the bottom corners and midpoint of the top bunk's rear rail
  • D and E - the upper edges of the bottom bunk where it interfaces with the top bunk

*F, G, and H - the top corners and midpoint of the bottom bunk's rear rail

The easiest way I think would be to cut braces at 45 degrees that go from D to somewhere between A and B, and from E to somewhere between B and C. I feel like it would be stronger though if I went from D and E meeting at the middle point B. Or am I completely backwards? Should I be attaching 2 points from the top to one point on the bottom?

Any help or guidance is greatly appreciated.

20:42 UTC


What to do about Joist Crack that runs to the end?

Picture Here

The crack is right up to where it rests on the beam. What is the route to fix this? Sistering another board next to it?

Would love to hear some opinions!

20:23 UTC


Silicon suction cup help!

Hello everyone, I need your help to find this sort of suction cup, for a similar piezo mix project, any idea what this can be? Checked online Silicone Suction Cup Microphone - Mini but no luck.



20:01 UTC


Is the dragon 12 board better than arduino when it comes to learning about microcontrollers and microprocessors?

Im looking for a good microcontroller to learn on because my microprocessors class was super lame and the professor just passed us along without teaching us hardly anything about microprocessors or microcontrollers. The other professors at my school who is amazing recommended an hcs12 when I asked him if I could learn some of what I missed out on by learning arduino.

Some people are telling me dragon 12 and some people are telling me arduino, what are the pros and cons to both?

19:56 UTC

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