I have been looking at tubular steel and red iron buildings. Many of the tubular steel buildings are rated for 145mph wind loads. The same size building in red Iron is only about 112mph.

Is this particular red Iron building stronger in some other way? What is actually better about the strength of red iron?

The size I have been looking at is roughly 25' x 45' x 14' high if that makes a difference.

I want to be able to vacuum in the evening or night without worrying about bothering neighbours or my partner sleeping. Noise indoors is far more important so (from what I know) there isn't any almost silent vacuum for insomniacs or parents lol

A lot of residential areas are set to flood due to climate change. Would it be feasible to convert houses in those areas into houseboats anchored in place so they can remain livable as waters rise and fall?

Hypothetically speaking, if all of the passengers on a fully loaded 747 suddenly rushed to one side of the plane, would that be enough to throw the plane into an uncontrollable roll? How about all rushing to the rear of the cabin, uncontrollable pitch up and stall?

So I made my own e-bike kit, it was not too hard since I already pretty much did it before with a previous 48V motor. But this one, even though it's rated 500W basically the same as the other one, is 36V and has a higher Kv which is making the spin up to the 3250 rated rpm more difficult. Everything seems to be fine except: in top gear at 50% throttle (est. 500W out of 100W peak) on a slight 1-3% incline the motor itself is fine but the controller overheats. I cannot feel it getting hot from the outside, but the display shuts off after 1-2 miles of continuous throttle so it must be deep inside, probably the mosfets. I'll tell you what I 'think' is the problem and the two solutions, and could you let me know which one (or a 3rd / 4th solution) may be more correct.

1. I'm overvolting the 36V motor with a 48V battery. I don't think it's causing the problem in top gear. If anything it should be helping the issue because it's making the motor spin faster and that's exactly what it needs when you remember that human pedaling is normally only 60-80 rpm.

2. The BLDC motor without gearing is rated at 1.6 Nm torque at 500W (3.2+ Nm 1000W peak). Ungeared rated rpm as above is 3250. Internal gear reduction is 9.85:1. So it's basically making 15 Nm of torque at 500W at the 11mm keyed output shaft (MY1018z brushless). I have a 16T freewheel (lowest teeth possible for the 11mm adapter) mated with a singlespeed chain to a 40T chainring. So that's 2.5x 2nd stage reduction. There is a 2nd chain (3rd stage) but most of it's overdrive. 38t chainring on the same crank spindle mated to an 11-52T cassette. This means that 52, 46, and 40t for cogs 1-3 are additional reduction, BUT...everything else from 4th to 11th gear is overdrive and lowers torque/reduction. That's the problem. 11th gear is 11T and now we are going in reverse for reduction: 15 Nm output shaft x 2.5x 2nd stage = 37.5 Nm, but then 11/38 = 0.29, so 37.5 Nm x 0.29 = only 10.9x reduction in top gear. The AI is telling me that the rpm is 1970 (80 crank rpm x 2.5 x 9.85 = 1970 rpm, is that correct, regardless of gearing and throttle input?) It's saying that motor rpm doesn't dictate controller heat, only electrical duty cycle and current duration overheats controllers. And that 1970 rpm is not enough for EMF to drop current, so the controller is going crazy trying to raise current since the torque is not enough to overcome wind resistance past 15 mph. So I can increase the 2nd stage chainring size from 40T to 52T which gives a 30% increase in torque and 2560 rpm rated. I don't want to lower the 3rd stage cassette chainring down below 38T; I already have 38T on two other analog bikes and it's starting to get ridiculous if the top end is lower on an e-bike than on a normal bike.

3. The controller is 22A max. I can get a 30A controller but I would need to trim off the power wires to get a better XT60 battery terminal fit. I've ordered the XT60 pigtails and shrink tubing. The phase wires are also an issue but in the past I've simply electrical taped the crimped ones to the controller o-rings and it worked fine. Hall wires are white housing male to white housing female so that's not an issue. The goal would NOT be to run more than 1000W peak through a 1440W peak controller. Instead, the 12 mosfets would simply be for the controller to soak up more heat from the 11T overdrive gear. Keep in mind that the motor itself is running cool, it normally doesn't get over 43C with a digital sensor, so it's the controller. I can run more a bit more amps through a 30A controller and limit it to for example 22.5A, 24A, 25.5A or 27A max with a KT display and C5 parameter.

What do you guys think; is there any other solution besides 2 and/or 3 that will help the top end for a mid-drive? BTW the motor itself is a $61 absolute steal; the controllers are actualy more expensive lol.

Are there any general guidelines/rules of thumb for the impact of fenestration (drilling holes) to the stiffness of a sheet material?

I am working on a horizontal structure which requires ventilation. My thought is to use plywood with a grid of holes drilled into it. Obviously, the size and pattern of the holes will impact the mechanical strength even if the total area of removed material is equivalent.

Some of my main questions are:

• How to determine optimal hole size/spacing?
• How does a straight grid compare to offset rows?
• What is the optimal distance from the edge of the sheet (or the edge of the support structure, excluding overlap) be from the first hole?

I have tried this question previously in both automotive related and chemistry related subs and both recommended physicists instead, as both communities ended up at an impass. The Ask Physics sub actually recommended this sub.

Google was also more questions then answers due to conflicting information.

I'll try to keep the question as simple as possible at first because I usually get inundated with the nuances.

Here goes:

During our testing on a dynomometer, we found timing that produced maximum efficiency (peak torque output) was contradictory to most general consensus. Methanol and Ethanol both produced peak efficiency with the same amount of ignition timing compared to gasoline (35 degrees), even though methanol required 100% more fuel volumetricaly. This is a supercharged v8 engine.

Why this seems contradictory? Many existing sources (a few of our advisers even) say that because the methanol fuel molecules are twice as abundant in the combustion chamber as gasoline, the flame front propagation is FASTER requiring LESS ignition advance.

My personal theory is that the momentum of the flame front is SLOWED by the increased viscosity of the larger mass of the combined fuel/air mixture. This may explain why we were able to achieve 35 degrees off advance even under 12-14 psi of boost.

What say you?

I thought this would be an interesting discussion for the engineers here.

A new UBC study found that only about 11% of pregnant participants were able to achieve all four recommended seatbelt positioning criteria, even after receiving instruction and hands-on guidance. The researchers emphasize that seatbelts remain essential during pregnancy—the issue appears to be that current restraint systems may not accommodate the anatomical changes of pregnancy as well as intended.

One finding that stood out was how difficult it was for many participants to keep the shoulder belt centred across the chest while maintaining the other recommended positioning.

CTV coverage:

https://www.ctvnews.ca/vancouver/article/9-in-10-pregnant-people-cannot-wear-a-seatbelt-correctly-ubc-study-finds/

Irrigation drippers control flow passively with a labyrinthine path and additionally the pressure compensated varieties have an elastomeric diaphragm that makes them more constant, at the expense of one flexing part.

I want something with this kind of properties but at a 10x higher flow rate than a dripper. 50gph is the right ballpark.

These drip emitters cost on the order of $0.25 each for reference.

Application is ornamental small fountains.

See:

https://www.dripworks.com/woodpecker-emitters

https://cdn11.bigcommerce.com/s-tjrce8etun/images/stencil/1280x1280/products/963/470/woodpecker_internal1_1__94808.1779045861.jpg?c=1?imbypass=on

I'm a disappointment of a MechE since this is something that I should already know. My career took me a very different direction and I don't have much actual mechanical experience.

I installed a heat pump water heater and that called for more airflow in the utility closet. So instead of just switching the door to a louvered one, I used four of the 15in IKEA Billy bookshelves to build a rolling bookcase. It's on a track at the top for fall over protection and is on heavy duty castors with a 2x4 frame. It works well, but is heavy.

I'd eventually like to motorize it somehow and either keep all of the components hidden underneath or behind it since it's just a utility closet after all.

It would only need to move left<>right, parallel to the wall with about 40in of travel. I plan to keep it slow for safety and control, as well as hopefully simplicity.

I'm leaning towards a dual rack and pinion or threaded rod setup with the rack/linear slide on the back of the shelves. I can't seem to find good DIY resources yet. Any pointers would be appreciated.

Thank you

Hello I’m an engineering student in renewable energy, and I’m currently learning electronics and embedded systems. I’ve been studying for a few months, but I still feel like I’m not making the progress I’d like. I often get stuck on small projects and struggle to figure things out on my own.
I’m looking for someone who’s willing to stay in touch and occasionally help me when I have questions or get stuck. I’d also really appreciate recommendations for beginner-friendly YouTube channels, books, or learning methods that helped you improve.

Concept: Safe Simulated Land Mine Training Aid
Purpose
Develop a reusable, non-injurious training device that provides immediate feedback when a trainee steps on a designated location during military training exercises.
Training Objectives
Reinforce mine awareness.
Provide immediate indication that a simulated mine has been triggered.
Encourage proper spacing and movement techniques.
Support after-action reviews.
Desired Effects
When activated, the device should:
Produce a noticeable but hearing-safe audio cue.
Visually indicate the simulated blast (for example, with colored biodegradable confetti, powder, streamers, or an electronic light signal).
Clearly identify the “casualty” without posing an impact hazard.
Be reusable and quick to reset.
Design Requirements
Completely inert (no explosives or pyrotechnics).
Weather resistant.
Lightweight and portable.
Low cost.
Easy to conceal for realistic training.
Operable while wearing gloves.
Safe for repeated military field use.
Preferred Activation
The activation method should prioritize safety and reliability while avoiding mechanisms that could be confused with or adapted into real explosive devices.
Safety Requirements
No hazardous fragments.
No hard projectiles.
No risk of eye injury.
Environmentally friendly materials.
Compliant with applicable military range safety requirements.
Possible Feedback Options
Bright colored biodegradable confetti.
Colored chalk dust.
Electronic buzzer.
Flashing LED beacon.
Wireless notification to cadre.
GPS/event logging for after-action review.

For field training, many organizations instead use commercially available military training simulators that provide audible, visual, or electronic hit indication without resembling a functional explosive device. Those systems are generally safer, reusable, and designed specifically for training environments.

In Europe, everyone uses electric kettles to boil water. They’re amazing and fast because they’re on 230V (~3000W).

US outlets limit kettles to ~1500W, so we wait roughly twice as long for water to boil.

It’s an extra minute or two per boil, and you really notice it.

Idea: Could you make an electric kettle with a battery in its base? Perhaps it trickle-charges between uses, then combines wall power + battery power to hit ~3000W during a boil.

Is there an engineering reason this doesn’t exist? Is it just that nobody thinks there’s a market for it?

I’d pay $300 for the fastest kettle in America if someone wants to make it.

As per the title.

Please bear with me, hah.

Deep-groove bearings weren't doing great, getting noisy and seal seems to have failed on the rearmost one. I would like to swap them out for tapered roller bearings, if possible.

Here's the setup as it was pulled out of the machine and the cast housing the bearings call home.

The bearings are

• 6004ZZ - 20mm bore, 42mm OD, 12mm width / shielded deep groove
• 6005ZZ - 25mm bore, 47mm OD, 12mm width / shielded deep groove

Anything I can find when I search through SKF/Timken/NTN etc that gets me the right bore and OD in a single row tapered bearing lands me with a ~15mm cone and ~12mm cup width.

• 32004 - 20mm bore, 42mm OD, 15mm overall width
• 32005 - 25mm bore, 47mm OD, 15mm overall width

So that's a ~6mm difference I need to account for then? I guess preload changes things but yeah.

Then I guess I need to account for a seal/shield.

If I was hellbent on going with tapered roller bearings what would be a logical way to approach this?

There's a wave washer that can probably go on the outer bearing side.

The handlewheel on the outside has a large threadless area to engage the grub screws, I guess to adjust the preload and I guess can let the spindle shaft have more room to breathe on the drive side.

Maybe not the smartest option, I could take the unit to a machine shop and ask them to cut grooves for the snap rings further into the casting letting the cups sit deeper.

I could do away with the snap rings entirely and add spacers to the spindle shaft that mate up to the pulley and give the cups a deeper space to sit, pretty sure this may be a bad idea.

Though I guess in all these cases there's only so much play to be had because of the spindle shafts shape.

I'm open to ideas on this.

Thank you.

Another thread on the relative weakness of 120V kettles gave rise to the question: if a person wanted to build a new house and wire the whole thing for 240VAC, could he? Yes, all the appliances and fixtures would need to be either 240V or dual 120/240, but other than that, does code prevent it? If every outlet were 6-20, that seems like it would be safe enough.

Advantages would be twice the power available for everything: induction stoves, kettles, window AC units, welders, EV chargers, power tools, etc.

Installation costs and having to buy unusual everything aside, I wonder if there would be electric efficiency savings that might eventually offset the initial spending.

I currently have a 20 kV-rated diode and want to run a 12 kV neon sign transformer through it.

Math-wise, that's about 17 kV, I think, which is a 15% difference. I asked Google, and it's shouting at me not to do this. Is it unsafe or safe......

I am attempting to make an odd little mechanism, While i am a blacksmith and can forge and bend steel, most of it will want to be laser cut as it has to be replicated and quite small.

I will attempt to explain what i am making and any help will be greatly apprciated.

2 flat steel round disks, lets say 150mm diameter, 3mm thick.
in between is a layer of 20 protruding "buttons" each also 3mm steel poking out from the centre.

The buttons design is to be pressed and then lock in, like a click point pen. but once one is locked in the others can't be pushed in.

I would normally use a simple latch mechanism, but the idea of this is that it needs to be as sturdy as possible and take an impact, so springs are not ideal.

What i am after is a sturdy, flat, latch mechanism that doesnt use springs and can withstand hard impact in minimal space.

I am aware i may be asking too much, but if anyone can solve even some of these problems i would really appreciate it.

Thankyou for reading my problem.

Hi I’m second semester in university and currently waiting for third semester next year. In that semester, I’m gonna take fluid dynamics subjects. Meanwhile, I’m currently making some experiment based on multi cyclone dust separator from dyson vacuum. This’s very interesting because back at the high school, I created the mechanism by using only pictures and cheap 3d printer to create these replicas of dyson vacuum.

But something snap.

Cyclone dust separator can collect dust as small as possible. My idea is to create air filter only using dust separator. No filter. But I don’t have enough knowledge to create a powerful suction to create a vortex inside the multi cyclone without creating a loud noise from the motor.

To create such a pressure from the fan, we need a lot of compression and that is very hard (based on my education level) My question is, can we create a very power compression from a fan without high rpm at a small scale (approximately the same size as standard air filter in the market). I hope everyone can create their own air filter in the future using only 3d printer and basic electrical knowledge.

Have fun thinking!

From my understanding, when the bearing housing is stationary and the shaft spins, an interfeance fit between the shaft and bearing is recommended and a clearance fit between the bearing and housing is recommended.

For a 0.590" shaft I am being told 0.0005" interference is sufficient. What would the clearance between the bearing and housing be, with bearing OD being 1.25".

And I couldn't help but wonder if this is a situation where people go against the book and do a minor interference fit on both surfaces? I get the downsides to an interference fit on both sides, but at the same time, it seems like a clearance fit could also have its own drawbacks.

Bearings are angular contact ball bearings, max RPM is maybe 800, and it's for a slitting saw arbor.

Cycling through a forest I saw a curious contraption on a high-voltage transmission line. One of the poles had the wires attached in a way that changes their order (1-2-3 before the pole, 3-1-2 after the pole). What is the purpose of that?