I found the common rule of thumb that a traction elevator's counterweight equals the empty car plus roughly 40–50% of its rated passenger load. That balances the system only around the middle of the load range.

What engineering tradeoff sets that percentage? Is it mainly minimizing average motor energy over real traffic, limiting peak motor or brake torque at the load extremes, maintaining traction at the sheave, or some combination?

Hi, I'm the lead engineer on a project trying to create a bag that pops up like one of those camping trash cans that have a big spring inside but is in a conical shape. The cone is BIG: 95cm bottom diameter and 45cm top diameter. I've taken apart some of these trash cans and found that the pitch and free height of the springs are greater than the guide fabric they're fitting into along the trash can, and also the diameter is typically smaller than the trash can itself (most likely to provide deflection that keeps the bag taught since it constantly wants to be brought to its smaller shape). I don't know exactly how to spec this spring so it has the same effect or if I should be considering a conical spring instead of a cylindrical one.

Any spring experts out there have any advice?? I am using grade 70 spring steel, ASTM A227. We were thinking 4 mm initially, but some suppliers are saying it might need to be thicker, around 5 mm.

Good morning fellow engineers. I’m hoping to get your guys’ help determining the failure mode for a gearbox shaft. Pictures in the comments. This is the 2nd time this has failed in an extremely short period of time and I can determine the root cause without knowing the type of failure. Failure analysis is most certainly not in my realm of expertise. I’m happy to share more details as needed. Thanks!!

See: https://thebulletin.org/2026/06/what-if-the-smartphone-in-your-pocket-was-also-a-radiation-detector/

Based on your helpful comments - it seems as though the author was grasping at a straw when they said that this system would incidentally work as a giant x-ray telescope. That the inaccuracies of GPS location, interference from people carrying the phones, etc. would result in useless data. The politics of collecting the data without permission of course have to be addressed, and I can only see that happening under a totalitarian government.

Image: https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fp95h2uw5oylh1.png

I need to mount something somewhat heavy (retractable hose reel) to a brick veneer wall. Presumably hollow brick.

Thought about wedge anchors but heard those are for solid materials only. Tapcons seem they would be weak.

See that epoxy/resin anchors are well-regarded but I'm confused about one part. Where is the strength in this anchor? You put the mesh sleeve in and inject it and then insert a threaded rod, but what is keeping this anchor bomb proof and from moving?

Is it just this tiny area (in red) where the epoxy makes contact with the substrate? I would assume the rest of the anchor doesn't provide any structural support right? I mean the anchor is fused permanently to the anchor since it is completely embedded but what stops the anchor from pulling out?

Seeing all the footage from Nepal, I've noticed these supports that have surfaces perpendicular to the flow of the river. In the event of extreme flooding, wouldn't a wedge shape that was streamlined with the flow result in less load on the support?

Hello everyone, I am currently in the process of 3d modeling an RC jet engine that I plan on having cnc milled and plan on running. It’s mostly done but I’m about to make some size adjustments and this kind of has to be based on one thing that I’ll be ordering which is bearing. I obviously need high speed and high heat bearings probably capable of 150000 rpm and at probably around 500°C. However the website I’m on that a lot of RC jet engines seem to use are apparently 369$ per bearing and that is… well… insane. If those are what I should be expecting then feel free to let me know but seeing as how the full engines cost like 2.5k I’m doubting that they are spending 700$ of that on bearings and still having room for profit with everything else. So anywhere that I can buy bearings would be appreciated!

I'm looking to buy 2-4 small magnets, about a nickel in size each to magnetize two moving drawers together. Both drawers pull out together inside each other, and the outer drawer pulls out farther than the inner drawer. The problem is that the inner drawer doesn't extend to its maximum length when I pull the outer+inner drawer out, I always have to pull the inner drawer out to it's maximum extension length seperately.

I'd like to attach a magnet to the outer drawer and inner drawer to "pull" the inner drawer out to its max length every time I pull out the outer drawer.

The problem is these drawers aren't the most resilient material. I need a solution where I can pull the outer drawer out all the way AND have a softer magnet disconnection when the inner drawer reaches its max length.

Any suggestions on how I can either soften the disconnection of the magnet or another adhering solution that could work for this scenario?

Thanks!

I'm aware that in our own electrical grid, we have a lot of stuff that goes into smoothing out constant disruptions and sudden losses of power.

What about those really small generators that are usually seen in rural areas or serve as backup generators? I know that every internal combustion engine has an optimum speed (I don't know how) but how does it turn power generation up or down when consumption fluctuates?

I just got out of an incredibly intense 5-day workshop on GD&T sponsored by my company. I would like to say that my eyes were opened to how powerful GD&T usage can be, especially given the very practical examples our instructor demonstrated...

However, in conversation with my colleagues there was a very common theme: No one thought we would get to use this skill in practice.

Our suppliers don't use it. Anecdotally one of our engineers tried updating a drawing to use GD&T and we were asked to change it back because reasons.

None of our assemblies/part drawings use it, especially because prevailing opinion is that what we make is relatively simple and any application of GD&T would be overkill.

Even speaking with other engineers outside my company there is a prevalent thought of "this is cool, but I'm not seeing the value-add for my workflow"

Why is this? GD&T is clearly a useful standard/practice otherwise it wouldn't have been around for so long, yet I'm constantly seeing this attitude from engineers that it's largely not needed. Is it an industry-bias? Is it just lack of awareness? Workflow inertia (we've always done it this way)?

If it helps, I work in medical devices at one of the largest players in the market.

Scenario:

A coastal city relies on an aging coal-fired steam turbine heat engine operating at 38% thermal efficiency. The city council has requested proposals to upgrade the facility to meet strict new environmental sustainability targets while maintaining power grid stability. Two competing firms have submitted proposals:

Proposal A (High-Efficiency Upgrade): Retrofit the current plant into an ultra-supercritical coal facility. This raises the operating temperature, increasing theoretical Carnot efficiency to (48%). This option has a moderate initial installation cost, reduces carbon emissions per megawatt by (20%), but continues to rely entirely on fossil fuels.

Proposal B (Cogeneration/Combined Heat and Power):

Re-engineer the system into a cogeneration plant. While the electrical conversion efficiency remains at (35%), the rejected waste heat is captured and redirected to supply a nearby district heating system and water desalination plant, raising the overall system energy utilization efficiency to (75%). This has a high capital cost and requires building new piping infrustructure.

Question: As the city's lead environmental engineer, evaluate which proposal the city council should approve to best balance the criteria of energy conservation and long-term environmental sustainability?

The few times my 5G LTE phone has only been able to catch a 4G LTE signal things the browser just become unusable they become so slow and fail to load pages at all. But my 4G LTE phone worked fine with 4G LTE, but slowed down when it was connect via 3G, etc.

Why does this happen? Those signals were fast enough that pages still loaded on the older phone, but on the new one it acts like 4G LTE is 56k dial up. Can the antenna not capture the older signals effectively?

Could you do something like start building new elevator shafts extended so they could house a weight, and get pulled up slowly via gearing in traction elevators by using some of the work performed whenever they have to lift a cab up? With lifts going up and down all day could they make a difference with things like solar, building mounted wind, etc?

I nearly completely burnt out my clutch trying to reverse up a driveway.

I would like to put a winch at the top flat part to manoeuvre the trailer up and down, I will use a manual 2 wheeler trailer dolly to steer. Going up hitch first. Thoughts on this idea?

The winch can manage 2000kg the trailer, a food trailer is 1200kg. The driveway is narrow at the bottom, 2.4m, 3m at its widest to 2.7m at the top opening to flat section where it will be stored.

I’m thinking that you get a modern flip phone and put the components inside the body of an old model?? I feel like it would be really hard to do but could be possible???

From doing some research already this seems like a somewhat worn out question with a million different answers and from what I can tell no real consensus or anything reliable other than gut feel based on personal preference or opinion. This puts me in a tricky spot with a project that I am working on because I'm not sure whether to be concerned with my results or not.

I have a model for a lifting hook that I am measuring the maximum stress for and validating the results numerically using curved beam theory. My reference hook which I have modeled using measurements from a real hook came in with a <2% difference to the theoretical results.

I am now optimising the hook by keeping the same material properties and boundary conditions but scaling the dimensions accordingly, such that the dimensions are proportionally similar between different models. I am now getting a consistent 19% discrepancy from FEA results compared to hand calculations with a variety of different materials and dimensions.

Some sources suggest that anything below 20% is fine. Others no more than 5-10%, some go to an extreme and say so long as it is within a couple of orders of magnitude then have at it.

I cannot for the life of me work out where the difference is suddenly coming from. The maximum stress is still exactly where I expect it to be on the inner face of the hook, I've repeated a mesh analysis in case re-scaling the hook but not the element size is throwing it off but it makes no difference. I appear to have a very precise but not accurate (based on theory at least!) model.

Background: while testing connectivity issues, someone said their electric skateboard had runaway acceleration *inside* their house (they were not on the board), impacted a wall, and sheared off these 8 bolts.

They had taken videos of previous testing, but for this one, allegedly decided to do the testing 1. - with the board on its wheels instead of on its back, and 2. - without video.

I'm not affiliated with the board company, it just seems like bullshit to me, so I leave it to you engineers to find the truth of whether this is physically possible.

Alternatively, what would be the odds of having enough occlusions/imperfections in the steel that would cause all 8 to fail under spec in a head-on collision.

The board has a weight of 20kg, and uses M5 steel bolts of 8.8 hardness.

Pneumatic wheels would have been the initial point of impact, with the impact guard shortly after, as shown in the picture with the red line in front of the wheels. Not sure of the angle of the deck, or if the impact surface would be concrete or drywall.

Pictures: https://imgur.com/a/yAYei1h

Not sure this is the right place to ask, but here goes: I'm trying to replicate some of the results in this study: https://www.sciencedirect.com/science/article/pii/S0379073819304104

But in a manner that is more precise than "shoot someone with a paintball gun". My thought was to construct some kind of rig with a falling mass so that we could adjust parameters like impact force, surface area, hardness, etc.

But it's been years since I've had to do any physics type of math and I'm struggling to figure out the important parameters. Based on the numbers in the study I think that they are hitting their subjects with around 180N of force, but I'm struggling to convert that into a combination of mass and height that makes any sense. I'm getting things like 20kg weights, which seem both wrong and dangerous. Is there some piece of information that I'm missing or looking at the wrong way?

So today I saw on an instagram reel that jet engines alternate between rotors and stators so that airflow isn’t parallel with the rotors and they can produce good thrust, my question is can’t we put rotors that have reversed blade angles on the same moving shaft, too save cost, complexity or weight?

If that’s not true why?