Gallery, Projects and General > How do I??

Electric motor question

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vtsteam:
Any hammer pounding or vise wrenching going to be happening on this bench, or is it strictly for electronics/soldering, etc?

Cable suspension only supports down loads. Seems like a locking telescoping leg mechanism (rachet, pin in hole, etc.) would be helpful as separate from the actual lift mechanism, unless it's a jack screw lift.

appletree:
Would a variation on the scissor action bike lift suffice?

Phil

AdeV:
OK, I think I'm going to rule out hydraulics. It's an interesting idea, but I don't like the idea of having all that oil kicking around in an office space, it's going to be dirty enough as it is, and I can guarantee I'll add a few leaks along the way. I may build a rise/fall bench for the workshop one day that uses hydraulics.

Counterweights - yes, I could build in counterweights I guess, but I don't really want things hanging down under the bench where my knees will go if I'm sat at it, besides, I don't think I'll need them. I'm hoping that speccing 100kg for the weight of the bench is total overkill... so the 5Nm motor should be more than capable (and if I do buy the expensive one, and it IS capable of providing up to 25Nm for brief periods, then it'll well lift the bench even if I lie down on it!

So, I have another thought, which is basically a variation on the linear actuator: Rather than having individual actuators, have a long ACME screw in each leg driven by a sprocket at the top. Then run a chain all the way around, driven by a single motor. That way, all the legs would rise/fall at the same rate (provided the chain stayed on!). Going around corners would be easy with additional sprockets. I can probably get away with using bicycle chain & gear sprockets which should be cheap as chips on eBay. Plus I can adjust the gearing (on the fly if I put a Shimano gearset on the motor  :lol:) This would also be self-locking, and the legs wouldn't need to be ginormous. The only "interesting" part would be the screws; but I have a lathe.... so I could make my own  :thumbup: Furthermore, if I didn't fancy running a chain all the way around the underside of the bench, I can always run a long driven shaft & simply take drive off it next to each leg. That would require bevel gears to turn the drive 90 degrees (I would want the sprockets horizontal, not vertical), it would also mean shorter chains = less sag between each leg, but it does make it a bit more complicated.

Re: the wire rope & safety (i.e. if it snapped) - each leg would have it's own rope/drum, albeit driven off a common shaft. So if one snapped, it's not ideal, but the bench should stay up on the remaining legs. However, as it would be effectively suspended on the wire ropes, it's possible there will be some "bounce". There will be no hammering or pounding (other than in frustration!) going on, it's purely for electronics & computer stuff.

Phil - that's also a very interesting idea, a bit like the "go go gadget shoes" as seen here: A threaded shaft could be used to drive them up & down.... the only thing that puts me off is, the mechanism would have to be left on show, and I suspect it might be susceptible to getting kicked/rammed with a chair, etc. This would be the same with round legs, but they could take a knock or two as they're purely support, not mechanism. Plus, to make 3 or 4 of them move the exact same amount, they'd have to be made to pretty exacting tolerances, something I'm not all that good at...

Anyway, lots of food for thought, please keep the ideas coming, I'm getting quite excited at the thought of building this thing!

vtsteam:

--- Quote from: AdeV on June 23, 2017, 02:38:47 PM ---So, I have another thought, which is basically a variation on the linear actuator: Rather than having individual actuators, have a long ACME screw in each leg driven by a sprocket at the top.

--- End quote ---

You could reduce the length of the screw to just longer than the adjustment range needed, with the rest of the leg being solid. Or maybe a pipe with a cap welded on. You could then use a standard bit of threaded rod. We can get that as Acme or just ordinary all thread.

If thick enough the ordinary stuff would work. 3/4" by 10 tpi is available in hardware stores here in 3' lengths. Metric must be available similarly.

Weld some long nuts to a plate for a pipe cap and you have the mechanism.

awemawson:
Or you could be less of a Wuzz and settle for a wind up/down stool like the rest of us  :lol:

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