Gallery, Projects and General > How do I??
Electric motor question
PK:
--- Quote from: awemawson on June 22, 2017, 06:04:46 AM ---This sort of thing:
http://www.ebay.co.uk/itm/linear-actuator-heavy-duty-screw-jack-24-inch-travel-/182630112771?hash=item2a859a5e03:g:HskAAOSw1WJZM9bx
--- End quote ---
Seconded, these are neat and can produce prodigious force. The ebay ones tend to wear quite quickly in gate opening applications (YMMV) but for raising a bench every now and then they should last forever. You need two DPDT relays to drive them and they often have limit switches built in.
PK
AdeV:
Thanks for the ideas!
Tom - that's probably not a bad idea... and will be way cheaper than the motor I found. I've actually got one kicking around somewhere out of an old Ford. The only thing I'd be concerned about is whether they've got the strength in them.
Linear actuators - very interesting indeed! They'd make the mechanism much simpler, that's for sure. The only downside is, I reckon I'd need 3 or 4 of them, one per leg, and getting them perfectly synchronised might be tricky? Don't want the bench going up wonky, all my stuff might roll off!
Dave - I was being a bit disingenuous about the pulley... it would actually effectively be a winch drum, around 1cm diameter, with one end of the rope attached to it. There would be one "drum" per leg. Each wire rope will then be routed via pulleys (of any old size) to the legs. The bit I realised last night that I'd got wrong... the rope will have to go down to the bottom of the inner leg, then come back up between the legs and be fixed somewhere near the top of the outer leg. Otherwise it'd be like trying to lift yourself off the ground using your bootlaces! :scratch: Gravity will allow the bench to descend (speed controlled by the motor/worm drive), and if I put a pulley inside the bottom of the inner leg, the rope can be guided into a machined slot (see what I did there? :lol:) to the attachment point on the outer leg. I can make the legs quite fat, so fitting a small pulley in should be no problem. Other than stretch in the rope, which might be an issue early on, and which I will have to be able to adjust out, it should mean each leg moves by the exact same amount - in theory at least...
Constraining the bench left/right - a while back I bought some linear bearings (another aborted project, I can't even remember what the project was now!) I can use them, screwed to the wall, with the bearings attached to the bench, to hold everything square, and there'll be as near as makes no odds, no friction. If the vertical load on the bearing seems excessive, I can put a leg or two at the back of the bench as well, although it's going to start getting a bit messy with all those ropes under there...
I guess I could use linear actuators, and a computerised level sensor... which tweaked the voltage to each motor to keep everything square, that could be a fun project... :proj:
awemawson:
Fat legs each with a hydraulic cylinder inside, where the floor end tube surrounds the table top tube sliding one in the other. Commoned up to a small hydraulic pump. Power steering pump would probably do. No complex mechanics to jam and heavy loads should be no issue.
AdeV:
Like the idea Andrew - a couple of issues though; the rams are chuffing expensive (for the stroke I want, you're looking at pushing on for £100 per ram, and I need 3 or 4); unless they're identical, tuning them might be tricky? Plus then I need control valves etc.
Even so, definitely worth a look... and it would make for a neater under-bench installation...
awemawson:
Perfectly feasible to make your own hydraulic cylinders - all the bits can be bought - precision tube and rod, pistons, seals etc
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