Gallery, Projects and General > How do I??
Electric motor question
AdeV:
I'm trying to find a DC gear motor (worm drive) capable of lifting up to 100kg via an Xcm pulley (size dependent on RPM). So 981newtons. Assume I need a range of about 75cms, and I'd like to be able to traverse the range in about 20 seconds.
So, if I had a 1cm diameter pulley, I need to find a motor capable of pulling 5Nm at around 75rpm. The closest match appears to be this wee fella: http://uk.rs-online.com/web/p/dc-geared-motors/7736771/ However, the datasheet claims a "nominal" torque of only 3Nm, but a "starting" torque of 25Nm (at 34 amps :bugeye:) I'm thinking this will probably do what I want it to do, but I'd just like confirmation from someone more knowledgeable than me: If I were to need 5Nm continuously for up to 30 seconds, would I be asking too much of this motor?
The application (you may have guessed already, if you saw my office thread) is a self-build rise-and-fall workbench... I'm going for 100kg as the likely maximum load, I'm thinking of having pretty much the entire 3m length of bench move up & down. To make sure everything's in sync, it'll all be driven from one motor, using thin wire rope and pulleys. Er, hopefully. I think I may have just spotted a flaw in my plans...
tom osselton:
Hell of a price! Try a car window motor from the junkyard its probably the same thing!
awemawson:
Ade,
There is a chap on the MIG welding forum who not infrequently sells second hand electric actuators, a bit like a hydraulic cylinder but contains a screw and nut and electric motor. I think they come from scrapped hospital beds and bath lifts. Perhaps you can find something similar as they sound ideal for your job and are cheap and compact.
DMIOM:
Ade,
Just a couple of thoughts:
1 cm seems an awfully small pulley- if it is conventionally-rigged the wire will only have just over 1.5 cm in contact with the pulley, so you’d need to create something like the drum-end on a mooring winch with multiple turns.
How are you guiding the bench so it is constrained in X and Y – will that add frictional losses?
If it must be 'push' from underneath alone, then maybe add a set of gas-springs to reduce the load?
Is there any chance you can rig this as a suspension? – could make things easier and you could add a counterweight to null-out the static weight of the bench? And you could then even automate it with an aquarium pump or similar! – empty tank atop your counterweight, reservoir tank nearby, elevate = pump water into counterweight tank, lower = run water back into reservoir?
Dave
awemawson:
This sort of thing:
http://www.ebay.co.uk/itm/linear-actuator-heavy-duty-screw-jack-24-inch-travel-/182630112771?hash=item2a859a5e03:g:HskAAOSw1WJZM9bx
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