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ac motor

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acdc:
Your right, lots of $$$ for a harmonic drive.  Too much for my pocket.  For starters, what dc motor spec would you recommend?  Something with a good torque to turn the jack, reversible, and something that can be connected to a controller.

waltr:
good torque??
What torque numbers will turn the jack?

There may be some gear motors used in automobiles that may work and not cost too much. Especially if obtained from a junk yard.

jwatte:
You don't need a lot of torque in the motor itself, necessarily, if you can get a gearbox geared high enough and are OK with waiting longer. The main thing to do is to match the strength of the motor with the friction and losses of the gearbox so you don't get an entirely unreasonable combination. (I think this is why most gearheads are in the 30:1 - 300:1 range, and 1000;1 is kind-of hard to find.)

Without knowing the equivalent gearing of your jack / worm screw, there's no way anyone can calculate whatever motor you need.

Do this:
1) Put your expected load on the jack.
2) Get a foot-long handle for the crank on the jack.
3) Get a spring scales (the kind used to weigh caught fishes at sea, say)
4) Attach the spring scale to the end of the handle.
5) Pull on the scale until the handle just barely moves.

Now, multiply the "weight" you see on the scales, by the length of the handle from center of rotation to spring scales attachment point.
The product you get is the torque you need to move the jack.
Now, get a motor whose stall torque is at least 2x that amount, for intermittent duty, or 5x that amount, for more continuous duty.

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