Back-driven Gearbox and motor

PendGB · Dec 9, 2019

What kind of gearbox is best for being back-driven (driven in both directions - not sure if 'back-driven' is the exact term)? The driving torque would be quite small, to the point where the motor's rotor inertia needs to be taken into account. I wouldn't want a reduction ratio any greater than 20:1. I was informed that a cycloidal drive may be the way to go but I was hoping for a second opinion.

Thanks!

drawoh · Dec 11, 2019

PendGB,

Worm gears over 30:1 generally are not back-driveable. The problem is not the gear ratio. It is the worm's lead angle. As far as I know, most other drives are back-driveable, including harmonic drives. Talk to your gear/gearbox vendor, and/or read your machine design textbook.

The inertia of whatever is being driven is multiplied by the square of the gear ratio. For your 20:1 speed increaser, this means your driven inertia is multiplied by 400. That is a heck of a lot! An output shaft that does not budge will turn when you apply enough torque, perhaps with a wrench.

I worked with a system that had a 500:1 MicroMo gearmotor. I was unable to grab and rotate the output shaft. I was able to turn the scanner housing the shaft was attached to. I felt comfortable applying 100[ ]lb.in of torque to the thing. I worked out the torque needed to accelerate the very tiny motor armature to its maximum allowable torque. This proved to be 40[ ]lb.in. I asked, and I was told that gearmotors were breaking.

Do you have a mechanical engineer on site? This can be complicated.

--
JHG

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