I’m completely new to this but trying to see what the best option would be for moving a rope back and forth about 2-4" at a rate of 2 movements per second. The object being moved would be 15-40lbs, tilted away from the motor so it’s own weight would be pulling against the motor. It needs to be small, fit in your hand and battery powered. I’ve included a link to a picture diagram for reference. Any help or suggestions are greatly appreciated.
I doubt you will find a suitable motor and battery combination that small.
If you want this to work, you will have to measure the force required to move the rope, for example using a luggage scale, and convert the force to torque. Then start looking for suitable motor/gearbox combinations.
Intro to force and torque: https://www.pololu.com/blog/10/force-and-torque
It shouldn’t be that bad. Here’s a rough order-of-magnitude calculation.
A 40lb weight at 8 inches per second is 18kg at 0.2meters in one second.
So, let’s say we have a cable connected to a pulley on the motor and the pulley is 2cm in diameter, how much motor torque do we need? distance = (acceleration * time^2)/2 so the acceleration is about 0.4m/s/s.
The mass is 18kg so the force needed is 18x.4 = 7.2N, so and the motor torque required is 7.2x0.02 = 1.4N-m at 400RPM.
Using an online converter (I was lazy!) that’s 63 in-lbs of torque required.
Maxon has a small one about the size you want for under $300: http://www.maxonmotorusa.com/maxon/view … SL0103CPLW