How do all of you get so much stall torque with your motors??
Lots of gear reduction. Physics is your friend if you want it to be.
So we have an arm that is about 18 something pounds roughly, and 1 cim motor geared down 768:1 and the arm still has no stall torque
How long is the arm, and is the CIM plugged into a 30 or 40amp breaker.
Also can you describe what you mean by “the arm still has no stall torque”? Does it not move, can you not hold it in position, does your breaker trip, do you brownout, etc? Perhaps stall torque and the arm back driving when power is removed are being mixed up here?
What do you mean by stall torque?
Normally, this is the torque generated by a motor being driven at its nominal supply voltage in a stall (non-rotating) condition. A CIM driven by 12V with 768:1 reduction should be able to generate some 1800+ Nm or 1300+ ft-lb of torque at the gearbox output, enough to lift your 18 pound arm two or three times over if it were the length of the field - assuming you didn’t break some component along the way.
Added: the free* speed of that gearbox output would be a bit under 7rpm, so it would take over 2 seconds (more likely three) to travel 90 degrees, even if there were no load.
* Free speed is the speed of a motor driven by its nominal voltage when there is no load on the shaft other than the internal friction and inertia of the motor.
Try to describe more articulately what you are observing, and how that is different from what you were expecting to observe.
The phrase “the arm still has no stall torque” is much too vague.
There are a lot of folks on CD who can probably help you if you make a bit more effort to be clear.
It would help a lot if you posted some photos of your robot with some zoomed in on your motors and gearboxes.