[Travis Schuh]

If I got it correctly from the video, you have a 63 to 1 reduction with a 2:1 reduction after that. The bags are about 1/5 the torque of a CIM, so 1/10th the torque of a 2 CIM drive. I am going to use a drive ratio of about 10:1 for comparison. Also, your driving pulleys on the arm looks about 1/3 the size of the output pulley in the drive. Given those rough estimates, you are running slightly more torque through each belt at stall (about 1.3 times), with the force at the teeth being significantly higher (about 4 times).

You also have a lot of inertia in that arm and a less backdriveable mechanism (due to the high reduction and planetary), so as the mechanism suddenly stops you are going to get peak loading that is higher than the stall torque of the motor, which is not going to happen much with your drive transmissions. This matches with your slipping appearing to happen most often when you are stopping the arm suddenly going down (down being more prevalent than up because you have gravity adding to deceleration forces).

I think the belt slipping is coming from your application being outside of what those belts and pulleys are rated for (and beyond what you are asking of the drive belts), although you could work through the exact calcs yourselves to check this (Gates light power and precision manual is a good resource on this). Some thoughts on solving this problem is you could go to wider belts and larger belts, or switching to something like #35 chain (hopefully combined with larger sprockets). You could also try motion profiling your arm to reduce the loads on the belt when lowering the arm.