[Nathan Streeter]

The CIM's a very powerful motor... A 20:1 reduction with a CIM should be capable of lifting an elevator with 4-6 totes on it IF (and maybe only if?) the drum/winch is fairly small (think 2" diameter or so... smaller means more torque, less speed), your elevator is moderately efficient, and your gear reduction's not binding badly (due to a poorly manufactured gearbox, big side-loading from the spool belt/chain/wire tension, no greasing, or a variety of other things).

If you have a relatively large drum/spool - which it looks like you may have - then you'll need extra gear reduction... this may be a big part of the problem. I've never made a custom worm gearbox, but they introduce a variety of axial (thrust) and bending loads that you don't have with ordinary spur gears. These need to be handled well (bearings, stiff enough housing, well toleranced design & fab, etc.) or you'll get some bad binding/wear. I'm guessing the combination of large drum/spool and an inefficient gearing are combining to cause your issues... to check if your elevator itself is inefficient, does your carriage fall down by itself? Does it still fall by itself when you have tote(s) on it? Can you grab the cable (with the robot off!) and pull the carriage up and down by itself? Perhaps with a tote on it? It should at least fall by itself most of the time (although it's best to drive it down anyway!), otherwise you probably have serious binding in the elevator itself.

For reference, we're using a CIM in a WormBox (16:1 AndyMark Worm Drive gearbox with a 2-start worm and a 32-tooth helical gear) which we have modified to put a needle thrust washer at both ends of the worm... it now runs butter-smooth but had worked well without this improvement (we had kind of abused the gearbox last year so we wanted to be darn sure it lasted in this application). We then have a 30t HTD Timing Pulley (1.88" PD) cantilevered .25" away from the gearbox. This goes over an idler pulley at the top, and drives our top carriage, which has ball bearings riding on 80-20. Webbing then connects this to our lower carriages. This elevator system can pickup and hold 4 totes very easily... it's all efficient enough that 3 totes (and sometimes 2 totes) can backdrive it, so we actively hold position. The CIM has gotten warm - but not hot - to the touch after a day of practicing. So far we're very happy with it.

TL;DR, you shouldn't need more reduction... you probably have some considerable inefficiencies in your gearing (very likely) or your elevator (likely, but probably not as detrimental), which combined with a large spool/drum diameter are giving you problems. I recommend switching to a different gearbox (go COTS, probably!) and a smaller spool.