Best way to figure out motors and gear reductions

[frizzen]

I'm just a hack who had to have someone else make my conversion parts.

If you didn't already have drums made, I'd suggest finding a series of suitable gearmotors first just to make sure it can fit the form factors, then you can kinda fine tune speeds with the drums and esc endpoints. So like a 1" diameter cable bed on a drum pulls 3.14" of line per rev, 100 rpm motor at full speed pulls 314" of line a min. Smaller drum more torque, larger drum more speed.

Might want to pick up a Fish or Luggage scale to see what kind of line forces are involved with digging in the surfaces you want. If you run a line from the control through all pulleys, around the drum, then tie a loop and hook to the scale. 'X' pounds of force on the line x 'radius of drum' = inch pounds torque.
So like a 15 lb pull on a 1" drum is 7.5 inch pounds or 0.625 ft/lb. Then add in some working and safety margins.

I know on some of the smaller machines some are running nylon cord from blinds. I like the inner strands of 550 paracord, (mil-c-5040 type 3). Just make sure whatever you use is able to lay without birdnesting on your drums. Wire ropes have a lot of spine at this scale, unless you build something big enough to walk itself to work. Keep your first wrap tight and perfect, use enough cable that full extend won't touch that wrap.

https://emce.com/about-winches/winch calculation