[gbalcita]

Consider the distance the ball "rolls" along the guide while in contact with the wheel. The longer the distance the more energy lost to "rolling drag". Try reducing the contact time/distance. Also, you are pulling the ball up. Is there a way to feed the ball such that it is pushed/pulled from left to right vs. from bottom to rightalmost level to the wheel

During this rolling stage the ball looses a lots of energy/momentum. I think the drill's power rating compensated for the lost momentum and the banebot motors lost a lot of the momentum to the "rolling effect".

If the wheel was slipping against the ball then more compression should transfer more power. If you increase compression I recommend reducing contact time (noted above) to minimize energy loss. If the ball was not slipping, then more compression will result in no benefit or increased "rolling drag" along the guide.

Hope this helps.