[ThaddeusMaximus]

Originally Posted by asid61

Assuming that your gearbox is direct driving the center wheel, here's a list of forces:
1. upward force from the effect of gravity on the wheel shaft
2. forces between gearsets (look up calculating the force of a spur gear)
-These translate into forces on the bearings, and thus the holes in the gearbox plate.
3. forces on the sprockets going to the front and back wheels (although this might cancel out, I'm not sure).

There might a couple more but those seem to be the major ones.

Point 3 may cancel out in best-case loading but it does not in worst-case loading. (think: one wheel off the ground) (Actually, it doesn't truly cancel out in best-case loading because a moment is still produced in the vertical axis since sprockets are offset...)

Point 1 may need to be treated as an energy rather than force. It's definitely an impact in a game like stronghold...

For point 2 be sure to account for pressure angle. 14.5 deg means it isn't huge but it's there.

Another force: Turning scrub is a force, depending on the gearbox application.