FEA on Gearbox Plates

[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.