Firstly, I underestimated (more like failed to estimate) how much force there would be trying to separate the final stage gears of my crusher. At some point I changed my design to make the front forks, and the shaft columns one piece. When I did this I moved the columns closer to the center line of bot, leaving the gear cantilevered at the end of the shaft.
The second problem I encountered is that the gear-motor I purchased is not capable of producing its advertised torque. Instead if you stall the output shaft and continue to run the motor, you will blow teeth inside of the gear box. I've now been able to reproduce this twice. It may be due to the end of the motor shaft being unsupported, but after seeing the tiny size of the gears inside the gearbox I suspect it is simply under engineered.