I'm surprised that VexPro doesn't have a small magnetic/slip clutch attachment for the VersaPlanetary Gearbox. Hint hint cough cough.
Building robots would be so much easier.
This is what you need.
http://www.mcmaster.com/#torque-clutches/=lx8mgg
Bryce,
I've made one from a delrin spacer. I parted the shaft into two pieces Reamed one end of the spacer to the shaft diameter and .002 over the shaft on the other end. I also cut a oring groove on the outside of the spacer with the bigger hole. I band sawed the spacer across the diameter and used a small oring over the outside to create the tension. I pressed one the spacer to the one shaft and inserted the shaft into the spacer. It worked pretty good.
We later changed out the mechanical spacer clutch and used a Jag in current sensing mode to make a software clutch.