pic: 20's IRI Carnage

[apalrd]

I agree this is a torsion failure. I was saying previously that I had never seen such a failure of the AM stainless dog.

You are only considering torque originating from the motor. Hitting another robot at high speed can cause very fast acceleration on the robot, which results in a huge force on drive line components. While all of the steady-state math would see the wheels spinning and such, there is still a shock on the drive line components momentarily (and it is HUGE).

I would additionally guess the dog had been failing for some time, and there were already stress cracks at two or all three of the fracture locations, from repeated shock loading.

I still believe the cause of failure is improper material selection or component design more than anything else, not improper use of the gearbox (it should be able to handle this). 7075 is a significantly weaker material, and without changes to the dog design (e.g. increasing thickness, additional hardening, etc.) the overall strength is significantly lower vs stainless steel.