Quote:
Originally Posted by llamadon
Our team actually does not have any mechanical engineers as mentors, in fact the entire robot was CADed, and manufactured by students (under the supervision of a few qualified parents.) We have addressed the issue by ordering a new gear, fashioned from steel instead of aluminum.
It seems that vex pro has already been notified of this issue, which is why they offer this gear in a steel variety.
Thanks for the wise words!
It definitely was a stall condition that caused the failure! We'll have to be a little more careful this week in Wisconsin 
What happened was our operator and driver were pushing for a faster cycle time, and I believe the operator had driven the elevator down and stalled the gearbox in this haste. It is powered by two CIM motors at a 9.52:1 reduction, with a stall torque hovering around 350lbs. Looking at the gear teeth it is apparent that they are a little wimpy for high load applications  . We'll have a steel replacement when we get to competition and replace it on Thursday. |
The broken gear: 7075 Al ~70ksi yield strength
Common steel gear: ~40ksi yeild strength
You can't fix this problem by replacing the gear. The pinion is overloaded and the best fix is a redesign that reduces load.
-Adrian
Edit: I went on a gear strength rant a while back, it could help you.
http://www.chiefdelphi.com/forums/sh...4&postcount=15