Just wanted to add this...when I get a chance I'll test my other idea...not that what I am about to post here is anything magical as it's basically similar to what's on the robot already...but something to consider as it would seem faster and designed for precisely the sort of protection we are talking about.
http://circuitprotection.ru/upload/p...04-Hbridge.pdf
Costs about $5.50 in small quantity:
http://www.mouser.com/ProductDetail/...9dFfZLyw%3d%3d