[pfreivald]

We covered our barrier with aluminum flashing to simulate the coefficient of friction and rounded edge in an affordable manner -- it made no difference to our drive train...

But yeah, a lesson I had to learn a half-dozen times in FIRST and am now paranoid about is this: never engineer anything so that it barely works. All values are nominal, and assume that if they're off, they'll be off in a manner disadvantageous to your robot.