In 2008 (Overdrive), I was a programmer for 339. Our autonomous had been working well for most of the regional, often crossing four lines. But during this match, things were different; the robot ran full speed into the opposing alliance's wall and rammed into their driver station, knocking one team's controls off the shelf. The refs warned us to either fix our autonomous or disable next time.
When we got back to the pit we quickly discovered we had lost the entire 5 V bus on our IFI controller. This bus provided power to the encoders, without which we had no idea how far we had driven. Unable to fix the problem immediately, we flipped our "disable autonomous" switch on and prepared for the next match.
Literally about two seconds before the match started, we realized something: the disable autonomous switch also requires the 5 V bus. Oops. We watched helplessly as our robot slammed into the opposing wall yet again...a rather embarrassing moment.
In 2009 (Lunacy), we had just finished a match and I asked the driver, did you notice any problems with the robot? He replied, "the drive system was acting weird, and the shooter wouldn't pivot." I initially didn't think these two problems could be related, but a quick look at the code proved otherwise. I had left the drive system in tuning mode, which reused the pivot control to change one of the PID constants. Hence, the more the driver tried to use the pivoter, the more out-of-whack the drive system became.
