[Chris is me]

We try to eliminate sensors as much as possible, but sometimes they are useful. We have basically only used limit switches and encoders, though this year we used an IR sensor.

2013: Open loop shooter speed control. Because the discs slip on the shooter wheels repeatably, and because discs fly into the goal on the "upward" part of the trajectory, this works just fine.

We used an encoder + limit switch on our arm almost exclusively for autonomous mode. Probably could have used a pot, but meh. Arm goes down, zeros on the limit switch, goes up until we hit our preset encoder count, fires. This style of arm and shooter could have been done completely without sensors using pneumatics, but we liked being able to use the camera and a drawn crosshair to shoot from anywhere we wanted, so we made an aimable arm.

For our disc path, a limit switch and IR sensor would help us detect what state the hopper was in.

2012: Only sensor was our shooter wheel encoder. We had something resembling PID working for our offseasons, but it wasn't stellar. Software isnt' our strong suit.

2011: Zero sensor feedback. Robot was a pretty crappy arm-bot that we have all tried to forget since. Set points would have been nice.

2010: Zero sensor feedback. Robot was basically just an 8WD base with a piston kicker and a suction cup. There was no need.