When we were designing our vehicle for the 2004 DARPA Grand Challenge, we considered installing a guitar pickup on the frame to sense vibration. Early plans for the Grand Challenge involved more off-road driving, and we wanted something to give us a sense of surface roughness. In practice, the off-road aspect wasn't important and we were overdesigned in that area. We had a 6-wheel drive vehicle and a windshield washer/compressed air cleaning system for the sensors, which were totally unnecessary.