SpaceX's recent
interesting test result of the F9R got me wondering about fault tolerant design. SpaceX said the loss of the rocket was a single point failure of a sensor, where on a Falcon 9 enroute to orbit,
that sensor would have been voted out.
I deal with similar architectures in my day job quite a bit. Some parameters (airspeed, for example) are very important to how things fly. If you are actually at 400 knots, and the airplane thinks it is at 150 knots, you will get an unexpected response!
The idea of a voting scheme is pretty straightforward. A simple FRC example would be having a very low geared arm with 3 potentiometers. If potentiometer A says it is at 120 degrees, potentiometer B says it is at 120 degrees, and potentiometer C says it is at 360 degrees, potentiometer C is most likely wrong, and the robot will vote it out and act as if the arm is at 120 degrees. If you had a single bad potentiometer, your low geared arm might rip the robot apart!
Another common FRC example is to have a potentiometer & limit switches. That way if your closed loop feedback can't keep up, the limit switch will protect your structure.
We've done the potentiometer and limit switch before. What have others done? I bet there's some pretty fancy fault tolerant magic out there...