Sensors

[apalrd]

Originally Posted by theawesome1730

Accelerometer:
Useful for things this year like balancing the bridge, it determines angle so you can tell if the bridge is level or not.

An accelerometer does NOT return angle. It returns the sum of all acceleration applied to it in the axis it measures. If you are NOT moving in any way (or at a perfectly constant speed... very hard to do in FRC), the only acceleration you will see is that of gravity, from which you can determine the angle of gravity relative to the axis of the accelerometer with one or two accelerometers.

If you are trying to balance a bridge using the accelerometer, you will also see acceleration from the driving, which will make the sensor see gravity as being in a different place.

While I have seen 6-axis IMU algorithms which can accurately keep track of their position in 5 dimensions indefinitely (it's hard to keep track of yaw indefinitely without any other sensors), that is far too complicated for an FRC robot (as cool as it is)

A gyro is most likely the right sensor for auto balancing.

As for useful sensors, consider the interface. For absolute sensors, an analog interface is the easiest to interface with the current control system. For incremental sensors, a quadrature or single-phase digital output is the easiest. Anything else (especially USB) is significantly more difficult. My favorite sensors of all time would probably the 1 or 10 turn analog potentiometer, and the Banner reflected light sensor.

Final thought - We on 33 have a policy against using an incremental sensor for measuring absolute position. This means that any mechanism that has a defined, fixed limit (such as an arm or elevator) MUST use an absolute sensor. We do this in case the robot ever reboots during a match, so it dosen't have to re-initialize itself.