VEXpro 2016

[ozrien]

Originally Posted by nuclearnerd

There's a big asterisk on the "absolute encoder" thing. It's still a relative encoder, but it includes it's own counter. It's nice not to have to implement a counter on the rio, but you would still have the problem of the zero changing every time you start up the robot. An actual absolute encoder would give the proper reading no matter how often the sensor had been turned off and moved. (see page 22 of the encoder user guide here: http://content.vexrobotics.com/vexpr...User-Guide.pdf)

The sensor provides both an absolute and a relative position. The "absolute position" is an absolute 12bit encoded value that wraps every rotation. This works similarly to the MA3 absolute analog encoder which gives you an absolute voltage (0 to 3.3V) for one full rotation.

You can think of it like having an MA3 analog encoder and a relative quadrature encoder both kitted in one, which solves several challenges in closed-looping.

If you don't move the mechanism and you power cycle the sensor, the bottom 12bits of the analog position remains unchanged.

Yes both the absolute and relative positions count the wrap arounds. But this doesn't mean you lose the benefit of absolute position. If you're application does not need wrap-around counting (like a continuous swerve) its pretty easy to add in the number of whole rotations to your 12 bit target position to achieve what you want. In fact this gives you the benefit of absolute position, plus you get to decide which direction you want to servo (always clockwise, always counterclockwise, or choose the path with smallest distance.)