The MT rotator can drive itself past the software position limits into a direction inhibit limit switch.

We managed to make this happen using the following command sequence in the command-line utility rotator_commander:

• move -90 # From -89 degrees; the CCW was not following well, so we made our way here in a series of 1-3 degree moves. This move seemed to work fine.
• ramp -90 0 1 # This means follow a path of speed 1 deg/sec from -90 to 0 deg.
• # observe that this did not work well (as described below), so a few seconds later:
• stop

When we issued the ramp command we observed the rotator move slightly in the negative direction (presumably that is when it hit a limit switch) and report demand position < -100 degrees.

Note: as we watched, the demand position very slowly climbed from its minimum, even though nothing else was happening – the rotator was not moving and the rotator commander was not sending commands (at least not after the stop command). This is a minor problem, since the rotator was not moving. Still, I hope it can be fixed, because it is confusing and suggests additional problems in the rotator.

The trajectory generator should never command a motion that exceeds the software position limits, nor the velocity, acceleration or jerk limits.