This page has some notes on how things actually work and what we may need to do to make things work better.
Tracking into the prelimits:

Tracking into the prelimits: (26may06)

    When tracking into the pre limits the little stars are moving to stop mode.  The tiedowns will move from stop mode to moving mode if a new command is sent. When inside the prelimit, only positions that move away from the limit are acted on.  The PI loop is not used to hold the tiedowns at a fixed position inside the limit. Instead, a fixed dac value is output  that should keep the tiedowns stationary. I guess this was chosen so that encoder failures would not continue to drive the system toward the final limit.
    The drawback with this technique is that everytime we change a dac or analog output signal conditioning board, we need to make sure that this zero velocity offset is set correctly (it changes). If it is off by a little then the tiedown will drift into the final limit (at either the top or the bottom). If this happens then you need to go down to the tiedowns, bypass the final limit switch, and drive the  tiedowns out of the final limit (after fixing the original problem). I'm not sure which method is better in practice.
    Another problem is the tietrk commands interaction with the tiedowns running into the prelimit.   When the tiedowns stop, i don't think the tietrk mode is sending another command to move again, it is just sending tracking positions. The operator has to manually execute the tietrk command (or some other command) that tells the tiedowns to move to tracking mode (i need to verify that this is really true).
    This is becoming more of a problem since the platform is low and during the summer days we can go into the prelimits.

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