Okay, I think I have the answer to the zero-calibration problem with drawbots.
I made an eyelet out of a piece of music wire. The drawbot string will be run through the eyelet. There will be a bead threaded on the string that will push the music wire.
This will trigger a micro-switch and presto we have a consistent reference point.
I’ll just use one micro-switch. There will be a thread running from each piece of music wire down to the micro-switch.