ELL spontaneously homes (and does not return to destination)

[ddkohler]

We don't know what triggers it, but during experiments we have noticed the ELL will spontaneously move to a position that we did not command it to. The occurance seems random, perhaps happening ~once per day.

After the motor is moved, we can detect that it has moved (e.g. position = 0, but destination is 55) and the daemon reads not busy.

Possibly a hardware issue; on power up the elltec motor will home, so if power is spuriously interrupted, we should get homing.

[ddkohler]

We have found this behavior testing an ELL14 unit. I have also heard that something similar may happen with a ELL18 unit we have.

[ksunden]

I would suggest running in the foreground or otherwise enabling logging, as we do log unexpected serial replies/error conditions that we get from the device

[untzag]

Consider adding a case to toggle busy back to true if destination and position are different greater than tolerance in update_state.

Ugly, but functional when hardware cannot be trusted.