Celestron motor focus issues, for the record.

[ollypenrice]

This is just for the record to help anyone who might have a similar problem.

The Celestron RASA motor focus on a setup based here stopped giving decent focus and eventually drove the scope right to one end of focus then stopped doing anything.

On investigation I was relieved to find the grub screws locking the motor shaft to the focuser shaft were no longer fully tight, so I tightened them and we ran the focuser calibration routine. It failed to complete the process and subsequent attempts also failed. In the end it stopped responding to requests to calibrate and we feared a bent focuser shaft as quite often described on various forums. If you get to this stage, don't give up. We found that when the motor failed to respond there was no indication that it was fighting to turn a jammed shaft. No vibration, no heat, no sign of energy at work. Also, the focuser shaft turned easily with a spanner on the flats so we continued to suspect a control, rather than a mechanical, problem.

Rebooting the USB, changing ports and replacing the power supply had no effect.

We then wound the focuser shaft round for maybe ten full full revolutions with the spanner to get it away from the end of its travel and tried the calibration command again. We also loosened and re-tightened the two screws bolting the motor unit to the scope. It worked and the focuser then did a couple of excellent autofocus routines so, for now, all is well. We can't be certain which of the operations was the critical one but we don't think it was loosening-tightening the motor screws. (I broke the golden rule of one test at once!)

We think the step in bold type was the breakthrough and that the problem may have started with the loose grub screws.

Olly

Edited October 17, 2021 by ollypenrice
clarification

[tomato]

Good to hear you got it running again. @Tomatobro did my initial set up and it has performed faultlessly ever since, but I do seem to recall him manually moving it to the the centre of the travel when performing the initial calibration.

[Tomatobro]

That's correct. I think its in the Celestron setup instructions but its been a while since I did it. I also machined up a centring ring for the shaft to hold it central while tightening the cross head screws. Better than doing it just by eye I thought.