On the face of it easy, but in practice less so.

In my case my drive system has been slightly lagging the stars and I'm trying to work out exactly where the error lies. It looks like the error is around 2% so worm wheels on their own don't account for it, but it could be part of the problem

I thought it might be that the worm wheels got swapped when the mount was refurbished, in which case the mount would be running a tad slow.

So how do you count 360 teeth?.. and trust your answer when you're done..

Solution: reprogram the drive to slew the mount through 360 degrees.... then I know it's done 360 worm revolutions, if the mount has come back to the exact same spot it started at then it's a 360 tooth worm wheel.

Result:

359 teeth.

So it's not that.

I did however establish that it slews at 2.5 degrees per second... I can live with that :D

So why is it slow?.. well analysing the various processor signals it looks like it might have been missing an interrupt every so often, and these are used to get the timing spot on. At 40 interrupts per microstep and one missed interrupt per microstep that makes a 2.5% slippage.

So a bit of assembler to speed up processing and now there's no lost interrupts.. I won't know if it's right until I can star test it again.

It's bound to be cloudy for the next fortnight.

Sorry...

Derek