Quote:
Originally Posted by Rod
Thanks Bojan,
I do have a question at this point. It sounds like you used friction rollers to drive the scope. Did you have any problems with microslippage? Or did the encoders fix that? It's the reports of microslippage that put me off the roller system but if encoders fix it, I would seriously consider it.
Thanks,
Rod.
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When looking at installing a GOTO system for the 16" Tridob (though eventually I went with a commercial unit to avoid having to use a laptop), I did lots of research and a bit of experimenting of my own. Basically, a friction drive will always have some microslippage, especially when slewing rather than tracking, so you either need to have encoders attached to the axes to "update" the position of the scope or make sure the drive system uses some sort of geared arrangement to avoid pointing errors.
For example, the Servocat system uses a knurled wheel that presses a bit into the wood of the ground ring for the AZ and a cable wound twice around a roller for the ALT. It needs the encoders mounted on each axis to make it a "closed loop" system, with the Argo Navis or Sky Commander telling it where it is pointing and correcting for any slippage.
Precise Goto seems to need more accuracy than just OK tracking.