Hi Rowland,
I've been down a similar road, you could have a hi-res encoder on the RA axis and ensure tracking accuracy with a closed loop to make sure the tick frequency is a constant. but there is a problem with this.
the tracking rate varies based on where you're pointing due to refraction and other factors as explained by Gary in this thread
http://www.usdigital.com/products/en...otary/shaft/S6
you'd have to track at a slightly amended rate from sidereal called the king rate.
geared encoders are prone to backlash errors, I'd suggest using a usdigital 10,000 cpr encoder on a 2:1 timing belt geared setup. so you'd get 20,000 ticks per RA rev with minimal backlash.
tHis resolution is still low for RA as you ideally need 1,296,000 ticks per rev.
http://www.usdigital.com/products/en...otary/shaft/S6
But the easiest and most accurate is autoguiding as that corrects for a number of errors, not just tracking and its a lot easier to do.
so once you achieve a constant tracking rate through any method, it could be a stable resonator based clock source for the stepper or other methods and you achieve accurate polar alignment, all you need is autoguiding to correct either tracking errors or mechanical errors,
with accurate polar alignment, you may not even need dec guiding.
I'm using just RA guiding with my fork mount.
for a double sided quadrature system, the wheels will have to be aligned extremely precisely which I doubt is possible manually.
would be good if you post some pictures of your setup.
there is a software to generate encoder wheels, which you could print on a transparency sheet. But you'd need the right spaced sensor.
that's why the usdigital ones are ideal.
http://www.iceinspace.com.au/forum/s...t=74481&page=2
Cheers