With a fibreglass dome and astrophotography you have the pain of having to rotate the dome at regular intervals - or very regular intervals depending on what part of the sky you're imaging.
For around £150 in parts, Tom How put together a dome rotator for me that actually works - commercial products cost 10x more and are notorious. This prototype rotator grabs the RA and DEC from the Sky6 and sticks the dome aperture right in front of the mini-WASP telescope array. This is a bit of a Godsend as the array is a bit big for the dome aperture and it would have meant manual dome rotations every few minutes in certain parts of the sky.
But what's the REALLY clever bit? Tom uses a solid-state compass to check the aperture position. So what? Well this means that if the stepper motor misses a step (or 10) or if the friction wheel slides - it doesn't matter - the compass will say the dome isn't in the right place and it will keep on stepping the motor until it is. As an added bonus - jog the dome and the compas will tell the stepper motor to compensate. It works like magic - and you can see the prototype in action here:
http://www.youtube.com/user/newforestob ... SXm05qEuFg
P.S. If you don't know what the mini-WASP array is, check it out here:
Nexstar 11 GPS, 2 x Sky 90, M25C, MaximDL, Photshop CS3, Noel Carboni's Photoshop actions, 7 foot Pulsar fibreglass dome, Canon 40D, 100mm macro lens, 28-200mm zoom lens, 17-55mm f#2.8 zoom lens, 100-400mm zoom lens, 1.4x converter, 2x converter.