For right-ascension we fitted a standard Slo-Syn NEMA23 unipolar stepping motor by machining a mounting plate and shaft adapter for the pulley. We used the same mounting scheme as the Vixen motor mount, one bolt from underneath pulls the mounting plate into a groove to prevent it from moving(the plate can be seen in the above picture between the motor and worm block, features were machined into the bottom to match the pattern on the mount to prevent it from sliding). A small steel plate bolts the motor to the side of the aluminum plate, and has slotted holes on one side to allow the motor to slide and adjust the tension of the belt. The last component is a shaft adapter that allows us to attach a pulley with a 1/4” bore to the 6mm shaft on the mount. This also functions as a slip clutch; when the screw on the pulley(gold knurled piece) is loosened the RA axis can be manually controlled by the knob on the other side of the mount.
Initially we ran the motor without a gearbox and at full steps(200 steps per rev). As the Vixen's worm gear assembly is a 144:1 reduction, this gave us .75 arc minutes per step. These steps were sent roughly once every three seconds, which wasn't nearly smooth enough to image. To fix this we added a Pittman 10:1 gearbox reducer, and half-stepped the motor. This reduced each step to 2.25 arc seconds, which is enough resolution to image at a 560mm focal length. The ideal solution is to use DC servos that don't step, and I plan to switch over to these in the future.
After mounting the motors we build the control electronics. The computer to telescope interface was based on an ATmega644, communicating with the computer over serial through USB. The AVR interfaces with the motors, and the software on the computer handles autoguiding, goto calculations, and watches the tracking rate. Posts on the circuitry and computer software will come later.