Research for mobile satellite tracking on a bike.
general thoughts on building a rotor ourselves: http://www.eham.net/ehamforum/smf/index.php?topic=60746.0 Lets see, you will need: 1. A reversible motor. 2. A braking system. 3. The necessary gears. 4. A weatherproof housing. 5. Transformer. 6. Direction switch. 7. Starter capacitor.
The bottom line is that unless you have a machine shop and a bunch of materials laying around it will probably be less expensive to purchase a rotor. they basically say: go for a rotor you can buy, it is worth the money.
For automatic selection of satellites and tracking of inclining satellites. Ready for yagi and radar antennas. Intelligent self-learning control system. Designed for commercially available linear motors (actuators) with any discretional lift as well as for heavy geared motors (AC as well as DC motors, e. g. 3-phase models). http://www.egis.org/autot_us.html
diverse rotors incl prices http://www.eham.net/reviews/products/24
An Antenna Rotator Controller A very simple controller circuit, with fairly smart performance! http://www.qsl.net/zl1bpu/MICRO/ROTATOR/Index.htm