Dear James, Read my August 1993 issue of Hight Power Rocketry. If you need a schematic design I can cook you one up.
Basicly you go to radio shack and get a 10 Kohn 10 turn resisteers, several 555 timer chips and a few 741 operationa amps. its an easy circuit. I have a 20 year background in instrumentation so I can help you along.
Basicly you use 4 photoresisters as your horizon sensors,. And you want those amplified and balanced . So a gright light dead on to your noce cone as you adjust the pots is really important. Now you going to feed that pitch and yaw signal to your two 555 timers to devekop a 20 ms pulse. That is dead zero on a R/C servo.
There is also a NARTS report on a Sun seeker as well. If you can not get a copy of the Aug 1993 HPR issue email me back and I'll send you one.
Dave Ketchledge NAR SR 57237