For me the decision was easy - EM400 mount to carry a 35KG load - specification on tracking accuracy and low periodic error.
Points to note if considering heavier mounts:
1. The EM400 mount's operation gives cause for concern when manual operation is used in the high speed(24V) mode. The motors are merely started and stopped - starting is fine, the motors "wind up" under full power (slowly because of inertia limiting the acceleration) But when you stop? well that's another matter! The motors stop but the load wants to continue and as a result the whole pier torques - not a good thing for the gears. In the automatic mode the TEMMA-2 system emulates (sort of) a slightly under damped control system and seems to work reasonably well.
2. Ideally the mounts controlling medium loads,(50 - 100KG), should be run with high speed DC servo motors (with in built tachometers) and the pointing critically damped with the appropriate feed back (position & velocity for pointing and acceleration for tracking). Price to buy? I'd hate to think. But this is what I would design for a customer.
Jerry.
