RC24 Focuser
The RC Optical Systems 24-inch Ritchie-Chretien telescope at Moore Observatory (MORC24) is focused with a motor-driven secondary. The original electronics was a TCC instrument control package that connected to the motor on the secondary, controlled the fans behind the primary, and read the thermistors on both primary and secondary mirror backs. The unit malfunctioned in August 2014 when it stopped reading the motor encoder and it was removed from service. This page documents our replacement.
We also note that a custom replacement part may be available from RA Limited LLC. We chose to develop a control that used hardware similar to that on our other telescopes.
[Wiring]
The telescope was originally wired through the primary mirror cell using an 18-pin Amphenol connector on the back plate. The pin assignments on this connector were not documented by the manufacturer, but they include these functional groups:
- Secondary mirror motor power (12 V)
- Secondary mirror encoder power (5 V)
- Secondary mirror encoder phase A
- Secondary mirror encoder phase B
- Secondary mirror thermistor
- Primary mirror thermistor
- Primary mirror fan power
The secondary mirror motor power is divided over 3 lines for DC + and 3 more for ground in the original ribbon cable. The polarity determins the direction the motor rotates so that is ambiguous and effectively set in software. The encoder has 5 lines and 4 are used:
- Black - Ground (pin 1)
- Green - Index (pin 2, clipped at motor)
- Yellow - Channel A (pin 3)
- Red - Vcc for encoder (pin 4)
- Blue - Channel B (pin 5)
The colors and pins are those assigned in the Pittman documentation for their brushed DC motors. The motors are the same as used on the CDK20 drives. Pins are numbered from the left looking on the back of the motor or encoder with the connector down.