Servo Motor Drive System

The SiTech Servo System

Dan Gray's SiTech controller appeared a good solution for the motorization needs of the 110 cm Cruxis telescope. Servo motors with plenty of power, a controller that does not require a laptop, and a wireless handpad for comfortable operation without the cabling hassles.

Gearing

The standard gearing was too high for the 110 cm, but Dan swapped some of the gears. The final configuration gives about 14.5 million encoder ticks per revolution in altitude and 9.5 encoder ticks per revolution in azimuth. In other words 0.09 arc-seconds per tick in altitude and 0.14 arc-seconds per tick in azimuth. Even with this very fine resolution, the system is capable of slewing at speeds above 3 to 4 degrees per second.

First impressions of the system after arrival and testing

I have spent some time testing the system after its arrival. This appears to be a very well designed and elegantly executed system:

• Plenty of features including a local search routine, backlash control, ASCOM driver, and even PEC correction.
• Great flexibility, e.g. the system can be driven at any voltage between 12V and 24V
• Powerful motors that operate without noise or vibration (quite a change compared to the stepper system used on the 406 mm).
• Very well finished boxes and cabling.
• A configuration application ServoConfig with some color madness, but very functional to finetune the motors and providing a lot of feedback about the motor's state (voltage, currents, position, etc).
• An amazing wireless handpad with buttons that glow very faintly in the dark, and incorporates a LED flashlight with adjustable brightness. It works like a charm - the radio handpad is very responsive and reacts instantaneously. Since this is the only part of the system that will actually be manipulated during observations, the wireless handpad is a key feature and will be a lot of fun to use!

Here's a picture of one of the motors and its gearing for the 110 cm:

Installation of the motors on the telescope mount

The full installation:

The altitude roller drive:

The azimuth rim drive with tensioning device to adjust the drive force:

Some pictures of the finished installation: