Kenko NES Eq Mount Modification - Motor & Encoder

 I have a Kenko NES equatorial mount for 15 years. It is quite old and have some shortages. I plan to enhance it. This first thing to modify is the stepping motor.

The original stepping motor is unipolar type. Unipolar stepper requires at least 5 wires to control and the output torque is smaller than bipolar type since only half the coils are driven. So, I open the wiring of motor and cut the central tap. By this way, it becomes a bipolar stepper with only 4 wires.

The new motor controller will drive the RA and DEC motors in bipolar mode. Modern stepper drivers are more efficient to drive bipolar steppers. Btw, dynamic micro-stepping and driving current will be used for different tracking speed.

Optical encoders are added since the gaps inside the gearbox is pretty large. Two encoders with 2000 PPR is used for RA and DEC, respectively. The firmware (of the new controller) will hand both raising- and falling- edges of both phase A & B. The equivalent resolution will be 8000 PPR. The reduction rate of the mount is 144:1 and the encoder will be attached to the manual rotation rod. So, the resolution is 1.125" (arc-second). This is good.

The connector is also replaced by RJ45. RJ45 connectors and cables are popular and easy to get. It has 8 pins. 4 pins are used for motor and 4 pins are used for encoder. So, one RJ45 for RA and one RJ45 for DEC. No extra cable needed for encoders. That's great.