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My astronomy project:
Stepper motor focus driver


Content:

  1. Collecting information
  2. To be continued

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

1: Collecting information

Now when I'm almost finished with my mechanical design of a stepper motor focuser I need to build a hardware driver and control logic for that motor and it must also be able to use INDI drivers. I have to draw some plan for it and I start to collect some information that I need to be able to build this.

They who built a controller board from the ground and up looks to use the Arduino processor and there is something called OnStep to use. I have to investigate further. Now I have at least started with this. And the construction must be a stand alone solution, it must not be dependent of the Raspberry to do all the control of the stepper motor. The Raspberry is already on the limit to handle all the needed tasks.


Stepper motor focuser driver

I have a NEMA 17 stepper motor in my boxes that I plan to use. Maybe it's an overkill and a NEMA 14 stepper motor is better suited for this. But I start with this stepper motor, the camera system is heavy and I plan for a weight of 5 kg. I want it to operate at 13 Volts direct, not as I have for the earlier focuser that need 8 Volts.

With my earlier USB-Focus unit I have learned a lot about motor focusers. When having the driver setup to half step mode the torque is much higher, you can use a smaller stepper motor. The extra torque comes from that all the motor's coils have a current run through. With this setup it takes a lot more power, you can never let it go down to zero because then it loose its position if it's between two full steps. Without current it takes a half step back or forth. The rest positions are only in full step. Even better had been to have it setup for half step but only stop at full step, but I'm not sure there are any driver that let this be done. I want to save power and then I have it to work in full steps with its lower torque, one big reason to have a big NEMA 17 stepper motor.

More to read about stepper motors:

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