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Focus motor driver - compact, simple and complete

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First of: Happy new year. May there be lots of clear nights available for imaging! B)

I've been creating an auto-focus motor controller that will fit SCTs and other telescopes as well (I also use it in a Crayford style focuser, for example).

The idea is simple: - one wire (USB) to the focus motor that has the controller & driver all integrated on the back side.
Additionally, the unit can be controlled by a small, cheap IR remote controller.This is much faster to adjust focus while near the telescope. At the same time, the position is communicated to EKOS.
This enables the focuser also to be used in standalone operation (for that one time you're visually observing :lol: ). The advantage: not touching the telescope -> no disturbing the image and thus better focus.

The stepper is powered from the USB directly, but a 12V connection is possible as well, selectable by a jumper.
Only during moving, the motor current is high ( 0.7 A RMS), after that it reduces the current to whatever value you set (I use 0.06 A RMS).
I'm still working on the code to incorporate (among other things) the beautiful feature 'Stallguard' of the Trinamic driver, to enable sensorless homing.
It uses a (surprisingly powerful) microcontroller: Seeeduino XIAO and a TMC2130 stepper driver. A TMP36 temperature sensor is connected via a connector (the three grey wires).
About accuracy: It's more than enough using microstepping. I usually need in the order of tens of steps for the minimal focus step.

I've also made a connector for a RC servo motor, in case I think of a SCT mirror-lock scheme or maybe something like a Crayford focuser clamp.

So... My intention is to further develop it. Publish the files for 3D printing/ firmware/ PCB files etc. (I can also snail-mail PCB's)

I've shared the firmware and some images here: github.com/speetb/scopefocus
Here are the files that can be 3D printed to connect the motor to the scope: www.thingiverse.com/thing:4670151
No housing just yet (waiting redesign for new PCB).

This is the prototype attached to a 8" Celestron:


Right now it is still a prototype soldered on a perf-board:


Today I learned how to use KiCAD, next I designed and ordered 10 PCB's for the 'beta batch'.


Any suggestions are dearly welcomed!

Cheers!
Bart

P.S. Now I've got the hang of this PCB designing, I'll think of making a dedicated tiny dew heater controller. Unfortunately it does need an 'extra' power cable.
The following user(s) said Thank You: Peter Sütterlin
Last edit: 3 years 2 months ago by Bart.
3 years 2 months ago #65356
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just a random thought: you ould share power between the focuser and dew heater if you chopped the dew heater while focusing. just to save the cord.
3 years 2 months ago #65400

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USB doesn't provide enough power for a dew heater, so it wouldn't work like that.

The dew heater controller can work stand-alone. What would be the benefit of controlling it from EKOS?

Only advantage I see is so they can be switched on and off remotely and change settings.
I would think of two operating modi (and anything in between):
a) a set amount above the environmental temperature
b) a set amount above the dew point temperature.
And by setting a small potmeter, any (resulting) value in between those modi.

Cheers!
3 years 2 months ago #65557

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