My astronomy project:
Stepper motor focus driver

Content:

1. Collecting information
2. Hardware tools for development
3. Arduino Nano and DRV 8825
4. Prototype setup
5. Setup Arduino system
6. Schematic / setup
7. Start assembling circuit board
8. Setup INDI for MyFocuserPro2
9. Enclosure
10. 5 kg load test
11. High impedance stepper motor
12. To be continued

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

10, 5 kg load test:

Now I can start doing some test. First test if it can handle a 5 kg load. Camera, filter wheel, off-axis adapter, field flattener etc.

Loaded with 5 kg:

Setup a test rig and load it with 5 kg pointing upwards toward zenith, the worst case. For a stroke of 67 mm I have 55000 step when setup as full step mode. One step correspond to a 1 my movement. That's high, for a f/4 optic system the focus zoon is 35 my wide and recommended at least a resolution of 3 my. My APO refractor where this focuser sits on it's a f/7 optic, it has a focus zone of 70 my.

The high resolution makes it a bit slow, but on the other hand it can lift heavy loads. From zero to 67 mm it takes 5 minutes. Normally it only moves +/- 500 steps around perfect focus.

Video from the test:

The stepper motor isn't optimal with its low impedance for 12 Volt. A better stepper motor will lower the noise and give more torque. The 5 kg load wasn't any problem to handle.

The push pull bar:

As it's now the stroke is limited to 67 mm, the full stroke is 100 mm. With my 1x field flattener I have focus at 27 mm, with the 0.75 reducer the focus is at 55 mm. The threaded bar has some Lithium grease on it to lower the friction and lower the wear.

End position:

At the end position, 67 mm and 55000 steps. If the PLA threads worn out too quickly I can replace them with brass threaded parts.