Arduino Focuser - Skywatcher Evostar 72ED

[Jasp05 (Aaron)]

Hi guys,

Just thought I'd share my design for an arduino focuser on my 72ED scope.

I've added a few pics of the 3d printed bracket and spur gears. (the stepper motor isn't bolted down. need a few longer bolts)

Still trying to decide whether to use the arduino focuser pro 2 projects code which allows for temperature compensation etc or just make it a simple focuser that I can control from the pc - basically a forward or reverse button type thing.

Will post some schematics of the pcb design once I have that finalised. planning on having it use an arduino nano or pro mini and the uln2003 breakout board. essentially make it so you can just plug the 2 boards into their respective sockets on the pcb and have it work. Should be less than $20 worth of parts for remote focus control.

I know a few people on this forum use the same scope, so if your interested in plans/ files to make one send me a pm.

[Pepper (Steve)]

Do you find the focus feels funny without the heavy fine knob? (When u manually focus?

I printed my gear (for belt but may go to spur gear) with the motor shaft hole big enough to fit snug over the knob.

I do like your bracket. Did you design it yourself?

[Jasp05 (Aaron)]

Hi Steve,

Yeah I designed the bracket in fusion 360.

The focus does feel a bit different without the fine focus knob, but Im pretty sure its just the weight difference. mechanically everything still works fine.

[ChrisV (Chris)]

You can do myfocuser pro2 without temp comp etc. Or there's onstep focuser. I use pro2 - with an Arduino Uno (eleven). It has a prototyping area- so you can just solder in a stepper driver. Nice and compact.

I made similar 3d printed brackets. But I direct drive the focuser with a coupler and use microstepping to get the resolution - much less backlash.

[Jasp05 (Aaron)]

Originally Posted by ChrisV

You can do myfocuser pro2 without temp comp etc. Or there's onstep focuser. I use pro2 - with an Arduino Uno (eleven). It has a prototyping area- so you can just solder in a stepper driver. Nice and compact.

I made similar 3d printed brackets. But I direct drive the focuser with a coupler and use microstepping to get the resolution - much less backlash.

Hi Chris,

I've been considering going to direct drive as the resolution is so fine on the 10:1 it takes a long time to move any real distance with the focuser.

They reference distance the draw tube moves per step and I'm at about ten times the resolution they recommend. which is just overkill and slowing the system down. Probably should of done the maths before I designed the mounting system


Did you direct drive to the 10: 1 reduced shaft or the standard one?

and being direct drive what stepper motor did you use? Nema 17 or something smaller?

[ChrisV (Chris)]

I direct drive to the standard shaft, not the 10:1.
I have a Nema 14 on a moonlite on my newt. But my refractor focuser needed a nema 17 - a bit more grunt. That's the payback for not using gears.

They are both x16 microstepping. So I end up with plenty of microsteps in the critical focus zone.