Motorized OAG focuser - Warning: Geeky post!

[Julien Lecomte]

Howdy!

First, a word of warning: If you are a visual astronomer, or if you have absolutely no interest in geekery — stuff that involves 3D printing, electronics, embedded software, etc. applied to the astronomy hobby — you might as well stop reading now...

For those of you who are still with me, I wanted to share my latest open source project, and let me tell you, it's a really fun one! First, the link to the GitHub repo, which has a very extensive "README" file that contains a ton of information about this project, including the WHY, WHAT, and HOW:

https://github.com/jlecomte/ascom-oag-focuser

Summary: This project is about motorizing the helical focuser of my ZWO OAG (Off Axis Guider). You might wonder:

1) Why am I using an OAG and not a guide scope? Good question! I answer it in the Introduction paragraph of the README. I can summarize it with only 1 word: flexure (if you are into astrophotography, you know what I'm talking about...)

2) OK, fine, but why would I need to be able to refocus my guide camera throughout the night? Another good question, and it's at the core of this project. I can summarize it with 2 words: filter offsets (well, it's a bit more complicated than that, and not everyone is facing the same constraints I am dealing with, but take a look at the Introduction paragraph of the README and you'll understand)

When I have some free time, I'll try and put out a full video of this project on my YouTube channel. Shameless plug: subscribe so you don't miss an episode ;-P

https://www.youtube.com/channel/UCh61RNGUv1O7BhOn6tYajIw)

Questions? Comments? Feedback? All are welcome!

I hope you like this project as much as I've enjoyed working on it! :)

- Julien, aka "Dark Sky Geek" on YouTube -

[Francesco Meschia]

What a great project, Julien! I have the same scope and I also deal with filter offsets. I’m using a guidescope at the moment, but I always wondered how to deal with offsets in the presence of an OAG – now I know! So, thanks for sharing this!

Francesco

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[Julien Lecomte]

Hi Francesco,

If you want to build this project, I can help you. I have a lot of spare parts (for example, you cannot buy a single 24BYJ48 stepper motor, you buy them in packs of 10 for $9... Same deal with ULN2003, etc.) and I'd be more than happy to give some of those parts (for free!) that I am not planning to use anyway to local astronomers who want to build this project. Also, since it's a relatively small project, I can even 3D print the parts for you, as long as not too many people ask for it ;-P

I don't know of anyone else doing this. Pegasus Astro SCOPS OAG comes close, but according to the N.I.N.A. developers, there is no good solution to deal with it (with N.I.N.A. at least, and I would suspect with other imaging suites) My ASCOM driver solves that, whether you use SCOPS OAG or the DIY focuser I propose in this project.

- Julien

To view this discussion on the web visit https://groups.google.com/d/msgid/sf-bay-tac/2132BA30-AD53-401B-8397-44D2DC600FB1%40gmail.com.

[Francesco Meschia]

Thanks, Julien! I don’t even have an OAG right now, but something tells me I should prepare for the future – so I may take you up on that :)

By the way, I looked at the CN thread you reference in the README.md file. I have the same type of guidescope, and for some time I had hard-to-pinpoint flexure. I think I managed to “kill it” from my system, after I found that the guidescope had a rotating coupling between the gudiescope OTA and the eyepiece holder, and that the “bearing surface” was… a rubber O-ring! After I removed the ring from the system, and I clamped down everything (at the cost – inconsequential to me – of losing the ability to rotate the eyepiece/camera relative to the OTA), flexure disappeared. I feel bad for not finding the thread before...

Francesco

To view this discussion on the web visit https://groups.google.com/d/msgid/sf-bay-tac/CAMf_mws%3DnKKw%3DExErmDjaY_t_Fg1xzVB%2BRVM7Ld3VLt0xvM6Yg%40mail.gmail.com.

[Julien Lecomte]

Haha, don't feel bad. Ever since I switched to an OAG, my guiding numbers have improved, regardless of the flexure. I'm not looking back :)

- Julien

To view this discussion on the web visit https://groups.google.com/d/msgid/sf-bay-tac/6503A4CC-CA4C-4890-84D4-4CDA7F1226F7%40gmail.com.

[ma...@astrospotter.com]

Nice solution Julien.     I enjoyed seeing the evolution, been there, have that (set) of T-Shirts.   The current rendition looks nice too.  I love those ULN200x darlingtons.

If you end up with issues with the gears, I can make you super fine resolution gears using the resin printer.  Contact me offline.

Recently made a RA drive system for a Great Polaris mount handed down to me by much missed James Turley.  Made the belt with NinjaFlex material.   3D printing opens the world to tinker times!

Again, great looking job and thanks for sharing

Marko