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INDI focuser driver for Waveshare Stepper Motor HAT for Raspberry Pi / Rock Pi

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  • Thank you received: 3
Very nice!  What stepper did you use?  I ended up using a larger stepper (NEMA-17) with a belt/loop under tension.  I really like the smaller stepper and worm gear arrangement you used.  And for this purpose, a larger gear ratio seems better since it enables finer control and decreases the required torque to move the focuser.
1 year 8 months ago #69443

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It's a tiny stepper motor I found on Aliexpress with a built in 50:1 gear box. The worm ratio is 120:1. Together it is a very high gear reduction. The position resolution is insane. A command for 100 steps barely has a noticeable effect on a bahtinov pattern. I had to use an initial step size of around 800 for the autofocus to get a good V curve.

I am thinking of selling my design as a kit.
INDI/KStars on Raspberry Pi 4, 4gb
Raspbian Buster with AstroPi3 script configuration
Skywatcher HEQ5 Pro Mount
Canon 600D Camera
Orion SSAG/ASI120mm @280mm Guide Scope
PHD2
Waveshare Stepper Motor Board - DIY Focuser
Adafruit GPS Module
Generic Bluetooth Joystick.
Startech 7 port powered USB Hub.
1 year 8 months ago #69444

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That is supercool! 
I had tried a similar design initially, but there was too much torque,  I could not make it work.  I used a different design instead, but it's more bulky. 

 

Yours is much more elegant.
Can you post the instructions and the STL files for building it?

Jo
 
Atlas Pro AZ-EQ, ASI1600MM-Pro, ASI120MM-S, ES102ED, WO-Z61, Nikon D3300, ASI-EFW, ZWO LRGB,Ha,O3,S2 filter set
Last edit: 1 year 8 months ago by Jose Corazon.
1 year 8 months ago #69450
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This is the motor I used. It is a minor miracle it actually has enough torque. But it manages with the very high gear reduction. It can get hot if it is run too much. And there was a one time issue when I left power to the HAT on while the Pi was shutdown. Thus my eNABL pin pull-up resistor bodge to prevent another meltdown.
www.aliexpress.com/item/32848283821.html...1.0.0.301c4c4dVCiy0M
INDI/KStars on Raspberry Pi 4, 4gb
Raspbian Buster with AstroPi3 script configuration
Skywatcher HEQ5 Pro Mount
Canon 600D Camera
Orion SSAG/ASI120mm @280mm Guide Scope
PHD2
Waveshare Stepper Motor Board - DIY Focuser
Adafruit GPS Module
Generic Bluetooth Joystick.
Startech 7 port powered USB Hub.
The following user(s) said Thank You: Jose Corazon
1 year 8 months ago #69452

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Thanks for the link.  It looks like I was on the right track with this eBay listing I found ;)

ebay.us/mzsqFl
Last edit: 1 year 8 months ago by Eric Brown.
1 year 8 months ago #69453

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Thanks, Andrew!  

I was actually wondering whether you would be willing to share your 3D files for the worm gear.  Designing a worm gear in Blender is complex and time consuming, having the final STL file would go a long way.
I don't think I will replace the focuser I already have on my WhiteCat, it is working perfectly, just as well as yours is, but I would like to adopt this to some manual Nikkor lenses that I also use for wide-field imaging.  Torque does not have to be so high for those, they move more easily.  The ring around the lens will have a different diameter, though, but I can scale the worm gear accordingly in Slic3r.

Thanks for considering,

Jo
Atlas Pro AZ-EQ, ASI1600MM-Pro, ASI120MM-S, ES102ED, WO-Z61, Nikon D3300, ASI-EFW, ZWO LRGB,Ha,O3,S2 filter set
1 year 8 months ago #69466

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I haven't looked yet, but I bet there are decent gear/worm gear generators available for OpenSCAD that could be imported into your Blender project.  I've done that for regular gears in other projects.
1 year 8 months ago #69467

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Simple worm gears, yes. Globoid worm gears with variable gear ratios are a different story. But perhaps I am too much of a perfectionist here.
Thanks anyway.
Jo
Atlas Pro AZ-EQ, ASI1600MM-Pro, ASI120MM-S, ES102ED, WO-Z61, Nikon D3300, ASI-EFW, ZWO LRGB,Ha,O3,S2 filter set
1 year 8 months ago #69468

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Now you've got me curious.  I have no idea what those are and assumed a simple worm gear would work in this case.  It sounds like I've got some reading to do.
1 year 8 months ago #69469

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This is a globoid worm gear with a 1:120 ratio.

www.stlfinder.com/model/another-worm-gea...-1-pWx6wsw1/1842347/

I suspect that may even be the one Andrew used. I have used it before as well with a similar design as the one Andrew posted, but as I wrote, I had difficulties taming the torque.
I have not found a gear generator yet that allows me to adjust the dimensions for different diameters and different gear ratios so I gave up on that approach and moved to my simpler, but less elegant solution. Which works perfectly, really, but is not nearly as compact as Andrew's.
Atlas Pro AZ-EQ, ASI1600MM-Pro, ASI120MM-S, ES102ED, WO-Z61, Nikon D3300, ASI-EFW, ZWO LRGB,Ha,O3,S2 filter set
1 year 8 months ago #69470

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Wow... those are really cool.  I'm with you.  Nothing less will do now that I know/understand what they are.  I did find this on thingiverse, though I have no idea how good / applicable it is here:

www.thingiverse.com/thing:2776688
1 year 8 months ago #69471

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My worm and ring gear are in fact Globoids generated with OpenSCAD. I am hesitant to share the original STL files at this time as everybody I have shown this to has encouraged me to market it. But I do encourage others to take inspiration from it. I'm honestly surprised I have not seen anyone else use this mechanism yet.
I used the following script to generate a custom set that I added features to in other 3D modeling software. www.thingiverse.com/thing:2776688
*But this is an updated version if the script that may be better.
www.thingiverse.com/thing:4197625
You will want to unhide the Customizer under the View Menu. And I had to scale down the gears it created to the right diameter.
INDI/KStars on Raspberry Pi 4, 4gb
Raspbian Buster with AstroPi3 script configuration
Skywatcher HEQ5 Pro Mount
Canon 600D Camera
Orion SSAG/ASI120mm @280mm Guide Scope
PHD2
Waveshare Stepper Motor Board - DIY Focuser
Adafruit GPS Module
Generic Bluetooth Joystick.
Startech 7 port powered USB Hub.
1 year 8 months ago #69474

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