Final Thoughts
Overall, I'm pretty happy with how this turned out.
To test the platform, I set it up and aimed it at Jupiter. I used the hand controller to put the edge of planet's disc right at the edge of the field of view. It stayed right there, edge-to-edge, for over 20 minutes. Jupiter's angular diameter is currently about 40 arcseconds. I think I can claim that the platform drifts much less than 1 arcsecond per minute. And with the controller it should be easy to make any compensations. I was hoping to try some imaging but due to lack of both knowledge and opportunity I was not able to do that.
The platform is built for 40°N latitude but I am at just under 30° so I had to elevate the south end by over 10°, which moves the center of gravity significantly off the axis of rotation. Even with that instability the platform had no trouble maintaining robust rotation.
As long as Polaris is in view, the polar alignment with the laser is super easy. It took less than 60 seconds.
The drive mechanism comprised of the polyurethane roller, contacting the flat hardwood bearing surface, with pressure provided by the spring, worked out really well. It's simple and there is no slippage whatsoever.
The momentary slowdown/speedup feature provided by the hand controller is really handy. I had not seen that feature in many of the platforms I'd seen.
The hardest part was the electronics. I had to do quite a bit of fiddling to get the motor to turn at all, and to establish the UART connection with the TMC2209 controller. I suspect I had some loose connections on the breadboard. With no prior experience with stepper motors or Arduino, there was quite a bit of a learning curve. (I did have some limited experience with electronics, and my background is software, so I did have a good foundation.)
I'm looking forward to my son using this platform and getting his feedback.
There are a lot of concepts for DIY platforms out there but I did not find anything close to a full step-by-step recipe, so it took me a long time to get traction on the design. I decided to do this write-up hoping that it could be of benefit to someone in a similar situation, so I hope someone finds it to be useful.
I welcome any questions or constructive suggestions. Please leave them in the comments here.
Happy platforming!
Alan Davis
Houston TX
December 2023
Thanks so much for your incredibly detailed instructions! I just happened to find a link to your design on a CloudyNights thread today. Years ago, I’d started a different build for my previous 8” dob with the Fort Worth Astronomical Society, but before I finished it, I upgraded to an Orion XT12i and never got around to making one. Really looking forward to trying your design. Only change I’m considering so far may be to go with a white OLED screen and add a red film for reduced night vision impact, as i couldn't find one with a native red output.
ReplyDeleteJohn, thanks for the comment. I'm excited someone is going to use my design. I used a blue OLED with the programmable brightness set to minimum and it was not an issue at all. If anything the green power LED is brighter; perhaps a higher pull-up resistance would be better. If you have any questions please let me know. Are you planning to use the spreadsheet? If so I'd be happy to look it over for you once you do your edits.
DeleteI’ll definitely be using the spreadsheet. I’d had to tweak a similar spreadsheet when we were doing our earlier build as it wasn’t completely accurate, but it was a Gee/Poncet design rather than a d’Autume design. The d’Autume is definitely a bit more complicated to cut the north bearing segment but I have a woodworking shop so the table saw work isn’t an issue.
ReplyDelete(And I actually have a truss tube XX12i — Orion’s naming convention always throws me off and I couldn’t edit my post)
Great post. Thank you so much for putting all of these details together. I enjoy bringing my 16" dob to public outreach events and it is always a challenge keeping the object in the FoV. I learned about this from John (above) and plan on building it this summer. I glanced over the spreadsheet and still need to wrap my head around the determination of the CoM location for the rocker base.
ReplyDeleteI'll be eager to see if the design scales to something as big as a 16". Please let me know what you decide to change, if anything. For the rocker base I just hung it from a fish scale using a C-clamp, moving the clamp until it hung level (vertical axis parallel to the ground), then measured from the bottom of the base to the position of the clamp.
DeleteI expect that like most spreadsheets that use formulas, it could be a bit confusing; I'd be happy to answer any questions.
Hi Alan, I was referred to this post by John Adelman. Have you considered building this for sale? I would be happy to buy one. I have a Celestron starsense 8 inch dob (I see the same brand in the picture). This will help with outreach events, we don't need to keep adjusting the scope!
ReplyDeleteThanks Muru
Muru, I am flattered by your interest, but I am more of a tinkerer and not set up for production. I think Ed Jones produces his design in limited quantities but I can't find the link (anyone?). Also, I have a prototype for the one featured here -- it's basically identical, but lacks the drive system and is not as pretty. I'd happily sell that for the cost of materials (maybe $150 plus shipping) but you'd have to put the drive together.
DeleteAlan, thanks for the response. I was looking for more complete setup :-) It does not have to be pretty as long it is functional. I don't have the tools nor the expertise. I could learn those things, but I am short on time too! Let me think about it though. BTW, Ed's page is https://opticaleds.com/custom-made-equatorial-platforms/platforms/
DeleteThanks!
Muru, what is your latitude? The prototype is just gathering dust in my shop so maybe we can work something out. If you submit a comment with your email address I won't publish it but then we can communicate directly (unless you know of another way to do PMs here).
Delete