SpaceMount

Controls Planning, Preliminary Firmware/Drivers, Wiring Diagram, and Finishing Touches.

Submission is upon us. Well, just me.
I planned out the full control scheme in a spreadsheet so that I could keep track of it all.

Top level is PINS https://github.com/nitr57/pins, which controls the entire shooting session, stages photos, etc.

Plate solving is handled by ASTAP https://www.hnsky.org/astap.html . This is how the polar alignment mount figures out where it needs to move.

Guiding is handled by PHD2 https://openphdguiding.org/. This is how the equatorial mount figures out where it needs to move to look at targets and track them.

Mid level is handled by Indiwebmanager https://github.com/knro/indiwebmanager . This hosts an INDI server that communicates control signals between PINS and my mount drivers.

Then we have custom drivers https://github.com/ProgrammerTurtle/SpaceMount/tree/main/Control/drivers here that handle transllating control instructions from PINS into actual signals the SKR pico can parse.

Lastly, the lowest level is the firmware on the SKR pico, which is here https://github.com/ProgrammerTurtle/SpaceMount/tree/main/Control/firmware . This is low level motor control, mainly.

That’s it! The last two were written during this session.

Lastly was the wiring diagram and final prep for submission. The diagram is pretty simple, thankfully. Otherwise I just double checked submission requirements and everything in my repo. I think this is the last entry before I ship.

Godspeed!

Instruction Manuals!

I wrote complete assembly instruction manuals for every part of this project. One for the Polar Mount, one for the Equatorial Mount, and one for the Guider Scope.

The polar mount manual is 47 pages, the equatorial mount manual is 24 pages, and the guider scope manual is 15 pages.

It took sooo much time but I am glad I did it as they are pretty neat to have! I doubt anybody will ever use them besides me but that’s ok!

I actually discovered a few errors while I was doing it too, since I hadn’t spent as much time thinking about assembly. Mainly errors on the internals of my gearboxes, as assembly planning for those is a nightmare due to the complexity and sheer volume of parts. So, I am glad I took the time and discovered those before the full release/ship!

Attached is one example page from each manual!

BOM, Readme, Renders, Finishing touches, and More.

This was a long session! I started off with some finishing touches here and there like an adapter plate for the arcaswiss mounting so that I can actually put this mount on a tripod.

Then, I wrote the BOM. Boy oh boy. I thought i was doing so well on budget! Turns out, I am at the full 1000 dollars. Oops. I mean, when you think about it, this kind of setup commercially would be well over double that. So it isn’t actually that bad? But it is a bit rough. I was looking into some DIY imaging scope stuff earlier because I thought I had the budget spare but boy was I wrong.

Anywho, I got the BOM done, including accurate counts of every single screw type. That isn’t something I have done before, but I feel like this project deserved the effort.

Then I wrote the README and thus had to take some renders for it! I took one of the whole project and this really cool one of the gearbox exploded - they are attached to this devlog. I am pretty happy with how they came out.

Anywho, we are getting very close to submission, I just need to write some preliminary firmware for the SKR pico. And then I think we are good to go? Not sure.

Nonrotating Helical Focuser

I designed a new focuser for my guide scope, a Non-Rotating Helical Focuser. This basically means there is a nut/dial that you spin and it pushes/pulls the lens WITHOUT rotating it. This keeps a much clearer image during focusing, thus making focusing easier and faster.

I also designed an additonal mounting clamp option in the form of Mini-Vixen, in case I want to use that. I think I will end up using the first clamp I designed, but still.

Time for the scary part - writing a BOM.

Electronics!
I designed the electronics assembly and guider scope for this project.

The electronics assembly is an SKR pico with a Raspberry Pi 4b. I chose this pair because they are identically sized boards, so they stack well, and the SKR pico has 4 motor drivers, the exact number I need. The raspberry pi will allow for onboard plate solving/tracking control and lessen the need of always being connected to a laptop. I already own the pi and the skr pico is cheap enough. The two boards are mounting into one assembly and that gets mounted to the rear of the polar mount.

I also added HDMI to CSI connectors for the polar mount camera so that I can just run an hdmi cable between the mount and my electronics, which will handle the motion way better and be way less fragile than using a long ribbon cable. So that’s nice!

As for the guider scope. I am using an IMX290 camera sensor, a 182mm focal length 50mm diameter lens, and a custom wound carbon fiber tube for the body. This allows for higher rigidity and lower mass, and is completely overkill but it looks awesome. This scope is heavily inspired by the OpenAstroGuider scope but mine has a simpler focusing mechanism.

I designed the Equatorial Mount section. For this, I just used two of my cycloidal gearboxes stacked at 90 degrees with a bit of fancy mounting. I honestly could have done something a lot more complex, but the fact of the matter is I don’t need to! I do worry a little about strength of my gearboxes, but that’s what iterating is for.

Long story short, I got sidetracked for the first while of this recording by a red herring on an issue with my gearboxes. I was seeing concerning numbers on the calculator when it came to pressure angle on the gear teeth, but I determined that the calculator maybe can’t be trusted so I don’t know how accurate it is. I’m just gonna send it tbh, and if something goes wrong we iterate.

The mount is made up of more 1/4” aluminum, this time with me trying to spice up the shape a little. I also used more Vixen mounting hardware on the output and mounting.

Finished up the polar mount.
I added a camera module from aliexpress as well as some final structural touches to complete the mount. I decided that for tensioning I am going to try the fight during assembly thing, but if that doesn’t work out then I do have an aluminum extrusion crossbar that I added that I could either use to add tensioning or use the mounting holes of to add tensioning. Either way there are options to solve my problem. Now, I move on to equatorial.

I designed the altitude axis in its entirety, minus belt tensioners and the alignment camera. It is constructed out of more lasercut aluminum and a few aluminum extrusions with minimal printed parts to maximize load capacity. I need to think of a clean way to do belt tensioning - maybe i just undersize the belt a bit and fight it during assembly? No clue. I will think about it.

Mount assembly and altitude work. I worked on integrating the gearbox into the mount, mounting the altitude motor, and then some more detailed work on the altitude axis. I have this cool idea to use a 4040 extrusion as the “shaft” with lasercut alu for the actual bearing interfacing part. I think it will be cool and hopefully will be quite strong.
I added an aluminum plate to the bottom of the module as I felt iffy about all the weight being supported by plastic. So now, it gets 1/4” aluminum, and I am not worried in the slightest. It does make me need longer screws but thats ok.

I designed a dual stage, 81:1 reduction cycloidal gearbox to replace the huge 41:1 from yesterday. Not only is this more compact (in xy), it is a much higher reduction. It should stall somewhere around 35-40 Nm, which is a great safety margin for this project. It uses two stacked 9:1 reductions (9x9=81).

I worked on a bit of gearing for the altitude axis, mainly adding pulleys, bearings, and the shaft, and then decided to make a custom cycloidal drive gearbox for the azimuth axis that bolts to a slew bearing, replacing the entire existing bearing assembly of thrust bearing with normal bearing and pulleys.

Began work on SpaceMount today. I am starting off with the polar alignment portion of the mount since it is basically a high load turret. I am heavily inspired by the Zenit Align Mini https://zenit-astronomy.com/products/zenit-align-mini for this portion of the mount. I am unsure if it will be standalone from the main mount or not, though. Decent bit of research and some design.