7 ms·

Custom telescope mount using harmonic drives and ESP32

310 points by waerhert 1y ago

ryanong 1y ago
This post reminds me of the beauty of open source. Well done build and a great project summary!
ddahlen 1y ago
This is really impressive! I considered buying a big harmonic drive mount for my scope, but the cost is really prohibitive. I have experienced the pain of getting ekos/kstars/indi tools to work well on my personal scope. If you want to try driving indi devices via python I have some python code (it's not super polished, but it does enough for my needs): https://github.com/dahlend/contindi https://github.com/dahlend/contindi
- waerhert 1y ago
  Cool project. What prompted you to write this? Asking because EKOS already has pretty good scheduling features (I've seen, not used). Along the way I did vibe-code a TUI for controlling the INDI server running on the MeLE 4C minicomputer attached to the telescope: https://www.svendewaerhert.com/content/blog/telescope-mount/inditui.png https://www.svendewaerhert.com/content/blog/telescope-mount/... - I switched to a headless setup using a remote indi server after having a bad experience with reliability using remote desktop in Gnome. I'll probably put this TUI on Github once I clean it up a bit.
  - ddahlen 1y ago
    I am a professional astronomer, and I am running a survey for asteroids. This needs to be controlled from python, as it decides every night which objects to observe. I also heavily use Jupyter for analysis, and with this code I can take over the telescope and command it in a jupyter session, allowing me to do live data analysis.
mrgaro 1y ago
I'm most impressed with being able to order the CNC'ed metal parts. I'm just a novice cad designer and I'd love to learn that capability.
- 4gotunameagain 1y ago
  It's super easy actually ! 1) Upload step file, 2) see what's possible: https://jlccnc.com/cnc-machining-quote https://jlccnc.com/cnc-machining-quote
  - zokier 1y ago
    Xometry and pcbway are alternatives, among many others
- dylan604 1y ago
  I joined my local Maker's Space specifically for the machine shop. They had a CNC machine that I took the classes on to be certified. I designed my first simple plate design piece for cinema camera support gear in the CAD software they had connected to the machine. There was even a bit of software that generates the G-code with a simulator to check for head crashes. However, every time I went up there to actually try to build the piece the unit was down because someone crashed the head and destroyed bits. Instead, I wound up using the regular metal working machines to hand make the first piece. It ended with square corners instead of rounded, and some of the hole alignment wasn't as precise as intended. I wish I would have known of one of these types of sites to have the piece still CNC'd instead.
fusslo 1y ago
I've been using freeCAD for about 3 years now. Looking at what he was able to make with it blows my mind. I love freeCAD, but I don't think I've ever been so continuously frustrated by a piece of software
- imtringued 1y ago
  Three years should be more than enough time to have learned how to perform a few simple extrusions and pockets. What we're looking at here is essentially a pipe with a cap. Free cad gets really complicated the moment you want to do surface modeling.
- Klaster_1 1y ago
  For real, I've been using FreeCAD for small hobby stuff for 7 years and still often find extremely frustrating UX issues in features new to me, stuff that wouldn't pass QA (I'm a FE dev and know a thing or two about that). When I proceeded to understand why overconstraints are an error and not a warning, I immediately discovered a multiple page thread on FreeCAD forums with regulars gaslighting how everything was exactly as needed because "performance", despite this being a deliberate choice, not a solver limitation. This gatekeeping attitude is really off-putting, the project needs a UX expert and a good community manager to root out that power user crap.
  - fidotron 1y ago
    That was the classic GIMP problem too. Meta comment: damn it's good to see something worthwhile at #1 on HN this morning.
- eurekin 1y ago
  Can concur. I jump between OnShape and FreeCAD in my free time. OnShape feels very polished. I go back to FreeCAD, because I've bought some models, I don't want to publish in OnShape's free tier. It's amazing how much can be done, but anything that I think will take an hour, lasts 6. Many times into the night.
- waerhert 1y ago
  Though very grateful for projects like FreeCAD, I did encounter a fair bit of frustration while designing this. Especially random crashes, which only got worse as the project got more complex. As far as usage goes, it's mostly a matter of knowing how to do things in FreeCAD. I haven't encountered anything I could not achieve in FreeCAD. Having no experience in other CAD software probably helped sticking to it.
Aaargh20318 1y ago
Cool project. Strain wave mounts are fantastic. Just ordered a wave 150i myself. Can’t wait to not having to waste time balancing my scope anymore.
artgship 1y ago
I love this so much. Is there any open-source software that calculates where a given planet or star might be (based on your coordinates) and automatically finds the star / planet and then follows it? Can these mounts be used with such software if it exists?
- waerhert 1y ago
  Stellarium and Kstars (which has EKOS built in) are both very good planetarium software. Both can interface with indiserver, which can talk to many astronomy devices such as mounts, filter wheels, cameras. I use Kstars mainly for controlling the mount, and Stellarium mainly for finding nice targets.
  - artgship 1y ago
    Thank you!
- krisoft 1y ago
  > Is there any open-source software that calculates where a given planet or star might be (based on your coordinates) Sure. Skyfield is a python library to calculate that (among others). Right on the front page is an example how to calculate the azimuth and elevation of Mars: https://rhodesmill.org/skyfield/ https://rhodesmill.org/skyfield/
  - artgship 1y ago
    Thank you!
- teamonkey 1y ago
  Yes, the OnStep firmware used here has drivers for ASCOM and Indi, which are communications protocols commonly used by most astronomy software on Windows and Linux. It also speaks the older Meade LX200 serial protocol, which is another common method. For example, Stellarium on your phone can connect to the mount’s wifi station and control it.
zokier 1y ago
One thing that I'd be interested in is having telescope mount suitable for doing quantitative measurements, basically doing astrometry from first principles. To me solving the orbits of planets (etc) based solely on my own measurements sounds very compelling. It would be like retracing the steps Kepler etc did.
- waerhert 1y ago
  Sounds like a really interesting potential project. I've been pondering a system that would make amateur observations usable beyond pretty pictures. Single frames captured could be shared in raw form along with metadata (time, coords, calibration frames), potentially allowing aggregators to process it for scientific research (or even prettier pictures). The Vera C. Rubin Observatory is now able to capture the entire southern hemisphere in a couple of days. Imagine having our capturing software contributing to a planet-wide crowdsourced telescope array.
  - dekhn 1y ago
    We did this for a recent eclipse- we had thousands of photographs along the path of totality upload photos with GPS and timestamps then registered/aligned/scaled all the images and made one long "movie of totality". It turned out not so great due to the huge variability in camera quality and the resulting images.
- Finnucane 1y ago
  Kepler did it without a telescope, using Tycho's naked-eye observations.
  - zokier 1y ago
    Brahe did have large quadrants (and armillarys) though, which in this context is not all that different especially when you factor in how much light pollution impacts observations. Not to take away from Brahes exceptional ability at naked eye observations, but the key here is having some sort of instrument that enables precise measurements, be it telescope on a mount or huge mural quadrant.
davidhyde 1y ago
Loved the write up, well done to the author. I get the same feeling building stuff with freecad and then printing it. Feels like there is no limit to what can be done. After going through the growing pains of designing stuff that was just poor and difficult to print I’m now confident enough to send it to be printed by jlcpcb or pcbway. And when they tell me to accept the risk of a failed print then I think, “I feel your pain, good luck”. So far I have never gotten a failed print back. Maybe a little warped but way better than my attempts. If I never have to use my large resin printer ever again I will be happy. On the pcb front, I dread going through those final steps in the pcb ordering process. No matter how many parts I preorder, there is always something that is unavailable. So much churn in component availability.
- waerhert 1y ago
  Thanks, glad you enjoyed this. It's good to be in a place where you're confident things will turn out alright when you send your designs halfway across the world to be manufactured. I've so far only had positive experiences with JLCPCB, especially with issues that turn up during their review process. I forgot to add a fillet around the edge where the DEC axis sticks out of the tube and they sent me a quick message to say "We can't guarantee a 100% right angle here cause of the minimum radius of our bits". I assumed they would just gloss over this and manufacture it anyway, but they gave me a chance to review it just in case it was important to the design (it wasn't in this case, but still). On the PCB side, I used a plugin for KiCAD that automatically generates the production files and the bom.csv - It's really critical to review this when you load it into their tool because the automatic recognition/matching with components sometimes has mistakes in it.
  - jcims 1y ago
    I built a small two axis direct-drive mount (https://mjbots.com/ https://mjbots.com/ controllers are great) to track satellites and aircraft with an RF antenna. One of the things that stood out in the article for me was the yolo send to JLCPCB. It spoke volumes about your confidence in the CAD design, maybe one of these days I'll get there hahaha. Great design and writeup btw, it looks as good if not better than most of the commercial designs out there. You might enjoy Bruce Van Deventer's vids on youtube: https://www.youtube.com/@djcheckonetwo/videos https://www.youtube.com/@djcheckonetwo/videos (direct drive mount with 26 bit renishaw ring encoder might whet your appetite a bit)
dylan604 1y ago
After using standard EQ-mounts for so long, seeing something without a counter weight just looks wrong to my neanderthal brain. My current mount weighs 40lbs, the counter weight is 17lbs, and the tripod legs are 20lbs. So that's over 75lbs of weight and size of gear to move around every time it goes on a road trip. This design looks like it was a fraction of that. Color me intrigued
- waerhert 1y ago
  I estimate a load capacity of 8-10kg. It's not designed for the really big equipment cause I also would like to take it on camping trips. If I were to do this again I will definitely add a threaded hole to mount a counterweight bar. I've noticed the tracking accuracy drop slightly when the mount is in the most overhanging positions.
  - dylan604 1y ago
    It looks like you have a typical OTA attached, what camera are you using with that? I've only ever used my DLSR attached to the OTA for prime photography, but it is heavy. I've learned to test the position by hand of the camera through the full rotation to see how the orientation of the camera will change throughout the night to prevent hanging situations and so it has forward tension. I noticed more backlash type issues when it had reverse tension. The one thing I haven't done yet, is to just attached the camera to a small ball head to do tracked wide angle images. However, I really haven't done any dark sky shooting in many years, pre-Starlink. I wonder if long tracked exposures with wide angles would ever not be affected by Starlink trails
    - waerhert 1y ago
      I switch between the cheap Byomic 76/700 newton and my Sigma 600mm lens (Canon EF but using an adapter to fit the Olympus body). I tried to get the DSLR looking into the newtonian but it was just too heavy, causing the plastic focuser to simply bend way off axis. I've since bought a dedicated astro camera (Neptune C II) which fits alright on the newtonian. I'm keeping the Byomic 76 only for visual observations now. Looking to buy a proper refractor of around 480mm. The Sigma 600 does alright with the DSLR but isn't very sharp, hard to focus and suffering from some coma. It's good enough to learn the ropes for now.
HorizonXP 1y ago
Amazing project and write up, very good timing too! I’ve been into amateur astronomy since I was 13, owning a few telescopes and spending many hours with family at star parties. This week I pulled out our big Meade 10” SCT and our small Meade 4” Newtonian to show my 7yo son the moon and Saturn from my parents Bortle 8 backyard. It was wonderful seeing his awe and surprise, and the fact that my parents were there to see it too. That 10” SCT is on an old fork mount which is motorized but has no GOTO capabilities at all. I’ve also gone down the rabbit hole of researching mount options, thinking I could just buy my way out of it. However, as much as I like the idea of GOTO, a big part of the fun is finding the objects. So I’ve never been able to pull the trigger. I did buy a ZWO 585MC though, I’ve always wanted a dedicated cooled camera. That said, we have lost way too many hours to trying to find objects. The Telrad isn’t always enough! I’ve been looking into using my 3D printer and electronics know-how to build my way out of this. I was even thinking of swapping the motors for NEMA 17 steppers. Then I stumbled upon PiFinder, and I think this project is going to be the exact balance of automation and Push-to guidance that I would like. https://www.pifinder.io/ https://www.pifinder.io/ It’s a wonderful hobby and I think the latest in 3D printing and PCB manufacturing does mean we’re going to be able to solve a lot of these problems soon.
- waerhert 1y ago
  Thanks! If you hook your ZWO up to Kstars/EKOS you can use plate-solving in software to find out exactly where your scope is pointed at and then adjust accordingly.
- jcims 1y ago
  >However, as much as I like the idea of GOTO, a big part of the fun is finding the objects. I love reading this because it shows how different people are and how much room there is in the hobby for different interests. I am grateful for goto mounts specifically because finding the object is one of my least favorite parts of it. :D
  - ahazred8ta 1y ago
    Irony: I have a 1960s 100mm "Goto" refractor made by what is now the Goto planetarium company of Fuchu City, Tokyo. It's a headache to search for online. https://www.goto.co.jp/english/about/ https://www.goto.co.jp/english/about/
stavros 1y ago
This is great! I never understood how people learn how to make solid PCBs, I've made a few things but I think I must be missing some decoupling capacitors or resistors or whatever, because my microcontrollers aren't very stable. How do you all just know what stuff to put on the PCB? Do you read the datasheet for the component and add whatever is there?
- Palomides 1y ago
  basically every part will provide a minimal schematic in the datasheet or have a reference design you can copy from some stuff may be somewhat glossed over, like usage of ground planes or which traces you're supposed to keep short, but when those are important they'll usually be mentioned, or even spelled out in a application note
- waerhert 1y ago
  Checking the datasheet is essential, they usually show the “must-have” parts around a chip. Beyond that, good habits are adding decoupling caps close to the pins, keeping ground solid, and following the reference layout. I also learned a lot just by listening to experienced designers explain their choices, like here: https://www.youtube.com/watch?v=aVUqaB0IMh4 https://www.youtube.com/watch?v=aVUqaB0IMh4
  - stavros 1y ago
    Thanks, I'll read more datasheets, as I've kind of just been winging it (with terrible results, as you saw).
    - mkipper 1y ago
      If you're pulling the datasheet from the vendor website, you can also skim the list of documentation and see if there are any application notes available for the part. For more "complicated" parts (e.g. lots of signals, high frequency, high power, etc.), integrating the part into a board design isn't necessarily straightforward. Rather than putting a ton of detail in the datasheet, the vendor will sometimes have an entirely separate document with design guidelines for the part.
donkeybeer 1y ago
So is the accuracy and stability he achieved better or worse than the commercial mount?
- waerhert 1y ago
  Short answer: it's in the same ballpark as other mounts of the same size. The theoretical accuracy for RA is 0.198″ (65,536 steps and 100:1 reduction) and for DEC is 0.253″ (256*200 steps, 100:1). In practice many things will reduce this accuracy: seeing, proper polar alignment, sturdiness of the wedge and tripod all account for some loss in accuracy. My highest achieved accuracy was probably around 1″ during brief moments, I'm sure with excellent seeing this could reach <1″ performance.
  - donkeybeer 1y ago
    So do you think that complex mechanism ended up no better than the normal mounts? It could be execution too, I am no good at experiments and sometimes even "proven" designs end up a bit subpar, so it could be the design was alright.
    - waerhert 1y ago
      Not sure what you mean with complex mechanism. The mount has a similar architecture to other commercially available mounts like the HEM15 iPolar for example.
      - donkeybeer 1y ago
        Oh ok. I didn't know harmonic drives were standard in commercial mounts.
        Aaargh20318 1y ago
        They have become popular in the last few years. They are smaller, lighter and thus more portable than traditional mounts. They also don’t need to be balanced with a counter-weight (although they usually allow for a counter weight to increase payload capacity, they don’t need to be perfectly balanced). This all saves in set-up time. One disadvantage compared to traditional mounts is that they absolutely need guidance, and with a pretty fast guide loop at that (like 0.5s). You can’t do long unguided exposures with a strain wave. But anyone who’s serious about astrophotography is guiding anyway so that’s not really a big deal.
bhouston 1y ago
You could sell kits for this btw. There would be demand. And I think you could be quite successful. The reason is that Trump is tariffing the hell out of the main Chinese telescope accessories manufacturer, ZWO. So if you can provide a non-Chinese alternative.... Think of trying to be Prusa 3D solution in the astrophotography area.
sfeng 1y ago
One tiny nit on this amazing project / write up. He mentions that the traces have to be extra wide to support 24V. In truth though, the higher voltage means lower current, which means if anything the traces can be less wide. The size of the traces is determined by the current they carry, the voltage determines how much space must be between the traces (but it’s unlikely to be an issue at these voltages).
- waerhert 1y ago
  Good catch and explanation!
- prudhvis 1y ago
  The IPC-2221A[1] specification standard, should have all the sizes/voltages/current for trace widths etc. [1] https://www-eng.lbl.gov/~shuman/NEXT/CURRENT_DESIGN/TP/MATERIALS/IPC-2221A(L).pdf https://www-eng.lbl.gov/~shuman/NEXT/CURRENT_DESIGN/TP/MATER...
rightbyte 1y ago
Nice. Harmonic drives are my 'favourite' machine element. The lash is silly and watching the carrier(?) deform is hypnotic.
contingencies 1y ago
I would encourage the author to share the kicad board and freecad parts on github.
_Microft 1y ago
Great project! The cost of the PCBs must be driven by assembly, right? The board itself should qualify for JLCPCB's budget offer at least: 2 layers (judging by the KiCAD-screenshot), < 100mm, HASL, nothing special about solder mask or board thickness either from the look of it. I'm not not sure about the plated slots of the USB connector, though? Do these cost extra? How many did you get assembled per version? Just two of the boards or all five of them? Did you try to stick to using the standard parts or extended library? Which difference would it have made to do some work on the PCBs yourself, e.g. by soldering the through-hole connectors by hand? Either way, it is definitely an amazing project! Edit: as soon as any part is from the extended library, all different components (even standard ones) incur a cost for loading them into the pick and place machine, right? So minimizing number of different components is the only way of keeping the cost down, I guess.
- waerhert 1y ago
  Indeed the cost is mainly from assembly. The board itself is 2 layers, all default settings at Jlcpcb except for the color which is now black as opposed to the default green. This increases the cost of the board a bit. You can experiment with their calculator to find out more. I've ordered 5x each version, which is also the minimal order amount. I did try to stick to the standard library as much as possible but it's not easy once you go beyond standard passive components. Can't currently tell the exact difference it would made if I had soldered the THT by myself, likely not enough for me to bother. You could be right on that last part. The details on it are not as fresh in my head anymore. It is definitely true that you want to minimize the amount of different components. If you need 4k and 6k resistors you're better off buying 2x2k and 3x2k instead.
topspin 1y ago
From the blog: "Not surprising once you understand that slewing to a target significantly increases the number of pulses per second sent to the motors, and everything became just too much to handle for our little ESP32." A hobby application of mine involves driving multiple steppers at high-ish frequencies, following sigmoid curves precisely and no tolerance for glitches, because the mass and the cost of the device(s) is too great to risk any failure in pulse output, and there is no feedback, so I must not suffer "missed" steps, glitches, etc. The big hammer that solves this is obviating the MCU core (ARM or otherwise,) in motion control and using timer peripherals with DMA. Ultimately, I ended up turning to STM32G4 MCUs because of the ACT (advanced control timer) peripheral. These timers can generate arbitrary waveforms using DMA in a relatively simple manner: the ARM core and its code/RTOS/whatever can suffer whatever overload, priority inversion, sleep mode, etc. happens to emerge, and the timers are unaffected. Today I would consider using RP2350 and the PIO peripheral, which is also capable of achieving this, I believe. ESP32 has its MCPWM peripheral, but I determined that with MCPWM you can't do the sort of arbitrary acceleration/deceleration profiles I needed in a 100% "core-free" manner without either a.) cascading timers or b.) using interrupts. The former is, comparatively speaking, complex[1], and the later gets you back into the MCU core, and possible glitches[2]. With the ST ACT peripheral, the problem is self contained to one timer per motor: simple and straightforward. At least one of their MCUs has three of those timers (G474, in larger packages, for example.) The other way to go is specialized motor driver ICs. Analog Devices, by way of their Trimanic line of devices and low cost breakout boards, has great products there, widely used with 3D printers, CNC and similar. The driver software is much more complex than my simple ACT peripheral solution, however. [1] I know it's possible and others have done it. The ST peripheral is far easier to get working and get right, if you can deal with CMSIS and the ST reference manual. [2] I know about interrupt priorities. I also know about code evolution, bugs and other ways that dealing in interrupt priorities can get fragile.
- waerhert 1y ago
  OnStepX is very much pulse based as far as I understand it. I haven't encountered offloading techniques like you mentioned yet. Since both motors support (multiturn) positon modes, it should be possible to completely forego the pulsebased approach and only drive the motors using regular (and less frequent in comparison to pulses) position instructions over CANBUS. I spent some time reading the code in OnStepX to understand how to implement it in this way but hooking it up in pulsemode was just too easy to get started.
Neywiny 1y ago
So a note on the capacitor bank. Basically the power cable from the USB-C supply acts as an inductor. Meaning, it has an LC (C from its capacities) filter which acts as a low-pass. The capacitors on-board basically are here to counteract that. If you think about it, let's say the motors do start taking a high amount of current. Where would it come from? In an instant, an inductor can't change how much current goes through it, so it'll basically look like an open. That's where the capacitors come in. They'll provide the current while the inductor is responding. Eventually the inductor will allow current flow out of the supply's capacitors.

310 points by waerhert 1y ago

This post reminds me of the beauty of open source. Well done build and a great project summary!

This is really impressive! I considered buying a big harmonic drive mount for my scope, but the cost is really prohibitive. I have experienced the pain of getting ekos/kstars/indi tools to work well on my personal scope. If you want to try driving indi devices via python I have some python code (it's not super polished, but it does enough for my needs): https://github.com/dahlend/contindi https://github.com/dahlend/contindi

waerhert 1y ago
Cool project. What prompted you to write this? Asking because EKOS already has pretty good scheduling features (I've seen, not used). Along the way I did vibe-code a TUI for controlling the INDI server running on the MeLE 4C minicomputer attached to the telescope: https://www.svendewaerhert.com/content/blog/telescope-mount/inditui.png https://www.svendewaerhert.com/content/blog/telescope-mount/... - I switched to a headless setup using a remote indi server after having a bad experience with reliability using remote desktop in Gnome. I'll probably put this TUI on Github once I clean it up a bit.
- ddahlen 1y ago
  I am a professional astronomer, and I am running a survey for asteroids. This needs to be controlled from python, as it decides every night which objects to observe. I also heavily use Jupyter for analysis, and with this code I can take over the telescope and command it in a jupyter session, allowing me to do live data analysis.

mrgaro 1y ago

I'm most impressed with being able to order the CNC'ed metal parts. I'm just a novice cad designer and I'd love to learn that capability.

4gotunameagain 1y ago
It's super easy actually ! 1) Upload step file, 2) see what's possible: https://jlccnc.com/cnc-machining-quote https://jlccnc.com/cnc-machining-quote
- zokier 1y ago
  Xometry and pcbway are alternatives, among many others
dylan604 1y ago
I joined my local Maker's Space specifically for the machine shop. They had a CNC machine that I took the classes on to be certified. I designed my first simple plate design piece for cinema camera support gear in the CAD software they had connected to the machine. There was even a bit of software that generates the G-code with a simulator to check for head crashes. However, every time I went up there to actually try to build the piece the unit was down because someone crashed the head and destroyed bits. Instead, I wound up using the regular metal working machines to hand make the first piece. It ended with square corners instead of rounded, and some of the hole alignment wasn't as precise as intended. I wish I would have known of one of these types of sites to have the piece still CNC'd instead.

fusslo 1y ago

I've been using freeCAD for about 3 years now. Looking at what he was able to make with it blows my mind. I love freeCAD, but I don't think I've ever been so continuously frustrated by a piece of software

imtringued 1y ago
Three years should be more than enough time to have learned how to perform a few simple extrusions and pockets. What we're looking at here is essentially a pipe with a cap. Free cad gets really complicated the moment you want to do surface modeling.
Klaster_1 1y ago
For real, I've been using FreeCAD for small hobby stuff for 7 years and still often find extremely frustrating UX issues in features new to me, stuff that wouldn't pass QA (I'm a FE dev and know a thing or two about that). When I proceeded to understand why overconstraints are an error and not a warning, I immediately discovered a multiple page thread on FreeCAD forums with regulars gaslighting how everything was exactly as needed because "performance", despite this being a deliberate choice, not a solver limitation. This gatekeeping attitude is really off-putting, the project needs a UX expert and a good community manager to root out that power user crap.
- fidotron 1y ago
  That was the classic GIMP problem too. Meta comment: damn it's good to see something worthwhile at #1 on HN this morning.
eurekin 1y ago
Can concur. I jump between OnShape and FreeCAD in my free time. OnShape feels very polished. I go back to FreeCAD, because I've bought some models, I don't want to publish in OnShape's free tier. It's amazing how much can be done, but anything that I think will take an hour, lasts 6. Many times into the night.
waerhert 1y ago
Though very grateful for projects like FreeCAD, I did encounter a fair bit of frustration while designing this. Especially random crashes, which only got worse as the project got more complex. As far as usage goes, it's mostly a matter of knowing how to do things in FreeCAD. I haven't encountered anything I could not achieve in FreeCAD. Having no experience in other CAD software probably helped sticking to it.

Aaargh20318 1y ago

Cool project. Strain wave mounts are fantastic. Just ordered a wave 150i myself. Can’t wait to not having to waste time balancing my scope anymore.

artgship 1y ago

I love this so much. Is there any open-source software that calculates where a given planet or star might be (based on your coordinates) and automatically finds the star / planet and then follows it? Can these mounts be used with such software if it exists?

waerhert 1y ago
Stellarium and Kstars (which has EKOS built in) are both very good planetarium software. Both can interface with indiserver, which can talk to many astronomy devices such as mounts, filter wheels, cameras. I use Kstars mainly for controlling the mount, and Stellarium mainly for finding nice targets.
- artgship 1y ago
  Thank you!
krisoft 1y ago
> Is there any open-source software that calculates where a given planet or star might be (based on your coordinates) Sure. Skyfield is a python library to calculate that (among others). Right on the front page is an example how to calculate the azimuth and elevation of Mars: https://rhodesmill.org/skyfield/ https://rhodesmill.org/skyfield/
- artgship 1y ago
  Thank you!
teamonkey 1y ago
Yes, the OnStep firmware used here has drivers for ASCOM and Indi, which are communications protocols commonly used by most astronomy software on Windows and Linux. It also speaks the older Meade LX200 serial protocol, which is another common method. For example, Stellarium on your phone can connect to the mount’s wifi station and control it.

zokier 1y ago

One thing that I'd be interested in is having telescope mount suitable for doing quantitative measurements, basically doing astrometry from first principles. To me solving the orbits of planets (etc) based solely on my own measurements sounds very compelling. It would be like retracing the steps Kepler etc did.

waerhert 1y ago
Sounds like a really interesting potential project. I've been pondering a system that would make amateur observations usable beyond pretty pictures. Single frames captured could be shared in raw form along with metadata (time, coords, calibration frames), potentially allowing aggregators to process it for scientific research (or even prettier pictures). The Vera C. Rubin Observatory is now able to capture the entire southern hemisphere in a couple of days. Imagine having our capturing software contributing to a planet-wide crowdsourced telescope array.
- dekhn 1y ago
  We did this for a recent eclipse- we had thousands of photographs along the path of totality upload photos with GPS and timestamps then registered/aligned/scaled all the images and made one long "movie of totality". It turned out not so great due to the huge variability in camera quality and the resulting images.
Finnucane 1y ago
Kepler did it without a telescope, using Tycho's naked-eye observations.
- zokier 1y ago
  Brahe did have large quadrants (and armillarys) though, which in this context is not all that different especially when you factor in how much light pollution impacts observations. Not to take away from Brahes exceptional ability at naked eye observations, but the key here is having some sort of instrument that enables precise measurements, be it telescope on a mount or huge mural quadrant.

davidhyde 1y ago

Loved the write up, well done to the author. I get the same feeling building stuff with freecad and then printing it. Feels like there is no limit to what can be done. After going through the growing pains of designing stuff that was just poor and difficult to print I’m now confident enough to send it to be printed by jlcpcb or pcbway. And when they tell me to accept the risk of a failed print then I think, “I feel your pain, good luck”. So far I have never gotten a failed print back. Maybe a little warped but way better than my attempts. If I never have to use my large resin printer ever again I will be happy. On the pcb front, I dread going through those final steps in the pcb ordering process. No matter how many parts I preorder, there is always something that is unavailable. So much churn in component availability.

waerhert 1y ago
Thanks, glad you enjoyed this. It's good to be in a place where you're confident things will turn out alright when you send your designs halfway across the world to be manufactured. I've so far only had positive experiences with JLCPCB, especially with issues that turn up during their review process. I forgot to add a fillet around the edge where the DEC axis sticks out of the tube and they sent me a quick message to say "We can't guarantee a 100% right angle here cause of the minimum radius of our bits". I assumed they would just gloss over this and manufacture it anyway, but they gave me a chance to review it just in case it was important to the design (it wasn't in this case, but still). On the PCB side, I used a plugin for KiCAD that automatically generates the production files and the bom.csv - It's really critical to review this when you load it into their tool because the automatic recognition/matching with components sometimes has mistakes in it.
- jcims 1y ago
  I built a small two axis direct-drive mount (https://mjbots.com/ https://mjbots.com/ controllers are great) to track satellites and aircraft with an RF antenna. One of the things that stood out in the article for me was the yolo send to JLCPCB. It spoke volumes about your confidence in the CAD design, maybe one of these days I'll get there hahaha. Great design and writeup btw, it looks as good if not better than most of the commercial designs out there. You might enjoy Bruce Van Deventer's vids on youtube: https://www.youtube.com/@djcheckonetwo/videos https://www.youtube.com/@djcheckonetwo/videos (direct drive mount with 26 bit renishaw ring encoder might whet your appetite a bit)

dylan604 1y ago

After using standard EQ-mounts for so long, seeing something without a counter weight just looks wrong to my neanderthal brain. My current mount weighs 40lbs, the counter weight is 17lbs, and the tripod legs are 20lbs. So that's over 75lbs of weight and size of gear to move around every time it goes on a road trip. This design looks like it was a fraction of that. Color me intrigued

waerhert 1y ago
I estimate a load capacity of 8-10kg. It's not designed for the really big equipment cause I also would like to take it on camping trips. If I were to do this again I will definitely add a threaded hole to mount a counterweight bar. I've noticed the tracking accuracy drop slightly when the mount is in the most overhanging positions.
- dylan604 1y ago
  It looks like you have a typical OTA attached, what camera are you using with that? I've only ever used my DLSR attached to the OTA for prime photography, but it is heavy. I've learned to test the position by hand of the camera through the full rotation to see how the orientation of the camera will change throughout the night to prevent hanging situations and so it has forward tension. I noticed more backlash type issues when it had reverse tension. The one thing I haven't done yet, is to just attached the camera to a small ball head to do tracked wide angle images. However, I really haven't done any dark sky shooting in many years, pre-Starlink. I wonder if long tracked exposures with wide angles would ever not be affected by Starlink trails
  - waerhert 1y ago
    I switch between the cheap Byomic 76/700 newton and my Sigma 600mm lens (Canon EF but using an adapter to fit the Olympus body). I tried to get the DSLR looking into the newtonian but it was just too heavy, causing the plastic focuser to simply bend way off axis. I've since bought a dedicated astro camera (Neptune C II) which fits alright on the newtonian. I'm keeping the Byomic 76 only for visual observations now. Looking to buy a proper refractor of around 480mm. The Sigma 600 does alright with the DSLR but isn't very sharp, hard to focus and suffering from some coma. It's good enough to learn the ropes for now.

HorizonXP 1y ago

Amazing project and write up, very good timing too! I’ve been into amateur astronomy since I was 13, owning a few telescopes and spending many hours with family at star parties. This week I pulled out our big Meade 10” SCT and our small Meade 4” Newtonian to show my 7yo son the moon and Saturn from my parents Bortle 8 backyard. It was wonderful seeing his awe and surprise, and the fact that my parents were there to see it too. That 10” SCT is on an old fork mount which is motorized but has no GOTO capabilities at all. I’ve also gone down the rabbit hole of researching mount options, thinking I could just buy my way out of it. However, as much as I like the idea of GOTO, a big part of the fun is finding the objects. So I’ve never been able to pull the trigger. I did buy a ZWO 585MC though, I’ve always wanted a dedicated cooled camera. That said, we have lost way too many hours to trying to find objects. The Telrad isn’t always enough! I’ve been looking into using my 3D printer and electronics know-how to build my way out of this. I was even thinking of swapping the motors for NEMA 17 steppers. Then I stumbled upon PiFinder, and I think this project is going to be the exact balance of automation and Push-to guidance that I would like. https://www.pifinder.io/ https://www.pifinder.io/ It’s a wonderful hobby and I think the latest in 3D printing and PCB manufacturing does mean we’re going to be able to solve a lot of these problems soon.

waerhert 1y ago
Thanks! If you hook your ZWO up to Kstars/EKOS you can use plate-solving in software to find out exactly where your scope is pointed at and then adjust accordingly.
jcims 1y ago
>However, as much as I like the idea of GOTO, a big part of the fun is finding the objects. I love reading this because it shows how different people are and how much room there is in the hobby for different interests. I am grateful for goto mounts specifically because finding the object is one of my least favorite parts of it. :D
- ahazred8ta 1y ago
  Irony: I have a 1960s 100mm "Goto" refractor made by what is now the Goto planetarium company of Fuchu City, Tokyo. It's a headache to search for online. https://www.goto.co.jp/english/about/ https://www.goto.co.jp/english/about/

stavros 1y ago

This is great! I never understood how people learn how to make solid PCBs, I've made a few things but I think I must be missing some decoupling capacitors or resistors or whatever, because my microcontrollers aren't very stable. How do you all just know what stuff to put on the PCB? Do you read the datasheet for the component and add whatever is there?

Palomides 1y ago
basically every part will provide a minimal schematic in the datasheet or have a reference design you can copy from some stuff may be somewhat glossed over, like usage of ground planes or which traces you're supposed to keep short, but when those are important they'll usually be mentioned, or even spelled out in a application note
waerhert 1y ago
Checking the datasheet is essential, they usually show the “must-have” parts around a chip. Beyond that, good habits are adding decoupling caps close to the pins, keeping ground solid, and following the reference layout. I also learned a lot just by listening to experienced designers explain their choices, like here: https://www.youtube.com/watch?v=aVUqaB0IMh4 https://www.youtube.com/watch?v=aVUqaB0IMh4
- stavros 1y ago
  Thanks, I'll read more datasheets, as I've kind of just been winging it (with terrible results, as you saw).
  - mkipper 1y ago
    If you're pulling the datasheet from the vendor website, you can also skim the list of documentation and see if there are any application notes available for the part. For more "complicated" parts (e.g. lots of signals, high frequency, high power, etc.), integrating the part into a board design isn't necessarily straightforward. Rather than putting a ton of detail in the datasheet, the vendor will sometimes have an entirely separate document with design guidelines for the part.

donkeybeer 1y ago

So is the accuracy and stability he achieved better or worse than the commercial mount?

waerhert 1y ago
Short answer: it's in the same ballpark as other mounts of the same size. The theoretical accuracy for RA is 0.198″ (65,536 steps and 100:1 reduction) and for DEC is 0.253″ (256*200 steps, 100:1). In practice many things will reduce this accuracy: seeing, proper polar alignment, sturdiness of the wedge and tripod all account for some loss in accuracy. My highest achieved accuracy was probably around 1″ during brief moments, I'm sure with excellent seeing this could reach <1″ performance.
- donkeybeer 1y ago
  So do you think that complex mechanism ended up no better than the normal mounts? It could be execution too, I am no good at experiments and sometimes even "proven" designs end up a bit subpar, so it could be the design was alright.
  - waerhert 1y ago
    Not sure what you mean with complex mechanism. The mount has a similar architecture to other commercially available mounts like the HEM15 iPolar for example.
    - donkeybeer 1y ago
      Oh ok. I didn't know harmonic drives were standard in commercial mounts.
      - Aaargh20318 1y ago
        They have become popular in the last few years. They are smaller, lighter and thus more portable than traditional mounts. They also don’t need to be balanced with a counter-weight (although they usually allow for a counter weight to increase payload capacity, they don’t need to be perfectly balanced). This all saves in set-up time. One disadvantage compared to traditional mounts is that they absolutely need guidance, and with a pretty fast guide loop at that (like 0.5s). You can’t do long unguided exposures with a strain wave. But anyone who’s serious about astrophotography is guiding anyway so that’s not really a big deal.

bhouston 1y ago

You could sell kits for this btw. There would be demand. And I think you could be quite successful. The reason is that Trump is tariffing the hell out of the main Chinese telescope accessories manufacturer, ZWO. So if you can provide a non-Chinese alternative.... Think of trying to be Prusa 3D solution in the astrophotography area.

sfeng 1y ago

One tiny nit on this amazing project / write up. He mentions that the traces have to be extra wide to support 24V. In truth though, the higher voltage means lower current, which means if anything the traces can be less wide. The size of the traces is determined by the current they carry, the voltage determines how much space must be between the traces (but it’s unlikely to be an issue at these voltages).

waerhert 1y ago
Good catch and explanation!
prudhvis 1y ago
The IPC-2221A[1] specification standard, should have all the sizes/voltages/current for trace widths etc. [1] https://www-eng.lbl.gov/~shuman/NEXT/CURRENT_DESIGN/TP/MATERIALS/IPC-2221A(L).pdf https://www-eng.lbl.gov/~shuman/NEXT/CURRENT_DESIGN/TP/MATER...

rightbyte 1y ago

Nice. Harmonic drives are my 'favourite' machine element. The lash is silly and watching the carrier(?) deform is hypnotic.

contingencies 1y ago

I would encourage the author to share the kicad board and freecad parts on github.

_Microft 1y ago

Great project! The cost of the PCBs must be driven by assembly, right? The board itself should qualify for JLCPCB's budget offer at least: 2 layers (judging by the KiCAD-screenshot), < 100mm, HASL, nothing special about solder mask or board thickness either from the look of it. I'm not not sure about the plated slots of the USB connector, though? Do these cost extra? How many did you get assembled per version? Just two of the boards or all five of them? Did you try to stick to using the standard parts or extended library? Which difference would it have made to do some work on the PCBs yourself, e.g. by soldering the through-hole connectors by hand? Either way, it is definitely an amazing project! Edit: as soon as any part is from the extended library, all different components (even standard ones) incur a cost for loading them into the pick and place machine, right? So minimizing number of different components is the only way of keeping the cost down, I guess.

waerhert 1y ago
Indeed the cost is mainly from assembly. The board itself is 2 layers, all default settings at Jlcpcb except for the color which is now black as opposed to the default green. This increases the cost of the board a bit. You can experiment with their calculator to find out more. I've ordered 5x each version, which is also the minimal order amount. I did try to stick to the standard library as much as possible but it's not easy once you go beyond standard passive components. Can't currently tell the exact difference it would made if I had soldered the THT by myself, likely not enough for me to bother. You could be right on that last part. The details on it are not as fresh in my head anymore. It is definitely true that you want to minimize the amount of different components. If you need 4k and 6k resistors you're better off buying 2x2k and 3x2k instead.

topspin 1y ago

From the blog: "Not surprising once you understand that slewing to a target significantly increases the number of pulses per second sent to the motors, and everything became just too much to handle for our little ESP32." A hobby application of mine involves driving multiple steppers at high-ish frequencies, following sigmoid curves precisely and no tolerance for glitches, because the mass and the cost of the device(s) is too great to risk any failure in pulse output, and there is no feedback, so I must not suffer "missed" steps, glitches, etc. The big hammer that solves this is obviating the MCU core (ARM or otherwise,) in motion control and using timer peripherals with DMA. Ultimately, I ended up turning to STM32G4 MCUs because of the ACT (advanced control timer) peripheral. These timers can generate arbitrary waveforms using DMA in a relatively simple manner: the ARM core and its code/RTOS/whatever can suffer whatever overload, priority inversion, sleep mode, etc. happens to emerge, and the timers are unaffected. Today I would consider using RP2350 and the PIO peripheral, which is also capable of achieving this, I believe. ESP32 has its MCPWM peripheral, but I determined that with MCPWM you can't do the sort of arbitrary acceleration/deceleration profiles I needed in a 100% "core-free" manner without either a.) cascading timers or b.) using interrupts. The former is, comparatively speaking, complex[1], and the later gets you back into the MCU core, and possible glitches[2]. With the ST ACT peripheral, the problem is self contained to one timer per motor: simple and straightforward. At least one of their MCUs has three of those timers (G474, in larger packages, for example.) The other way to go is specialized motor driver ICs. Analog Devices, by way of their Trimanic line of devices and low cost breakout boards, has great products there, widely used with 3D printers, CNC and similar. The driver software is much more complex than my simple ACT peripheral solution, however. [1] I know it's possible and others have done it. The ST peripheral is far easier to get working and get right, if you can deal with CMSIS and the ST reference manual. [2] I know about interrupt priorities. I also know about code evolution, bugs and other ways that dealing in interrupt priorities can get fragile.

waerhert 1y ago
OnStepX is very much pulse based as far as I understand it. I haven't encountered offloading techniques like you mentioned yet. Since both motors support (multiturn) positon modes, it should be possible to completely forego the pulsebased approach and only drive the motors using regular (and less frequent in comparison to pulses) position instructions over CANBUS. I spent some time reading the code in OnStepX to understand how to implement it in this way but hooking it up in pulsemode was just too easy to get started.

Neywiny 1y ago

So a note on the capacitor bank. Basically the power cable from the USB-C supply acts as an inductor. Meaning, it has an LC (C from its capacities) filter which acts as a low-pass. The capacitors on-board basically are here to counteract that. If you think about it, let's say the motors do start taking a high amount of current. Where would it come from? In an instant, an inductor can't change how much current goes through it, so it'll basically look like an open. That's where the capacitors come in. They'll provide the current while the inductor is responding. Eventually the inductor will allow current flow out of the supply's capacitors.