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Custom telescope mount using harmonic drives and ESP32

svendewaerhert.com

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Re: Custom telescope mount using harmonic drives and ESP32

#101

Post by dekhn »

waerhert wrote: post #27
zokier wrote: post #14

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.

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…

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.

Re: Custom telescope mount using harmonic drives and ESP32

#102

Post by coryrc »

ejp wrote: post #71
alnwlsn wrote: post #46

Earlier quoted context omitted.

I came to FreeCad with some years background in Inventor, NX and SolidWorks. The jump from any of these to FreeCAD is not very big; you're doing a lot of the same things. But, most of the problems FreeCad has are solved in those, so you can sort of do anything in them and be none the wiser. In FreeCAD, you need to think a little bit more on how it's going to do things. But most people don't learn the big CADs first,…

OpenSCAD is great for functional parts, built of basic components. It can start to be good for moderate complexity components with the BOSL library (I use BOSL2) including chamfers/fillets where needed. And the parametric/customization aspect is second to none - IF it's built with that in mind. Where it really falls down is when you need to somehow get data OUT of the model to feed to other shapes. I would love to be…

> I've also tried to spend some time performance optimizing for render/output. It is not cooperative at all.

Have you started using a recent nightly build with the Manifold backend and not the "stable" (aka obsolete) release?

Re: Custom telescope mount using harmonic drives and ESP32

#103

Post by benhurmarcel »

alnwlsn wrote: post #46
waerhert wrote: post #18

Earlier quoted context omitted.

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.

I came to FreeCad with some years background in Inventor, NX and SolidWorks. The jump from any of these to FreeCAD is not very big; you're doing a lot of the same things. But, most of the problems FreeCad has are solved in those, so you can sort of do anything in them and be none the wiser. In FreeCAD, you need to think a little bit more on how it's going to do things. But most people don't learn the big CADs first,…

I've used Solidworks and Catia quite a bit, and for home use Fusion doesn't give me nearly as much frustration as FreeCAD.

Re: Custom telescope mount using harmonic drives and ESP32

#104

Post by ddahlen »

waerhert wrote: post #49
ddahlen wrote: post #3

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

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/... - I switched to a headless setup using a remote indi server after having a bad experience w…

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.

Re: Custom telescope mount using harmonic drives and ESP32

#105

Post by fest »

topspin wrote: post #90

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…

When I was doing stepper control on rp2040 I looked into using PIO but the 5 bit counters and 32 instruction limit made it too awkward to use. What worked better for my needs was dedicating 2nd core for just motion control and bit-banging the step/dir signals- simple to implement and good enough for the modest needs I had (just trapezoidal velocity profile for single axis motion).

Re: Custom telescope mount using harmonic drives and ESP32

#106

Post by mnw21cam »

zokier wrote: post #14

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.

The best way to determine the exact position of a planet is not to have a highly calibrated telescope mount that knows exactly where it is looking. Instead, it is to take a decent picture with the planet approximately in the middle, and feed it into a piece of software that looks at all the surrounding stars (with known positions) and calculates the planet position from that.

Getting a telescope mount calibrated that well is nigh on impossible. Calculating position by relative position of nearby stars is incredibly accurate.

Re: Custom telescope mount using harmonic drives and ESP32

#107

Post by zokier »

mnw21cam wrote: post #106
zokier wrote: post #14

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.

The best way to determine the exact position of a planet is not to have a highly calibrated telescope mount that knows exactly where it is looking. Instead, it is to take a decent picture with the planet approximately in the middle, and feed it into a piece of software that looks at all the surrounding stars (with known positions) and calculates the planet position from that. Getting a telescope mount calibrated that…

Yeah, I know plate solving is a thing. People did it even manually back in the days when plates were just film photographs, you don't need fancy computers for that.

Tbh this is the sort of thing why I would want to do this experiment, to determine what observations/measurements you actually need.

As you noted, to do plate solving successfully you need accurate and comprehensive star catalogue. But if you are starting from first principles then can you build such catalogue without precision aiming? Maybe you can, but it is all bit difficult to wrap your head around without concrete experimentation.

Of course historically afaik this sort of work was done with precision transit instruments. But that is interesting question, can we bypass that step if we use photography and some computation

Re: Custom telescope mount using harmonic drives and ESP32

#108

Post by Neywiny »

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.

Re: Custom telescope mount using harmonic drives and ESP32

#109

Post by mnw21cam »

zokier wrote: post #107
mnw21cam wrote: post #106

Earlier quoted context omitted.

The best way to determine the exact position of a planet is not to have a highly calibrated telescope mount that knows exactly where it is looking. Instead, it is to take a decent picture with the planet approximately in the middle, and feed it into a piece of software that looks at all the surrounding stars (with known positions) and calculates the planet position from that. Getting a telescope mount calibrated that…

Yeah, I know plate solving is a thing. People did it even manually back in the days when plates were just film photographs, you don't need fancy computers for that. Tbh this is the sort of thing why I would want to do this experiment, to determine what observations/measurements you actually need. As you noted, to do plate solving successfully you need accurate and comprehensive star catalogue. But if you are starting…

In this case, a precision transit instrument can be the two corners of two houses (or some other structure that won't move) that are separated by a reasonable distance, an eyeball, and an accurate time. Stand at one and sight along both edges looking South past the other wall, and mark the exact time when a star disappears behind the far wall. That'll give you a load of pretty accurate relative right ascension values. If you can measure the time the the star disappears to within about a second, that gives you an accuracy of 15 arcseconds. If you use a video camera and frame-count, you can get better than that. It'll be best if the far wall is accurately straight and vertical and accurately due South from your observation position. You can get declination values by marking how high on the far wall the star was when it disappeared, or indeed the position in the video when it disappeared, and that accuracy will be the zoom level of your camera. (Make sure you calibrate out the distortions of the camera lens. Creating a panorama in daytime and processing it in something like hugin will give you this.)

Re: Custom telescope mount using harmonic drives and ESP32

#110

Post by topspin »

dekhn wrote: post #100
topspin wrote: post #90

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…

I think the ESP32 also has an RMT, did you also exclude that as an option?

Good question, and yes, I did. RMT can work, but ACT has a key advantage. Motion curves are naturally segmented into phases. With ACT, the Repeat Count Register (RCR) defines how many cycles to hold a given frequency and duty, so each phase is exactly 64 bits: PSC, ARR, CCR, and RCR. A full curve reduces to a compact precomputed table that can be hardcoded, generated once, or streamed with negligible core load for continuous motion.

With RMT, you either need a large table of individual level/duration symbols or involve the core to manage phase pulses.

It’s entirely feasible to do this with ESP32 using MCPWM, RMT, etc. Its been done and has worked well. But I value the dead-simple, hard-to-get-wrong invariants of ST's timers.

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