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Custom telescope mount using harmonic drives and ESP32

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Re: Custom telescope mount using harmonic drives and ESP32

#91

Post by ted_dunning »

teamonkey wrote: post #78
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.

First principles it is not, but people use the Seestar S50 roboscope with a distraction grating to get readings on the emission spectra of stars.

Did you mean diffraction grating? Or is there something I haven't heard of?

Frankly, distraction grating sounds like the perfect name for an amateur astronomy accessory.

Re: Custom telescope mount using harmonic drives and ESP32

#92

Post by ted_dunning »

stavros wrote: post #42
bongodongobob wrote: post #31

Earlier quoted context omitted.

Yeah, you have to read the data sheets. Beyond that, use decoupling caps for all power pins, as close to the chip as you can, and make one side of the PCB a ground plane. These 2 things should solve most of your issues.

Excellent, thank you. I already do the plane, but not the caps. Thanks!

Based on seeing lots of beginners (me, too, at one time) do ground planes wrong, this video may help:

https://www.youtube.com/watch?v=EEb_0dja8tE&t=746s

Hans Rosenburg explains some tricky concepts very clearly. The upshot is

a) 4 layer boards are much easier to get right

b) you really need an unbroken ground plane for return currents. This is often incompatible with having just two layers.

c) putting the ground plane much closer to the protected signals is a really good thing. Again, that means 4 layer boards.

Re: Custom telescope mount using harmonic drives and ESP32

#93

Post by waerhert »

_Microft wrote: post #88

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), 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.…

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.

Re: Custom telescope mount using harmonic drives and ESP32

#94

Post by waerhert »

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…

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.

Re: Custom telescope mount using harmonic drives and ESP32

#95

Post by waerhert »

ted_dunning wrote: post #91
teamonkey wrote: post #78

Earlier quoted context omitted.

First principles it is not, but people use the Seestar S50 roboscope with a distraction grating to get readings on the emission spectra of stars.

Did you mean diffraction grating? Or is there something I haven't heard of? Frankly, distraction grating sounds like the perfect name for an amateur astronomy accessory.

Works great on cheeses too!

Re: Custom telescope mount using harmonic drives and ESP32

#96

Post by teamonkey »

ted_dunning wrote: post #91
teamonkey wrote: post #78

Earlier quoted context omitted.

First principles it is not, but people use the Seestar S50 roboscope with a distraction grating to get readings on the emission spectra of stars.

Did you mean diffraction grating? Or is there something I haven't heard of? Frankly, distraction grating sounds like the perfect name for an amateur astronomy accessory.

Alas, autocorrect.

I really need the distraction grating to be something that distracts me before I buy more astronomy gear.

Re: Custom telescope mount using harmonic drives and ESP32

#97

Post by topspin »

waerhert wrote: post #94
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…

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 unde…

> 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

Since that capability is present, it's probably worth your while to apply it. Good motion control is hard, but important. Unnecessary vibration due to phase noise in the pulse train is an example of the subtleties that matter at high frequency. Excessive force generated when moving large masses can prematurely wear drive components and, over time, backlash increases and you get precision and repeatability problems. Well managed motion control will mitigate these things.

Re: Custom telescope mount using harmonic drives and ESP32

#98

Post by mrheosuper »

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…

For anyone wondering how much they can push their MCU controlling stepper, take a look at Merlin 3D printer FW, they used to run on a little 8 bit AVR MCU and do complex math(for delta printer)

Re: Custom telescope mount using harmonic drives and ESP32

#99

Post by nullc »

sheepscreek wrote: post #55
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 genuinely great for the right kind of user. If you’re familiar with CSS and have experience with animations in the past, you already possess the skills to be productive with OpenSCAD. In my opinion, the most challenging aspect is getting accustomed to the disconnect between visualizing something and manipulating it, as it’s done through code.

I used OpenSCAD a long time ago because it felt very natural having spent a lot of time with POVray as a teen.

But I found it to be very difficult to design parts with specific dimensions that were needed to line up with objects in the real world.

In FreeCAD (/Solidworks/Onshape/solvespace/etc.) it's easy to just create a logical sketch of your part, fix the require dimensions, angles, symmetries, etc and it solves for the geometry.

Re: Custom telescope mount using harmonic drives and ESP32

#100

Post by dekhn »

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?
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