DIY Equatorial Mount

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Re: DIY Equatorial Mount

Postby Jerry » Sun Jun 29, 2014 11:15 pm

hjd1964, a member of the CloudyNights forum, has been working on the code to get his OnStep software package working on a Teensy 3.1. It is working for the most part so far.

I powder coated the last batch of parts for the scope mount last night and mounted the dovetail today. Now comes the fun part of pulling the OTA off the old forks. Whee...

Here is the breadboarded Teensy 3.1, line driver, and bluetooth module:

ImageScope mount control prototype by macona, on Flickr

I did some gizmo triage and recycled a bunch of stuff, I now can see some of my desktop:

ImageParts powdered and ready for baking. by macona, on Flickr

Here are the parts just after being coated and ready to bake. 400F for 30mins.

ImageParts powdered and ready for baking. by macona, on Flickr

The dovetail mounted on the OTA. Funny thing, I went to bolt it down and I found my holes to be 1/16" off. I milled out one end turning the holes into slots and reinstalled it. Now the bolts fall in to where they were supposed to before. I have no idea what happened. Oh well.

ImageIMG_8909 by macona, on Flickr
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Re: DIY Equatorial Mount

Postby Jerry » Mon Jun 30, 2014 9:18 pm

The OTA popped off the forks very easily, I did it in about 10 minutes last night. I went down to the hardware store and picked up the bolts for the saddle today and put it together. Some pics of it assembled.

At this point I would say it is mechanically finished. Now I need to put together the controls.

A bit overkill for a 10", I think. It weighs in at 96lbs without the scope. It has gone from portable to luggable.

ImageIMG_8911 by macona, on Flickr

ImageIMG_8913 by macona, on Flickr

ImageIMG_8910 by macona, on Flickr
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Re: DIY Equatorial Mount

Postby Donovan Ready » Mon Jun 30, 2014 10:53 pm

Yeah, but super-stable, especially after you shoot down the tripod stays... :mrgreen:

Awesome job, seriously. Image You'll post some stunning time exposures soon after you get the controls calibrated, won't you?
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Re: DIY Equatorial Mount

Postby Doug Coulter » Wed Jul 02, 2014 1:58 pm

Knowing Jerry, and that set of optics, I'd bet quite a bit we'll be seeing some great pix soon, even though he lives in a place, errrm, not that well suited to looking at the sky if I read my weather maps right. That might be why he made it so adjustable - he might take it to a mountain somewhere with clear air and low sky light pollution...I know that's why I'd have done that.

The scope has a rather long focal length, eg, it's easy to have too much magnification for it - it's not a wide field of view unless he rips out the current eyepiece holder and puts in a larger diameter one...not a big deal from him, but it frustrated me when I owned that scope.

Someday, I hope to convince him to build "Coulter's stochastic smoother" for it. I'll put details of that on another thread, it's why I got the thing myself, but that project petered out here - I was busy also running a business at the time. But the main idea is simple. Use a really fast sample rate (about 2-300hz is right for the turbulence cells in the jet stream), and simply toss out the frames that have smear, adding the rest together instead. A more-advanced version might deconvolve simple smears where possible, and there's a point source guide star in the FOV. But looking at, say, the moon or Jupiter at high magnification with that was like looking at something at the bottom of a swimming pool just after someone cannon-balled into it - multiple smears inside the eye's averaging time = the FPS required for movies has nothing to do with this problem. I did bother to do the math and a few hundred hz (or the inverse for a shutter speed) is about what you need to get above Nyquist for the air effects. This might require a multichannel plate with high quantum efficiency, close-coupled to the camera sensor. And it'd have lousy dynamic range, so you put a third layer on the front (that loses you 2/3 of the photons, so now you really need that light amplifier) - which is a B/W LCD screen - you make pixels in it dark to keep from "clipping" the bright spots in the image, and that data can then be combined with the sensor data to give you more dynamic range than the sensor alone has...This also has the advantage for deep space work of only keeping pix that have a photon from the object of interest, but you then have to be careful you don't only see what you expect. At least, you get rid of hours of sky light pollution per kept frame - only keep the ones with real data in them.

I've been trying to sell this idea to astronomers and guys at NASA for decades, but no. Back then - long exposures are it, we just live with the sky background and smear. No need for that, or a laser fake star if you know your DSP - which was, admittedly, a lot more expensive then than now.
I've also agitated with the two guys I know who have access to fabs to make this fancy 3 part sensor. No takers yet...but it would be a huge breakthrough if someone bothered to do it all in one "chip" as you could have all the pixels aligned perfectly between the layers.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: DIY Equatorial Mount

Postby Jerry » Sun Jul 20, 2014 1:56 am

One thing about a lot of japanese stuff is they really like to use more of the odd-ball connector. In the case of this it uses 20 pin MDR connects for all of the IO for the drive. So I ordered some of those off ebay and ordered some mating connectors for the servo motors from mouser. Or so I thought. In the manual it shows the part number for Molex MiniFit Jr connectors but they are really AMP Mate-n-lok connectors. They look the same but they keying is different and they use different pins. So I ordered the right ones and was able to get the servo cables made up.

For the box to hold all the drive electronics and controller I used an old box from a communications package for a ScanEagle drone. Nice aluminum case with connectors already on the side. I got the wiring finished​ tonight, now I need tie it all together and see if it works.

ImageTelescope controls by macona, on Flickr
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Re: DIY Equatorial Mount

Postby Doug Coulter » Sun Jul 20, 2014 3:49 pm

Oh, it'll work - those who won't be stopped can't be. It's just a matter of time (pun intentional). How much power is that all gonna draw? I guess these days people bring all sorts of tech to star parties and have access to much more power than back in the day when a gel cell was the biggest thing you'd lug.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: DIY Equatorial Mount

Postby Jerry » Sun Mar 08, 2015 3:12 pm

I have finally started working on this mount again. I got an old Quick-Set Hercules 5302 tripod from a friend. It is rated for 150lbs but I am betting it will hold a bit more.

I took another piece of the scrap 17-4 stainless and machine a spud that adapts the 1/2-13 threaded hole in the center of the mount to the 1-1/4" spud on the tripod column. A set screw in the spud locks in a steel socket in the column.

A couple of days ago my SiTech Servo 1 controller showed up. First thing I am going to try is making a 2nd order filter to attach to the motor outputs of the controller to smooth out the PWM and then scale it to the +/-10v analog input the servo drives have. Then the encoder feedback from the drives will connect to the encoder inputs on the SiTech. If that does not work I will use the SiTech to drive a couple small dc servo motors to and then use another encoder to drive the Mitsubishi servo drives through their pulse inputs, they can be configured to take quadrature signal inputs as well as CW/CCW and step/dir modes.

ImageTripod Mount Adaptor by macona, on Flickr

ImageMount on tripod by macona, on Flickr
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Re: DIY Equatorial Mount

Postby Jerry » Mon Mar 09, 2015 5:39 pm

I used LTSpice last night to do some circuit simulation. I hooked up the SiTech controller to the scope and found it uses a 23.45khz base frequency. Popping this info into LTSpice allowed me to come up with a pretty simple 2 pole low pass filter that should give me reasonable ripple and good step response with a 10v max output.

ImageLTSpice filter by macona, on Flickr
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Re: DIY Equatorial Mount

Postby Doug Coulter » Tue Mar 10, 2015 9:47 pm

Must be a pretty high impedance load, I always use inductors otherwise.

You gotta know you're just making us all BEG for pix from the scope.....
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Re: DIY Equatorial Mount

Postby Jerry » Wed Mar 11, 2015 10:52 pm

Input impedance of the servo drive is about 10-12kohm.
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