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snaarman
17th September 2015, 09:37 PM
I made myself a star tracker for astrophotography. It is a real bodge involving the wood router, an old table, some ball bearings, worm drives, a computer driven stepper motor and a program in "C" (my first...)

Here is what happens if you point the 75mm lens at the sky for 60 seconds.

http://e-group.uk.net/gallery/data/622/P1010580.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/86431)

Well, that's not a surprise.

But here's what you get if you mount the camera on a star tracker.

http://e-group.uk.net/gallery/data/622/P1010578.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/86430)

Coo. It sort of works. 60 seconds and a tele lens and the stars are reasonably sharp.
Yes, it is a right old nerd-fest to get it aligned with the pole star and there's a shed load of backlash to sort out .. but it sort of works. I am so chuffed I am going to have a sit down.

:-)

Pete

Mark_R2
17th September 2015, 10:05 PM
That's a fine display of DIY mechanical, electrical and software engineering. Well done. Can I ask what sort of stepper drive you are using?

Mark

Jim Ford
17th September 2015, 10:14 PM
Details of your tracker would be interesting.

Arduinos are very useful for driving stepper and servo motors and use a C++ like language. They're also cheap and very simple to interface.

Jim

Graham_of_Rainham
17th September 2015, 10:27 PM
Can we see the rig please

*chr

snaarman
18th September 2015, 06:23 AM
Oh dear, I am going to have to take a picture of the lash up aren't I :)

Tech details first. It's an 8051 micro on a development board, 11 from China. Motor is the "standard" 4 phase 5 wire type with built in reduction gears, about 2 from China, including driver electronics. Worm gear (2:50) about 2 from China. Meccano gears 2 and leftover wood and bearing found in the garage.

I have lots of previous when it comes to 8051 processors, I have used then in countless designs at work but always written in assembler (real man mode).

The reduction gear means 4070 steps to one revolution, and coupled with the worm gear you end up needing about one step per second. The cute trick - I can control forward, back, stop and speed via USB from my tablet.

Proper pictures in a short while so you can have a good laugh..

Pete

Phill D
18th September 2015, 06:36 AM
Sounds really neat to me Pete. All the better for being diy. I bet getting that image was really satisfying. Put me down on the want to see pictures list too.

Wee man
18th September 2015, 07:14 AM
Super DIY skills again I would like to see the equipment.

IainMacD
18th September 2015, 07:20 AM
Great result Pete; you lost me when you got to "old table"...

Wally
18th September 2015, 07:53 AM
Great result Pete; you lost me when you got to "old table"...

You're lucky, I fell by the wayside after 'Coo.' ;)

I've just posted a thread that might add to this topic... something to aim for those if interested in astronomy /astrophotography.

snaarman
18th September 2015, 08:29 AM
OK, here's the dirt:

General view with camera mounted.

http://e-group.uk.net/gallery/data/622/EM585870.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/86433)

A: is a standard Manfrotto mount with holes drilled. It bolts to a brass hinge on the wooden support. This allows you to adjust elevation on the camera.

B: is the turntable, part of the old dinging room table, made circular with the router. Round the edge I fitted four ball bearings to prevent it rocking. These are attached to the turntable with 8mm wood dowels and are glued into V grooves routed on the underside of the turntable.

Under the turntable is a Meccano 27 gear (the one with holes it it) that is screwed to the turntable. This is where the synchronous drive happens.

The rubber band is not driving the turntable, it is acting as a soft brake to take all the backlash out of the system :-)


C is my micro computer - this has a 6v input (will be batteries eventually). It has a plug leading to the turntable assembly so it can be disconnected. It also has a flying USB lead for control.

Part two next...

snaarman
18th September 2015, 08:31 AM
Tech stuff part two:

http://e-group.uk.net/gallery/data/622/EM585871.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/86434)

Close up shows D: one of the turntable bearings

and E: the motor drive electronics.

How they can sell the stepper motor and the drive card for less than two quid amazes me...

Pete

Wee man
18th September 2015, 08:36 AM
Super. .

snaarman
18th September 2015, 08:37 AM
Finally part three:

http://e-group.uk.net/gallery/data/622/EM585872.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/86435)

Underneath the thing. The main plate is made from two sheets of hardboard glued back to back. I wanted thin but flat. It didn't turn out to be either. :-(

You can see the stepper motor, it is a 28BYJ-48. If you google that you see they are all over the place and therefore dirt cheap.

What I can't show is the worm drive, also bought dirt cheap off eBay.

So: Is this the way to do it?
No: Here is what I will change... Driving the turntable from the centre is a bad idea. It would make more sense to drive it from the edge with a toothed belt. Problem is, where would you get a huge toothed cog? Answer, don't bother. Buy a slightly smaller belt, turn it inside out and glue it to the turntable. It then becomes its own cog. Excellent. I wonder if that is actually possible?

P

Graham_of_Rainham
18th September 2015, 08:38 AM
Something you may want to consider:

http://deepskystacker.free.fr/english/index.html

*chr

Wally
18th September 2015, 08:49 AM
Nice to know that Heath Robinson is alive and kicking in another body. ;)

British DIY at it's best.

Graham_of_Rainham
18th September 2015, 09:01 AM
I really like DiY solutions, especially when they are done on the cheap. It's so much more gratifying when you produce a result from your own efforts.

For a MkI rig to produce results as good as yours, is clear indication of the skill in working out all the requirements of the project.

Well done Pete. *clap

snaarman
18th September 2015, 09:23 AM
Tnx everyone. It has been a long project punctuated by periods of sloth...

As to the build quality, I am reminded that of the two, Grommet was the brains of the outfit. I do have a copy of "Electronics for Dogs"

P

OM USer
18th September 2015, 11:54 AM
Super stuff Pete. Using a stepper motor was a stroke of genius to provide control and reduce the amount of gearing needed by a continuous drive system.

snaarman
20th September 2015, 08:10 AM
Well - here is a second attempt. This time with the 12mm lens pointing upwards. This is a random bit of the Milky Way, plus a passing jet. It reveals that the main problem here at Snaar towers is light pollution and humid air. Still, it works well enough with a wide angle. This is the result of combining two 1 minute exposures. I aligned them manually, they only needed a movement of 2 pixels to line up. Not bad considering I had to handle the camera to start the second exposure.

http://e-group.uk.net/gallery/data/622/P1010584a.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/86479)

However, this beast is going to be stripped and rebuilt using a toothed belt drive method to sort out this backlash problem. Hmm. More woodwork. More routing. More dust. More complaints...
I wonder how much old dining room table I have left?

Pete

PS. This had a load of processing on it to reveal the Milky Way. How do those astro heroes get their wonderful colourful images? Two hour exposures? Full frame cameras? Liquid nitrogen cooling?

Phill D
20th September 2015, 08:27 AM
Excellent shot Pete from a really cool rig. You are definitely in danger of giving me some project ideas for retirement. Keep it up :)

Wally
20th September 2015, 09:10 AM
Looking at the last picture post I would say that the time and effort put in has been worthwhile. I'm sure you have probably started something that others could take up if interested in astronomy photography. Would certainly be much more interesting and time better spent than watching TV repeats and other rubbish programs etc.

Graham_of_Rainham
20th September 2015, 09:18 AM
If you are going to build a MkII you may want to consider using only 3 bearings at 120, rather than 4, as this will provide a slightly more stable rotation platform.

As for light pollution and atmospherics, if you do go for a battery powered version, then alternate locations

http://www.darkskydiscovery.org.uk/dark-sky-discovery-sites/map.html

*chr

Wally
20th September 2015, 12:39 PM
For variations on the theme of Pete / Snaarman's idea, and the interest shown. For those who fancy having a go. Try -> Here (http://www.instructables.com/id/Build-a-star-tracker-for-your-DSLR-and-make-your-o/)

The link leads to other links which should suit various abilities in DIY

crimbo
20th September 2015, 03:56 PM
Nice one Pete
DeepSkyStacker will help with image alighnment
Also for an alternate design google scotch, haig or barndoor mount... you could even consider a twin arm barn door mount...

snaarman
20th September 2015, 04:15 PM
I did research the various types of barn door tracker but then I bought three stepper motors and set off on the trail of a x y time stage. Then I found that a x y stage can indeed track any point in the sky with enough maths, but the sky rotates about the selected star. Not what I wanted, so I ended up with a stepper turntable.

Long story :)

Graham_of_Rainham
20th September 2015, 10:24 PM
Get the maths right and do all the research and you never know what you could end up with... :D

http://dpnow.com/galleries/data/500/The_Moon_ISS.jpg (http://dpnow.com/galleries/showphoto.php/photo/28072)