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Home made astrotrac

MooMoo

By MooMoo
in DIY Astronomer

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MooMoo

MooMoo

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Does anybody know if anybody made a home made version of a Sissor mount like the astro trac at a fraction of the cost?

I was going to make a single or double arm barn door but now I have decided to look into a Sissor tracker like astro trac.

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MooMoo

MooMoo

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Good luck with that. If you find a cheap way of doing this I am sure quite a few of us will be sending you begging letters! :grin:

Two bits of wood, precision motor and drive, same as a barn door except arranged as a sissor tracker like an astro trac.

Has anybody even tried it?  I plan to but currently cannot now, but I am trying to find out if anybody has even tried.

It doesnt have to be to the same quality of machining as astro trac but one similar :)

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AstroTux

AstroTux

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Interesting one this. I've been thinking along similar lines recently and think I have a solution but have not got around to trying it.

I have recently built some micro-controller based boards to handle stepper motors for barn door mounts ( each costs about £2-£3 to make ) and a simple change to the code means that the tangential error associated with these can be programmed out. It is simply a case of speeding up the motor as the mount opens, and is all handled by maths in the code. An analysis of the maths indicates that tracking could be good for up to 2 hours.

The other benefit of using a micro-controller is that the design of the mount becomes much more flexible. The length of the arm and the gearing are all taken into account when the code is compiled, meaning that the design is not locked into the traditional 1 rpm motor with an arm length dictated by the pitch of the drive screw.

The maths would be slightly different for a scissor design, but should not present many problems and I believe the accuracy could rival that of an AstroTrac.

If you want yo give this a try ( you produce the hardware and I'll produce the controller ) then I'm quit willing to give this a bash. Just PM me if you are interested. I would also be quite willing to post any results as an open source project for others to use or improve upon.

all the best,

Alan

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StuartJPP

StuartJPP

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The AstroTrac uses a very fine pitch screw, not sure how fine it is but much finer than UNF. The fine pitch allows precision and the length of it the tracking time (2 hours).

The screw is turned using a micro stepping controller (16 steps per full step or 3200 steps per revolution, assuming it uses a 1.8° step motor) and there are well over 1.6 million 1/16th steps during the 2 hour tracking time.

On top of this, the step rate changes depending on the arm position (using a tangent function) as mentioned.

Good luck matching the precision, it is this that makes the AstroTrac what it is.

You should be able to achieve decent tracking by following a similar design though I think that a LOT of effort went into the scissor/folding design.

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MooMoo

MooMoo

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Thanks for the replies.

I honestly don't think it is a big task, I dont even require a full 2 hours precision so even 15 to 30 minutes decent accuracy will good enough
.

It is simple geometry, even simpler than the barn door design that everybody uses

It would make a fun aruino project which I am looking for.

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Viewmaster

Viewmaster

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If one had the knowhow a guiding camera could be fitted to control the RA tracking speed,

just as the big EQ trackers do these days. 

I don't know how they work but a small computer must be 'looking' at the star used for tracking

and which pixels it is on. Any wandering is passed to the tracker motor I guess. 

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  • 1 year later...
helium

helium

Posted
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Does anybody know if anybody made a home made version of a Sissor mount like the astro trac at a fraction of the cost?

I was going to make a single or double arm barn door but now I have decided to look into a Sissor tracker like astro trac.

Yes.

atrac

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  • 11 months later...
SilverAstro

SilverAstro

Posted
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5 hours ago, m.tweedy said:

I would suggest caution on this thread as the Astrotrac has Patent Protection!

Surely that only protects it from being manufactured and sold/resold ? Doent stop anyone DIY building something similar for own use, nor telling how they built it.

Anyway an AT is only a BarnDoor that has been put into a bacon slicer end on ! Stack lots of (2D) ATs together on their polar axis and you get a (3D) BarnDoor.

What new bit of it is the patent for ?

 

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SilverAstro

SilverAstro

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23 minutes ago, Markusc said:

I removed it

Oh that's a shame, I would have liked to see that, doesnt look like an AT to me no holes ! !

Did  you code it yourself in Arduino or similar ?

 

On 10/02/2014 at 11:06, AstroTux said:

and a simple change to the code means that 

That is what they all say ! I know this is an old post, did you use trig functions in a math capable processor or a look-up table to save proc power but needing bigish ram ??

 

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Markusc

Markusc

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11 hours ago, SilverAstro said:

Oh that's a shame, I would have liked to see that, doesnt look like an AT to me no holes ! !

Did  you code it yourself in Arduino or similar ?

 

That is what they all say ! I know this is an old post, did you use trig functions in a math capable processor or a look-up table to save proc power but needing bigish ram ??

 

It's similar but nowhere as nice as the AT, the AT is a work of art

The processor is an Arduino nano and a easy driver for the stepper. Yes coded it myself and using the trig functions instead of lookup

This was built using a taig lathe, bandsaw and hacksaw, which I owned a milling machine

I've attached the pictures again, just want to be clear I'm not trying to sell anything

image.jpeg

 

image.jpeg

image.jpeg

 

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SilverAstro

SilverAstro

Posted
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3 hours ago, Markusc said:

It's similar but nowhere as nice as the AT, the AT is a work of art

The processor is an Arduino nano and a easy driver for the stepper. Yes coded it myself and using the trig functions instead of lookup

This was built using a taig lathe, bandsaw and hacksaw, which I owned a milling machine

I've attached the pictures again, just want to be clear I'm not trying to sell anything

@m.tweedy was right to say caution - wrt. commercial activities,,  as you say if it is clear that you are not about to make a batch of nn etc&etc lol! no harm in discussing HowTos.

Very nice work, thanks for showing, my workshop is not nearly as well equipped as yours :( ( I have lathe and a hacksaw :) ) The beauty of the ( 3D as I call it) BarnDoor is that it exchanges elegance  for length and simplicity. The length of the hinge means that it can maintain pointing accuracy without fine tolerance engineering. The AT design means that a well engineered bearing is needed to avoid pitch and roll   yaw (oops edit ! senior mo. got my spatial co-ords muddled :) ).

However, the drive requirements are the same for both ( the conversion from a linear screw to circular motion) so when I get all my other projects and my roundtuit in line I will be looking for suggestions for code,  that is the critical bit I fancy, for any budding DIYers on this bit of the forum :)  - I wonder what happened to @AstroTux and his simplicity model :)

 

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