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Motorized Stars Tracker

by pchretien, published

Motorized Stars Tracker by pchretien Sep 12, 2011

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Summary

This type of astrophotography mount is often called a barndoor mount, a scotch mount or a Haig mount. This mount allows you to take long exposure of the night sky by canceling out the apparent motion of the stars in the sky.

You can get more information on this type of device on Wikipedia:
http://en.wikipedia.org/wiki/Barn_door_tracker.

The version displayed here is made using soft wood (pine) but the final assembly should be made of hard wood such as maple.

Note: The mechanism is working as expected but I am still having some vibrations transmitted to the camera. I have to eliminate these before to try taking any pictures. Improvements are on the way ... stay tuned.

Instructions

  • Print all parts. You may have to design a specific mount for your motor.
  • Cut one 9 1/4"" long 3/4" x 3/4" piece of hard wood.
  • Cut one 12"" long 3/4" x 3/4" piece of hard wood.
  • Bind a 1/4" filted rod with a radius of about 11.45" (291mm)
  • Assemble all parts as displayed on the pictures. The distance between the center of the bearings and the center of the rod must be 11.45".

The electronic is built using an Arduino, an Alegro 5804 driver and a cheap stepper motor. I did this some time ago and, as of today, I would use different parts such as the Adafruit motor shield and the Nema 17 motor. You'll find more informations about this on my blog at: http://basbrun.com/2009/07/10/arduino-timer-interrupt/

Following is a short video of the mount in action:
http://www.youtube.com/watch?v=q-sFi-ZAZ7o

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OK, so a 291mm radius arm at 15deg/hr means 0.0213mm/sec, 1.279mm/minute, or about 1.023rpm on a M8x1.25 or 0.992 RPM on a 1/4-20 bit of threaded rod. Cool.
I think my dad once had something like this driven with a cheap synchronous motor driven by a 555 putting an amplified ~59.53Hz square wave backwards through a 12V:120V transformer.

I suspect from the photos you are using a 7.5 degree per step (or thereabouts) stepper. If that is the case, upgrading to a 1.8 degree per step might help.

A couple of ideas to minimize the vibration...
A vibration suppression mount (essentially a shock absorber) right under the camera, and one between the board and the camera's mount will go a long way in this configuration

A mount where the camera sensor is in line with the board will help.

Use soft wood with plastic bolts and rubber vibration suppression mounts.

Use a brushless DC motor mounted as far away from the camera as possible. Then add another gear set. Idea being to get the frequency of the vibrations into the suppression mount's sweetspot.

Hey!

I was thinking all weekend about designing a nice open source star tracking mount that can be 3D printed, but I never found this Thing because you never mention the word "telescope" and thats what I was searching for. Perhaps tag it with that or mention it in the post? Clearly this is technically for a camera and not a telescope, but people searching for telescope related items would probably be interested in this! Though I see now I should have just searched for "astronomy". Not sure why I didn't really.

Anyway I'm thrilled to find that there are actually star trackers on here! I'll have to build one of these when I get my Ultimaker. :)
-Taylor

Eh, thanks for your comment! I added the telescope tag.

I'll publish a new version in the next few days. The mechanism will be a lot simpler and much more compact.

I still have a lot of work to do but my weekent at the ohsummit and the Maker Faire gave me the push I needed ...

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