DIY Autoguider for Long Exposure Astrophotography (Part 2)

Well I got around to take some photos of the upgraded astrophotography tracker and to describe my progress.

Tracker-2222

A few months ago I abandoned work on the tracker due to mechanical instability and started playing with a mini-mill to make a large worm gear and worm. The process has been reasonably successful but I think that I can only use about 1/4 of the worm gear due to concentricity problems. As I used a small mill as a lathe to try to get the worm down to a perfect disk, some flexure in the setup caused the machined aluminium disks to be less than perfect. The cutting of the 130mm worm gear went very well and only took about 1 1/2 hours to cut and polish. See some of the previous posts for the detail.

I had to assemble the worm and stepper motor assembly to the mount and it looks a bit “wonky”, but it works. I have not done any testing yet except to see how smooth the gear operates. It becomes quite sticky and I marked out a quarter of the worm gear disk as useable. That’s ok as it represents 6 hours of continous tracking and it is very fast to backtrack with the controller to the beginning of the “good” section of the worm gear.

The mount makes provision for my imaging camera (normally a Canon 600D or modified 350D) with a set of Canon and Tokina lenses. Tracking is done with a webcam mounted on a Canon lens. The rest of the setup is described in previous posts.

Tracker-2226

Tracker-2223

Tracker-2225

I will now try some bench testingĀ  to see how accurate this mount will be. I will also have to re-calibrate the stepper driver to get the correct stepping rate for the specific gear ratio (1:269).

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6 thoughts on “DIY Autoguider for Long Exposure Astrophotography (Part 2)

  1. Pingback: DIY Autoguider for Long Exposure Astrophotography (Part 3) | stars*in*photos

  2. Pingback: Building a new Astrophotography Tracker Mount | stars*in*photos

  3. Lasse Lolk Larsen

    Hey.
    Love your blog on your sky tracker. I’m thinking on making my own tracker but i’m having some trouble with the calculation of gear/motor/earth rotation. How do you do that?

    Kind regards-
    Lasse Larsen
    Denmark

    Reply
  4. Theo Post author

    Hi Lasse,

    The tracker assembly is like a gear box. The objective is to let the RA shaft rotate once every astronomical day.
    A small stepper motor is used with a gearbox (worm gear and belt drive with combined gear ratio of ~400). The stepper is a 400 step motor and the electronic driver (Big Easy Driver) allows for a 16th step micro stepping mode. This allows me to run the stepper at 400*16 = 6400 steps per revolution. A single step of the stepper motor will turn the 20mm steel shaft approximately 0.892 arc seconds. The rotation of earth is 23 hours, 59 minutes and 4.09 seconds. I have calculated the delay period between individual steps to be in the order of 0.0328 seconds. It can be worked out exactly if you know the ratio of the “gearbox”. This may sound difficult to achieve but with an Arduino processor it is quite simple. Let me know if you need more help and I will try my best.
    Good luck,
    Theo

    Reply
  5. anantkale711

    Hey
    Really amazing work!
    I too really enjoy building things and got some great ideas from your blog.
    I am actually planning on making a worm gear pair myself for my goto telescope(http://thethinkerundertherock.blogspot.com/) I am in the process of upgrading my telescope. Which stepper did you use?
    I saw some of the astropics that you took and they are crystal clear! I use a motorized barndoor tracker but its never as good as yours. Which software do you use for image processing.
    If I use ISO 600-800 and use only 30 sec exposures, still the entire image becomes orangish and very saturated. The camera I am using is an old nikon D70s with a 55mm lens.

    Reply
    1. Theo Post author

      Hi there,
      I used a stepper motor from Australian Robotics.
      http://www.australianrobotics.com.au/products/stepper-motor-60-ozin-400-steps-rev
      You will be able to download the specifications of the stepper motor from their website.
      I generally take as many light frames as I can (or have time for), a few dark frames and then process the best images with DeepSkyStacker (http://deepskystacker.free.fr/english/index.html ). This software is free and used by a large number of astrophotographers.
      I don’t process the resulting stacked image with DSS but sometimes I just increase the saturation a little bit before I save the image for further processing in Photoshop CS2 and Lightroom 4. I think that your problem with orange saturation may be to do with light pollution. Try to get away from the city lights to a dark spot and you will see a huge improvement.

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