Thursday, September 07, 2017

The Barndoor Tracker Revisited

Well, I got a chance to put the Barndoor Tracker to use this summer. On August 21st, I was privileged to observe the Great American Eclipse from Glenrock, WY. The weather was sparkling, except for some high, wispy clouds that showed up just in advance of the eclipse and continued to grow a bit right after. However, photographic opportunity was perfect and the eclipse occurred right on schedule.

In advance of the eclipse, I did a considerable amount of testing and work to get the tracker properly aligned to track the sun. I learned a lot about both astrophotography and the tracker. One thing is that the tracker has got a bobble to it. It tracked ok but not perfectly. The sun stayed in frame but it would move a bit from one picture to the next. I was taking pictures every two minutes and the sun would move one way and then the other. I think that there were two things that contributed to this. One was that the geometry is too complex. I plan to rebuild it this winter to align the pivot points with the lead screw. This will get rid of some of the calculations needed and also will make it easier to get the pivot points straight. That leads to the other possible problem, that at least one of the pivot points is not straight, which makes the door open at an inconstant rate.

The other thing I learned about the tracker was how to get it aligned. I had to do it the night before by sighting on the North Star (Polaris) with my camera attached to the tripod and shooting a timed exposure of about 30 second. Then I zoomed in on the image and adjusted the tripod to get the star to align perfectly with the center of the image. When this was correct, and the tripod was completely locked down against movement, I retired and, in the morning, attached the tracker to the tripod without disturbing it. After this, it tracked quite accurately, except for the aforementioned wobble.

So the other day I was at the Fry’s here in Wilsonville, Oregon, where we are visiting now that the eclipse is memory and photos, and I bought a Raspberry Pi. I guess I will be exploring this next and figuring out what I can do with it. Fun.


Friday, May 19, 2017

Barndoor Tracking Mount Part 5

The tracker is pretty much finished now and has been field tested with excellent results. The electronics are mounted on the bottom and covered by a shell, the lighting has been added where it is visible from the top, and I have added bubble levels to aid in getting the platform level and at the proper angle for the latitude. I have run some test programs which run the platform through some known angles and it came out spot-on. The only difficulty I have had is in setting up the tracker on the exact polar axis. So far, I have not used it in a location where I could see Polaris. I have used a compass and measuring angles with my phone to set it up, with mixed results. There is a little movement of the images but not much, many because I performed mostly short exposures. However, to aid in this setup, I have added two bubble levels. One is attached along the long axis to get the bed level. The other is adjustable on a protractor so it can be adjusted for the current latitude. Then I should be able to use the bubbles to set the correct angle. I would still need Polaris to site on or a compass to get the azimuth angle correct. This would also have to be the way to set up in daylight (as I will be using this tracker during the solar eclipse this summer).

Here are some final pictures.

Bubble Level

Bubble Level

Completed Tracker

Completed Setup in Test