Return of the Barn Door Tracker

After last time's rather lackluster tracking, I decided to try out the barn door tracker again. I used essentially the same hardware as before, but greatly simplified the electronics. I added another 1:3 gear reduction stage so the final ratio was 1:15, allowing me to run the drive motor faster. Instead of having closed loop feedback with the PID like before, I just used a cheap buck-boost converter from eBay to provide a constant voltage that should keep the motor turning at a fairly constant rate.

I adjusted the voltage so that the final gear rotated at one revolution per minute. Power came from a small LiFePo4 battery.

Battery, buck-boost, and LEGO gears.

With this much simpler setup, I was able to mount everything to the tracker so that when it was running I didn't have to any physical contact with it, which could introduce vibrations.

I took the setup for a spin in my front yard. This time I was able to do a somewhat proper polar alignment since Polaris was actually visible. After a bit of eyeballing, I decided the hinge was close enough in line. I tested taking photos with and the tracker on and off, and after a bit of fiddling, sure enough, the tracker was working. Sure, the stars weren't nice pinpoints, but the trails were significantly reduced.

Tracking off. 135mm f/5.6 20" ISO 400

Tracking on. 135mm f/5.6 20" ISO 400

Finally!

However, the setup was not without its flaws. The whole thing lacked any rigidity, so after handling the hinge I had to wait about five seconds for the whole thing to stop wobbling before taking a photo.

I initially had the drive direction close the hinge over time, but the threads would get stuck in the hole in the wood and the hinge wouldn't close. I swapped the polarity on the motor to drive the hinge open since this would guarantee that the hinge has to move.

There is also periodic error in the drive mechanism. Looking at the movement of the stars in each photo, it's clear the hinge is moving very slightly in axes other than the polar axis. The movement repeats itself every minute (the drive gear turns once per minute hm...), leading me to think that the main drive gear is not concentric with the threaded rod. I did just eyeball the position of the nut and hole on the main gear so it's no surprise.

Wobble wobble.

I tried to do some imaging of the Orion nebula, but only a few frames didn't have any extreme streaking. I stacked the twelve "usable" frames, did some basic editing in Photoshop and got this:

135mm f/5.6 12x10" ISO 800 (and 21 darks)

To improve the setup, I would likely need a much more rigid hinge that wouldn't allow any movement other than opening and closing, so any other wobbling movement from the threaded rod wouldn't be able to actually affect the setup. I also need a better tripod so any movement from the wind is minimized.