Telescope Reviews: Dome automation hardware

Ok yesterday I said I would post some pictures of the dome rotation sensor relocation for my Sirius dome. I hope that Tomo will forgive me my posting all this to his thread.

First I will give a little background. The Sirius dome rotation is done by a 24 volt gear motor (running at 12 volts. This motors are commonly used as window motors for cars. Sirius uses a righthand side motor) that drives a flat gear attached to the dome. The flat gear can be seen at the top of the image. (Note the gears). I also strongly recommend you cut a hole in the dome lip as shown in the picture. This will allow you the tighten the dome wheels in the future without having the lift the dome off the walls in order to get to the screw on the wheels. I cut my hole near the door area. When the dome is put back together the hole is covered my the black retaining piece so it's not seen anyway.

The next picture shows my spare rotation motor. Notice the white area on the shaft above the gear. The other half is black (not shown). This will present a while/black pattern to the sensor so the controller can count the motor revolutions in order to keep track of the dome's position.

If this area is not painted or taped correctly or the sensor is misaligned so it doesn't see the alternating white/black sequence the dome will not operate correctly. The symptoms range from improper and inconsistent dome positioning to the dome stalling during manual or computer controlled rotation.

The factory installed location of the sensor is behind the motor box between the dome wall under the gear. This location makes it vary difficult to service the sensor (realign, clean grease off of it, etc.) I have had to realign my sensor a couple times as it is only held in the stock location by a single screw. Over time the vibration of the dome rotation can cause the sensor to slip and point downward, away from the white/black target on the motor shaft.

To correct this problem I moved the sensor from behind the motor box to inside the motor box. The problem here is there is no exposed area on the motor shaft to paint a white/black target. After I built the LesveDome controller I learned a few things from that design. That design uses magnets on the drive reduction gear. So I removed the plate that covers the reduction gear and made a new cover out of cardboard.

While the cover was off I painted an area on the white plastic reduction gear black. This will present the required while/black pattern to the sensor. I cut a hole in the cover over the gear area. I then covered the cardboard with duct tape to protect it. The sensor was then mounted to one of the gear cover attachment screws on the motor via a small "L" bracket purchased from the local hardware store. Since the reduction gear is attached to the other end of the gear shaft that had the original white/black target the number of revolutions per motor turns didn't change. My dome sees 228 white/black patterns per one full revolution of the dome.

When the motor box cover is put on the sensor is shielded from stray light that might interfere with the white/black pattern. This picture is a wider view of the motor inside the factory motor box.

The last picture is just the reduction gear cover used as a template for the replacement cardboard cover.