Motorized Observatory Roof

When I first built my observatory it was a breeze to roll off the roof. Of course that was before I finished all of the boxing and trim but even after that it was manageable. Over the past year and a half the 4x6 rails that support the roof have twisted and warped a bit. That's made it harder to operate. This year I decided to add some light insulation and an AC unit to keep my equipment in better condition through the hot and humid Texas summer. This was the last straw. I needed a better way to roll the roof. I had seen many plans for roof openers based on garage door operators and on winches with cables but I really wanted something a little cleaner with a small foot print. I had seen the gear rack opener that Backyard Observatories sells but it's pretty expensive so I decided to build my own. The total cost for my solution ended up being a bit over $200.
 
I saw in my Harbor Freight flyer a 110V AC reversible hoist that looked about right on sale for $59. This is the "440 lb" hoist. This rating is based on doubling the hoist cable so it's really a 220 pound straight line hoist. I removed the spool and found a hexagonal shaft. I opened the gearbox and removed the shaft.
This is what the shaft and bearing looked like once removed from the hoist. I had found a spur gear from McMaster-Carr (part # 5172 T32) with a 5/8" bore so I needed to turn down this shaft to 5/8".
Fortunately for me my neighbor owns a Bridgemill and doesn't mind me using it.
Another shot of the shaft during turning.
The finished shaft. I cut off a couple of inches of it on my horizontal bandsaw.
The shaft with the gear in place. I had to drill and tap two 10-24 set screw holes in the gear. Then I repacked the gearbox with lithium grease and reassembled the hoist.
The gear rack arrived a few days later from McMaster-Carr (part # 5174 T23). The rack comes in 6 foot lengths. My observatory is about 12 feet long so I needed two pieces.
I drilled holes for the 1/4" lag screws that I would use to secure the gear rack to the rolling observatory roof supports.
I cut the second piece of gear rack to length and installed the rack onto the interior rolling roof support. I had to add a 2x2 wooden support to get the rack clear of the bolt heads and tye-down hardware that were already installed.
I devised a limit switch arrangement. Not an absolute essential but a good idea in case my attention should waver while operating the roof.
A close-up of the limit switches. These are 120V/5A snap-action switches purchased from a local electronics supply house.
All done. The opener works fantastically. The speed is just about perfect. It take about 30 seconds to roll the roof off. The only real issue is the start-up jolt. It is so strong that it shakes the walls a good bit. I would like to add some sort of soft-start circuit but I don't think this would be a trivial undertaking with an induction motor.
Addendum. To get the limit switch working properly in both directions I needed to locate the second limit switch in the circuit between the cap and the switch that were in the controller. So, I cleaned it all up by moving this stuff into a new box that's permenantly mounted on the wall. Here is a crude circuit.

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