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.
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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". |
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Fortunately for me my neighbor owns a Bridgemill and doesn't mind me using it. |
| Another shot of the shaft during turning. |
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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. |
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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. |
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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. |
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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. |
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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. |
