My Exploradome came with plastic ring segments that go under the dome skirt to keep the dome from lifting in strong winds. The dome is actually quite aerodynamically stable, as well as being heavy, so I have seen no tendency for it to lift. However, given the value of the equipment it is protecting, a retention system is a good idea.
This photo shows one of the retention ring segments lying on the roof below the dome skirt. The retention ring is about 2" wide. Because of the poor fit of the roof panels, there is only 1" clearance between the done skirt and the upturned inner edge of the roof panel. There was a lot of bending and rubbing, and the ends of the ring segments would catch on the corners of the roof panels in places.
As long as I was using the big geared DC motor supplied by Exploradome for rotation, there was unlimited torque available, and the motor was able to force the dome around anyway. However, when I switched to a stepper motor for rotation, the available torque was much less. I had to remove the retention ring to reduce drag.
Keeping the dome on in storms has never been a problem. I had installed removable tie-down turnbuckles that have successfully held the dome on through hurricanes. But they have to be removed before
flight using the dome, so I was always concerned about a wind coming up while the dome was open. (The yellow cord attached to the bottom of the turnbuckle tethers a shorting plug, which, when inserted into the rotation controller, tells it to refuse all rotation commands.)
I considered modifying the original retention rings by cutting them down. However, that would have taken a lot of fiddly work with jigs and a jigsaw, plus they are a pain in the butt to install.
My solution was to install aluminum brackets on the inside of the observatory. They are attached to the roof framing, and have a 90-degree bend at the top that goes over the ring gear. I would have been happier if I could have made the overlap at the ring gear larger, but the radius of the dome varies by several inches, and there isn't room for anything that extends past the ring gear itself.
The brackets will hold the ring down. The dome itself has to be secured to the ring in order to prevent it flying off. I had always had a couple of screws holding the dome to the ring, just to prevent it rotating relative to the ring. I added six more, for a total of eight, to actually provide some significant hold-down force in the event that it tries to lift. Because there is no access to the underside of the ring to install nuts onto bolts, I used self-tapping screws into pre-drilled holes.
This modification gives me peace of mind when a wind comes up while I am doing unattended imaging.
Edited by kathyastro, 30 November 2020 - 09:36 AM.