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  1. I'm in the planning stage for my own observatory and have been looking at Roll-off designs, but am now having a think about a possible DIY dome. My design would be based on a geodesic. At present I am thinking about how the dome rotation would operate. Having looked at several online dome builds, most people seem to sit the dome on a circular base, which either rolls on casters mounted on the walls somehow, or the base actually has the casters which roll on the top of the wall in some way. For the sake of discussion, let's imagine that there are two circular rings, one on which the dome rests and which has 6-8 casters on the underside that roll on an identical circular ring attached to the building walls. When I exert a tangential force on the dome in an attempt to rotate it, it seems to me that the dome will actually want to move sideways (not rotate), which several online sources seem to confirm. People seem to solve this issue by making the castors roll on some kind of track, or they fit guide casters to keep everything in the right place, essentially forcing rotation. So, because rotating is not the natural tendancy of the dome, it seems to me that the caster wheels are continually being forced to steer round a curve when actually they just want to go in a straight line tangential to the circular rings. Thus, I would expect them to kind of skid a bit as they operate, a bit like a bicycle might do if it had to follow a circular path but I wasn't allowed to turn the handle bars at all. (Actually, the bicycle probably wouldn't be able to follow the path in that case as there would be no guide force to make it skid). This leads me to believe that flat bottom wheels would be a bad choice because they'd create too much friction and make it hard to turn the dome. Much better wheels would be rounded ones (donut-shaped) that have minimal surface area in contact with the rolling surface so that skidding friction is kept as low as possible. Is my thinking logical here, or am I just not on the right track at all? Assuming I'm understanding what is going on well, it seems to me that the best thing I could use would actually be spherical ball bearing castors (think like mouse ball) that could rotate however they needed to help the dome rotate with minimal friction. I'd be looking to automate the dome rotation later, so having something that moves easily would be fairly important given that I'd probably go for a friction drive wheel. Does anyone have any experience here or a good understanding of the mechanics involved to give some good advice on how to make the dome easy to rotate? David
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