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Russ,
Thanks, I've been looking for something like that for my lightweight eclipse mounting and my Polarie. I've been thinking about custom making one for some time. Thanks for the hint. I found a possible supplier (Profilium) on line. I'll give them a try first rather than put you to the trouble of having to freight the stuff to me.
When you make that double arm drive, get in touch. I have an excel spreadsheet for optimizing the dimensions and modelling the error profiles of the type 4 isosceles platforms. It isn't very user friendly. I didn't make it for distribution so it needs a fair bit of driving.
Many years ago, I came up with a modification to the type 4 that greatly increases the drive time to almost 4 hours with theoretical ±1 arc sec drive error, plot also attached. I have my doubts that it would be quite that accurate unless you were very precise with the construction but even if you fall a bit short it would be pretty amazing.
I would be happy to optimize a set of construction dimensions and produce an error plot for you. I've attached a couple of examples of the sort of performance you can get from a type 4.
cheers
Joe
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