Re: [ATM] Gimbaled Secondary mirror

["Bob May" <bobmay@nethere.com>]

The reason for a 3 point mount is easy.
Three points define a plane.  This plane can be moved about without any loss
of accuracy or "looseness" in the system and doesn't require the
compensation with other points to do a move.
For example, the next number requires the push by one actuator and the exact
same pull by the other actuator to do a move.  If you fail to provide the
exact opposite motion, the surface is stressed by the motion being different
between the two actuators and this ends up with an incorrect motion at the
best and a deformed mirror at the worst.  You can compensate for this a bit
by putting springs on the opposite of two actuators but if you don't provide
a center point (making it a 5 point mount) you then end up with complex
motion calculations to do the job.  In addition piston motions become a bit
more difficult.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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