[ATM] Question About Dobsonian Design

["Michael Wolfson" <m_wolfson@rogers.com>]

Hi.  I'm a relative newbie re ATM.

I'm planning on building a lightweight dob for a 16 in mirror, mainly using aluminum tubing of various sorts.  I already have a Dob Driver II which I'd like to use.

My main question is the necessity of using Teflon bearings.  I've read and reread Kriege and Berry, and I think I understand the principals of friction, stiction, moment arms and such in order to get the "buttery" feel for manual use.  However, I understand that the Dob Driver would be 'happier" on frictionless (i.e. ball) bearings.

Idea -- why not use ball bearings, and develop clutches for the Dob Driver, and adjustable sources for additional friction as needed.  When the scope is being driven by the motors, only the ball bearings would be in use.  However, when the Dob Driver was not at work (via some sort of mechanical clutches that disengage the drive belt for alt, and drive wheel for az), there would be some sort of mechanical clamp (e.g. with a thumb screw or spring) that would press, say 2 square inches of Teflon, against an aluminum surface with an 8 or 10 inch moment arm in alt and in az?  This would then switch the scope into a mechanical mode that reproduces the kind of friction advocated by Kriege and Berry.

Any thoughts or suggestions would be most appreciated.  Thanks -- Michael
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