[ATM] Re: Question About Dobsonian Design

["Lee Buse" <lcbuse@comcast.net>]

It is possible to do both.  I use an 1/2 inch thick idler wheel with
ball bearings that is driven by a motor from the rocker box. The idler
wheel, in turn,  slides, using ebony star laminate, on the Teflon pads
attached to the base. No clutches are necessary and you can move the
scope manually anytime you want. I use a similar arrangement for the
vertical axis that works about as well.
Lee


> Date: Fri, 1 Apr 2005 23:21:34 -0500
> From: "Michael Wolfson" <m_wolfson@rogers.com>
> Subject: [ATM] Question About Dobsonian Design
> To: <atm@atmlist.net>
> Message-ID: <023201c5373b$7491d680$6400a8c0@statcan.ca>
> Content-Type: text/plain; charset="iso-8859-1"
>
> 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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