RE: Mel's TriDob (was Re: ATM Oregon Star Party telescope walkabout for 2002)

[Benjamin Robbins <benjaminr@highwire.com>]

Here is the link to "Jane's 16"

http://www.tms-usa.com/grayarea/janes16/jane16.htm


 -----Original Message-----
From: 	John Sherman [mailto:shermj@netzero.net] 
Sent:	Wednesday, September 11, 2002 1:41 AM
To:	atm@shore.net
Subject:	Re: Mel's TriDob (was Re: ATM Oregon Star Party telescope
walkabout for 2002)






Hi List,

>
>The genius of the flex rocker is that it moves the requirement and
>subsequent construction efforts from the rocker to the ground track.

For those who asked what a flex rocker is. Most dob mounts have three feet
on the bottom to make up for uneven ground. They have four altitude bearings
supporting the weight of the tube. Somewhere in between has to be a piece
that is stiff enough to convert the four points of weight into three points
of support. Usually it is the rocker box. Many of you have seen very flimsy
looking groundboards under a stiff rocker box. The three pads are directly
over the feet, so the force is transmitted directly from the pads to the
feet. But if the stiffness is built into the groundboard, then the rocker
box can be built very flimsy. All that is really required is that you have
four azimuth pads, each right under an altitude pad, and a means to hold
them there. The force on each altitude pad is transmitted directly to the
pad below, through solid material. In my case, you can see that each side
panel of the rocker has two pads on top and two on the bottom. One 3/4"
plywood panel supports half the tube. Of course the stiff groundboard will
flex a bit, and it is not perfectly flat anyway. So as the telescope moves
in azimuth, the rocker has to bend to keep all four pads on the ground. If
you can picture one pad out of four hitting a hole and dropping a bit, now
the two side panels are not parallel. One side has twisted, putting a torque
on the rocker, and flexing it. The two side panels do most of the work, the
rest of the rocker structure just has to keep the two sides vertical  (it
would be embarassing to have your telescope come crashing down).  Also my
rocker goes around a regular azimuth bolt, instead of a track.

If you're setting up on a sidewalk, there is no need for the three feet. You
can use the hard, smooth and level surface as the rigid ground board, and
all you provide is the top surface if you need one. This allows you to have
a flex rocker and no groundboard at the same time. I saw a picture of such a
scope on the net a couple years ago, I believe it is called "Jane's 16"
String Telescope".

>Can't predict the action of others, but I
>am convinced that this is the future of dob design

I agree to both things. The flex rocker can be made so flimsy
it is almost non-existent.  Flex rocker, ground ring,


Thanks Mel,

John









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