Re: [ATM] How to find Centre of Gravity of an existing telescope

[Dale Eason <atmpob@yahoo.com>]

While another has answered the question as to how to
find the COG they did not answer what happens if your
COG does not meet the table conditions.  It will not
create an optical alighnment or tracking problem.  It
will create a telescope falling off the table or both
tipping over problem.

Dale Eason

--- Bruce MacDonald <brumac@gmail.com> wrote:

> I'm starting to work on making a poncet (equatorial)
> platform for my
> existing commercial 10" dob.
> 
> My starting point is here:
>
http://home.wanadoo.nl/jhm.vangastel/Astronomy/Poncet/e_index.htm
> 
> Before I even start planning, though, I'm up against
> this:
> 
> "As shown in figure 1 the virtual polar axis passes
> through the axis
> of the altitude bearings. Idealy this axis passes
> throught the center
> of gravity of the telescope-dobsonian mount
> combination. In most cases
> these points will almost coincide. If the virtual
> polar axis passes
> through a point too far above the center of gravity
> the motor will
> have to push the telescope uphill. It is not
> unlikely that the
> movement will stop. If the virtual polar axis passes
> through a point
> too far below the center of gravity, the telescope
> will be top-heavy
> and, in the worst case, will fall from the platform
> in its most
> extreme (East or West) position. "
> 
> Questions:
> How does one go about determining the CoG of the
> telescope/mount combination?
> 
> Once found, assuming that the CoG does NOT coincide
> w/ the altitude
> axis, what are the consequences.  I still need to
> build the table so
> that centre of curvature of the arcs is the centre
> of gravity,
> otherwise we have the problems mentioned above.  If
> the altitude axis
> is significantly distant from the centre of gravity,
> will the ability
> to track be compromised?
> 
> I can always raise or lower the centre of gravity by
> adding or
> removing weight either above or below as necessary,
> but in any case, I
> still need to figure out how to find the centre of
> gravity.
> 
> Thanks,
> Bruce M
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> ATM mailing list http://www.atmlist.net/
> 



       
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