RE: (ATM) ATM Remember the 'Bigfoot' mount?

[Kerwin Robert <P24493@gegpo7.geg.mot.com>]

>From: owner-atm
>To: atm
>Subject: (ATM) ATM Remember the 'Bigfoot' mount?
>Date: Friday, October 06, 1995 11:09AM
>
>I would like to discuss, ie, receive info about the BIGFOOT mount, a
>German equatorial available from an Arizona builder circa 1986.  I
>wrote then, and was informed that they would not ship out of state
>(?).
>
>It looked a little like a sawhorse, very low to the ground at one
>end.  The 'beam' of the sawhorse pointed at the north pole.  It used
>very large (3" dia ? tubular?) shafts on ultra-high molecular weight
>(UHMW) polyethylene bearings (bushing type).  It was touted as
>strong enough for a 17.5" f/4.5, I believe.
>
>I am thinking of a derivative design for a 12.5" f/8.  Suggestions
>welcome.  I can easily construct a Dob mt, but that is not the point
>of this note.  I am pondering a German equatorial.
>
>Larry Manuel, Calgary, AB.
>

 ----------
Larry,

I purchased a light-weight version of the "Bigfoot" mount back in 1990 (or 
was it '91??) for my 8" f/6 scope.  The Bigfoot mount is made by Pierre 
Schwaar of Phoenix, Arizona.  The version I purchased was similar in design 
to the full-size Bigfoot.

The Bigfoot is indeed built somewhat like a sawhorse, with the north end 
(I'm assuming you're polar aligned :-)) having two legs and the south end 
having only one.  The shafts are made out of ordinary pipe.  In my mounting 
the shafts are 1.5" diameter; in the full-size mounting, I believe they're 
 3". I'm not sure of the bearing material on the full-size mount, but on 
mine  they are made of brass. I think Pierre simply cut a hole of the 
appropriate size in a block of wood, cut it in half lengthwise, then epoxied 
a strip of brass
to the inside of each section.  Wing nuts are used to adjust the amount of 
friction in the bearings by tightening the two sections against the shaft.

The drive consists of a steel worm and a plastic (Bakelite?) sector gear. 
 The sector gear is good for about three hours tracking before it needs to 
be reset.  To reset, you loosen the south polar bearing, which causes the 
sector to unmesh from the worm.  Turn the scope east, re-tighten the bearing 
and you're set.

After using this mount for five years, I have amassed a list of areas for 
improvement:

1.  After years of use, 99% of which has involved stuffing the mount into a 
vehicle in some awkward position, I have found that the sector no longer 
meshes well with the worm.  It seems to work fine at one end of the sector, 
but as the sector advances towards the middle, it unmeshes.  Could the mount 
be warping? Or perhaps the sector is simply wearing out.

2.  The mount makes generous use of triangles as structural members, but 
there is a weak point where the south leg joins the main part of the 
mounting.  This causes some flexure.

3.  The mount was built for a shorter instrument than my f/6 (I don't think 
Pierre builds anything longer than f/5!).  The tube runs into the mounting 
at certain positions.

4.  The motion of the mounting is a little jerky.

5.  The mount is not equipped with setting circles, although you could 
certainly rig something up easily enough.  I usually don't bother with 
circles anyway.

6.  (Kinda nitpicking) The mount LOOKS crude and improvised.  Doesn't matter 
in the dark I suppose.

All in all, it has been a serviceable mounting.  The full-size Bigfoot will 
carry a fast 16-20" scope, though I haven't actually "test driven" one that 
big.  If you would like more information, I would be glad to send pictures, 
measurements, etc..  In fact, I believe Pierre will be at the All-Arizona 
star party in a couple
of weeks, so I could get more specifics on the full-size mounting.

Clear skies,

Robert Kerwin