Mounting encoders on dob base

[Tiotion (Jack)]

Hi all,
Ive got a problem mounting an encoder to the Az axis of my 12" GSO dob. Basically, the bracket holds the encoder a few mills above the pivot bolt, so that the shaft of the encoder does not fit into the pivot bold all the way in. So when i tilt the tube, the edge just nips the encoder and pushes it about 2mm deeper into the pivot bolt. Once it passes, the bracket springs back up. Not a major issue i guess, but over the years this is just going to cause unnessesary wear on the encoder.

The bracket is one supplied by Wild Card Innovations, but this isnt their fault at all. I bought the scope used, and the previous owner had US digital s2 encoders, which are a few mm thinner. In my defence though, the s2 description does say that the s6 superceeds the s2 and to use it rather than s2. When i realised it was a little thicker than the s2 the encoders were already en route to Syd. Whoops!

So basically does anyone know how i can mount the bracket a bit better? Any easily obtainable hardware that could do the job? Or self made brackets?

A cheap and nasty fix is to file down the edge of the tube but yeh...cheap and nasty indeed.

[gary]

Hi Jack,

Thanks for the post.

The encoder installation for the GSO Dobs is designed for the S2 encoders which
have a lower profile than the S6. The lower profile of the S2 series makes them
preferable for many telescope installations and the GSO Dob which provides
minimal clearance is a good example. The S2 is still a current line item and we
stock them ourselves.

On GSO Dob kits manufactured in the past 18 months or so, the far end of the
tangent arm bracket is designed to float on a shoulder screw a few mm
above the inside base of the rocker. In any case, the encoder should mate all
the way into the Az pivot bolt up to the beginning of the threaded section above the shaft.
If the kit does not have the shoulder screw arrangement and the far end of the
tangent arm bracket has been fastened tight to the inside base of the rocker,
you might want to consider providing the tangent arm with a different height.
One way to do this is to remove the encoder from the arm and in a virtual
sense, gently pull both ends of the arm so that the bends are no longer at 90
degrees but at some larger angle. This will then reduce its effective height.
In a practical sense, rather than pulling both ends, one might position the
bracket on the workbench and press down on the apex of each of the bends,
first one a little and then flip the bracket and press down on the the other so that
the sum of the angles remains 180 degrees.

If the encoder is being hit by the OTA, eventually the encoder is very likely to
fail.

On a normal unmodified GSO, even with the encoder mated all the way into
the Az pivot bolt and with the current style floating Az tangent arm arrangement,
there is only a couple of mm clearance so the S6 may never quite fit.

We CNC fabricate custom brackets on demand.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au

[Tiotion (Jack)]

Thanks for your reply Gary. I thought of that, flattening the bracket so to speak. But then the distance between holes on the bracket would slightly increase wouldn't it. May need to muck around with a vice and drill!

[gary]

Originally Posted by Tiotion

Thanks for your reply Gary. I thought of that, flattening the bracket so to speak. But then the distance between holes on the bracket would slightly increase wouldn't it. May need to muck around with a vice and drill!

Hi Jack,

Indeed it will so you will need to reposition the screw at the far end or increase the
length of the slot. Any improvisation that prevents the OTA from hitting the
encoder is a move in the right direction.

Best Regards

Gary

[bobson (Bob)]

The way I fixed the same problem with my GSO 12" Dob. I added 3 peaces of wood approx. 1cm thick bought from Bannings between the base and top part of the mount. This gave me enough clearance between fan and encoders from Gary.

cheers