Thursday, July 15, 2010

Construction Details: Meade DS Motors on Vixen Great Polaris

I've written this documentation on how I mounted the Meade DS motors to my Vixen Great Polaris equatorial mount. My key constraint was that I do not have ready access to a variety of metal brackets, and I don't have much in the way of metal-working tools. All the metal-cutting for this project was done using a Dremel with a carbide cutoff wheel.

First: the dimensions of the Declination and Right Ascension mounting plates. These can be made of sheet aluminum of appropriate thickness, or, in my case, I used angle aluminum for extra stiffness.

Also, I re-did the Declination mounting plate by extending it opposite the motor so the plate would "grip" the dovetail saddle and be more secure against rotation, since it's secured by a single bolt.

Here is a detailed view of the Declination mounting plate:

The Declination mounting plate from the other side, showing how the motor is mounted (using ordinary bolts going through holes in the motor casing) and the 6mm shaft coupler. The DS motor shaft is more than 6mm in diameter, so I had to file it down a bit by chucking it in a drill and pressing a file against it while the drill was spinning.

Also, the shaft on the Great Polaris is slightly less than 6mm diameter, so I had to put in some flat tie-wire inside the coupler so that it wouldn't slip. Note that my couplers are friction-fit (the set-screw doesn't bear on the shaft but instead tightens down the entire coupler hole) and if you're using a set-screw coupler, you will not experience my troubles.

Here is the Right Ascension mounting plate. I had to put one-and-a-half thicknesses of 9mm plywood so that it was mounted just the right distance from the (original) RA motor mounting area, so that the DS motor's shaft aligned with the RA shaft. I got the half-thickness of plywood by splitting the plywood edgewise with a kitchen cleaver.

Another view of the Right Ascension mounting plate. I drilled a couple of holes in the Great Polaris itself in order to secure the plate. Since my GP is old and cost $200, I didn't feel too bad about putting two small holes in it.

Yet another view of the Right Ascension plate, showing the one-and-a-half thickness of 9mm plywood.

I used a plastic box that I found in an electronics shop to hold the connector panel. The box is screwed into my plywood 6" half-pier. The half-pier is needed because I live at a very low latitude (1 degree North) and the Vixen SX pier costs as much as my entire GP mount!

1 comment:

orly_andico said...

Update: the straight brackets cause mount collisions in certain areas of the sky, e.g. the Northern sky above about 40 degrees of altitude.

So this mechanism isn't desirable. I will have to revise it.