Balancing Big Bertha 2.0

Balancing Big Bertha 2.0

Getting a telescope on an equatorial mount balanced is a bit of an operation--and I have not been completely happy with my efforts so far. One side effect of being unbalanced is that the motors just don't have enough power to move the telescope in either axis if they are unbalanced. You can disguise the lack of balance by tightening down the locks on both axes of the mount, but the motors still won't have enough power--especially when the telescope is up at the upper limits of the mount's capacity, as is the case with Big Bertha 2.0 and this Celestron CI-700 mount.

Balancing a telescope on a CI-700 mount involves loosening two clamps and moving the telescope back and forth--but that's harder than it sounds when the tube assembly weighs 55 pounds, and is 6 1/2 feet long. Even worse, when you replace a light eyepiece with a heavy eyepiece, or worse, a camera, the balance changes--again.

A common solution to this problem is to put a balance adjustment weight on a bar that you can move back and forth. I found a somewhat simpler solution. I took two pieces of scrap black nylon, cut them so that they were a bit wider than the bottom rail of Big Bertha, then used a 3/8" end mill to make two slots in each so that they would slide up and down on the bottom rail.


Click to enlarge

Sorry it is such a lousy picture--flash was too bright, and without the exposure dragged on too long.

And here's a full picture of it.


Click to enlarge
I had originally thought of using aluminum or Delrin, but the nylon has the advantage of:

1. It is scrap that cost me almost nothing.

2. Easy to cut and machine.

3. Because of its flexibility (even relative to Delrin), I didn't need to add a fastener to hold it on the rail. It is a friction fit, and I can move it back and forth with a wave of my hand.

I still think the CI-700 mount is too small for Big Bertha 2.0, but at least it tracks objects across the sky okay now. My big problem now is wind, which tends to whip it around a bit. There's less wind on the south side of the house--but perhaps a wind screen or a heavier mount makes sense. Unfortunately, from CI-700 size mounts to the next step up--the Losmandy Titan--is a leap of enormous size. (The Titan mount lists for $6000--far more than I can justify until I get the spare house in Boise sold, and even then, that's a lot of money.)