I have put a discussion of why this is an issue on a separate page.
I have two telescopes mounted side by side on my GEM and this causes problems with balance when I swap OTAs because, as well as balance about the RA axis, I have two directions to adjust to get the declination balance correct. This is supposed to be done by sliding the two telescopes and the saddle on which they ride through their respective dovetail clamps. This involves loosening the clamps which in turn encourages the assembly to fall off the mount. Preventing this fall presents some difficult times and small adjustments are very difficult. I need to be able to add extra adjustable weight. However, I am close to the maximum weight recommended by the manufacturer so I am reluctant to adjust the balance by adding weight to the telescope side of the mount. But the manufacturer says I can add as much weight as I like on the balance-bar (as long as I maintain balance about the RA axis). The problem is how to add that weight off axis. After a suggestion from one of the customer-service technicians at the manufacturer, I came up with the following solution.
|Figure 1||Figure 2|
The counterweights are secured to the balance bar by a bolt that passes through the edge of the weight. These are metric 8-mm bolts with a plastic knob at the top. I removed the bolt and substituted an 8-mm threaded rod onto which I could mount a weight. The pictures above show the result of my first prototype arrangement. I could not remove the knobs from the original bolts so my initial solution is to use wing nuts locked onto the threaded bar. (I have ordered some suitable knobs but they are coming from China so may be a while.) The weights are 1.1 kg training weights I happen to have lying around; their central holes are much too big so I made wooden inserts with 8-mm holes in their centres. They are held in place by a nut on each side (figure 1). The arrangement shown in figure 2 is what was needed to balance an extra DSLR camera and lens that I added on top of the RC.
I had hoped I would not need to have the rods any longer than this, but I suspect that I may substitute longer ones when the plastic knobs arrive. I thought I would need two balance weights (one on each of the original weights supplied with the mount), one to correct an error in the positions of the telescopes, the other to correct for an error in the positioning of the saddle. However theoretically one will do since its position can be adjusted around the rod. I shall experiment to see which is easier once the plastic knobs arrive. I have an extra 5-kg weight which can be seen in figure 2 which is needed to balance my heavy loads.
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