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Adjustable magnetically attached counterweights for steel dobs.
Using a finder scope or large eyepieces on my 16” Lightbridge caused big imbalance. The need for a counterweight is clear.
This magnetic counterweight incorporates a battery and solves a second problem:
The second problem with dobs is conveniently getting power to the dew heaters and primary mirror fan. This counterweight uses a 12V battery (for power and mass) that makes the wiring to the fan and the dew heater very simple. The battery can easily be removed for swapping out and charging.
Magnets are used to make it easy to reposition the counterweight, depending on what’s at the top of the scope. Simply slide the counterweight up or down the scope.
See pic Counterweights 002 fitted (you probably need only one counterweight for a 12” dob.)
Each counterweight consists of:
• a 12V battery sandwiched between
• two pieces of timber
• a couple of magnets (from a dead microwave) to hold it to the scope
• some “rubbery” drawer liner material (to stop the magnets scratching the scope and give grip)
• fasteners to hold it together (T-nuts, threaded rod and threaded knobs) and
• a handle for convenience
See pic counterweight disassembled.
Magnets: You can pick up a dead microwave on council clean-ups. All microwaves contain 2 strong donut shaped magnets. These magnets are in the magnetron which is encased in metal and is close to the chamber. (Not the transformer, the other large part.) To get the magnets out, remove the microwave’s cover. Prise open the magnetron’s metal case. Pliers may be best.
TIP #1: definitely avoid putting a screwdriver through your hand when prising!
TIP #2: When you get the magnets out, do not test how well they attract – they will drag themselves out of your hands and smash. The pieces can’t be glued together again.
After that construction is pretty straightforward. Araldite glued the magnets to the timber, and silicone sealer attached the draw liner to the magnets.
TIP #3: Don’t put the magnets on the ground, they will pick up stuff that scratches your scope.
Ideally the counterweight should be positioned in the same plane as the elevation axis so that it is independent of the scopes elevation. In practice, this wasn’t a problem - I do not use the “brake.”
Questions welcome, but response might not be quick.
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