My EQ8 works very well, but has some dec backlash that cannot be adjusted out due to slight (bearing?) runout. It is easily managed by adding bias weight to ensure that the worm always meshes with the wheel on one side of the gear teeth. If this is done, there is no undefined backlash region and it guides very well.
However, that requires that I be there to change the weight bias when doing a meridian flip - possible but annoying. So I made up a spring device that applies a consistent torque to the dec axis to keep the gears firmly meshed regardless of the dec angle. It now can easily handle meridian flips without my presence.
Pleaser don't laugh, but the kit itself is self explanatory from the images, consisting of some copper waterpipe to hold the spring and shaft from a window blind, the spool and bearing set from an old fishing reel (driven by the spring loaded shaft) and some fishing line wrapped around the spool. the fishing line also wraps around an old record player turntable platter that is sandwiched between a short dovetail bar and the main OTA support bar - the fishing line transfers reasonably constant torque from the spring to the dec axis. The spring was initially tensioned up by rotating the spool to the point where it provided just enough torque to reliably move the dec axis in any scope position. It has worked without intervention for about 20 hours to date and makes the system easier to use, with very good dec guiding behaviour(particularly in wind). The drive motor is huge and gives no indication that it is even aware of the slight added torque.
I measured/calculated the required torque before building the thing, but found that it was occasionally unable to overcome axis bearing stiction with the heavy-handed bearing preload setting that came from the factory. That turned out to be easy to fix - remove the main cover plate, loosen the three set screws holding the bearing retainer nut and carefully thread the rubber strap from a small strap wrench around the nut to loosen it slightly for adjustment (be careful of the wires in the way).
something like this could possibly be used on other systems that do not have spring loaded worms (EQ6, G11 etc). It turned out to be quite easy to make using stuff that I had lying around and now the mount tracks a little better, as well as leaving me asleep while it does meridian flips
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thanks for reading. regards Ray
That is a fine/basic piece of engineering , pat yourself on the back Ray .
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