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Friday. Cold, grey and windy. I decided to look at the RA drive worm to try and reduce backlash. The strong spring I had used was either on or off. 15lbs to achieve midway stretch. So I found another spring in my marmalade jar collection of springs.
This one took only 4-5 lbs to stretch half way measured on the fisherman's "spring balance." I duly fitted it in place of the stronger spring but gained nothing obvious. The stepper motor still stalled if I tensioned the spring too much. So I slacked it right off until there was no stretch at all. And still the motor stalled going both ways in RA.
Another asymmetric balance problem methinks. The telescopes wanted to match the counterweights for level. One on either side of the PA. They should balance completely irrespective of position or pointing angle. This needs urgent attention with the clutches let off.
Another asymmetric balance problem methinks. The telescopes wanted to match the counterweights for level. One on either side of the PA. They should balance completely irrespective of position or pointing angle. This needs urgent attention with the clutches let off.
Have paused for lunch and then it is back to balancing and testing for stalls on slews. Fortunately the "Simple handset" [paddle] is all that is needed to slew the mounting. No laptop, computer or IH2 required. More on this later.
Completely freeing the worms was essential, as usual, rather than just the clutch screws. There is still too much friction on the shafts even with the clutch screws loosened. The clutches are simply plastic plugs pressed against the shaft by three radial screws in the wormwheel boss. Originally supplied with only one clutch screw by Mount Beacon.
The balance proved to be fine with only a very slight bias in favour of the telescopes. I tried hanging very small weights off the counterweights on a cord but it made no difference to the RA motor stalling.
Gently "helping" the telescopes in either direction also has zero effect on stalling. It's not an inertia thing either. Stalling often occurs mid slew rather than at the beginning of a paddle button press. I am using white grease to lubricate the worms and it seems to remain in place. The motors do not [usually] stall if I allow some backlash. The stalling problem is due to my desire to avoid any "slop."
Thanks to the 50mm bore, self-aligning, flange ball bearings, friction is very low on both axes when freed from the drag of the wormwheel clutches. I can only assume that there is variable friction between the contact surfaces of the worm and its wormwheel. Perhaps I should lap the worm against the wheel for a few hours? Perhaps make up a simple jig for the lathe? There isn't much room for a motor to drive the worm in-situ. Though it would make most sense to lap the worm while still attached to the mounting. The geometry between the worm and wheel would change under any other circumstances.
Completely freeing the worms was essential, as usual, rather than just the clutch screws. There is still too much friction on the shafts even with the clutch screws loosened. The clutches are simply plastic plugs pressed against the shaft by three radial screws in the wormwheel boss. Originally supplied with only one clutch screw by Mount Beacon.The balance proved to be fine with only a very slight bias in favour of the telescopes. I tried hanging very small weights off the counterweights on a cord but it made no difference to the RA motor stalling.
Gently "helping" the telescopes in either direction also has zero effect on stalling. It's not an inertia thing either. Stalling often occurs mid slew rather than at the beginning of a paddle button press. I am using white grease to lubricate the worms and it seems to remain in place. The motors do not [usually] stall if I allow some backlash. The stalling problem is due to my desire to avoid any "slop."
Thanks to the 50mm bore, self-aligning, flange ball bearings, friction is very low on both axes when freed from the drag of the wormwheel clutches. I can only assume that there is variable friction between the contact surfaces of the worm and its wormwheel. Perhaps I should lap the worm against the wheel for a few hours? Perhaps make up a simple jig for the lathe? There isn't much room for a motor to drive the worm in-situ. Though it would make most sense to lap the worm while still attached to the mounting. The geometry between the worm and wheel would change under any other circumstances.
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