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Monday 40-43F, cool and grey. I set up a dial gauge to measure the run-out of the PA wormwheel. It has a habit of stalling the stepper motor drive without warning. While it could sometimes be imbalance of the mounted instruments it could also be eccentricity in the wheel. This would casuse tightness in the engagement and raise the friction substantially.
The "teeth" of the wormwheel make it difficult to follow the rim with a measuring tool. I seemed to be getting a 7 thou difference in radius over 180° but can't be certain it has anything to do with reality.
The "teeth" of the wormwheel make it difficult to follow the rim with a measuring tool. I seemed to be getting a 7 thou difference in radius over 180° but can't be certain it has anything to do with reality.
What I should do is pivot the worm housing. Then use a strong spring to pull the worm into the wheel. Provided the pivot is firm enough there should be no loss of drive due to backlash. At present I have to slacken off both motor housing fixing screws. Which is really rather hopeless. There is no control over backlash even if the present spring pulls the worm in tightly.
The worm housing has to be firmly located lengthwise in both directions. Or it might pull itself back and forth relative to the wormwheel. Which would spoil the accuracy of any Goto slews.
The problem was the shallow depth of the 5mm thick, motor housing, box section. The fixing screw had to be countersunk in the lathe to fit into the tight space available against the stepper motor body. I elected to use the original countersunk screw but apply the pivot to the nut. So I used a large headed, furniture nut. The long body provides the pivot in both the support plate and motor box.
Tuesday 21st. Another grey day. The body of the furniture nut needed shortening and reducing slightly to fit tightly in a 7.5mm hole bored in the 10mm support plate. I had to dismantle the whole motor and drive belt assembly to modify the motor box to take the tip of the furniture nut to provide the precise, pivot location. Reassembly and drive trials were positive. No stalling occurred. I moved the earth lead and terminal to another screw to avoid any slack in the motor clamping system.
If I were starting again I would add packing to the motor box to provide much greater depth of material around the pivot. The wormwheel would then need to be moved down by the thickness of the packing used. Though that is easily achieved with a ring of the same material. Another job for a rainy day.
Wednesday promises to be partially sunny. A chance to do some imaging?
The worm housing has to be firmly located lengthwise in both directions. Or it might pull itself back and forth relative to the wormwheel. Which would spoil the accuracy of any Goto slews.The problem was the shallow depth of the 5mm thick, motor housing, box section. The fixing screw had to be countersunk in the lathe to fit into the tight space available against the stepper motor body. I elected to use the original countersunk screw but apply the pivot to the nut. So I used a large headed, furniture nut. The long body provides the pivot in both the support plate and motor box.
Tuesday 21st. Another grey day. The body of the furniture nut needed shortening and reducing slightly to fit tightly in a 7.5mm hole bored in the 10mm support plate. I had to dismantle the whole motor and drive belt assembly to modify the motor box to take the tip of the furniture nut to provide the precise, pivot location. Reassembly and drive trials were positive. No stalling occurred. I moved the earth lead and terminal to another screw to avoid any slack in the motor clamping system.
If I were starting again I would add packing to the motor box to provide much greater depth of material around the pivot. The wormwheel would then need to be moved down by the thickness of the packing used. Though that is easily achieved with a ring of the same material. Another job for a rainy day.
Wednesday promises to be partially sunny. A chance to do some imaging?
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