Changes between Initial Version and Version 1 of MaintenanceFeb2020


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Timestamp:
Jul 30, 2021, 7:41:27 AM (14 months ago)
Author:
trac
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  • MaintenanceFeb2020

    v1 v1  
     1== New Dome Motor ==
     2
     3In January 2020 we suffered a failure of both the telescope and dome, with neither one being able to move.
     4Investigating, we discovered that the dome motor was tripping the circuit breaker (located in the larger electrical box in the dome, to the left of the DC !MaxDome box). We removed the motor, gearbox and wheel assembly from the dome and brought them down to investigate the issue.
     5
     6We discovered that the motor was burned out, and needed replacing.
     7We had to use a hydraulic jack to remove the wheel from the gearbox shaft, as it was impossible to remove by hand. Over time the wheel had slipped down the gearbox shaft, to the point that the edge of the gearbox was cutting in to the rubber wheel.
     8After removing the wheel I was able to open the gearbox, and found it was in remarkably good condition, with the only issue being an oil leak.
     9
     10To bring the dome back in to service we ordered a new motor, a ½ hp Marathon AC motor (model no 5KC42GN0018X) from [grainger https://www.grainger.com/product/21YZ93]
     11We also ordered oil for the gearbox (Mobil 1 synthetic gear lube 75w-90) and [https://www.grainger.com/product/38R340 gasket material] to replace the gaskets.
     12Finally, I ordered a [https://shop.servicecaster.com/10-inch-rubber-drive-wheel-p/scc-rss1030-1-kw-2ss.htm replacement wheel] from servicecaster.com. It’s a 10”x3” rubber wheel, with a 1” keyed bore.
     13
     14The gearbox/wheel is held against the dome by a spring.
     15To mount the gearbox to the dome, undo the nut that’s constraining the spring and remove the nut, washer and spring. The spring is not under any force when the nut is at the end of the bolt, so you don’t have to worry about it flying off.
     16You can then swing the mounting plate for the gearbox forwards and secure the gearbox to it. We used 5 washers to help space the wheel off of the gearbox, and prevent the gearbox cutting in to the rubber.
     17Install the wheel on to the gearbox shaft (you can do this before mounting the gearbox, but it adds considerable weight to the gearbox), and tap in the key.
     18Swing the mounting plate back in to position against the dome, reinstall the spring and washer, and tighten down the nut.
     19
     20The motor mounts to the gearbox. Install the gear towards the end of the motor shaft, insert it into the gearbox and then attach the 4 bolts to hold the motor on to the gearbox.
     21Note that if the motor is attached to the gearbox, you won’t be able to swing out the gearbox as noted above to mount/dismount it. The motor is just long enough to hit the dome wall when you try.
     22
     23We had to get electricians from facilities to install the motor for us as it’s not straightforward to get it to run in both forwards and backwards directions. It required installing an extra relay to properly reverse the motor wiring. Marco Rodriguez performed the work.
     24
     25== Telescope !Balancing/Greasing ==
     26
     27We discovered that the telescope was not moving because it was shaking/juddering while moving, and this was shaking loose the set-screws on the RA motor.
     28We found that physically pulling against the direction of motion stopped the shaking, but pushing in the direction of motion had no effect.
     29We disconnected and removed the torque motor from the telescope, and verified that this was still working. The telescope showed no difference in behaviour with the torque motor removed.
     30We rebalanced the telescope in the RA direction, but this had no effect on the issues.
     31Finally, we re-greased the RA gear and worm gear. The telescope manual calls for annual regreasing, but Jon H. didn’t think this had been done in recent years. This immediately improved things. For future reference, the recommended grease is a molybdenum disulfide (moly) grease. I ordered some off of [https://www.grainger.com/product/6ZKW4 grainger].