Mounting update 2: Drive Slew Testing.


Sunday: Dry and 42F: Finally a chance to dismantle the big mounting. I also stripped the stepper motor and worm assemblies and tidied up the motor backing plates. I had left them rectangular and raw after rough shaping. Which prevented the assemblies from being released without withdrawing the axes shafts.

Thanks to fixing the front plate I can now fine adjust the polar altitude angle with the turnbuckle for the first time. The large round aperture in the front plate allows my hand to reach the turnbuckle adjuster. No great effort is required provided I have slackened off the altitude pivot nuts first. I deliberately chose a bulky turnbuckle design to make it easier to turn without tools.

The image shows the PA drive. With 1:2.4 ratio, [14:34] timing pulleys, toothed belt with urethane, jockey pulley, 287t x 11" Ø wormwheel driven by the large, brass, single start worm. The large stepper motor lives in the aluminium box behind the small pulley. The steel flanges on the pulleys are proving rather rust prone. As are the mounting's flange bearings.

Monday is cool but bright. I spent a couple of hours replacing all the worm assembly fixings with stainless steel, hex socket head screws. Added stainless steel spring washers beneath all the nuts to avoid them loosening with motor vibration.

The worm assemblies feel very solid and secure. While [hopefully] looking quite 'tidy' thanks to the sturdy 10mm sections of aluminium plate and the square al. tubing, stepper motor housings. My usual 'belt and braces' approach helps to ensure rigidity. I still have to smooth the edges of the newly cut motor plates. A bench, disk sander would have been handy but an expensive investment for a decent one. Not sure how to apply worm mesh, fine adjustment yet.

The single, tiny grub screw on the Beacon Hill, Declination worm housing could not hold the journal bearing in place. So I drilled the housing close to the bearing. Then added two screws with washers both sides and doubled lock nuts for security. The bearing can no longer work its way steadily outwards during slews. Over-tightening the grub screw merely locked the ball bearing solid so that it could not rotate. Beacon Hill was very mean with the worm shaft overhangs.

The Declination drive, stepper motor is visible just below in its box section housing. It was sheer luck that I found the square tubing at the scrap yard just when I needed it. The clearance between the motor and housing is ideal. The height of the square tubing is also perfect for presenting the worm to the wormwheel.

Wednesday, 45F, mild, dark and windy with showers. Spent a couple of hours in the workshop balancing and testing the mounting and AWR drives. Before balancing, the RA motor was apt to complain about having to work 'uphill.' I also fastened off the stepper motor cables with zip ties to provide some strain relief. The Dec motor cable will need to be 'dressed' to allow rotation without tension. This should not be too much of a problem because the telescope(s) would be upside down if allowed completely free reign.

I have photographed and printed off the AWR IH2 menu in several sizes to have reminders of the cascaded steps required. Having not used the drive system for months I had forgotten much of it. When I finally have the observatory set up properly I shall be pointing to objects for Goto slews on the computer screen.

Thursday and Friday: Testing drive slews with the AWR IH2 handset.

With the mounting raised on a bench the sheer scale and mass of it is quite overwhelming. The buzzes occur when starting and stopping the motors. I wasn't sure whether to shim the motors for better conduction or leave them more fully exposed to the air. I ought to have used a more neutral background for the video but had no other, lightweight tarpaulins left to quickly hide the workshop clutter. White always confuses the camera. PS: I have invested in sheet of neutral grey cloth for pocket change at a charity/thrift shop.

Dressing the divided, stepper motor, drive cables is proving slightly awkward. Both cables presently exit the access hole provided for PA altitude adjustment. The RA cable need only be quite short but the Declination cable must not hinder rotation of the PA over a rather large circle.

I have already managed to stall the drive during slews when I allowed the Dec cable to become tight. With only short, primary motor cables, from AWR, this places a rather large plug and socket dangling in mid air not far from the motor.

Unable to obtain them locally, I have ordered a boxed assortment of Nylon P-clips online. This will improve my chances of sorting out the cable problem neatly. There is no need for the main cables to be readily removable because the mounting will be permanently installed on the pier. So the heavier, main sections of cable can be clipped neatly onto the mounting. With plugs easily removable from the drive boxes at the far end when desired.

Click on any image for an enlargement.


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