Last month I wrote about a design I had been working on for a large German Equatorial Mount for astrophotography, to be machined this summer.  After I finished the design I called Ed Byers to order the right ascension gear, and we ended up discussing the design.  He gave me an amazing amount of advice, and I decided to redesign the mount to fully take into account what I learned from speaking with him.

Pictured above is a Solidworks render of the mount with an 80mm APO telescope pictured for scale.  During operation it will (hopefully) carry a much larger instrument.  Below is a summary of the features of the mount.

  • Mostly Aluminum and Steel construction.  Most panels are 3/8" aluminum, a select few are 3/4", and non-structural plates are 3/16".  Bearing blocks are 1.25" aluminum.  The aluminum plates are all machined from 6061-T651.  All fasteners are Type 18-8 or Type 304 Stainless.   The axis shafts are 7075-T651 aluminum. The worm-wheel cover sides are made from heat-formed acrylic, to display the beautiful Byers gears.
  • Swiss made Maxon RE-025 Motors with German made Maxon gearboxes on each axis.  These are from the same series of motors used on the Curiosity mars rover and the Astro-Physics German Equatorial mounts.
  • 11" "Star-Master" 440 tooth anodized aluminum worm wheel on right ascension, machined by Ed Byers in California.
  • 10" 360 tooth anodized aluminum worm wheel on declination, again machined by Ed Byers.  This worm block has a spring loaded worm to take up backlash.
  • Nylotron slip clutches on both axes, from Ed Byers.
  • 3 Thin-section Kaydon slewing ring bearings.  Two at the front of each shaft, and one on the back.  I am told this is the configuration used on the Byers Series I mount.
  • A Heidenhain sinusoidal encoder on RA for real time periodic error measurement and correction.
  • An Avago absolute encoder on each axis, so the telescope knows where it is (to within about an arc minute) upon start up.  This also helps it keep track of its position if the clutches slip, either due to a collision or manual adjustment.
My original design had incorporated 3.75" 6061-T651 aluminum shafts on both axes, each around 8" long.  In the newer design I chose to reduce the shaft diameter to 2.75", but increase the distance between the bearings to 12" on each axis.   The general consensus among bearing literature is that bearing spacing is significantly more important than bearing diameter(within reasonable limits).  Ed also recommended I use 7075-T651 aluminum for the shafts, instead of 6061.  At this point the design is done and I should be machining parts in the next few days.


 


Comments

10/14/2013 2:22am

it is very important that we have a proper way of processing metals

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