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    Default Dome Drive Upgrade - 107"/2.7M Harlan J. Smith Telescope Dome @ McDonald



    We completed the dome drive upgrade today on the 107"/2.7M telescope dome structure here at McDonald Observatory.

    The rotating dome and shutter structure weighs 435 tons, and incorporates a 20-ton bridge crane, ventilation system, and the 55-ton moveable shutter structure and wind-curtains.

    Over time, the dome drive system has evolved/devolved, most recently into something we colloquially call the "Windmill".

    The dome is driven through a primary pair of steel-on-steel friction drive rollers. The driven element is a steel wheel wheel, which impinges on the underside of the dome drive ring, a steel surface flat integrated into the circumference of the 'flange' on the underside of the dome. There are two drive rollers, and 26 idle rollers, which mount in pivoting bearings integrated into the structure of the dome's stem wall. There are 8 inboard guide rollers, two of which are integrated into the primary drive wheel assemblies. In the old system, these were driven by a Dodge 24:1 reduction gear, the output shaft of which was coupled to the input of the primary drive wheel, and input shaft coupled by a Jeep drive axle and universal joint assembly to the output shaft of a Baldor 15HP, 480VAC drive motor.

    In the past, failures have occurred that were both threatening to the structure, and to personnel, including a catastrophic drive shaft failure that allowed the shaft assembly to flail out of control and pretty much wipe out its surroundings.

    During early 2012, we worked with Ascendent Engineering Solutions, Inc. from Austin, TX on a reliable, safe, compact, and serviceable replacement. This is the photographic story of implementing that system.

    The drive systems are deployed as a pair of drives, one on the East stem wall, the other, directly opposing on the West stem wall.

    Here we are preparing to demo/de-install the East wall drive - this one did not incorporate any braking capability

    IMG_5977.jpg

    The existing drive motor is rigged to the dome crane, a component that we will reuse in the new system.

    IMG_5980.jpg

    The AES team prepares the old Dodge 24:1 reduction gear for use in an alignment jig/template that will be used to set the stem wall mounting plate, a weldment that attaches to mounting plates that were welded into the dome stem wall about two weeks ago.

    IMG_5982.jpg

    The AES team works on the dry-fit template for the stem wall mounting plate.

    IMG_5988.jpg

    This is a brand new Dodge 24:1 reduction gear assembly - we elected to replace, rather than reuse the existing assemblies on the system, because the lifetime service on the existing units was uncertain.

    IMG_5990.jpg
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  2. #2
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    Default Re: Dome Drive Upgrade - 107"/2.7M Harlan J. Smith Telescope Dome @ McDonald

    Here, the thrust/taper bearings are being installed into the new reduction gear assembly prior to mounting on the drive wheel input shaft.

    IMG_5992.jpg

    The reduction gear uses a pair of keyed, tapered, thrust bearings, one inboard, one outboard to secure it to the drive wheel input shaft. They are independent, and require precise alignment, and controlled torque as the bearings are assembled onto the input shaft. The unit weighs about 90 lbs.

    IMG_6000.jpg

    The AES team, and our Mechanical Engineer (yellow jacket) confer as the assembly is set plumb and level on the drive wheel input shaft.

    IMG_6001.jpg

    A wide shot of the work area on the East dome floor - this drive unit is behind the dome floor HVAC unit that cools the telescope and dome structure.

    IMG_6006.jpg

    The AES team sets level and plumb on the stem wall mounting plate. The stem wall mounting plate, and the backing plates that this structure are welded to are the most critical parts of the implementation.

    IMG_6009.jpg
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  3. #3
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    Default Re: Dome Drive Upgrade - 107"/2.7M Harlan J. Smith Telescope Dome @ McDonald

    Two of the McDonald team ready the reused drive motor for positioning on the new stem wall mounting plate.

    IMG_6014.jpg

    The next two shots show the reduction gear assembly, mounting ears, and stem wall plate in place, and ready for welding to the backing plate.

    IMG_6011.jpg

    IMG_6010.jpg

    Welding underway on the stem wall mounting plate.

    IMG_6015.jpg

    A shot of the reduction gear, brake rotor, and caliper in place.

    IMG_6018.jpg
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  4. #4
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    Default Re: Dome Drive Upgrade - 107"/2.7M Harlan J. Smith Telescope Dome @ McDonald

    Welding continues on the stem wall mounting plate.

    IMG_6022.jpg

    Final structural welding being completed on the stem wall mounting plate.

    IMG_6040.jpg

    The drive motor being set in place by one of the AES team.

    IMG_6046.jpg

    The mostly completed East dome drive assembly, sans one drive pulley on the input side of the assembly, in place, ready for static testing.

    IMG_6054.jpg

    Static testing underway. In this shot, the brake rotor can be seen spinning, in motion, at about 1750rpm. It is being driven by the existing West stem wall drive assembly, while we look at rotor run-out, vibration, etc. The drive belt is absent, and we are disconnected from the East drive motor.

    IMG_6058.jpg
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  5. #5
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    Default Re: Dome Drive Upgrade - 107"/2.7M Harlan J. Smith Telescope Dome @ McDonald

    Here are the final shots - in this one, we're looking at a close-up of the old drive system, on the West stem wall. Here is a shot of the infamous wobblin-gobblin Jeep axle.

    IMG_6063.jpg

    This is the top of the old West 'Windmill', this motor is gold in color, the replacement for the one that beat itself to death during the drive shaft failure of 'yore.

    IMG_6062.jpg

    The McDonald team demo'ing out the 'Windmill'

    IMG_6059.jpg

    The managing partner and director of development with AES stands proud with the completed and tested East stem wall drive assembly.

    IMG_6069.jpg

    The completed, tested, and approved West stem wall drive assembly.

    IMG_6072.jpg
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