I guess emails with attachments just don't make it, so here's a repeat:
Here's the story on the flexdisc ("Giubo") isolator: I learned about
flexdiscs because my race car used them on the rear (drive) axles in
place of CV joints, and this worked well, see
https://sportsracernet.smugmug.com/Events/1970s/1979-Runoffs/i-CSKMk8q.
Some interesting history is here:
https://eeuroparts.com/blog/driveline-vibration-on-your-bmw-replace-your-guibo/
I adapted the idea to a mast isolator using the same smaller BMW
flexdiscs BMW part number 26-11-1-106-113, as described on pgs 7-28 and
7-29 of my 1992 Yagi book. I noted that it's also possible to isolate
the entire rotator, but that carries the shock force through the
rotators gears. I used an inner vertical support bearing piece that was
somehow overlooked when it was adapted for a commercial design. This
created the need for separate vertical bearing support above and below
the isolator, which wasn't emphasized, so the results of that particular
product were disappointing. My own home-built isolators, with the
internal bearing supporting the mast weight, are still in use decades later.
More recently I became aware of much beefier 110 mm flexdiscs used on
bigger BMWs, BMW part number 26-22-1-229-065, and that's what I had
Kurt, K7NV, fabricate for my prop pitches. The bigger flexdisc is
available for around $75 to $90 at
https://www.bimmerworld.com/Flex-Disc-Guibo-E34-E39-E32-E38-E31-Z8-BMW-26111229065.html
or
https://www.fcpeuro.com/products/bmw-drive-shaft-flex-disc-giubo-540i-840ci-740-750-26111229065l
or https://www.turnermotorsport.com/p-374255-universal-flex-disc/ For
general info, see
https://www.turnermotorsport.com/c-941-bmw-guibos-and-flex-discs
I sent complete drawings of the mounting and mast clamp setup to Kurt,
and he had the parts machined. It has been up for quite a number of
years without incident, although I expect that sooner or later the
rubber disc will need replacement from wear and tear. I'm happy to share
the description and drawings of the prop pitch setup.
I have also considered how to create a remotely switched disc brake, but
haven't pursued it since the combination of DC motor braking and the
isolator has worked out in my particular situation. One possible
improvement that came up in my analysis of wind-induced antenna rotation
is that a longer mast will reduce the rotational resonant frequency of
the assembly, decreasing the shock force at the rotator.
If a large antenna were frozen in place without some rotational
flexibility, I would be concerned about tower fatigue and damage. The
standard anti-rotation guying (torque arm Stabilizer with double guys)
might be a good investment, see
https://www.3starinc.com/rohn_65g_tower_torque_arm_stabilizer_assembly_r-ta656.html;
I have that on one of our commercial towers, a Rohn 80 that I also use
for low-band antennas.
Dave, W6NL/HC8L
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