Hi Guys,
Here are the gear reductions for the different prop pitch gear trains to clear
up some of the confusion:
They are all mutistage planetary systems.
Small = 9576:1
Medium = 7063:1
Large = 7056:1
Extra Large = 5915:1
I have one guy that has been able to turn his small pp back through the gearbox
without the brake on it. He is turning a 30 ft diameter EME dish and if he
doesn't tie it down in winds over 40 mph it will move.
I have two guys with loaded 3 el 80m yagis and many with 3 & 4 el full size
40's and suitably large stacks that don't report any problems with a small pp
and no brake.
I have two guys with 80m yagis (not sure of the size, but they're real loud
here), using the XL pp and haven't heard of any problems.
I have quite a few guys with MonstIR's, small pp without brakes, with no back
driving problems.
Maybe the way to know if your antenna is really big enough is when it can turn
the prop pitch ;-) Kudo's to those guys!
Like K5GW, K5GO reports that his 100 ft + long boom 40m yagi can turn the XL
unit he built. The wind load (wind speed) at one end of a long boom is
certainly not always the same as the other end. The longer the boom, the more
chance for greater differences. I have built many "perfectly" torque balanced
yagis and can see them trying to yaw in the wind due to this phenomenon. Even
on 30-40 ft booms.
You will notice that the larger units have smaller gear reductions. The
difference between the motor bearing resistance to turning between the large
and small motors is not very much. So, that may be why the larger ones can be
turned by the bigger arrays.
They can all be fit with the brake and a separate actuating power source, if
one has the parts, but then you need to ask your tower what it thinks about
that. This would be a good place for a star guy bracket.
Hope to see some of you in Visalia!
73, Kurt, K7NV
P.S. Now, everyone practice "Safe Rotating" out there!
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