[TowerTalk] Prop Pitch Info (Used to be Mast Slipping)

Kurt Andress kurt at k7nv.com
Thu Apr 26 21:21:34 EDT 2007


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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