Towertalk
[Top] [All Lists]

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

To: <towertalk@contesting.com>
Subject: [TowerTalk] Prop Pitch Info (Used to be Mast Slipping)
From: "Kurt Andress" <kurt@k7nv.com>
Reply-to: Kurt Andress <kurt@k7nv.com>
Date: Thu, 26 Apr 2007 18:21:34 -0700
List-post: <mailto:towertalk@contesting.com>
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!
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>