I have used also a small prop pitch to turn my 3 el 80M yagi (home made)
with 82 ft boom.
But I should say that inside the 4.5"OD mast, I have square tube, and also
at the output of the small prop...
I had no problems at all for 10 years...and the weight of the yagi was about
875 pounds...
I am turning also a 3 el full size 40M beam here with another small prop
pitch...same set up for the mast...no problem at all. Props are strong...but
the DC motors are hard to find...I don't know why...
NOEL ve2ryy/VE2HQ
----- Original Message -----
From: "Kurt Andress" <kurt@k7nv.com>
To: <towertalk@contesting.com>
Sent: Friday, April 27, 2007 01:21
Subject: [TowerTalk] Prop Pitch Info (Used to be Mast Slipping)
> 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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