[TowerTalk] Biggest, strongest rotor that fits a Rohn 45, rotor plate?

[Kurt Andress]

Hi Guys,
KK9A sent me an e-mail about this discussion.......
He needs us to modify a unit for him, and some others that read the 
thread have contacted me.....
Here's some info from my perspective......
There is probably no other rotator that can compete with one of our 
properly built prop pitch units in its price range.
That is why we have been building them for over 3 decades. The first one 
I built properly was in my dad's (W6KUT, SK) tower for 27 years when he 
passed away, I had to rebuild the motor at about 15 years, Dad was a 
very active DX'er and used it almost every day. Right now we are 
building our 322nd-328th units, they are all over our small shop..we 
have rebuilt all sizes of them.
I buy everything I can find that may produce some useable parts, we have 
a huge crate of spare parts collected from all the cadavers, and piles 
of cadavers outside waiting to be broken down to see what can get out of 
them, we save every serviceable part we find!
When we run out of parts, we (my assistant & I) will retire, or maybe 
I'll just die first?

Dave Leeson, W6NL, & I did some calculations and we determined that the 
output torque of a small prop pitch is around 11,000-12,000 inch pounds. 
All of the parts in a prop pitch are aircraft quality heat treated alloy 
steel.
I had an old ham that worked for Curtiss-Wright, in New Jersey, 
assembling these things on the production line, when they were taken out 
of service around 1955. He told me the US Army Air Corps (remember that 
was round when the US Air Force was created) was paying something like 
$3200-$3300 for each unit at that time! You do the math to convert that 
into today's dollars.

A small prop pitch has a gearbox reduction of 9576:1 and it's output 
speed, at a full 24 vdc voltage, is around 3/4 rpm. The motor draws 
around 7-8 amps @ 24 volts DC, unloaded. We have many of them out there 
turning big stacked antennas on top of towers, and turning K0XG rotating 
rings, and 150ft-200ft tall rotating Rohn 45-55G towers with lots of big 
antennas on them. The larger units have much larger electric motors and 
lower gearbox ratios, and much larger & stronger gears & bearings.

I hope this little bit of info assists you folks with this discussion!
73. Kurt, K7NV
P.S. I need to get back on the bench & computer to design & build some 
more stuff for the folks that have ordered & need what we can do.....

Message: 7
Date: Thu, 28 Feb 2019 17:19:41 -0500
From:<john at kk9a.com>
To:<towertalk at contesting.com>
Subject: Re: [TowerTalk] Biggest, strongest rotor that fits a Rohn 45
	rotor plate?
Message-ID: <009201d4cfb3$b3eac470$1bc04d50$@com>
Content-Type: text/plain;	charset="us-ascii"

What will K7NV do when there are no prop pitch motors? I wonder how he got
so many surplus motors? Yes you should be able to make a killer rotator with
parts from Grainger. Telrex had an A/C motor and a separate gear box
connected with a chain. Mine held up much better than the many Hy-Gain
rotators that I owned. I thought about building a rotator similar to the
Telrex with a more modern control box but in the end I went with using prop
pitch rotators. They have an impressive gearbox which seems perfect for
antenna rotating and also holding in position, in comparison most ham
rotators are just toys.

John KK9A