The small pp is about 9576:1. I for one will be in trouble. I use one in the
crankup I have now and will be putting one in the base of a rotating tower
project later this year to turn it. They are not as difficult as some would
have you believe to rebuild.
Steve, WD8NPL
-----Original Message-----
From: jimlux
Sent: Thursday, February 28, 2019 4:54 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Biggest, strongest rotor that fits a Rohn 45 rotor
plate?
On 2/28/19 12:41 PM, Patrick Greenlee wrote:
Re-purposed prop pitch motors are definite contenders in the
strength/robust department but fitting in a small space???
On 2/28/2019 1:58 PM, Chuck wrote:
On 2/28/2019 1:22 PM, RVZ via TowerTalk wrote:
Pretty hard to find a better, more reliable rotor than the BIG RAK.
Chuck KØTVD
www.dxham.net
Please advise the rotor that will handle the biggest windload and is
likely to be the most reliable that will fit a standard Rohn 45 rotor
plate?
What will the ham world do when the last prop pitch motor dies??
Some years ago I was pricing big DC (and AC) motors with suitable
gearboxes and they are *really* expensive.
The BIGRAK as an example, is 4000 in-lb torque at something like 0.5
RPM, but as noted elsewhere prop-pitch tend to be somewhat higher torque.
The PP has a reduction gear of something like 7000:1 or 9000:1 - so the
basic DC motor is running at 5,000-10,000 RPM or thereabouts. It's
probably something like a 1/3 HP motor (240W @ 24V is 10A...not having
run one myself, I don't know if this is a typical current)
1/3 HP at 1 RPM is about 28,000 inch pounds.
(1700 foot pounds)
Typical AC electric motors have speeds around 1800 RPM, so an 1800:1
reduction is needed. Getting that in one step is unlikely, so figure
you need two gearboxes with 30-40:1 reduction.
So, a $500 3/4HP C-face TEFC electric motor, and a pair of $1000 speed
reducers will set you back about $3000. Plus maybe $500 for a decent
Variable Speed Drive.
At least, you're now using something that is a standard industrial
product and if you need to replace it, you can order the parts anywhere.
Will it fit inside the tower?
A 56C size motor is 6.5" in diameter. I don't think that will fit
inside Rohn 25 (barely).
(There are better solutions out there. using, for instance, a
worm&pinion reducer, but I didn't happen to have my catalogs handy).
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