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

[jimlux]

On 2/28/19 2:19 PM, john at kk9a.com wrote:
> 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. 

Indeed, that's where I was looking.. Grainger's selection of gearboxes 
didn't seem to have "inline" multistage planetary with the 1000-2000:1 
reduction you'd like to have.

Inexpensive variable speed drives make a 3 phase AC induction motor nice 
to use - they're cheap, common, and rugged.  You DO have to run 3 wires 
up to the motor or put the VFD up on the tower.. I don't know about that 
from a servicing standpoint.

I suspect you could easily interface something like a Green Heron to a 
VFD - most of them will take an analog speed input, for instance.

For very skinny fit situations - Franklin Electric does make skinny 3 
phase motors (for use in well pumps) - less than 4" OD as I recall. But 
if a standard 56C case will fit that would be the way to go.
I guess, you probably wouldn't want a 1/2 HP drive in Rohn 25 for 
structural reasons (you'd twist the tower?)


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.

An impressive gear box that would cost $10s of K to duplicate today.
And, they were volume and mass constrained - a tower application isn't 
as mass constrained. Cast iron is a cheaper housing material than aluminum.