John,
I say go for it.
I have a Prop pitch drive motor mounted at the 4ft level on my tower. This
is a good working level and keeps grass cuttings from covering the rotor
assembly. Mine is only a 50ft tower which places the TH6DXX at about 55 ft.
I also have a 14 element 2m beam on top of the Th6DXX. I am using 1 3/4 in.
Schedule 40 water pipe. (2 in would be better for your 70ft)
The schedule 40 is higher pressure pipe and as such is little stronger and
less apt to split because it does not have the weld joint along the side. I
use standard galvanized couplings. I pre-assembled the drive shaft on the
ground. I then drilled two 1/4 in holes through each of the couplings
through the assembled ends of each pipe. This keeps the couplings from
unscrewing. I then removed each section in order to install is inside the
tower as I assembled the tower sections. The schedule 40 is rigid enough
that in my case I only had to install one center side load bearing about
20ft above the rotor.
One thing is unique with my installation. I do not use any load thrust
bearings. At the rotor end of the assembly. I have attached a steel cable
with a turnbuckle to the bottom of the drive shaft. The other end goes up
the shaft to the support bracket of the side load support. This allows me to
adjust the turnbuckle until the weight is lifted from the thrust bearing of
the Prop Pitch drive motor. I positioned the cable straight at the half way
point in the rotation. So it is only lifted through 1/2 of the rotation. The
lift is only about 1/4 in, which is easily handled by the spine shaft on the
rotator drive gearbox. You can also accommodate this setup using a spline
slip joint portion of an automotive drive shaft.
* 73's Jim W5IFP *
>
>K5PGW Wrote:
>
>I do have one additional "question of the day" and that is if you
>have had any experience in installing a tailtwister rotator near
>ground level by running a mast from the top of a Rohn 25 tower about
>70 feet tall so that the rotator might be changed or worked on from
>near ground level? I know it has often been done, but I am not sure
>of the type mast, thickness of the material to use and how much
>bellying of the mast might occur. I have large thrust bearings that I
>can place near the top and strategically down the tower to prevent
>sway and bellying of the long mast. That would also take all weight
>off the rotator as well as as control the sway and bellying of the mast.
>
>You may see this as an ambitious project for a 70 year old, but I
>DESERVE IT after over 50 years as a HAM. Your support and
>encouragement is greatly appreciated. 73, John, K5PGW
>
>-0-
>
>John,
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