Bill,
Good afternoon. Just back from a West Coast trip and thought I'd provide
some of my own experiences with the 135' of Rohn 55 + K0XG rotating base and
guy rings.
My tower has been up for about 3 years now and performs fine - but only
after paying attention to various details and performing a few "engineering
modifications".
Guy rings: Yes, I did a pre install inspection and found that some of the
bearings did not want to easily rotate - the fix was to remove the white
plastic PVC cap and using an allen wrench, back out the screw to the point
where rotation was possible. Also, the dip galvanizing had some high and low
spots that caused the ring to become difficult to rotate - as the coating is
soft, a careful sanding or filing took off the high spot without
compromising the galvanizing. Richard did inform me that the six welded
torque arm stubs were laser drilled and that the resultant hole was tapered
so the combination of the taper + the galvanize coating made the hole too
small in diameter to accept the bolt. The fix was to use an adjustable
straight reamer to properly open up the hole. Once done, the torque arm
assembly was easy.
Rotating base: The stainless sheet metal covers did not fit together well
and required a bit of filing and some additional holes/hardware to satisfy
my needs. The big problem was that the rotating table (with the 3 welded
bosses to accept the first tower section) was concave based on over torque
of the bolts. Some adjustment got this right and now you can lay a "flat"
across the table without seeing a 1/4" space in the middle.
Control system: I opted for the Green Heron controller with the speed
control/ramping option. I am pleased with the performance so far. Setup was
a bit tricky as you need to specifically know the complete turns ratio
number of the various transmission boxes and gears. Once known, the value is
programmed into the controller and all will properly operate. I did add some
additional EMI filtering and a metal NEMA box to house the green Heron PWM
control boards - this helped with electrical noise that the 180VDC motor and
controller generates. All wiring to the tower base and electrical panel is
run inside of metallic, flexible EMT (Sealtite). I still have a bit of motor
EMI to eliminate in the near future.
Tower bearing conditioning: So, I will give credit here to K3TUF as he has
gone through similar experiences and we have compare notes working through
the punch list. We both noticed that the rings and torque arms tend to seize
and release during rotation (at any speed). At the time I noticed this, I
had 6M and 432MHz yagis + feed lines installed (but no rotor loops connected
yet). According to K0XG (I believe), you need to condition the bearings with
continuous, low speed rotation over a week's time. First, all mechanical
limit switches are disabled (remove the actuator arm from the turn table)
and the 180VDC motor is connected to a variable voltage (0>24VDC) power
supply - I believe mine is rated at 6A maximum. The power supply is powered
on and the voltage adjusted so that the tower just creeps along its rotation
- let it rotate for 24 hours in one direction and then reverse it. Continue
for 7 days. I had the guy wires a bit loose at the beginning of this process
and increasing the tension over the 7 days. You can monitor the current
meter to see where the "high spots" are and that they smooth out over time.
When complete, re-connect the limit switches and the Green Heron control
electronics.
Hope this information is helpful to all. I will also add this to my web page
http://manitousys.com/rotating-tower/
73,
Steve W1SMS
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