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Rotating Tower

Here are some W1SMS experiences with the 135′ tall Rohn 55 + K0XG rotating base and guy rings.

R55 tower section being hoisted

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”.

Rotating Tower Components in Truck Bed Rotating Tower Base on Tractor Rotating Tower Rings on Tractor 

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 Ring on Test Stand Rotating Ring on Test Stand 1 Rotating Ring Bearing Adjustment 

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.

Truck Bed with Concrete Rotating Tower Base on Tractor 1 Rotating Tower Base - Ready for Installation Rotating Base Sprocket and Chain

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.