It is very difficult to keep water out of the gearbox of a prop pitch motor that is mounted upside down. I have one of those and one that is mounted right side up with a chain drive. The latter has never given me any trouble, and others I've spoken with a similar setup have also had good success.
Most prop pitch motors used as rotator are mounted upside down including those by K7NV (SK). There are ways to seal the opening to the gearbox against water incursion but none seem foolproof. There are numerous channels and seals that serve its design in aircraft but are trouble when used as a rotator .The hydraulic pressure of wind driven rain and ice damming in winter causes water to overcome the barriers I made and pool around the crown bearing where it eventually migrates to the interior of the gearbox.
I gave it a shot with the materials that I could work with in my home workshop and my various attempts weren't good enough. For the second time the gearbox for the prop pitch motor turning the upper yagis of my 15 and 20 meter 5-element stacks froze this spring.
After taking it down and doing an inspection I found extensive water fouling of the reduction gears and two stuck bearings. I am retiring this prop pitch motor. The pieces, along with a spare motor, are now boxed up. They can be used as spare parts should I need to service my one remaining prop pitch rotator or those of my friends. There seem to be no commercial service options since the passing of Kurt K7NV. I receive many queries due to this blog and there is little that I can do other than offer advice.
I don't want to deal with the issue again so I've been preparing for this day. Last winter I acquired a used Yaesu G2800 in excellent condition and a Green Heron RT21 controller. The stack is within the specifications for what the rotator can handle, though not by a lot. However, there is no weight bearing on the rotator since I have an industrial sealed bearing under the mast to do that. This arrangement eases service of the mast and rotators. In any case, prop pitch motors are not designed for substantial axial loads.
I locked the mast where it was which left the yagis pointing at 15°. That's not an ideal direction but I have lots of antennas and there were no important contests or DXpeditions of great interest to me in late spring and early summer. It was simply going to stay like that until I had time to devote to the rotator system. Tower work is not ideal this time of year due to the intense heat and clouds of insects in the hay field where the towers are located. I did most of the work described in this article at temperatures around 30° C. Autumn is when I prefer to do tower work, but you don't always have that option.
The central hole in the support plate for the prop pitch motor was too wide for the bolt pattern of the G2800. The plate was therefore removed and a new one made from ⅛" galvanized steel found in my scrap pile. It already had many holes in it though none where I needed them! The sheet is barely wide enough to reach the mounting holes on the tower girt. I've discussed centering of bearings and rotators on tower plates in several other articles so I'll move on.
I used the removed plate as a template and then used the pattern of the mounting bolt holes to locate plate centre. Positions for the 4 bolt holes were calculated from plate centre then checked by mounting the rotator. Never assume you did it right; it is surprisingly easy to make mistakes. Validate before and after punching the holes. Last year I had to do the same for a friend's Yaesu rotator with little time and few tools. It didn't go so well so one of the holes had to be extended. Take the time to do it right since alignment is critical in many installations.
Centering of the rotator is critical in my case since the rotator barely fits between the girt and the mast coupler hanging below the bearing plate above (see below). An error of even 1 or 2 mm can stress the rotator and potentially bind due to flexing of the plate and coupler. The alternative was to place the rotator on the next lower girt. The mast is already very long and I preferred to avoid adding 40" (100 cm) to it. Too long a mast amplifies torque induced oscillations that can stress the antennas, mast and rotator.
The picture below shows the tight fit. There are just a few centimeters between the top of the mast clamp and the mast coupler. I made the coupler out of 1.9" OD aluminum (6061-T6) schedule 80 pipe. The same ⅜" grade 8 bolt that pierced the coupler for the prop pitch motor is reused. That is the only hole in the pipe. When I came to tighten the jam nut on the bolt it sheared. Grade 8 bolts are hard but can be brittle, especially at the threads. The bolt was carefully selected so that the load bearing surfaces (the 4 points where it contacts the pipe walls) are unthreaded.
Grade 5 bolts, although tougher, are weaker in shear. I'll have to replace the bolt or secure the nut another way (e.g. hose clamp). Lock washers are ineffective on round surfaces.
Looks simple? It took me 3 tries, each involving a tower climb. On the first try I made a simple recording error and the coupler was precisely 1" too long. On the second try I failed to account for the "seat" on the rotator mast clamp. I assumed that the mast rested on the rotator body. Oops!
Even seemingly routine tasks can become expensive when a tower is involved. I can't machine metal 130' up in the air. It wasn't as bad as it might have been since I had lots of other work to do on the tower so none of the climbs were solely to correct my mistakes.
I did not use the 4 centering bolts on the mast coupler. These were added several years ago when I found there was too much slop in the fit of the prop pitch motor coupler -- it was 1.66" steel pipe welded to the crown gear. That caused rapid wear and stress on the coupler through-bolt, which contributed to its shearing. At the time that was a 5/16" grade 5 bolt, since upgraded to ⅜" grade 8 as described earlier.
As you can see, the fit is pretty good and the coupler well centred. The centering bolts are still there, locked but retracted, just in case I decide to use them again.
The Yaesu mast clamp can handle a wider range of mast diameters than those of many other rotators. That comes at the expense of a multi-step alignment procedure. It isn't too complicated but must be done properly to avoid trouble. First, the two clam shells of the clamp are bolted together to grip the mast. When done properly, the width of the slot between both sides of the clamp should be equal on both sides and along their full lengths. It is well worth the time to fuss over it to ensure stress equalization and mast centering.
The bolts have only one correct orientation. Note the captivating tangs to fit the bolt heads -- that's how you know you've got it right. It is also handy since it takes just one 13 mm wrench to tighten the 6 bolts. The next step is to tighten the 4 bolts (with the same 13 mm wrench) that hold the mast clamp to the rotator body. When the mast is properly centred the positions of the bolts within their slots (not shown) will be identical for all 4 of them. If they aren't, something is amiss with the centering and you must recheck your work. Luckily mine were properly aligned so I was effectively done.
One point worth noting is that I left the 6 bolts holding the plate to the tower girt loose during the alignment process. That way the plate can shift within the small amount of play in the holes. Only after the mast alignment procedure was complete to my satisfaction were the plate mounting bolts tightened.
One part I did not use was the mast locking pin. I avoid those since there is a risk of damaging the rotator when a high wind applies a momentary high torque to the mast. Unless you are very confident in your calculations avoid these devices. It is preferable to occasionally have to correct a slipped mast than to deal with a broken rotator. Although the clam shell mast clamp on the G2800 appears to have a good grip, I'll have to wait and see how it deals with the wind load of two very large HF yagis. I am already close to the 'K' rating documented in the rotator manual.
I had previously completed the wiring of the rotator and tested it from the shack for full rotation, just sitting on the tower plate without the mast clamp. The wiring was interesting. Although the rotator came with almost 100' of cable it was not usable in my station. It's far too short -- the run is >300' or 100 meters -- and would have to be buried. Instead I reused the motor wires for the prop pitch motor and used spare wires on existing control cables.
I have a history of innovative wiring of Hy-Gain rotators and the same can be done for Yaesu. Ground is easy: tie it to the tower/antenna common ground, which is tied to electrical ground. Thus freed, the 3 wires of the 10/2 cable for the prop pitch motor provide the 3 wires to the motor: CW, CCW and motor common. For the two direction pot wires, a Cat5 cable was run from the G2800 to the one for the lower 15 meter yagi, patched in to a spare pair, patched into a spare pair on a buried Cat5 cable, then patched again at the far end to a spare Cat5 pair running into the house. Other than a some tedious cable tracing (I keep detailed cable wiring records) it was perfectly straight forward.
Before attaching the rotator to the mast, I re-calibrated the rotator controller to account for the resistance of the long cable. After confirming that all was working as it should it was time to test the rotator.
My initial plan was to be on the tower while a friend operated the rotator from the shack. I wanted to watch the rotation to check for any stress points or other problems. However I had to move quickly since I wanted the stacks ready for the IARU this weekend and it wouldn't be fair to ask someone to drive to my remote QTH on an hour's notice. I can do that test after the contest.
Suffice to say that there were no issues. I turned the large arrays at the rotator's slowest speed setting and then increased it to its midway point. For such large antennas it is unwise to turn them faster due to their high momentum when you remove power. The 90° over-rotation feature of the G2800 also must be avoided since the length of the coax rotation loops aren't designed to accommodate 450° of rotation.
I must now contemplate another rotator controller on the operating desk. The new addition makes 5: 3× Hy-Gain rotators, the G2800 and my home brew prop pitch motor controller. I now use the last for only the motor on the other tower -- 3-element 40 meter yagi and upper 5-element 10 meter yagi -- however, the mast operated direction pot on the 20-10 stacks still works but is redundant. I have no good reason to remove it. When they disagree I guess I'll have to look out the window to know which one is right.
I may replace my home brew controller with the Green Heron controller since it is more robust and has more features. That wasn't possible when my controller needed to support two prop pitch motors. I've heard rumours that Yaesu controllers are failure prone so I intended to keep the RT21 in reserve. Certainly they are electrically and mechanically complex. Time will tell.
A more serious issue is the proliferation of controllers on the operating desk. I would like to migrate to software control using PSTrotator, which I've used at other stations and it seems to work well. Most operators like physical controllers but they have to reach for them and pick the right one during hectic multi-op contests. Mistakes happen! The migration that won't happen quickly. It's a project to mull over during the cold winter months.




























