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Old 11-Dec-2016, 2:43 PM   #1
bobsgarage
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Review - CM 9521A Antenna Rotator system

I read a lot of reviews before I ordered my CM9521A. They were all over the place. Some had no issues, some said theirs never worked right from the start. I figured most of the issues were due to installer error. Not so it seems.

Actually, I bought two because I was setting up a new antenna system and my other array has an old Radio Shack (noisy box) rotator that has lost it range over the last 15 years. Also, the Channel Master 9521A has a remote, which I really wanted. Another thing, all the competitors don't market rotators anymore, so there is truly a lack of choice.

I bought 1 CM 9521A through Amazon, the price was right, I thought. I bought the other through Solid Signal a week earlier as it was on Sale with free shipping. I bought it in April 2016 and now by early December, I am already experiencing problems. Aside from losing it's calibration, it had lost it's it range and only rotates approx 270 out of a possible 360 degrees, when it rotates.

So, in the early days of a very cold winter, I was back up on my roof. I loosened the clamps and climbed back down the ladder, hit the remote control aiming through a window and remarkably, it began working. It still had only partial rotation but I was happy enough to get off the cold roof so I tightend the clamps and it worked a few times and stopped again. WTF? Oh well. I expected it wouldn't be that easy...

Having another hour of sunlight, I went back up the ladder and brought my other new CM9521A that I hadn't mounted yet- yay! My fingers were numb even though I had gloves on, I had to remove them for the little 1/4-20 mounting nuts. I replaced the whole CM9521A rotator and I now have a functioning full sweep rotator again. I plan to work it hard and get my warranty out of it. Thankfully, the fresh one worked.

Now some of you already know what I have, a very tall 21' 1 3/8" SS-20 chain link top rail reinforced with 1" SCH 40 galvanized water pipe internally for the antenna mast so, it is fairly heavy mast. Add to that, an AD 91 XG and a MCM 30-2476 antenna and it is unwieldy.

However, knowing that, I fabricated 2 support bearings that support that weight. Yes, they actually hold ALL the weight, so that the rotator only has to turn the mast, a much easier task with no weight pushing down on the rotator motor. There is actually a 3/16" gap between the rotator and the base of the mast.



This support system is so effective, I can change the rotator without moving the antenna mast-at all. I loosened the upper clamps , removed the lower clamps, slide it a few inches down the main mast, unplug the three wires and (quickly) install the new one, clamping to the main mast as fast as possible.

That is why I decided that replacing the rotator as cold as it was out, because the thrust bearings were not just like another set of hands, but really like two hands. These are industrial bearings that are meant to support thousands of pounds rotating at hundreds of RPMs if not more.

I plan to send the 9521A back in Monday after I contact Channel Master. I am shocked that it could not even make it a year.

I'll possibly change my Amazon rating depending on how Channel Master handles this.

From what I understand, Channel Master is no longer manufactured in the US, it is a Chinese manufacturer distributor. They may be US owned but really just a marketer for Chinese manufacturing.

My old Radio Shack rotator is 15 years old and it still working.

I did some searches, and it appears that without getting into the bigger HAM radio stuff, which can be very costly, are there any recommendations?

Thanks, Bob
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File Type: jpg 2016-06-05 Both Arrays (cropped & RS).jpg (99.4 KB, 2073 views)

Last edited by bobsgarage; 12-Dec-2016 at 11:28 AM.
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Old 12-Dec-2016, 11:59 PM   #2
WIRELESS ENGINEER
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You have way too much load for that light weight rotor

If you could install the rotor close to the antennas and use no more than 3 feet of mast pipe, you might get by but even then the square feet of wind load with those long boom antennas would eventually strip the drive gears

You have created a giant flywheel effect with that heavy pipe and
trying to stop the rotation is likely going to destroy any light duty rotor

Something like the Hygain AR40 might last undertaken those conditions and they are over $300

In the 9521 instructions it says "use no more than 3 feet of mast above the rotor"

Last edited by WIRELESS ENGINEER; 13-Dec-2016 at 12:13 AM.
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Old 13-Dec-2016, 4:09 AM   #3
bobsgarage
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Quote:
Originally Posted by WIRELESS ENGINEER View Post
You have way too much load for that light weight rotor

If you could install the rotor close to the antennas and use no more than 3 feet of mast pipe, you might get by but even then the square feet of wind load with those long boom antennas would eventually strip the drive gears

You have created a giant flywheel effect with that heavy pipe and
trying to stop the rotation is likely going to destroy any light duty rotor

Something like the Hygain AR40 might last undertaken those conditions and they are over $300

In the 9521 instructions it says "use no more than 3 feet of mast above the rotor"
I see, I had not thought that the inertia of the mass of the mast stopping.

Well, I am already in the market for a new type of rotator. I found the Yaesu, but I don't think there is a remote:

http://www.ebay.com/itm/Yaesu-G-450A...gAAOSw5cNYSEIF


You are correct the AR-40 is comparatively expensive:

[url]http://www.hy-gain.com/Product.php?productid=ar-40[/url
]
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Old 13-Dec-2016, 11:37 AM   #4
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The use of the thrust bearing arrangement eliminates the need to limit the stub mast length. That restriction is in place to limit the lateral loading on the rotor motor's output shaft bearing.

WIRELESS ENGINEER is completely correct about the mass of the antenna system that the rotor can handle. When that much mass has to either be started or stopped, there is a tremendous amount of inertia that must be overcome and it will cause the drive unit to fail very prematurely.

For antenna arrays this large, an entry level "ham" rotor is recommended, they're going to start in the $300-400 price range and will probably last a lifetime barring storm damage.
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Old 14-Dec-2016, 10:16 PM   #5
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.,.................

Last edited by WIRELESS ENGINEER; 14-Dec-2016 at 10:59 PM.
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Old 15-Dec-2016, 12:10 PM   #6
bobsgarage
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Mounting tab

Quote:
Originally Posted by WIRELESS ENGINEER View Post
Did a little more research and saw someone had a similar issue
They dealer he bought it from said if they are using thrust bearings, they needed to break off the tab on the rotor body just above the u clamps

He did that and it would turn 360 degrees again
Thanks for your continued interest in my rotator fiasco.
Early on I knew to remove the tab on my CM 9521, it is absolutely necessary for my type of install.

The tab is of course if you are mounting to the top of your main mast. It makes it easy to leave the rotator loose while positioning it. It also may be responsible for weight bearing, but once the clamps are tight, I don't think it will make a difference.

I actually checked for binding in my support bearings while my rotator was slid down . I could easily spin the mast by hand.

I read through the CM9521A instructions and saw nothing about weight limits, although I agree there has to be a weight limit.

Still looking for a deal on a better rotator.



Thanks, Bob
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Old 15-Dec-2016, 12:19 PM   #7
bobsgarage
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Quote:
Originally Posted by ADTech View Post
The use of the thrust bearing arrangement eliminates the need to limit the stub mast length. That restriction is in place to limit the lateral loading on the rotor motor's output shaft bearing.

WIRELESS ENGINEER is completely correct about the mass of the antenna system that the rotor can handle. When that much mass has to either be started or stopped, there is a tremendous amount of inertia that must be overcome and it will cause the drive unit to fail very prematurely.

For antenna arrays this large, an entry level "ham" rotor is recommended, they're going to start in the $300-400 price range and will probably last a lifetime barring storm damage.
I fear you are correct, the starting and stopping inertial force are too great for the CM 9521A.

I am researching the rotator choices as I have time. As for now, I may set the rotator for it's strongest signal and leave it all winter.

Todays temps are -1 F and wind chills of -25 F with 8" of snow coming over the weekend... Glad I got that rotator changed last Saturday when it was a balmy 25F
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Old 15-Dec-2016, 3:44 PM   #8
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Given your current configuration, the only rotor out there looks to be the Yaesu G450

It has over 200 ftlbs of braking force though it can only handle 22lbs of mast weight

Also look at https:\\swap.qth.com

I see is several very heavy duty rotors listed for reasonable prices there
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