Faux motor backlash problem – SOLVED (1 Viewer)

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TRG

SatelliteGuys Pro
Pub Member / Supporter
Jul 19, 2007
3,089
2,053
Albuquerque, NM
I’ve been fighting what I thought was a motor backlash problem. About a month or so ago I pulled the motor and fixed the dish on 87W so my wife and I could continue to get our PBS fix. Looking at the motor and possibly sending it in for repair would have to wait for while.

I had noticed that when tightening the dish bracket onto the mast directly the bracket didn’t bottom out like it did on the motor shaft. I also noticed that the motor shaft was not sloppy as I had originally thought. Today I pulled the dish off the roof and started making some measurements. Sure enough the motor shaft was a smaller diameter ~ 1/8”. When I bolted the dish bracket to the motor shaft it never really got tight. The only thing really keeping me from spinning the mount on the motor shaft was the pivot bolt. And the bolt is ¼” verses the hole in the motor shaft ~ 3/8”. Basically this combination of things allowed the dish to rock back and forth a couple of degrees in each direction messing up my alignment. This was a real hassle when it got windy.

They say a picture is worth a thousand words so I’ll post a few with some commentary.

The first picture is of the dish (no motor) on the mast. See the gap between the two halves of the bracket? The mount is tight and the bracket is not bottomed out.

The second picture shows the same bracket mounted on my SG2100 motor. Notice that there is NO gap between the two halves of the bracket? The mount is NOT tight and the bracket IS bottomed out. I can easily make the bracket slip on the motor shaft even though the clamp bolts are tight.

The third picture is my fix to this problem. I used a piece of 1 ½” “economy discharge hose” from the Home Depot ($1.16) to build up the motor shaft a bit.

The fourth picture shows the bracket mounted on the modified motor shaft. See the gap between the two halves of the bracket? The mount is tight and the bracket is NOT bottomed out just like on the fixed post.

The fifth picture is another anomaly I discovered when re-assembling everything. First I used my receiver to move the motor to the center position. The pointer on the shaft is dead on zero. Notice that the bracket is off several degrees from the motor? Since the pivot bolt goes through the shaft there is no way to adjust this out. I assume it’s small flaw from the manufacturing process. They probably punch the holes in a flat piece of metal and then bend and roll to get the proper shape. Something might have been a little off during this process. The dish is one of the inexpensive 3ABN (Azure Shine) types.

The dish is back up on the roof and dialed in pretty good, not perfect yet though. We’ll see how it holds up. The forecast is calling for 40 mph winds for today.

[FONT=&quot]Oh and before I forget. I aligned the dish using my new Birdog. The Q meter is a lot less jumpy on the BD then on my Receiver/TV. In fact it’s not jumpy at all. And I don’t have to lug all that stuff up onto the roof anymore. :D [/FONT]
 

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Anole

SatelliteGuys Master
Sep 22, 2005
11,819
12
L.A., Calif.
first rate detective work

I read through your description, and the solution was so clear in my mind, I never did even look at the pictures.
(Okay, I will in a bit) - :rolleyes:

Nice job. Next time someone has this problem, we'll all be on notice that maybe your solution should be applied!
Thanks for sharing. - :up
 

Tron

SatelliteGuys Master
May 6, 2005
6,599
33
Metro New Orleans, LA
Wonder if its is a quality control issue with the 3ABN dishes... Mine mount perfectly to the SG-2100 and fit tightly to the motor shaft. Strange...
 

TRG

SatelliteGuys Pro
Pub Member / Supporter
Jul 19, 2007
3,089
2,053
Albuquerque, NM
Wonder if its is a quality control issue with the 3ABN dishes... Mine mount perfectly to the SG-2100 and fit tightly to the motor shaft. Strange...

It's quite possible there is (was) a quality control problem. If you look at my last photo and description you'll see that the mounting is off by a few degrees when the motor is set to zero. I'm wondering if this explains why I can never quite get the dish to track the arc perfectly. I always seem to compromise on one end of the arc or the other. I also think that there might be some pole flexing going on. Eventually this dish will come down off the roof and go on to a rigid pipe buried in the ground with concrete. I'm not crazy about the roof mount that the dish came with. Besides I've worn out the shingles around the dish. ;)
 

TRG

SatelliteGuys Pro
Pub Member / Supporter
Jul 19, 2007
3,089
2,053
Albuquerque, NM
I read through your description, and the solution was so clear in my mind, I never did even look at the pictures.
(Okay, I will in a bit) - :rolleyes:

Nice job. Next time someone has this problem, we'll all be on notice that maybe your solution should be applied!
Thanks for sharing. - :up

I think it was you that suggested I build up the motor shaft with PVC pipe. I figured the wall thickness of the pipe would be too much. But that's what got me thinking about my current solution. I guess thanks are in order, thanks!
 

Anole

SatelliteGuys Master
Sep 22, 2005
11,819
12
L.A., Calif.
I was just complementing your clear writing.

As for the PVC pipe, that's the standard fix used by SatGuys for years.
(I spend a lot of time reading the archives.) - :cool:
Your solution seemed dandy, as well. Congrats on a job well done.
 
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