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="]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.
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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="]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.
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