motor imprecision

hairybadger

hairybadger

Bricoleur
My Satellite Setup
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My Location
near Geneva, Haute-Savoie, France
I'm having issues setting up my motorized dish correctly. 7E is near as dammit due south for me, so I use this bird to get started. The pole is plumb (have just rechecked for the Nth time). Now - if I go to 30W and use "positioner setup", in "fine positioning" I need to dab "step east" 4 times to get maximum signal. If I use 31.5E, it's "step west" 3 times. This makes life difficult when I'm trying to get anything with more marginal reception (57E Durok for example). I'm using USALS and my co-ordinates are correct. The only thing I can think of is that the motor (Moteck SG2100A) is a bit pants and has some sag in it, although the dish at 1m(aluminium) is well within the design parameters (up to 1.2m). Thoughts?
 
could be a few things still not aligned correctly possible slight adjustment of the dish elevation or as you say the Motor could have some play in the stub and on the far east-west points even a light dish can weight the stub over more than it should be
 
I should think that it's a small error in dish backplate setting.

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Had this with my Technomate motor when I mounted my 1.2M dish on it. It was play in the gearing. The only other thing I can add to the other suggestions is that it could be the bolt holding the stub to the motor drive which has come slightly loose.
 
Tivù said:
I should think that it's a small error in dish backplate setting.
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Hmmm - so I can adjust the elevation of the motor on the pole and the dish on the motor, so it's conceivable that I have them misset so that although they're fine together at 7E, they're off further away from due south. Idem for E/W. Is this what you're driving at?
 
Pretty sure it's misaligned on elevation/declination like others said.

You can also cheat by changing your lattitude setting to manipulate the arc 'curve' but it's more of an alignment issue still.
 
If there's only a small error, it won't be evident across the central part of your Arc, only towards the ends.

Same applies whether it's the pole half a degree out, the dish half a degree out, or even the Motor Latitude/Elevation.

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Captain Jack said:
Pretty sure it's misaligned on elevation/declination like others said.
You can also cheat by changing your lattitude setting to manipulate the arc 'curve' but it's more of an alignment issue still.
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OK, I can go with that - unfortunately I find it pretty difficult to make fine adjustments, especially with the crocodile-mouth clamps. Tighten one bolt and it throws everything off :) I take care to tighten the bolts in sequence, a little at a time and still can't quite get it right...
Don't fancy my chances of correcting the error by cheating on the latitude....
 
It could also be your LNB, it may not be truly horizontal at the "Due South Satellite" if it was off a tad bit it will affect the signals at the far end satellites, as the motor skews the dish if the LNB was not true the skew will be off.
 
hairybadger said:
Don't fancy my chances of correcting the error by cheating on the latitude....
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No, but when my old motor started to move at the arc ends, I altered the satellite position to compensate. I.E. if you were looking for 57E and the dish was on say 59E, alter the position a couple of degrees so that the motor thinks it's looking at 55E then the freeplay in the motor has been compensated for. Mind you I was using USALS.
 
Could be a loose boom-arm on the dish, and this may not be helped if you are using a heavier (quad ?) LNB.
 
sonnetpete said:
No, but when my old motor started to move at the arc ends, I altered the satellite position to compensate. I.E. if you were looking for 57E and the dish was on say 59E, alter the position a couple of degrees so that the motor thinks it's looking at 55E then the freeplay in the motor has been compensated for. Mind you I was using USALS.
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Ah, now this is what I did in order to scan in 70.5E. Bit irritating though, because you have to be careful not to replace satellites.xml....
 
Just one further thought. When I set up my pole, I use a digital angle finder and ensure it's plumb to within 0.1 of a degree. Same with the motor, I put the angle finder on the motor backplate where it joins the pole and try to tighten the bracket to within 0.1 of a degree. I guess any difference would be more noticeable on my 1.2M. I take it you've tried flexing the dish/motor when it's at the end of your arc to see if you can perceive any play in the motor?
 
hairybadger said:
7E is near as dammit due south for me, so I use this bird to get started. [...] Thoughts?
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But you did send the dish to 7E, right? Your coordinates say 6.4E so that is not near as damn it. Correct way to set up is enter your coordinates, then move the motor to your nearest due south satellite. Then start your alignment. You don't do the alignment with the motor pointing at zero.
 
sonnetpete said:
Just one further thought. When I set up my pole, I use a digital angle finder and ensure it's plumb to within 0.1 of a degree. Same with the motor, I put the angle finder on the motor backplate where it joins the pole and try to tighten the bracket to within 0.1 of a degree. I guess any difference would be more noticeable on my 1.2M. I take it you've tried flexing the dish/motor when it's at the end of your arc to see if you can perceive any play in the motor?
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I've been using a simple spirit level - have just ordered a digital one to see if I get better results with that.
I *think* there is a bit of play in the motor, but I have nothing to compare it with so am not really sure. I'll try all the other ideas before replacing the motor, though.

Thanks to all for the suggestions :)
 
Huevos said:
But you did send the dish to 7E, right? Your coordinates say 6.4E so that is not near as damn it. Correct way to set up is enter your coordinates, then move the motor to your nearest due south satellite. Then start your alignment. You don't do the alignment with the motor pointing at zero.
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Sure - I meant I aligned using this satellite, 7E being the best candidate. I sent the motor to this position (USALS) using the receiver and played with the alignment until the signal was maxed out. However - now you've made me doubt exactly what I did to set it up. Seeing as I have a roughly equal but opposite error on each side I *suspect* that E/W isn't too bad and it's the elevation balance between the pole/motor and motor/dish that's the problem.
 
Motor elevation should be 43.2º, Holding the digital level parallel with the seam around the motor.
 
Huevos said:
Motor elevation should be 43.2º, Holding the digital level parallel with the seam around the motor.
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thanks - will have to wait for the digital level, the scale on the motor itself is a bit crude. Could you please explain to me why 43.2°?
 
hairybadger said:
explain to me why 43.2°?
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90º - 46.1º (lat) = 43.9º. But your southern satellite is 3600km closer to you than the satellites at the end of the arc so you need a bit of extra downward tilt. For latitudes between 35-55º that is always around 0.7º lower. So, 43.9º - 0.7º = 43.2º
 
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