servo motor test?

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elam budmore

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Sep 22, 2008
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sheboygan falls wi
is there a way to test a servo motor? i take it , if i switch polarity in the house, at the dish, i should be able to see the wire looking hook inside the feedhorn turn or move? should it move slow, or flip like a light switch?
 
Anole

Anole

SatelliteGuys Master
Sep 22, 2005
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-no-

I believe the motor needs +5 and ground on the marked wires.
Then, a stream of pulses is applied to the __|--|__ pin with the hat (pulse).

Narrow pulses cause the servo to rotate one way to a preset position.
Wide pulses cause the servo to rotate the other way to a preset position .
The servo may have a total movement of only 180° or so.
By varying the pulse width, the servo will go to and stay at any place you wish.
Then, if the pulses stop, the servo won't move.
 
skysurfer

skysurfer

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Dec 1, 2006
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are the pulses such that a human could imitate them by touching some wires together and separating them (such as one can when testing an actuator pulse circuit) or are the pulse timing such that no human could imitate it to test a servo motor?
 
Anole

Anole

SatelliteGuys Master
Sep 22, 2005
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L.A., Calif.
rough numbers

I don't have the specs, but if they're anything like the servos in model airplanes, the pulses are on the order of 1..3 milliseconds wide.
And they may be spaced 10...50 milliseconds apart.
That'll at least get you in the ballpark.
So, they need to be generated by some electronic circuitry.

I'd looked in manuals, and asked some members with those servos who had an oscilloscope, but never got a clear answer.
 
Hermitman

Hermitman

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Jul 2, 2006
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When you switch the polarity, you shoud hear a whirling sound at the servo for about 1/2 second. That's the servo re-positioning itself. Or if you really want to be sure, remove the servo from the feedhorn assembly, bring it inside and attach it directly to the receiver. Then you can sit there and watch it move as you play with the controls. Good luck.
 
voomvoom

voomvoom

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May 18, 2004
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Lizella, Georgia Republic
If you can get someone to change channel polarity in the house while you look down the throat of the feedhorn, you should be able to see the probe move, if it's working. Or you could take the servo motor or the whole feedhorn assembly into the house and hook it up to the receiver directly and watch the servo motor to see if it moves or look down the throat of the feedhorn to see if the probe moves....?
 
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melgarga

SatelliteGuys Pro
May 11, 2008
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SE Texas
If your an electronics DIY kinda guy, between your junk box and Rat Shack you should be able to throw the circuit on this page together for 3-4 bucks. A lot of other useful servo related info there too.
It is still unclear, at least to me if the polarotor servos are of the same dutycycle to position specification as their robotic cousins. Please posts any results you may determine in your testing.
Code:
h[COLOR="Red"]XX[/COLOR]p://home.earthlink.net/~tdickens/68hc11/servo/servo.html
Anole, 90 deg movement is all that is needed for a H to V swap. 180 would put the diploe back to it's original orientation, just upside down or reversed.
Also, if I understand it correctly, as long as the 5vdc is present, the correct dutycycle pulse must be present as well in order to maintain positition.
 
skysurfer

skysurfer

SatelliteGuys Pro
Dec 1, 2006
1,737
42
If you can get someone to change channel polarity in the house while you look down the throat of the feedhorn, you should be able to see the probe move,

Or just unscrew it from the feedhorn and hook it up directly to a receiver with a known working polarity circuit. It's nice those servos are so easy to remove/change out for testing or replacement.
 
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