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Old Nov 27, 2012, 02:23 PM
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United Kingdom, England, Birkenhead
Joined Nov 2012
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My servo is broken :-(

My Angell Airbus was never the same again after sharing a rather intimate moment with a tree a few weeks ago (DOH!). That's OK though because I fancied having a go at making something so the gubbins are now in an rc boat. I noticed though, that the servo was a bit hit and miss while I was putting the boat together. Perhaps that explains why the tree failed to get out of the way. I put it together anyway to try it out but the servo has finally given up. I see that replacement servos come with three wires, but the one with the Angell Airbus has two.

My questions are these; am I right in assuming that only two wires are required for power, the third being for communication, meaning that the circuit board from the Angell gives or takes power to or from the servo therefore removing the need for communication? If that is the case can I overcome the problem by just not using the communication wire? And If so is it correct to assume that the red and black wires are for power and the third wire whatever colour it might be is for communication?

Thanks for taking the time to help a newbie.
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Old Nov 27, 2012, 08:54 PM
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United States, AK, Fairbanks
Joined Aug 2009
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Quote:
If that is the case can I overcome the problem by just not using the communication wire?
No. It sounds like what you have is some basic type of bang-bang actuator rather than an actual servo. They're common in simple RC toys where proportional control isn't required, and they do that job pretty well.

Trying to use a real servo simply won't work because there's no PWM signal available to drive it. The red and black wires ARE for power, but the third wire tells the servo when to move and where to go. If you just give it power with no instructions, it might not do anything at all. It might also go to one endpoint and stop, or it might go to an endpoint and shred its own gears trying to keep moving. It will certainly not give you any kind of controllable reaction and, assuming your actuator worked in both directions, one direction on the stick will simply fry the servo's brain rather than make it move at all.

You could probably ditch the stock actuator from your plane and build your own simple magnet/coil actuator, but that might be a little more involved than you're looking to get.
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Old Nov 28, 2012, 05:04 PM
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United Kingdom, England, Birkenhead
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Originally Posted by C₄H₁₀ View Post
You could probably ditch the stock actuator from your plane and build your own simple magnet/coil actuator, but that might be a little more involved than you're looking to get.
That sounds interesting, is it as complicated as it seems? I get the impression that it might not be something for people with no clue. (like me)
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Old Nov 28, 2012, 10:47 PM
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Joensuu, Finland
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See this post: http://www.rcgroups.com/forums/showp...74&postcount=3

It is not difficult once you know what you are supposed to do: just wind some wire into a loop and put a magnet inside it.

Which brings up another point: an actuator is such a mechanically simple device that there isn't much to go wrong. You could first check if there are any broken wires or other mechanical damage. If you have a multimeter, you could disconnect the actuator and measure the output between those two wires - it should be zero when the controller stick is centered, some positive voltage for one direction and a negative voltage for the other direction.
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Last edited by jkettu; Nov 28, 2012 at 10:57 PM.
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Old Nov 29, 2012, 03:58 PM
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United Kingdom, England, Birkenhead
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My friend did that test we reckon the motor was broke.
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