Servo Wire Length?

Ok, you have convinced me to do away with the bellcranks on my 51 and install servos in the wing. My next question is.. I`ll have to use a Y harness and
extension since the servo lead will be about 6 inches short of reaching the center of the wing. How long can I go without needing an amplifier or some kind of help without worring about signal loss?
Thanks
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There should be no problem in what you are describing. I have used as much as 2 ft extra with no problems.
Gord Schindler MAAC6694

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SKYLANE42 wrote:

About 150meters at a guess :-)

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wrote:

Although it doesn't address signal loss, the IMAA High Flight archive article "Big Servos Need Big Wire" does concern voltage drop versus wire length/guage. It's at http://www.fly-imaa.org/imaa/hfarticles/electro/v6-4-43.html
FWIW. Cheers, Fred McClellan the dash plumber at mindspring dot com
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Fred McClellan wrote:

Yes. But you can make all that up with a 6V pack.
Signal; loss on a 5V pulse in the ms range will be very small over considerable distances. Eventually the edges will be rather smeared and the servo position will start to be a tad inaccurate.
Howvere, if it gets that bad add a second reciever, power pack etc, and just run the whole lot locally :)

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I've used servo wires in wings up to 4 feet long. The one thing I am careful about however, is to use four wire material and use the fourth wire as a ground. NEVER have had a problem.
MJC

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MJC wrote:

Neat trick. I'll remember that.

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Sounds like a clever idea. What do you ground the wire to? Just one end, I'm assuming?
Rein

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Correct. The fourth wire acts as a shield so soldering it to the ground wire at the receiver end but LEAVING IT OPEN at the servo end will keep an open loop which is what you want.
MJC

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Wait, when you say "ground" you mean the negative side of the battery yes? The same negative as is travelling along one of the 3 wires going to the servo already? Or do you have some kind of earthing system on your aircraft? Also, when you talk about 4 conductor cable, do you actually mean shielded cable?
Russ.

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Russ wrote:

He does, yes.

Yes, but that is carrying lots of spiky current from the servo.
Its complicated, but a piece of wire cobnnceted to what teh reciever considers a 'cold' place - and teh negative is usually the coldest - sucks up interference in teh neighbourhood.

Not necessarily, $ strip ribbon is better then nothing. Shielded cable would be marvellous, but expnsive and tricky to work with,

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Russ wrote:

You are missing something.
Thibk of a long pice of wire. Makes a great aerial doesn't it? How DOES it do that since its so thin...and has no effective aera to cover?
Well the tiny currents induced in teh wire by the signal, make a field of their won that radiates out, and cancels the signal all around. So an aerail that is a stragight piece of wire can pick up signals that actually when you measure the power, would seem to come from a big chink of space. If you tune the aerial to the signal you want, the effect is even better.
Now think that this aerial is earthed to the reciever. It sort of damps down energy, directing it to ground, in the vicinity. Not as good as a screen, but still a lot better than nothing. In fact its SO close to the other wires that there is quite a bit of capacitance directly between them, so that shorts out spikes a bit as well.
The maths is horrendous, and I have forgotten all of it, but I remembered the result - derived I think via tensor calculus from Maxwell's equations - but the result - that a load of earthed conductor near 'hot' wires gets rid of interference, is well known and proven.
Whether its the capacitance or the EM effect that dominates depends on geometry. My guess is that capacity does in this case. BUT it also stops the servo wires picking up other stuff that is floating around, and injecting it into the receiver...screening would be the ideal ion this case.

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