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?
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
the dash plumber at mindspring dot com
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 :)
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
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,
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
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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