What happens if multiple receiver channel signal wires run side by side? - RC Groups
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Feb 02, 2018, 11:36 PM
Registered User
Discussion

What happens if multiple receiver channel signal wires run side by side?


I believe their are members who can shed light on the following (please tolerate and forgive if my terminology is shabby):

If the wing of the rc model had 4 servos, on four different receiver channels, say, throttle, aileron, flap and retract, and;
if all four servos were powered off of a single pair of twisted heavy wires, one positive, one negative, and;
if the four signal wires for the four servos were unshielded and run, separated from the twisted pair, and instead side by side until each branched off to its servo,

Would the operation of one servo likely "interfere" (crosstalk or ??) with the operation of one or more of the other servos, and if so,
could that interference be reduced if each of the four servo signal wires was shielded, or if the four signal wires were twisted?
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Feb 03, 2018, 01:28 AM
Registered User
Quote:
Originally Posted by GoNavy
I believe their are members who can shed light on the following (please tolerate and forgive if my terminology is shabby):

If the wing of the rc model had 4 servos, on four different receiver channels, say, throttle, aileron, flap and retract, and;
if all four servos were powered off of a single pair of twisted heavy wires, one positive, one negative, and;
if the four signal wires for the four servos were unshielded and run, separated from the twisted pair, and instead side by side until each branched off to its servo,

Would the operation of one servo likely "interfere" (crosstalk or ??) with the operation of one or more of the other servos, and if so,
could that interference be reduced if each of the four servo signal wires was shielded, or if the four signal wires were twisted?
Too many variables I think. Would depend on the susceptibility of the particular servos, the drive capability of the rx, the rise time of the signal, the capacitance/impedance/insulation of the wire used etc. etc.

No easy answer IMHO.
Feb 03, 2018, 07:55 AM
No bounce, No play.
davidmc36's Avatar
I have done it both ways. Common power and just all the regular servo wires laying in a bundle.

Have never seen any problems either way.

I've done it with SJ and Spektrum radios and various servo brands.

Bonanza has four servos, retracts, Remote Rx, XBUS, all in one big Ty-Rapped bundle down the center, no issues.
Feb 03, 2018, 10:04 AM
Registered User
Quote:
Originally Posted by davidmc36
I have done it both ways. Common power and just all the regular servo wires laying in a bundle.

Have never seen any problems either way.

I've done it with SJ and Spektrum radios and various servo brands.

Bonanza has four servos, retracts, Remote Rx, XBUS, all in one big Ty-Rapped bundle down the center, no issues.
In your common power installation, what type of wire did you use for the signal, and did you cable or twist the signal wires in any way?
What factors would affect your decision on when to use common power wiring?

I am planning to use, for the first time, mpx multi connectors for the fuselage to wing connections; as I understand things, all the servo power leads are
connected to the same pins, one positive and one negative, so common power wiring from there to the servos in the wings might be more appropriate.
Feb 03, 2018, 10:42 AM
No bounce, No play.
davidmc36's Avatar
I went two gauges bigger than what is on the servos, whatever that is for any particular install.

I have never bothered twisting anything but there sure is no harm in it.

Hard to say what exactly would make me do it. I guess each one anylized for amount of work vs why I might want it; ie: weight savings, complexity reduction when there are many, many wires. DHC-6 had 16 conductors for each wing so servos and lights each got their own common power rails. Some I don't bother sinceit's actually pretty fast to cut all excess off and crimp pins on for multi conductor connectors.

I have been using the locking connectors from Hansen Hobby for most things. I have 4 to 12 pin to use depending on how many conductors. Multiplex or EC for the power buss.

It all makes for easy field set up. No messing with bunches of regular servo extensions, just two or three easy index connectors.
Feb 03, 2018, 11:33 AM
Registered User
Helpful info, thanks.
Don't know how I missed Hansen Hobbies; looks like excellent selection including some unique items, i.e., the Y connector pcb.
Feb 03, 2018, 12:43 PM
No bounce, No play.
davidmc36's Avatar
The PCB looks nice to Buss power together then signals are run separate, nice idea.
Feb 03, 2018, 02:09 PM
Registered User
If I reduce to a single pair common power line with multiple servos, it dawns on me that a failure in either line means all the servos served are out.

That seems unlikely, but my cautious side sees advantage in separate, conventional wiring.

I found an online calculator that might help with the issue of wire sizing in low voltage DC circuits:
http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

(It's not clear to me if the "length of run" is simply point to point or out and back. Doubling the length of run from, say 1 meter to 2, makes a significant difference in suggested wire size.)
Last edited by GoNavy; Feb 03, 2018 at 02:10 PM. Reason: typo
Feb 03, 2018, 02:46 PM
No bounce, No play.
davidmc36's Avatar
There is a valid point to the common Buss. I figure for most of my planes with flaps, all it would take is one single failure anyway to spell disaster.

Just measure one direction.

I use this most of the time:

http://www.calculator.net/voltage-dr...es=2&x=62&y=19
Last edited by davidmc36; Feb 03, 2018 at 03:18 PM.
Feb 04, 2018, 09:21 AM
Registered User
pilotpete2's Avatar
+1 on the locking polarized connectors
I use the 3 pin ones for all my aileron disconnects. Those Y harness pcb's are also excellent for splicing servo wires. I'm old school and won't bury servo connectors in a wing or fuselage, since resistance can build up over time.
Pete
Feb 04, 2018, 09:27 AM
No bounce, No play.
davidmc36's Avatar
Quote:
Originally Posted by pilotpete2
...won't bury servo connectors in a wing..
10-4.

Even if I don't want to reduce conductors, custom wiring to remove unnecessary length and eliminate connectors.
Feb 05, 2018, 07:16 AM
Mark LSF # 3792
I always have a connector at the servo in the wing. Makes it easier to replace if it fails...no soldering or other complex shop tools required. I usually tie a piece of button thread around the connector to prevent it from being disconnected accidentally.

Also, I have in some of my sailplanes run common power wires to the servos direct from the source on point. Signal only has come from the receiver. These have been in non-twisted bundles with no issues.
Feb 05, 2018, 07:51 AM
No bounce, No play.
davidmc36's Avatar
Button thread, perfect. I used to use floss. But I bought some string easier to tie.
Feb 05, 2018, 07:41 PM
Registered User
I use 3/8 inch heatshrink around mating plugs

Just received the mpx multi connectors. A real bear to take apart. No finger grip. Have to pull by pressure on the wires/pins.
Not sure these are the best answer. Have a pair coming that has a panel mount molded in. Might be better.
Feb 06, 2018, 06:50 AM
Mark LSF # 3792
For my most recent assembly of an aero tow glider I used a pair of these:

https://alofthobbies.com/6-pin-mount.html

Really slick. I too have some of the MPX 6 pin connectors that felt real tight. I had not used them before for that reason. Put a small amount of dielectric grease on each pin and after a few insertion/removal cycles they became much easier to use. It is the grease commonly used on automobile connectors and available in small or large quantities and most auto supply stores. First thought of it when I purchased my first Supra. It had Deans plugs for the wing that were a bear to remove. Never had a problem after I applied it.

Also, the MPX style connectors I have on one side of the male connector have a cutout to aid in removal. Haven't tried it yet, but it looks like that cut could easily be enlarged if desired. With the cutout, the mounts and the grease the connectors are fairly user friendly and keyed for polarity.


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