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Jun 22, 2012, 09:37 AM
Acacia II Lunar Lander
RCRod's Avatar
Question

Wire Gauge for Digital Servos


I'm starting a re-wiring project on my current F3F racer (Acacia II), and am preparing for a new build (Willow). I've come across a question I'd like some help with: wire gauge for running plumbing to the digital wing servos.

What gauge do you use?

I know the bigger seems better, but I'm finding that running 22 AWG through a single connector on my Acacia II's center panel is feeling very crowded. I have an 8-pin multiplex connector (like the green 6-pin ones we all know and use, but with an extra two pins) through which I'm trying to connect all four servos. With the fat 22 AWG stuff, it's pretty tough to get 12 leads crammed together around the little pins. I'm trying an experiment wherein I'm only running power (plus/minus) from two channels, and just signal wires from the other two into the fuse side of the connector. I'll branch the power on the wing side a little bit downstream from the connector, so I have room.

Is that silly? Am I over-killing it with the fat 22 AWG? Should I scrap the single 8-pin connector and go to two 6-pin connectors, so they're not as crowded?

Any experience-driven opinions would be appreciated!

Cheers,
Rod
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Jun 22, 2012, 01:38 PM
Hot Dawg Glider Pilot
schrederman's Avatar
I run 22awg for power and 28awg for the signal wire to save a bit of weight. I tax my wing servos pretty heavily during launches.

Experience:

I manage a large number of various types of radios that average 60 watts output, (railroad). Recently we changed the input wiring in a series of facilities from #12 to #8. These 100 watt radios were drawing enough current that the voltage was dropping below the minimum threshold. The change in input wiring guage solved the problem entirely.
Jun 22, 2012, 01:54 PM
F3B
satinet's Avatar
I wouldn't worry about the gauge too much. The stall current on the servos will be a lot less than the rating of even pretty thin wire.

I've haven't heard of or experienced having problems (f3b etc) running 6 digis off 1 servo plug in to the receiver, which powers the 6 servos. Unless you bypass the receiver an power your servos direct from the battery you are only running all your servos through a pair (or maybe two pairs) of servo pins going in to the rx. (Usually I put two leads in to the RX to be on the safe side. )
Jun 22, 2012, 02:28 PM
Registered User
I use 24 guage teflon coated for power and 26 for signal. Expensive wire but using stock 22 guage servo wire adds an extra ounce or more to a model.
Jun 22, 2012, 03:26 PM
Acacia II Lunar Lander
RCRod's Avatar
All good info, guys. Thanks a bunch!

I think I'll step down to a smaller gauge. Stuffing the crimped ends of the 22 AWG wires into the connector housings is a pain in the butt.

Satinet, you touched on a point I was considering, as well. It hardly seemed necessary to run so many power leads to the wing, when the entire system is pulling juice through only the wires from my BEC.
Jun 22, 2012, 03:43 PM
F3B
satinet's Avatar
well my point is merely that if you are running all your servos through one power lead that is the same rating as each individual servo wire, your problem is not your servo wires. not that there is a problem.

It's really solving a problem that doesn't exist. yes you can pull a fair bit of current on a winch launch because you have a lot of deflection on the surfaces and a lot of speed, but the wire can take high loads for a short period quite easily.
Jun 22, 2012, 03:48 PM
Eagle Butte User
PDX Slope Pilot's Avatar
Good topic and something I have always wondered about...
Jun 22, 2012, 04:10 PM
F3B
satinet's Avatar
some info about servo wire ratings here:
http://www.smservices.net/acatalog/Cable_and_Wire.html

in metric but you can convert it. I assume 0.34mm is the same as 22awg (looks like when I bought some). That takes 6amp continuous and 12+amp for 5m minutes. So even if you go down a grade i very much doubt you will have a problem.

IIRC the typical stall current of a digi wing servo is something like 1-1.5amps.
Jun 22, 2012, 07:26 PM
Acacia II Lunar Lander
RCRod's Avatar
Really helpful posts, Satinet! Thanks very much!
Jun 23, 2012, 01:26 AM
In F3J size does matter!
roydor's Avatar
In the following link you will find a chart with max current and a calculator for the voltage drop.
http://www.powerstream.com/Wire_Size.htm

In general it is wise to de-rate the wires by a factor of 2, this means that for a servo with a current draw of 1 amp you wouldn't use a wire with less than a 2 amps for its max rating.
Jun 23, 2012, 03:04 AM
F3B
satinet's Avatar
Quote:
Originally Posted by roydor
In the following link you will find a chart with max current and a calculator for the voltage drop.
http://www.powerstream.com/Wire_Size.htm

In general it is wise to de-rate the wires by a factor of 2, this means that for a servo with a current draw of 1 amp you wouldn't use a wire with less than a 2 amps for its max rating.
With this information plus the stall current of your servo you should have no problem working out what you need.
Jun 23, 2012, 07:54 AM
Acacia II Lunar Lander
RCRod's Avatar
Nice resource! Roydor, do you know if that data is for single- or multi-conductor wire? Servo wire is all multi-conductor.
Jun 23, 2012, 08:19 AM
Acacia II Lunar Lander
RCRod's Avatar
Here's another good resource...

Hansen sells wire and connectors. This PDF is his a how-to for creating servo leads and extensions.

http://www.hansenhobbies.com/product...Connectors.pdf

He includes a table of gauges and resistance. The only data missing is max amperage. Is there a formula we can use to determine that?
Jun 23, 2012, 11:04 AM
Registered User
J. Wydronek's Avatar
There is a formula it is current=voltage/resistance of wire per unit length. So if you are using a 3 foot piece of wire and it measures 5ohms

Current=6.0volts/5 ohms
Current = 1.2 amps
Jun 26, 2012, 07:32 AM
Hot Dawg Glider Pilot
schrederman's Avatar
I used the heavier wire not for current carrying capacity, but for the drop in voltage over the long leads.


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