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Old May 29, 2009, 06:49 PM
SOARMINDED
GNX430's Avatar
United States, OK, Mannford
Joined Jul 2006
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Long servo wire lead gauge??

Hey Gang,

I just got off the phone with a Dave at Hoopes Design trying to figure out a harness setup that would work. I have a 5 servo wing and I have ran twisted HD Hitec servo wire to all servos in the wing. My question is Dave is set up for 24 gauge wire and not the HD 22 gauge wire I am running. My main panel is 73" long and tip panel add another 29" to servo pocket. Would a 24 gauge wire be ok to run all the way there with a connector at the fuse and at the tip panel or would there be a bad volt drop this far with the thinner gauge? I am running 5125 digital servos in the tip panels and i think digital 5645 in main panels. I really liked Dave's honesty about not sure about my setup and asked me to do some research before i asked him to build my harness. I have tried to make my own harnesses in the past lets just say soldering BIG wires to small pins is NOT FOR ME Tired of plugging in 10 wires each time!
THANKS Jerry
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Old May 29, 2009, 08:46 PM
Registered User
New York
Joined Feb 2002
3,075 Posts
Why can't Dave use the HD Hitec servo wire which is excellent and what I use all the time. I can't think of any reason why he can't either crimp or solder it to whatever connectors you're using. Wherever possible I suggest crimping over soldering.

Steve
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Old May 30, 2009, 11:29 AM
SOARMINDED
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United States, OK, Mannford
Joined Jul 2006
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Hi Steve,

I don't want to speak for Dave but what he told me is he has a special high dollar crimper just for the 24 gauge wires. He also said he ONLY crimp's so maybe i should look into this myself. I could not gang wires easily ( WELL FOR ME ) on a single pin when soldering so crimping looks like a great idea. Now i am not going to gang the common wires and make my own harness if i can find a suitable connector. I would need a 15 slot connector or maybe the 12 he shows on his website would work with a couple common wires ganged?? I have a 1 1/4 x 2 1/4 area for a connector so size doesn't matter in this case Steve THANKS for help.
Jerry
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Old May 30, 2009, 05:09 PM
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New York
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Jerry, everyone in this hobby does things differently so I'm not saying my way is better than anyone else. I've evolved into it and find it is extremely reliable.

My general wiring approach is to create "home runs" for every servo. By that I mean running a set of twisted 3 Hitech servo leads to each servo and to terminate the other ends with an appropriate connector. I recently finished a 5 meter Thermic with an 8 servo wing which had 24 leads. I used a multi-pen male computer connector which mates the appropriate female connector mounted in the fuse so when the wing is attached all the servos auto-connect at once. I avoid ganging the reds and blacks for a number of reasons.

The mating connectors are D-Sub connectors from Digi-Key Corp. Depending on the available space for the connectors I sometimes use high density D-Subs with 3 rows of pins, otherwise the connectors have 2 rows.

All of the leads are crimped at the connector end and at the servo end. At the servo end I use female connectors from Maxx Products. Crimpers vary in quality. I find the Molex brand available from Digi-Key is by far the best.

With a little practice, you should find crimping very easy to do and if done right it produces a very strong and consistently reliable connection without the problems that soldering can produce if not done very carefully.

Let me know if you need any more info.

Regards,

Steve
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Old Jun 12, 2009, 04:32 PM
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solitairyman's Avatar
Antwerp, Belgium
Joined Oct 2007
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Servo in wing

Hi,
I use this system to connect servo's in the wing.
Maybe if the leads are about 60" a the special coils were you take the wires through to enable the wrong signals to the servo's.
Grts,
NoŽl
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Old Jun 12, 2009, 07:06 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
Jerry, my favorite subject!!!

So, to answer your question regarding 22 AWG vs 24 AWG, the bottom line is that you will see about 1.6 times the voltage drop across a specific length of multi-strand 24 AWG wire than you will with the same length of 22AWG equivalent wire.

Here are some "relative" data between the two wire guages (the actual values will change based on the actual properties of the copper, size of the individual strands etc so the data I will present here should be viewed as "relative" - relating 24AWG to 22AWG):

The voltage drop (V) across a length of wire is measured as a function of current flowing in amps (I) and resistance (R) in ohms. V = IxR

For 22 AWG wire, resistance is 16.14 ohms per 1000 ft
For 24 AWG wire, resistance is 25.67 ohms per 1000 ft

The smaller the guage wire, the higher the resistance per unit length.

Your wires are 73" + 29" = 8.5 feet

Therefore the resistance of the 8.5 feet length of wire for each guage is:

R for 22 AWG (8.5') = (16.14/1000ft)x8.5ft = 0.13719 ohms
R for 24 AWG (8.5') = (25.67/1000ft)x8.5ft = 0.21819 ohms

The longest lead is presumably the aileron one that has the HS 5125 servo on it. Under load, this digital will probably pull up to about a max of 1 amp (this is a guess as the only specs I have for the HS5125 is the no-load running currents at 4.8V (180mA) and 6V (230mA)).

So, IF the servo is loaded to draw 1 AMP, the voltage drop across the 8.5 feet of wire will be as follows for each guage:

22 AWG: V=IxR = 1AMP x 0.137 ohms = 0.137volts, or 137 mV
24 AWG: V=IxR = 1AMP x 0.218 ohms = 0.218volts or 218mV

The relative difference is that you will see 1.6 times more voltage drop across the 24 AWG wire than you will across the 22 AWG wire.

If the current was increased to 2 amps, these numbers would be double those stated above but still have the same 1.6 relative difference.

At 2 amps - 22 AWG = 2 amps x 0.137 ohms = 0.274V or 274mv (about a 1/4 of a volt)
At 2 amps - 24 AWG = 2 amps x 0.218 ohms = 0.436V or 436mv (close to a 1/2 a volt)

If you are operating a 4 cell pack with say a nominal voltage of 4.8V, the servo would see the following under 1amp current draw from the pack:

22 AWG - servo would see 4.8V - 0.137V = 4.663V
24 AWG - servo would see 4.8V - 0.218V = 4.582V

With a nominal 5-cell 6V pack, those voltages would be:

22 AWG - servo would see 6V - 0.137V = 5.863V
24 AWG - servo would see 6V - 0.218V = 5.782V

The bottom line here is due consideration to the complete system and an understanding of the current draw of the servo's. The HS5125 probably has a lower stall current value than the HS5645. If you were going to put the HS5645 out at the aileron and do 3D type work where the loads on the servo would be high, the commensurate current draw would also be high and therefore the voltage drop across the 8.5 feet of wire would be proportionally higher.

I assume this is a sailplane and a scale one at that. We generally don't do 3D work with our scale sailplanes and therefore, assuming good building skills and no binding hinges, our loads are generally smaller. Smaller loads = smaller current draw = smaller voltage loss along our wires.

Along with the relative data, bear in mind the number of cells you operate with and the relative losses across the 8.5 feet of wire. If you use 4 cells and you run the pack down to 4.8 or lower, your servos will start to see even lower voltages. With 24 AWG these would be 1.6 times lower than 22 AWG.

One last point, and the following are somewhat conservative numbers, the maximum current handling capability of each wire is:

22 AWG = 7 amps
24 AWG = 3.5 amps

There are many variables that need to be considered when calculating the maximum current a specific wire guage can handle but if you use these general values, you should have a conservative and relatively safe power transmission system for your model.

So, that's the data. Let me know if you still have questions.

Tony
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Old Jun 12, 2009, 07:39 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
So, after a few minutes thought, I'm guessing that this info may or may not help. If it doesn't, we can approach the subject from a different vector - how to use the data! Let me know. Tony
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Old Jun 12, 2009, 08:12 PM
SOARMINDED
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United States, OK, Mannford
Joined Jul 2006
410 Posts
Tony, Steve R,

THANKS for the help and Idea's. Funny I hadn't checked this subject till now. I went ahead and found the coolest prebuilt 20 connector at Fry's with wire already connected. I took pics and will post them once I figure out why my new camera software won't load ( screen not formatted for camera? ) This is great help Tony showing what real life is happening with the OHM values! This is a scale bird 1/3 Ventus and i do have dual 3200 mah 4 cell packs installed now. The new connector i found and wired in has like 16 or 14 Gauge stranded wire so the 20 Gauge servo wire from Hitec is the weak link now. I will give more data and info on connector when i can figure the new camera out. Tony I am going to PM you.
THANKS Jerry
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Old Jun 13, 2009, 07:10 AM
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Tony, as usual your engineering analysis is dazzling. But for those of us who are severely numerically challenged, let me ask an embarrassingly simple question. For the average flier, if we could test fly two identical sailplanes, one with 22 vs 24 gauge wire, do you think we could tell them apart based on how well they flew?

I pose the question sincerely. My personal belief is there are so many variables with model aviation that my guess is only the best of the best pilots might just be able to clearly identify one from another. Maybe.

I always make it a point at an aerotow to look closely at as many planes as possible to pick up new ideas about construction and installations. I'm amazed some of these planes get up and down in one piece or fly as well as they do given so many basic issues with construction, equipment installation, etc.

It's a great hobby,

Steve
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Old Jun 13, 2009, 08:09 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
LOL!!! Probably not (answering your specific question relating to "how well they flew").

However, that does depend on the type of plane and the flying you might do with it. For a sailplane, in general, you probably would not see any differences until your battery packs were real low. Once you have low levels of energy left in your battery packs, the pack no longer maintains the ability to provide the system with a stable voltage. If you needed to pull energy from a low pack for a demanding maneuver or to rescue from a troublesome condition, the voltage to the servo's would be further reduced by 24 AWG wiring over 22 AWG. That reduction in voltage would result in reduced torque available from the servo and a condition where you simply might not be able to perform the maneuver you needed to.

If you had a large aircraft and you wanted to do significant 3D work with it and fly very fast, high load, snappy maneuvers - you'd soon see the difference if you were using a low 4.8V pack and 24 AWG wiring for those same reasons.

I hear you say that one shouldn't fly with such a low pack - I agree. However, not all sailplane pilots have on-board telemetry that can provide them feedback about battery pack voltages. The variables are, as you note, many.

This is what happens when one is a designer/engineer - one has to analyze everything - where do you think the word anal came from

The real point of the dialog was to provide some data so that a person could draw their own conclusions. I am a believer that once armed with information - you can conquer the world!! Information is king as they say.

However, as I said in my second post, I'm not sure if the data helped or not because it could be quite a leap to go from the "now I know what voltages I'm dealing with" to "now I know how to design the system and what wire guages I need". Being a designer/engineer with a EE background, the picture is very clear for me. Hence the reason I indicated I would provide further help if needed.
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