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Written by Jim Hiller
RC Jets
As seen in the RC Jets 2020 issue of Model Aviation.

the electrodynamics one-clik multi-connex connector is shown installed between the front and rear half
The ElectroDynamics One-Clik Multi-Connex connector is shown installed between the front and rear half of the Mephisto’s fuselage at the break point. The fuselage easily breaks down into two halves for handling. Install four bolts, attach the two servo connectors that connect five servos, and you are ready to go.

LET’S DISCUSS SERVO EXTENSIONS or wiring harnesses for our larger, more complex aircraft that have so many servos located throughout them that it is intimidating.

My latest model, a CARF-Models Mephisto, is one example. It has more than 60 feet of servo extensions—a wiring nightmare. The Mephisto has a fuselage length of 123 inches, combined with a separate servo on each surface, plus flaps, and two-axis thrust-vectoring servos. It uses most of the available 18 channels.

What are our options for servo extensions? Maybe I should first discuss the requirements. For longer extensions to servos with high-torque ratings of 400 to 700 ounce-inches and more than 36 inches of length, I prefer 20 American wire gauge (AWG) wire. Normal wire is 22 AWG. I have been using wire with silicone insulation for its flexibility and temperature rating—a proven-quality wire insulator for any application. The thicker 20 AWG wire is needed because of the higher amperage that is required of these powerful servos. Lower-rated servos can use 22 AWG wire with no issue, especially with normal-length extensions.

Insulation options are changing. Until recently, we typically had the option of two grades of insulation on our wires: cheaper and stiffer PVC, or an upgrade of the more flexible silicone insulation.

PowerBox Systems has introduced a line of twisted servo wire with a thinner insulation based on full-scale aviation use. I haven’t used this product yet, but maybe I’ll give it a try on my next build. This insulation should be less affected by kerosene fumes as the model aircraft ages. Check out some of your older models that use PVC insulated wires. They might be getting brittle.

That was the basics on wire, so on to connectors. Servo connectors are not the only option, and we all use standard servo connectors at the ends that go to the receiver and the servo, but in between we have options.

I have been using the ElectroDynamics One-Clik Multi-Connex system. One connector can connect up to four servos, which is convenient. The One-Clik is made for simple installation with approximately 4-inch servo leads on either end, with the multiconnector in between. After it is installed, only the One-Clik is utilized.

This product is available in two, three, or four servo-connection options. The ElectroDynamics One-Clik Multi-Connex is made to fit between your standard servo extensions, acting as one simple connector for multiple servos. I secure the servo extensions to the One-Clik with ½-inch heat-shrink tubing to ensure that I do not accidently pull apart the servo connector.

I have been using the two- and threeservo connectors and have been happy with the convenience and reliability of these products on regularly used areas such as the wing panel connection, where there are multiple wires to connect. Using only one connector, I connect the aileron servo, flap, electric retract, and the electric brake. It’s sweet and simple.

electrodynamics has a simple solution for an easy connection between your wing panel and the fuselage when you have multiple servo connections
ElectroDynamics has a simple solution for an easy connection between your wing panel and the fuselage when you have multiple servo connections. The One-Clik Multi-Connex is available in versions for two to four servo connections.

Now let’s go on to the wiring harness itself, how to make up the wiring harness of servo extensions, and where to get the material.

Option one is to buy separate servo extensions of the lengths required for your model then route them throughout the airplane. This is a quick and simple way to procure your necessary servo extensions, but you might find the selection limited in terms of quality and length.

The next level of wiring harness is custom servo extensions that are manufactured according to your needs and specifications and sized to fit your model with all of the options that you want. This method requires you to lay out your needs, measure carefully, write up an accurate and detailed document of what you require, then source it out to be made.

I have sourced my harnesses multiple times with ElectroDynamics and have been happy with the company’s work. The staff’s knowledge and experience can help you avoid problems, especially with unusual installations.

this is an example of how to clean up your servo harness by using a simple hardware store grommet that protects the servo extensions from the abrasive fiberglass
This is an example of how to clean up your servo harness by using a simple hardware store grommet that protects the servo extensions from the abrasive fiberglass. The tie-wrap on the lower left secures the wire harness to the fuselage. Just drill two holes and wrap the tiewrap around the wires as you tighten it.

I had a 6-meter sailplane that had 8-foot servo extensions. The company’s technical experience showed with proper installation of the buffer-amplifier interface to improve servo performance. It pays to work with experienced and knowledgeable people.

Lately, I have been making up my own wiring harnesses, cutting the wire to length then installing my own connectors as required. It’s a time-consuming and tedious job, but convenient because there is no wait time while a supplier makes up my harness.

This process is not for everyone. You’ll need specialized tools, new skillsets, and patience. I enjoy making my own wiring harnesses as I go because it allows me to customize and fit the wire lengths accurately for my new aircraft. It’s not easy, but it’s just another part of the fun of modeling.

Hansen Hobbies sells a good starter kit called the Deluxe RC Connector Kit to make your own servo connections. The kit includes the tools and enough servo connectors for a typical model, so it’s a great starting point.

You will find learning to make quality crimps on the connectors difficult (it is more complicated than you think), but as your knowledge increases and skills grow, you’ll find that you can move along at a good and reliable pace.

The best advice I have is to find someone who has experience making his or her own connections and learn from that person. It will greatly reduce the learning time. Most of us have made the same mistakes until we figured things out.

Hansen Hobbies carries a nice selection of wire, servo connectors, and even its own multiple connectors. The company can serve as a good source as you learn this process.

Moving on, the servo extensions are all made to size, so let’s discuss how to route them throughout the model and secure them along the way. You don’t want them flopping around inside of the model as you fly aerobatics.

There are many solutions to the problem of securing a wiring harness to a model. Each is dependent upon the aircraft’s construction, the routing of the wires, and your preferences. I have used tie-wraps looped around the harness and through some type of fixture that is glued to the inside of the model. It works well, but don’t squeeze too tightly and damage the wire insulation.

Another method that I like is used by BVM Jets in its PNP line of jets. The company has a neat little laser-cut plywood package that you can glue to the model’s inner skin. An O-ring is then hooked over the wires to secure them. It’s simple and easy, so check it out.

In a previous column, I mentioned the use of a soft fiberglass sleeve to protect the wires from heat where they are routed through hot areas, such as through the turbine bay and in the aft area of the fuselage near the tailpipe.

These areas require good planning to protect the servo harness. Even the best wire insulation has its limits, so carefully routing and properly securing the wires to keep them clear is required. Take your time and do it right.

It is important that you protect your servo wires from heat and abrasion because our composite aircraft have a lot of surfaces that can damage the wire insulation.

These ideas should help you on your next build. The integrity of your wiring harness is critical to the success and enjoyment of your aircraft. If you think it through and do it right, it can be trouble free.

Experience has proven that what I’ve mentioned has worked well for me, and I hope it can also work for you.

SOURCES:

PowerBox Systems Americas

(904) 330-0145

www.powerboxamericas.com

Hansen Hobbies

chris@hansenhobbies.com

www.hansenhobbies.com

ElectroDynamics

(734) 422-5420

www.electrodynam.com

CARF-Models

www.carf-models.com

BVM Jets

(407) 327-6333

www.bvmjets.com

Jet Pilots Organization (JPO)

www.jetpilots.org

3 comments

Nicely done, as usual. Looks like DeWayne Jr. convinced you to get into a Mephisto. Eh?

Looks like a well worth while read.

Thank you for sharing your experience. Having a neat wire installation is applicable to all size models. I do agree that there is, in my case, a BIG learning curve when making my own extensions.

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