Building Techniques

REPLACING A SERVO PLUG

Kevin Crozier  |  Jul 28, 2021

Each time you assemble your favourite ARTF it's a good idea to check for wear and tear on the servo leads, especially where the wires crimp into the plug. If the wires are starting to break, then it's time to replace the whole plug. You could make new crimps but it's easier to solder on a fresh plug. The most economical way to obtain some new leads is likely to be to buy some 300mm extension leads and to cut them down to length. This size extension lead is by far the most popular, so they are likely to be cheaper than buying a servo lead alone. Female to female leads are also available, which can be cut in half.

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Cutting mats make horrible backgrounds for photographs but are useful for stripping back insulation by the same amount by gently rolling a sharp scalpel over each wire. Pull the cut insulation back by a small amount and then twist it clockwise to evenly twist the bare strands of wire.

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Use a 'helping hands' jig or a bench vise and soft jaws to gently hold the servo lead whilst you 'tin' each wire with solder. A 30W household iron is plenty for this job, or a smaller iron if you have one. Lead free solder, as used here, is more difficult to flow evenly along the wires. 60/40 leaded solder will probably help you do a neater job.

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Tin the wires of the damaged servo lead. Cut short lengths of fine bore heat-shrink tubing sufficient to cover the soon to be soldered joints. A piece of longer, larger bore tubing is used 'wrap' the wires back together. Use needle nose pliers to form hooks in each wire and connect each coloured pair.

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Use the pliers to nip up the hooks of each pair, then solder together. Try to avoid adding too much extra solder. Cut off the excess wire ends with wire cutters, then pull over the heat-shrink sleeves to cover each joint. Shrink carefully, making sure to avoid wafting hot air over airframe parts like this foam wing!

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After checking that all three joints are fully insulated pull the long piece of large bore tubing over the top and shrink it to pull all three wires into a neat and tidy package that is just a little wider than the original ribbon wiring.

YOU WILL NEED
Servo leads
Electrical wire cutters
Cutting mat
Sharp scalpel
Bench vise w/soft jaws
Soldering iron & solder
Needle nose pliers
Heat shrink tubing
Heat gun

DID YOU KNOW?
Since the introduction of the Restriction of Hazardous Substances Directive (RoHS) mass produced consumer electronic goods sold in Europe are likely to have been made using lead free solder, including our R/C sets and accessories. But for hobbyist use it is still possible to buy and use leaded solder, including the most popular 60/40 (tin/lead) types with a rosin (flux) core.

If you have good soldering technique and use high quality soldering equipment, usually in the form of a temperature-controlled soldering station, then you should be able to get very good results when hand soldering with lead free solder. There is no argument that this is the best method for the environment.

However, it's likely that most modellers will solder infrequently and not have terribly good or well-honed soldering technique, plus be using a cheap plug-in household soldering iron. In such cases you'll probably get better results and more conductive/stronger joints if you use 60/40 solder. (But not that 30-year-old reel that you found in the back of the man draw, please!)

One thing to avoid is mixing jobs with lead free and tin/lead solders. So, for this project, if you buy new servo leads with pre-tinned wires, they are almost certain to have been made using lead free solder, so you should only use lead-free solder to connect them. If you only have 60/40 solder, then please cut off the tinned ends and re-tin them yourself. This goes for other pre-tinned wires too, such as those supplied with ESC's.

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