Making servo extensions

Tutorials > Making servo extensions


If I need to lengthen a servo wire I will add a splice, but in cases such as a detachable wing where a servo must regularly be connected and disconnected I will use an extension for two reasons. One, it's generally easier to plug a servo into an extension than into a receiver. Two, it saves wear and tear on the receiver socket. Servo extensions can be purchased, but making them at home is cheaper, more customizable, more statisfying (to me, and least) and if you keep a supply of wire, pins and plugs they never go out of stock.

  1. Gather the required equipment and supplies.
  2. Tools and supplies*

    Top: Bulk servo wire

    Paper, clockwise from left: Scissors, hobby knife, crimpers, male pins (3), female pins (3), male connectors (2), female cover, wire strippers

    Start of Page

    Here's a closer look at the crimpers - these are from MPI, model ACC175.

    MPI crimpers with information*

    There are two set of jaws, both with peaks and valleys. I assume that the numbers refer to wire gauges, but what gauges are designed to fit the jaws are unclear to me. No matter - I only use the jaws nearest the tip. When crimping, the pin is fed through from this side, which means that the insulated wire protrudes from the side of the crimpers with the gauge numbers. The pins go in open side down - the dies in the valley that round them over and closed are visible in the above photo. When properly inserted, the front and rear crimping tangs will both be within the valley.

    Start of Page

    Here's a closer look at the male and female pins.

    Male pin Female pin
  3. Measure a length of wire approximately 1/4" longer than the desired total length. Hold all of the conductors together and cut them flush to one another.
  4. Measuring a 12" extension* Holding the conductors together Cutting the conductors

    Start of Page

  5. Strip 1/8" of insulation from the end of each wire. This is how 1/8" looks in my wire strippers. If there are loose strands, do not twist the strands together (this can create problems during crimping). Pinch the wire and pull it straight through your fingers.
  6. Stripping 1/8 in of wire*

    Start of Page

  7. Place the wire into the pin. Push the wire down into place from above rather than sliding it in - this stops strands from getting caught. The insulated portion should fit inside the rear tangs and end at the rear of the front tangs.
  8. Placement of insulation and stripped wire*

    Start of Page

  9. Hold the wire between the front tangs with the thumb and forefinger of one hand.
  10. 2. Hold wire in place with one hand

    Start of Page

  11. Pinch the rear tangs together slightly with the other thumb and forefinger.
  12. 3. Pinch insulation tang with other hand

    Start of Page

  13. Insert the pin from the numbered side of the crimpers with the open ends of the two crimps facing the bottom of the valley.
  14. Crimping the pins*

    Start of Page

  15. The properly crimped pin.
  16. Proper crimp - open end Proper crimp - closed end

    Start of Page

  17. When all three pins have been crimped, insert them into the connector. Regardless of the end of the extension, the ground pin (brown, in this case) goes on the right, the positive (red) in the centre and the signal (pink) on the left. Note that the crimped side of the pin will engage the tabs on the open face of the connector. When the pin is properly inserted there will be a quiet "click".
  18. Proper orientation of pin and connector

    In my limited experience, if a pin doesn't go smoothly into the connector it's for one of three reasons: The pin is bent from excessive crimping force (straighten by hand), the crimp is not fully formed (another pass through the crimper), or there's excessive insulation squeezing out (trim with hobby knife).

    Start of Page

  19. Repeat steps 3 to 9 for the other end of the extension with the opposite type of pins.
  20. The end of the connector with the male pins will require the installation of a female cover. The shape of the cover will ensure that the connector cannot be inserted the wrong way, but it will still be possible to insert the connector into the wrong end of the cover. Here's how it looks when correctly installed. If there's any doubt, tug the connector and cover in opposite directions. If the cover comes off, reverse it and install from the other end.
  21. Correct end - cover slides farther onto plug and stays in place

    Start of Page

  22. When the extension is complete, check that it is wired correctly by plugging one end into the other; the wire colours should match.
  23. Checking wire placement - correct

    Start of Page

  24. Test the extension further with a servo and servo tester.

Many thanks to my friend Peter for his patience and guidance while instructing me in this finicky procedure!