How to Use Crimp-On Servo Connectors

This how-to article originally appeared in Model Airplane News.  I've reformatted it for easy online viewing. 

Introduction:  Crimp-on servo connectors such as those marketed by Custom Electronics* are tremendously useful for accomplishing neat and reliable component installations.  With these connectors you can trim over-length servo leads to the ideal length, and you can make your own servo leads and extensions for sailplanes and giant scale models.  But there’s no denying there’s a learning curve for installing these little connectors.  As with most things, there are a few simple tricks that will allow you to get professional results.  Here’s how it’s done…


Neatly routed and bundled servo leads make any model look more professional.  By using crimp-on servo connectors, you need never worry again about where to hide all that extra wire.    


 

Here’s how the crimp-on connectors come packaged.  Custom Electronics* and MPI/Maxx* are two of the most popular and reliable brands.  Be sure and buy the correct style of connectors for your particular brand of radio.



Here are the tools of the trade: Metal contacts and plastic housings for both male and female connectors, an X-Acto knife and the required crimper.




This is the crimper of choice.  You can get a crimper like this at your local hobby shop for about $25, but the exact same crimper is available at Radio Shack for under $10.




Now we get to work.  First split the three wires apart for a distance of about 3/4”.  I strip my wires by hand so that I have better control over how much wire I expose.  I carefully score the insulation about 5/32" from the end and then sharply tug it off to expose bare wire.




Here's the perfectly stripped wire.  Note that I've exposed about 5/32" of wire.  The exact amount of wire you strip depends on preference, but it's important that it matches up with how far you insert the wire into the crimper.  After srtripping, I twist the bare wire to make it easier to slip into the metal contact. 




Here the metal contact is pre-loaded into the crimper.  I'm gently squeezing the crimper just enough to hold the contact in place without actually bending the tabs.  Note that the end of the crimp trough is flush with the front face of the crimper (i.e. the side that's stamped with the wire gauges).  For normal and fine servo wire I always use the end notch, which is for 24-28 gauge wire.  I use the larger notch only for heavy-duty servo wire.




Here's where it gets interesting.  I've inserted the end of the negative lead carefully into place.  I'm squeezing the crimper grips just hard enough to hold the wire in place while I check everything over.  Note that the end of the twisted bare wire is about 1/32" short of the folded tabs of the box-loop on the contact.  By using that point as a reference, I know I'll have just enough insulation inside the crimped contact, and I know all three contacts will be the same length.  Note that the correct sequence for crimping the contacts is negative, then positive and signal last of all.  When you're sure of the alignment, firmly squeeze the crimper closed to crimp the tabs.  A firm squeeze is plenty; you don't have to crush it.  Check the contact to see if it's bent to one side from the pressure of crimping.  If it is, gently bend it straight before opening the crimper.




One down, two to go!  Here's a perfectly-crimped contact. Note again that the bare wire comes just even with the folded-over tabs on the contact.  Note that the insulation stops exactly at the gap between the two pairs of crimp tabs.  This will be a strong and reliable connection.




Here I'm crimping the last of the three contacts.  This shows why I start with the negative lead and finish with the signal lead; the already-installed contacts are out of the way so that you don't crush them while crimping a subsequent contact (I learned this the hard way).




Nearly finished now:  Here I'm gently slipping the contacts into the plastic connector housing.  Note the correct sequence of leads.



It's crucial that the contacts be fully locked in place by the retainer tabs.  I sometimes have to gently work the contacts in with the tip of a hobby knife so that they click into place.


Here's the finished product - a perfect connector.  Note that the folded-over box tabs on all three contacts are captured by the plastic retainer tabs.  Gently tug on each lead to make sure they're properly locked in place.



The pin-style contacts for a female connector are crimped on in the same way as the contacts for a  male connector.  It can be a little confusing that a male connector has female contacts, and a female connector has male contacts, but this makes for a much more reliable connection that’s more resistant to vibration and strain. 

 

The contacts for the female connector are slipped into the same style plastic body as is used for a male contact.  Again, make sure that all three contacts are fully seated so that the plastic retainer tabs lock them in place. 

 

The plastic connector body is slipped into the outer female housing so that it’s locked in place by the barbs inside the outer housing.  Some brands may need to be secured with a very small drop of CA. 

 

Here’s the completed female connector, ready for use. 

 


Conclusion:  With the ability to install your own connectors, you can make servo leads and extensions of any length - far better than being dependent on the stock lengths of servo extensions that are commercially available.  Your radio installations will look more professional and will be more reliable.