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Bobble Build: Part 2 - Crimpin' ain't Easy

A project log for Bobble-Bot

Demonstration robot for learning principles of real-time control using Raspberry Pi, RT Linux, and ROS.

James HolleyJames Holley 05/19/2019 at 21:331 Comment

Is crimpin' easy?  Hell yeah!

Making cables is the WORST part of finishing a build.  We've all been there - adding the final touches to a project just to find out that some (or all) of the cables have a loose connection, bad crimp / solder, wrong pinout, etc.  Sometimes pins push back out of their connectors or, as you are trying to solder a pin, you melt the whole thing...  

Getting your cable assembly reliable and easy can be hard on DIYers.  Below is an image from customcable.ca that captures some of the pros and cons of soldering vs. crimping at a high level.

The biggest problem for hobbyists and DIYers... Crimping doesn't have a low initial setup cost?!?!?  Like I said, crimpin' ain't easy.  But wait!  It's not so bad - here's what we're using for Bobble-Bot.

If you take a look for this guy, you'll see its priced in the $425 range.  Yikes!  A little steep for some of us, but lets put it in perspective - Can this tool reduce the number of bad connections down the line?  Is it easier and more reliable than soldering?  

Right now I'm putting together 2 Bobble Bots, each with 60 crimped connections, making 120 connections total - when you have a lot of connections in front of you, any mistake can spiral into hours of lost time troubleshooting or repairing a poor initial job.  If I spend 5 minutes on each connection, I'm looking at 10 hours of work just putting together cables.  That's not super owesome at all.

The major takeaway: If you plan on doing a lot of cabling, get yourself a crimper.  It will cost a bit up front, but you'll see how much time it saves you down the line.  We reuse this crimper and different styles of the CLIK-Mate connectors for most of our projects that require small gauge wire.  The connectors themselves are cheap and reliable.

So, how does one crimp?  The first step is stripping the wire - don't strip too much.  The nice part about crimped connections is you can minimize the amount of exposed wire and not have to use heat shrink.  The back prongs of a CLICK-mate connector are designed to hold onto the insulation of the wire.  Here is a close up of the minuscule amount of wire I stripped off the end - for reference the wire is 28 AWG.

After that, I insert the connector in the crimper and close the crimper about half way - there is a piece of backing that is used to push the wire against to ensure it is inserted at the proper depth.  Closing half way makes sure the connector is removing most of the room where the wire could mistakenly push through past the backing.

After that, you just put the wire in and sqeeze the handles down.  Completed crimp below.

One of the best parts about crimping is you can inspect the connector after it has been crimped to verify your connection is in good condition.  Compare this with soldering, where you could end up with cold joint and the outside still looks OK.  Here's a pic of a good crimp.

You can see that the insulation has been grasped by the back tongs and the wire is smushed down under the front tongs.  I always do a pull test after each crimp after visual inspection.  Better to know that its going to come apart before it ends up in a cable.  Slide it into the connector and its done!

Rinse and repeat 120 times... Maybe a coffee break or two mixed in there and...


So we have more Bobble Bots on the loose - look for some updates on testing, software, and design refinement in the coming weeks.

-James

Discussions

Daren Schwenke wrote 05/20/2019 at 17:45 point

There is a reason connectors spec'd for areas with motion or vibration are crimped.  When you solder wires, the solder tends to migrate back up inside the insulation and produces an area of stiffness with a sharp cutoff just beyond your connection point.  This leads to bending being concentrated there and eventual failure.  Crimped connections, when done right, don't have this issue.

Then again, if you support your wires so they can't move relative to the board until after the solder wicking point, solder can actually work better then.

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