Let's Make Robots!

Wire and Servo Connectors

Hello,

I am currently am ordering parts for robot #2.  As robot #1 is a nest of wiring, this time I want to use cables that have 2 or 3 conductors and use the connectors normally used on servos.

This has leads to two questions which are:

Is there some reason to choose "twisted" wires (2 or 3 wires wrapped around each other) over flat ribbons (2 or 3 wires side by side)?

Is there a reason the connectors from Pololu are so cheap?  They want 69 cents for 25 connectors while Digi-Key and Jameco want around $10?  I am looking at the Molex 1, 2, and 3 pin housing with 0.1 spacing.



                                Thanks for your help,

 

                                        Hal  (Kingart3)

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I agree with the comments from birdmun and bdk6. I'll add to this.

Twisting wires is more important for longer runs. Twisting short runs can be kinda annoying, 

You can also reduce interference between signals by keeping some distance between wires, or crossing them at 90 degree angles.

If you are using PWM for your motors, the signal will be changing constantly, not just during starts and stops. So there's even more reason to twist those wires.

Lastly, some of my early robots were real wire messes. Moving to dedicated robotic microprocessors and/or shields that include motor drivers, terminals for servos, sensors and motors, etc., really cleaned things up.

the crimp on ends that will run you $6 for 100. So, you will run up a tab of about $8.40 + shipping for 100 complete ends that will still require you to assemble them. :)

Re: twisted wires.

I have seen it mentioned that for something like longer/longish motor leads, twisting the wires is a good thing because it cuts down on RFI. The long parallel leads act like an antenna, and if you get any kind of noise from the motor it could broadcast elsewhere. Twisting cuts down on the broadcasting.

Birdmun hit the nail on the head.  Twisting the wires decreases the RFI.  In fact, twisting the wires together in almost all circuits LMRians are likely to build is almost always a good idea.  It works both ways, too, helping keep circuits protected from outside RFI entering.  That probably isn't a problem to a motor, but to a sensitive circuit like a photodiode or microphone or something it can be important.

A very short and simplified explanation why if you or anyone else cares:  Every conductor that carries a current that CHANGES (like a motor switching on and off) broadcasts some radio signal.  The polarity of the signal follows the polarity of the current.  Since the current to and from a circuit is (close to) the same, the signals are equal and opposite.  The closer together the wires are, the more the two signals cancel each other.  The same basic thing works in reverse:  a radio signal hitting a wire causes a current.  If the current is the same in both wires they will cancel.  Any difference creates an unwanted signal in the wire.  There may be other advantages, depending on the circuit.  But in short it is almost never a bad idea to twist the wires.