Has anybody ever tried to use CAT6 network cables for wiring the stepper motors?
According to specification the 8 single strands of a CAT6 cable should be 23 AWG.
Every 2 strands are twisted together so that 8 of them form 4 twisted pairs. Around these pairs there is a shield that helps against electromagnetical induction (EMI?).
I just imagined that the ends of each pair could be soldered together in order to get an even bigger cross section. That would upgrade the 23AWG to 21AWG cables, wouldnāt it?
One problem could be the rigidity of the cables since they usually are not used in places where they have to move around all the time. On the other hand this could be a solution for good, cheap? cables that are shielded (less lost steps) and with little resistance.
Donāt, this route has been done by the reprap community for almost 10 years. The conclusion is always the same, cat5/6/etc cables are not meant for repeated flexing. Use silicone or ptfe wires.
My limit switches on the far axes have solid core ethernet wire connecting to a DuPont female connector so that theyāre the same length as the motor wires, but they go from the switch into the gantry tube, and never flex. ā or at least they SHOULD never flex, lol.
Stranded is more expensive, and generally only used for patch cables.
Still, if you are using drag chains, or at least appropriate strain relief, solid core ethernet should last a reasonable lifespan. The CNC does not move quickly, and with a drag chain, or even the tape measure trick, the bend radius should not be intolerable. The maximum speed we should be seeing with a Primo or LowRider is significantly slower than we would see on a typical 3D printer, and the wire runs are quite a bit longer.
As far as EMI rejection goes though, using one pair per conductor isnāt the way to do that. Each pair should go to 2 ends of a motor coil, so if the coils are A, Aā, B, Bā then say orange and green can go to A, while orange-white and green-white can go to Aā. Blue and brown can go to B while blue-white and brown-white go to Bā. In this way, any EMI that gets past the shielding affects each pair the same, so an increase in voltage at A will coincide to the same increase at Aā with no change in the difference, keeping current the same. Or at least it would if the twists were the same. Using more than one pair might actually introduce noise though. (Been a long time since signal theory class.) Probably youāre still better off using them individually, just use 2 pairs, ground one pair at the board, ground the other at the motor. Or use one pair for limit switch.
FWIW, I experimented with this and found that simply routing 4 22AWG stranded wires was much easier than working with the CAT5/6 cables. Even with the drag chain I ended up with some intermittent connectivity issues with the original wire harness. The simpler routing with soldered connections was recommended by others and I concur wholeheartedly.
In general, the only times EMI is really a huge issue is when you use a plasma torch. Or a really, really cheap/bad spindle thatās got some serious issues that need a lot to address before you get to the point of worrying about the EMI interference in your cabling.
This is all assuming your general shop environs are relatively EMI free. If you are set up in a HV lab with Tesla coils and Jacobās Ladders all around, then you really should have Igor shield everything for you. And put copper mesh in your boxers as a faraday cageā¦ :frankenstein: :thats_frahnkensteen:
I know it goes against best practice, but my printer has some strands of solid cat6 for a filament sensor that moves with the gantry. That wire has lasted for 1200hrs of printing. This is just an anecdote, and for sure ymmv. I wish I had stranded cat6 on hand when I installed that sensor. My mpcnc has 18awg strand for the motors, and 23awg strand UTP for switches (just torn apart cat6 strand).
Motors on an mpcnc thoughā¦ gotta watch ampacity. An mpcnc has rather long runs, and does not need to be lightweight. So bulking up motor wires is a good idea.
Also twisting pairs is normally not done on high current lines (like motor and power lines) due to inductive losses, and the fact that such lines do not usually need noise resistance. Usually you twist pairs for small signals because their lower current makes them more prone to noise, and less affected by inductance.
@kvcummins, lol I have a friend whoās workspace actually fits that description. He also is smart enough to prevent problems from the nearby Jacobās ladder. In fact, the same friend was supposed to make an mpcnc for jobs, which is what inspired me to make mine. He ended up not making one and is starting to push those jobs my way.
I work in power distribution (power lines) and this simply isnāt true. We use triplex and quadruplex (3 and 4 wire twisted sets) all the time in secondary applications. In fact is is much preferred to the old independent open copper.
Very trueā¦ I should have clarified power lines are not twisted for noise cancellation, however twisted arials are used for other reasons. The typical drop using triplex is much cheaper than the older alum mesh wrapped drops they used to use for example. Also, if arials were not twisted or otherwise bundled together, they might tangle in trees or abrade against each other as the wind blows them around. What I meant to say is we donāt twist power lines in efforts to fix noise problems.
Though there are very few places where we would create that much EMI. Stepper motors are in the unique realm where you have a device that requires a large current but can also switch direction on the drop of a pin. Power lines have to be switched carefully or they can overload and cause blackouts. Same with large 25+Hp motors. You donāt just switch direction so the emissions generated is smaller and more consistent.
Not saying that twisting the cables would or would not help (I would have to do some math to figure that out) just pointing out that it is a rare situation that we find ourselves in
Yep steppers do have a high slew rate for a high current line. That is no doubt a major source of noise on all Cnc machines that use them. Similarly inside a psu there are intense spikes of em radiation from the same kind of thing. I wonder if twisting would contain the noise though, or if it would just change the shape of the resulting field (more or less same energy output). When I wired my Cnc, I spent some time pondering those motor wires. I went with untwisted, thinking if I twist them my drivers would just have added inductive losses to sea with. Would be interesting to run a quick experiment with a scope to see how much noise is transferred from straight motor wires vs twisted.
Iāve used that kinda stuff working on real-world cnc machines a couple of times. But he kind of hardware and environments related to that also makes it necessary to use such cables.
Does it make sense in above cases? Of course!
For a MPCNC I donāt think so. Would involve a lot of other stuff youād have to mind, aswell for that to really make senseā¦
I just used shielded flexible wiring for my build.
But as others have posted, I think that normal quite flexible ethernet cables would work just fineā¦
I have no experience with CNC machines so far and that makes me a bit insecure when it comes to ordering parts for the lowrider build.
I just cannot judge what is adequat, over engineered or simply not up to its intended task.
Hope I will get more experience soon to overcome this phase .
That is why i am so glad when I get tips from you guys @snoop / @barry99705!
I have ordered now cables that are rated for drag chains just to be on the safer side. But I am quite sure that I could have come away with something cheaper that would be good enough for my hobby use cases.
Industrial cat6 is stranded(patch cable) with a chemical restent sheathing. Some might have a metallic shielding under the outer sheath for noisy environments.
All the machines I have made I have used Cat5 cable for the stepper motors as we use it everyday and I have it laying around to use for āprojectsā for free. My MPCNC has run for over 5 years now with no issues and my OX for about 3 years. Just do not want any tight bends that are going to flex too often. Cable chain probably helps. Had more issues with Cheap ramps 1.6 boards & Chinese Arduinos then cables.
:frankenstein: :thats_frahnkensteen:
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