Connecting to a CNC machine, pros and cons of USB vs PP vs Ethernet etc.

[Neale]

I suspect that the underlying UDP ethernet protocol is nearly as error prone as the USB protocol, however, the TCP/IP layer which sits above it and does the error correction is (as has been pointed out) extremely robust so the end result is much better.

I can see both sides of the argument but theory is worth nothing if it doesn't work in practise...

For what it's worth, I've got a 3D printer which is extremely noise sensitive on the USB connection (to the point I now download the print to a memory card and print from that) and a USB CNC controller which I haven't had a problem with but there are dire warnings on the website about using a good quality cable - see https://www.youtube.com/watch?v=NUu9xwDfJ9k

Looking at a USB cable, it appears to use ground, power, and data in and data out. So, single-ended connections. Typical Ethernet connections use twisted-pair and, presumably, differential signalling. That suggests that Ethernet, at a hardware level, should be intrinsically more noise-resistant (although my own 3D printer has run for many, many hours over USB without any problem, although that is in a domestic environment without machine tools and EMI generators nearby). I think FatFreddie has it right with reference to TCP, though. A typical USB connection will be using an application-specific protocol that assumes a reliable connection (I know my 3D printer does this as I've looked at the code) so any data corruption or loss will be catastrophic, where the TCP protocol gives a highly reliable connection; any packet loss or corruption short of losing the whole connection will be detected and corrected by resending packets. Ethernet-connected motion controllers appear to use IP as they need network addresses and I presume they also use TCP over this - why shouldn't they? So, an error-correcting protocol over a more noise-resistant hardware connection gives so much more safety margin than a simple protocol over less-protected hardware. Be interesting to see the Ethernet-level error counts in a noisy environment, though.
What you are losing, of course, is any claim to a real-time protocol, but as the network connection is being used to transfer, typically, high-level movement instructions which can be easily buffered, by buffering a couple of seconds'worth of data you can still withstand a short loss of communication during a noise burst, the TCP stuff does its job and makes sure the data gets there eventually, and the pulse generator bit of the motion controller chunters away happily working from buffered data.
Conclusion - theorist meets practical experience, shakes hands, and goes off for a pint...
Personally, I like learning from experience, and preferably someone else's experience 'cos that costs me less! But trying to relate that back to theory might give a bit more insight sometimes and lead to a better understanding and maybe a way to move forward. Cathedral builders used experience to create magnificent buildings but theory and better understanding of materials gives us skyscrapers. If that is an advance...

[Lee Roberts]

Looking at a USB cable, it appears to use ground, power, and data in and data out. So, single-ended connections. Typical Ethernet connections use twisted-pair and, presumably, differential signalling. That suggests that Ethernet, at a hardware level, should be intrinsically more noise-resistant (although my own 3D printer has run for many, many hours over USB without any problem, although that is in a domestic environment without machine tools and EMI generators nearby). I think FatFreddie has it right with reference to TCP, though. A typical USB connection will be using an application-specific protocol that assumes a reliable connection (I know my 3D printer does this as I've looked at the code) so any data corruption or loss will be catastrophic, where the TCP protocol gives a highly reliable connection; any packet loss or corruption short of losing the whole connection will be detected and corrected by resending packets. Ethernet-connected motion controllers appear to use IP as they need network addresses and I presume they also use TCP over this - why shouldn't they? So, an error-correcting protocol over a more noise-resistant hardware connection gives so much more safety margin than a simple protocol over less-protected hardware. Be interesting to see the Ethernet-level error counts in a noisy environment, though.
What you are losing, of course, is any claim to a real-time protocol, but as the network connection is being used to transfer, typically, high-level movement instructions which can be easily buffered, by buffering a couple of seconds'worth of data you can still withstand a short loss of communication during a noise burst, the TCP stuff does its job and makes sure the data gets there eventually, and the pulse generator bit of the motion controller chunters away happily working from buffered data.
Conclusion - theorist meets practical experience, shakes hands, and goes off for a pint...
Personally, I like learning from experience, and preferably someone else's experience 'cos that costs me less! But trying to relate that back to theory might give a bit more insight sometimes and lead to a better understanding and maybe a way to move forward. Cathedral builders used experience to create magnificent buildings but theory and better understanding of materials gives us skyscrapers. If that is an advance...

Really well said Neale.

[Clive S]

There is also the cable length issue with USB (just saying) ..Clive

[JAZZCNC]

Cathedral builders used experience to create magnificent buildings but theory and better understanding of materials gives us skyscrapers. If that is an advance...

Yes very well said but just one small detail.? . . . Those Skyscrapers where built by Master builders with years of experience.! Those builders would not use inferior products and therefore make sure those products where well tested by people experienced in testing material Theory.!!

Theory and Experience work together for advancement but experience "TESTING" ultimately Wins and as the final say on what works and what doesn't.!!!

[Neale]

Theory and Experience work together for advancement but experience ultimately Wins and as the final say on what works and what doesn't.!!!

I'm not sure that I agree with that (I think that testing has the ultimate say) but that statement is only based on my experience and there's no theory to back it up...

[HankMcSpank]

Would it be too presumptious that on a forum called mycncuk (which has a "mylittlepony" vibe to the name!), that most are hobbyists? In other words, not everyone wants to go to the far end of a fart over 'ethernet vs USB' (which would need a forum called IusemyCNCmachinetomillindustrialhardenedsteel.co.u k - which granted isn't as catchy)

I'm a dabbler (I use my CNC to make pcbs) & I was pleased to see the back of Mach3 ...putting on those retro stick-on Bradley Wiggen-esque sidebruns & a pair of massive Lionel Blairs just to do a CNC session was a bit much. It was therefore like a breath of fresh air to migrate to cnc-usb, which uses erhm USB ....& I've not had one bit of bother with it. For the sake of balance, that's not to say others haven't has problems, which prompted the owner of cnc-usb to illustrate what a difference the actual usb cable can make...

[Jon.]

My god i must be doing everything badly.. cheap ass 5m usb cable coiled up, wrapped around extension leads and all sorts and running off a laptop. I must be very lucky.

[JAZZCNC]

I'm not sure that I agree with that (I think that testing has the ultimate say) but that statement is only based on my experience and there's no theory to back it up...

Ok I'll amend it to what was meant and say Ultimately Experience testing wins.!!. . .

[Neale]

Ok I'll amend it to what was meant and say Ultimately Experience testing wins.!!. . .

I wasn't being very serious! My personal problem is that anytime someone talks about the value of experience, it reminds me of my father whose attitude was along the lines of, "That's the way I've always done it, so that's the way it has to be done!" Didn't leave him much room for improving anything... I cheerfully admit to stealing the results of other people's experience where they've been kind enough to publish it - which is why I have a CSMIO-IP/M waiting to be installed, complete with Ethernet connection and 24V differential signalling.

My god i must be doing everything badly.. cheap ass 5m usb cable coiled up, wrapped around extension leads and all sorts and running off a laptop. I must be very lucky.

FatFreddie said he had so many problems with USB and his 3D printer that he gave up using USB. I've been using USB with my 3D printer for more than 3 years now and I've never had a problem with it. There's nothing wrong in principle, it's just that the safety margins with respect to noise are much lower than with Ethernet. There are also issues if you rely on the 5V supplied via the USB port as this can be a bit flaky as well. My printer controller has a separate supply - maybe that's why mine is more successful? Don't know but it's a case where experience gives different answers depending on who you ask.

As for theory versus experience - I use Ethernet-over-mains to get a network connection to my garage as the layout of my house makes the wifi signal a bit flaky out there. That signal goes through two ring mains, 3 MCBs, and an RCD. I wouldn't expect anything to get through that lot (based on the principles of high-frequency signals getting through a bunch of inductors), but I tried it, it works, and it's really useful for moving Gcode files around and that kind of thing. Stops working as soon as I turn on the router control box and VFD, though!

[JAZZCNC]

I wasn't being very serious!

Yes I knew that neil, I wasn't exactly being too serious my self.! . . . And regards your Father experience then I fully it get it.!
To me it comes close or equal to "Can't teach Old Dog new tricks" in terms of irritation.! . . . .I'm so far removed from both it gets me in trouble at times But Experience applied with intelligence along with a good dose of common sense win every time over theory alone in my book.! . . . . But . . . . All my best ideas and achievements started with " In theory it should work" but it does take certain amount of experience to allow the theory to evolve.!! . . . .Chicken and Egg maybe.?