Kind of unrelated but I noticed I peak out speed in speed regardless of gcode when it comes to trochoidal milling. This is due to the acceleration limit in the firmware correct? The circles are awfully small so that’s what I would assume. Was thinking to changing to 16 steps but it’s not necessary I bet.
Yes, could be your acceleration setting and/or jerk settings.
I thought it was a memory thing. Those little loops take a shit ton of code compared to normal milling.
Dui look up a nema 17 torque curve, 60-100 rpms is the max before rapid decline in power. That is 32-53mm/s with a 16T pulley above that and the stepper gets weak fast. A larger pulley will have less power loss than the stepper itself, because you are keep the rpms down.
You can also turn down accelerations, or use a higher voltage power supply. In reality I just don’t think you should be trying to move such a large gantry at 190mm/s it is too low of torque and too close to the aduino limit. No need to push every single aspect of the build in one shot.
The “jerk” in Marlin isn’t the derivative of the acceleration. You might already know that, but I found that very confusing. Any speed below the jerk value doesn’t get the acceleration limit applied to it. So if you have jerk set to 1mm/s, then any movement from 0mm/s to 1mm/s is applied instantly, as opposed to using the acceleration value to smoothly move up to 1mm/s. These numbers are 100% independent of the 1/16 or 1/32 stepping, because the steps/mm will cancel that out.
So if the jerk was set higher than the speed you are cutting at (using trochoidal milling) then the acceleration value would not affect the cutting at all.
Well, another disappointing weekend with plasma. This thing is so frustrating, I really don’t know how to get it to finally work…
A reminder of the story: I tried for the first time a few months ago and the Arduino blew up instantly after the torch fired for the first time. Never had the time or the motivation to give it a try again until this weekend.
What I’ve done this time:
-Linking all tubes together, using some copper braided wire
-Attach this to the ground, together with the plasma ground
-Put the Arduino/ramps in a carton box, covered with several layers of aluminum tape (I had no metallic case available for this around)to create a Faraday cage
-Attach this box to the ground together with the others
-Put the plasma cutter as far as possible from the Arduino, and put the torch wires away from the motor wires as much as I could
Results:
-First attempt: normal configuration: the arduino is powered from the 220V (through the 12V power supply of course), the torch is fires from the relay. It started just fine, so I was super excited, cut a few letters from my test file, then crapped out suddently, the Arduino restarted… No damage to the arduino, I made a few other attempts but none of them was successful, the arduino kept restarting or acting weird
I thought it could be some interferences in the relay, so my next move was to disconnect it and try to control the plasma cutter using the manual switch.
Again, it started just fine, cut a few letters and then crapped out the same way.
So, I thought it could be a power supply issue, and decided to power the arduino and steppers through a scooter battery.
Same result, worked fine for a while, then stopped.
I tried several times using the battery, and at some point I guess something died in the electronics, the screen displays the startup logo and then blinks at a high frequency.
I really need some expert opinion here, I really cannot find out what is going on. I don’t want to give up on plasma, cuz it could be super useful in the shop.
This really puzzles me… Apparently it is not because of the relay, and not because of the power supply. I wonder what it could be… Any help would be greatly appreciated.
Here is the setup, the plasma cutter is on the right, the control box on the left of the machine, connected to the battery:
[attachment file=43097]
The Arduino is inside this box:
[attachment file=43098]
The results:
[attachment file=43106]
It doesn’t look very good, but I think that is because the plate I was using was pretty warped, so a lot of spots were too far. But the spots who were at the correct distance are actually very clean. Anyway, tweaking up to improve the quality is not the biggest concern right now, I need to come up with a way to make this work reliably, and if possible more than 10 seconds…
[attachment file=43107]
[attachment file=43108]
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I’m not an expert… but …
Shield the stepper motor cables … maybe … if you didn’t do that already 
or use those tb6560 drivers
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And the LCD cables.
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The motor wires are CAT 6 shielded wires, but I haven’t found a good way to connect them to ground yet. So basically, they are not really shielded.
For the screen wires, I want to shield them, but it is not really easy to find a proper way to do it.
Anyway, I just found out two things:
-My arduino isn’t dead: the extruder driver died, and it somehow conflicted with the Arduino. I just took it out and now everything works fine.
-I made the stupid mistake of forgetting to unplug all the unnecessary wires. I was using the MPCNC as a printer last week, so I had the thermistor, the hot end, fan, and extruder motor connected to the Ramps, with the cables going around the torch… No wonder why it crapped out, I’m actually surprized it was able to work for a few seconds. I guess it picked most of the noise from the extruder wire, since it destroyed it eventually.
So’, I’ve disconnected every unnecessary things and I’ll try again tomorrow to see if this makes things better (I really hope so). No matter what happens, success of failure, I will ground and shield everything properly to make sure it is reliable.
Fingers crossed!
You should be able to just strip off some of the plastic coating on the CAT6 and just ground it from there.
Putting the ramps and screen in a metal box with a screen cutout would be a better Idea I think.
You probably already know this, but just throwing it out there as general knowledge. Only ground one side of the cat-6 cables. You’ll get ugly ground loops otherwise.
Well shoot I didn’t know that!
I really hope it works… I have been wanted to try a plasma cutter too. (actually have an old one that’s just sitting in a corner).
Ferrite cores on the cables perhaps ? (I have no idea if that would help in this case 
)
There are a handful of videos of some really long plasma cuts with an MPCNC. I never looked to far into it but It must work. There was some talk of a tiny grounding wire from the nozzle to the work before to help with the HF start but I don’t think they needed it.
I would say If you want to get it going see what they did. I have a few linked in the gallery.
Tried again today, still no success… That’s really annoying, I wonder why I’m the only one having that much trouble…
I shielded everything I could, motor wires, motors, screen wires, etc.
I removed all the unnecessary wires, so the only ones I was left with were the motor wires, screen and PSU.
Same results, it works for a while, then as soon as it starts a new path, poof, the Arduino either freezes, slows down dramatically or restarts.
I’ve seen a method supposedly effective for getting rid of the HF start, by running a wire from the tip of the torch to the ground clamp. I tried that, didn’t seem to change anything.
I tried to manually fire the torch after removing all the wires: seems to work 80% of the time, crashes 20% of the time.
As soon as I plug any of the motor wires, it crashes about 80% of the time I fire the torch.
Only the firing phase seems to pose problems, if I never release the switch between different paths, then it continues to cut perfectly fine. I just need to get rid of this stupid torch firing up HF interference issue to make it work.
I really don’t want to give up on this, but I’m not confident at all that it will work one day, I think I’ve done a lot of things to shield and protect everything for almost no discernible result, so I wonder if spending more time and resources on this will actually make any difference. It really sucks, I’m super disappointed. I wasn’t expecting it to work perfectly, but I was expecting it to be much better than yesterday…
But yeah, for the shielding I know that only one end of it must be linked to ground (but thanks for the reminder), and I watched a lot of videos, forums and website to try to understand what I’m doing wrong, but so far I found nothing really helpful.
For instance, on the few videos I’ve seen about plasma cutters MPCNC, people didn’t seem to have taken any particular precaution to shield anything (the Arduino is just left outside in the open air, motor cables are connected with dominos without shielding or protection… My machine is way, way more shielded than that!), but for some reason, their machines work and mine doesn’t.
This one seems to be shielded pretty good: http://forum.longevity-inc.com/showthread.php?1971-High-Frequency-shielding-for-CNC-Plasma
Have you confirmed 100% that it’s radio interference and not some power/ground issue? Can you completely electrically isolate the Arduino/RAMPS and confirm that it still happens when it fires? If you’re running off of a battery, and you don’t share a ground, etc. A large spike in the ground would look like a drop in voltage to the Arduino, which would cause a reset.
Can you test another plasma cutter? Maybe there’s a shop that would have one (like a car repair shop) that would let you bring your Arduino near and fire it a few times to confirm that it’s not something wrong with your cutter?
W.r.t. the foil tape, is the adhesive conductive? If it’s an insulator, then you’re not getting a great faraday cage.
Are there any wires that you can twist? Twisted wires have a lot less RF area, because each loop cancels out the next since it goes through the loop the wrong way. This only works for differential things, like power, but it could help.
Don’t give up. You’re about to crack it. You might just need a calming bike ride to stew on it, but you’ll get it.
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I tried with the Arduino directly hooked up to a 12V battery, but it did the same thing, so I’m pretty sure this is some radio inducted noise at this point. The Arduino crashed while being connected to the battery, with no cable connected except for the screen and the two battery wires. So I’m pretty sure this is some really nasty radio noise here.
I have no idea where I could find an other plasma cutter, I’ll see if any shops have that around, but I have little hope.
For now, I’ve decided to rebuild all my wiring. I will get rid of all the ethernet wires and go for shielded 4 wires of higer gauge. Hopefully that will help. I will also use some copper breaded wiring to put everything to ground, instead of my skinny wires and aluminum tape.
I will also put the Arduino in a proper metal enclosure.
Any other suggestions are welcome, especially regarding possible modifications to the plasma cutter itself, since it sounds better to me to tackle the EMI issue from the source.
The tape adhesive is indeed not very conductive, but that was the best stuff I had on hand… I’ve used a ton of it, for nothing.
I have little hope that this will work anyway, the fact that the EMI is so intense that it can shut down the arduino without anything being connected shows that the level of protection I’ll need will be quite important.
When you did the battery test, you didn’t have the grounds connected in any way? Something like grounding the case to the Arduino and the earth ground? Or grounding both sides of some shield?
I don’t know if the motors wires are the most susceptible to noise. I would look hardest at the Arduino itself and the Arduino power. What would cause it to reset? Either the power is dipping, the voltage difference is dipping, or there is noise on one of the important signals leading to, or inside the Arduino itself. Would current flow on the motor coils cause it to reset? I would definitely try twisting the power cables. Is the power supply shielded?
You could also try without the LCD connected, although how would you know if it reset…
On a program I worked on, we had AC inverters in these vehicles we were using all the time, and we had radio communications (just normal, consumer band radios). The AC inverters had GFCI plugs built in. Turns out, when the radios turned on, there was a large EMF burst, and the GFCI would trip. Most of the users didn’t know it was a GFCI, so they would call in the engineers to fix the AC inverter, and by that time, the correlation to the radio was not noticed. It was months before someone figured out the correlation. The solution? Replace the GFCI with normal, unsafe outlets.
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