Grounding steppers
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Yes it could be a reason why drivers fail. Can you ground each motor to the nearest extrusion? This is assuming that your extrusions are joined using metal fittings, and the whole frame is grounded somewhere.
I wonder whether anyone makes antistatic GT2 belts? [EDIT: yes, e.g. [url]http://www.ebay.co.uk/itm/GATES-8008MGT-30-POWER-GRIP-GT2-TIMING-BELT-ANTISTATIC-TO-ISO-9563-NEW-115672-/181546325859.]
David, are you sure that anodized alu frames are good conductor? Mine are certainly not. I checked it with decent multi-meter (Fluke 289) it is 0.00nS! So now I have hard time devising how to ground frame, no good ideas at the moment. Maybe the anodized aluminium was a bad thing from the start. Robotdigg's Alu vertex are bad conductors as well. Anyway stepper could and would be grounded by wires with O-contact under one of mounting screws. Thanks for good point about grounding them.
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I've been doing some research into this phenomenon. I came across this which explains it very well. OK, it has nothing to do with 3D printers but the principle is the same. https://www.rchelicopterfun.com/tail-belt-static.html.
It seems it can cause RC helicopters to fall out of the sky, (not that that is an issue with 3d printers). Interestingly, the conclusion started with this -
Quote ….........
Static SummaryThe most important thing that you can do is to defeat the tail belt’s Van de Graff generator behavior by lubricating the belt.
This is intended to defeat the TriboElectric effect which determines how static charges get generated. ............end of quote.A bit further up it says this
Quote ..........
The most important thing that heli pilots can do is to keep the tail belt well lubricated which does an excellent job of nulling out the TriboElectric effect. Grease against grease has no TriboElectric difference. Lubricate all four surfaces of the belt. Experiments indicate that a good lubricant is more effective than graphite products selected for conductivity.
Another benefit of a lubricated belt is that it lasts forever, compared to a dry belt. E.g. a dry belt will try to climb the side walls of the pulley which results in most of the wear and tear, often resulting in loose strands of belt material. Use a dry silicon lubricant if you fly where dust is a problem or you don’t like cleaning up the grease that gets thrown off the belt. ............end of quote
I've always thought that lubricating my timing belts is a bad idea but I wonder........???
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Are we talking about grounding the metal stepper housing to
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mains earth, as in RCD/GFI protected neutral?
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or the NEGATIVE/GND of your 12V/24V DC power supply?
Because AFAIK the two are not connected (at least in my PSU).
My heated bed is grounded (mains neutral/RCD/GFI).
My 2020 frame is floating and has poor conductivity (at least on the surface without scratching it). -
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Anodization is an industrial process to make thick layers of aluminium oxide on aluminium elements. But in any case, this oxide naturally and instantly appears because of the oxygen contained in the air. And it is a good electrical insulator!
So, it is not easy to use it as ground…
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Are we talking about grounding the metal stepper housing to
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mains earth, as in RCD/GFI protected neutral?
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or the NEGATIVE/GND of your 12V/24V DC power supply?
Because AFAIK the two are not connected (at least in my PSU).
It depends of the class of your power supply. In most class I, GND of 12V/24V is connected to main earth.
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Ian, whilst you have some wiring to do with the steppers that move your head, and its follower, the extruder motor steppers should be much less prone to this issue as there are no belts running near to them.
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According to the article that I linked to it says
quote….............
Static can be effectively dissipated with 10 million Ohms, even as much as 100 million Ohms (e.g. humidity, static dissipative products). No need to sand off any paint unless you plan to use a multi meter to check wiring continuity.............end of quoteIf that is correct, then it shouldn't matter is the frame is a good conductor or not (as long as it's less than a few 10s of millions of Ohms). Even high humidity in the air can be enough -maybe we need to move our printers to the bathroom
It seems that I may have inadvertently opened a can of worms.........
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@fma:
Anodization is an industrial process to make thick layers of aluminium oxide on aluminium elements. But in any case, this oxide naturally and instantly appears because of the oxygen contained in the air. And it is a good electrical insulator!
So, it is not easy to use it as ground…
Thereby there is no sense grounding stepper to anodized frame. And how is it safe left a bulk metallic structure ungrounded, not mentioning possible signal interference problems?
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Ian, whilst you have some wiring to do with the steppers that move your head, and its follower, the extruder motor steppers should be much less prone to this issue as there are no belts running near to them.
Good point!! Thanks for pointing that out Simon. It's only the belts that can act as Van de Graff generators so, as the extruders have no belts it shouldn't be an issue (unless some smart ar*e says that the movement of the filament through the extruder can cause static to build up).
Just grounding the 4 XY motors and the Z motor should be a piece of cake. Alternatively, finding someone who can make me some metal mounts would also negate the need to cool the motors. That sounds like a better solution. Hmmmm….....
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According to the article that I linked to it says
quote….............
Static can be effectively dissipated with 10 million Ohms, even as much as 100 million Ohms (e.g. humidity, static dissipative products). No need to sand off any paint unless you plan to use a multi meter to check wiring continuity.............end of quoteThe situation is much worse, it is of order 10^11 Ohms or so. And you don't open a can of worms it is a good point. That is a possible cause of increased driver chip failure rate David complained of.
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@zov:
…..............................And you don't open a can of worms it is a good point. That is a possible cause of increased driver chip failure rate David complained of.
My thoughts exactly - That's mostly why I started this post.
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I've just done quick test on my anodized frame between 2 points about a metre apart. With the probes just touching the surface the resistance is greater than 10M Ohms which is the maximum range of my meter. However, if I just lightly scratch the surface with the probe, then the resistance drops to 0.5 Ohms. From that, I'd say that it's just a matter of scraping the anodised layer away (which is only a few microns thick) in order to make good contact for grounding purposes.
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Scratching is certainly an answer but to be real ground the frame should have unbreakable contact between all the extrusions it consists of and be connected to main power protective ground. Otherwise this has no sense from safety and static charge protection points. So you need scratch each and every single extrusion in your printer and connect them all with wires ended with appropriate crimped contact. Obvious but very tedious solution! But to my pity can't invent any better for a while. Anyway steppers SHOULD BE GROUND with or without the rest of printer.
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@fma:
It depends of the class of your power supply. In most class I, GND of 12V/24V is connected to main earth.
Are you sure?
This would mean a 24V 400W PSU "-" has a straight path to mains earth - which would immediately trip the RCD/GFI!
AFAIK to have any meaningful DC PSU the "-" should be completely isolated from the AC side.So the question remains - grounding to WHERE?
I guess a simple bleed-off to "-" via a high impedance path should do the trick. -
@fma:
It depends of the class of your power supply. In most class I, GND of 12V/24V is connected to main earth.
Are you sure?
This would mean a 24V 400W PSU "-" has a straight path to mains earth - which would immediately trip the RCD/GFI!
AFAIK to have any meaningful DC PSU the "-" should be completely isolated from the AC side.So the question remains - grounding to WHERE?
I guess a simple bleed-off to "-" via a high impedance path should do the trick.Do you know how RCD/GFI works? Any decent designed and manufactured electronic device should have connection between protection ground of mains supply and 0V (signal ground) of low voltage circuitry except very special cases. There is no problem for RCD/GFI in this case.
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@zov:
Scratching is certainly an answer but to be real ground the frame should have unbreakable contact between all the extrusions it consists of and be connected to main power protective ground. Otherwise this has no sense from safety and static charge protection points. So you need scratch each and every single extrusion in your printer and connect them all with wires ended with appropriate crimped contact. Obvious but very tedious solution! …............
No not really. It depends how you build the frame. I tapped the ends of the extrusions then used button head bolts which engage in the slot of the extrusion it fixes to. A clearance hole for a hex key provides access to the screw head and when tightened, it bites through the anodising and makes good contact. I've connected earth braids to several of the extrusion cut ends which goes back to the earth of the mains plug. I did the same with the aluminium build plate. So every frame member and the build plate is connected to earth. I remember checking this when I first built the printer as I was concerned that if the 240v mains bed heater developed a fault, it could potentially make the frame live.
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Thanks Ian, but I consider something like David's KosselXL style so no tapped holes to connect extrusions into frame. Keep trying to devise something appropriate for deltas.
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I have a possible solution (for people building new printers).
If a cable with a braided shield is used to connect the steppers, it is typically recommended to connect only one end of the braid to AC ground, for noise-rejection.
Could we then connect the other end of that shielding to the stepper motor body? There is still only one connection to ground on the shield, but we also piggy-back off the shield to ground the stepper frame as well.
Thoughts?
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@zov:
Do you know how RCD/GFI works? Any decent designed and manufactured electronic device should have connection between protection ground of mains supply and 0V (signal ground) of low voltage circuitry except very special cases. There is no problem for RCD/GFI in this case.
If you provide a low-resistance current path from 24V to Earth there should be an imbalance between the Neutral and Hot wire of your house, because some of the current finds its way back through the Earth wire.
And this should trip the RCD/GFI, or should it not?This means DC PSUs should have floating "+" and "-", otherwise it would trip all the RCDs/GFIs…
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Using braided shield as stepper ground wire is good solution but a problem remain where connect it on the motor? And how to ground frame witch the stepper is mounted on? BTW Duet board has no provision for connecting braided wire to signal ground.
