Grounding steppers



  • While I was looking for something else in the Wiki, I can across this -

    Note: it is highly recommended that the stepper motor casings be grounded, especially in belt-driven printers. Otherwise, motion of the belts causes static charge to build up, which eventually arcs over to the windings. If the motors are screwed to a metal frame, grounding the frame is sufficient.

    My printer is belt driven, the mounts are plastic and the motor casings are not and never have been, grounded. Should I be worried? Running separate ground wires to all 10 motors is going to be a real PITA but I'll do it if I have to.

    Could this be a reason why driver chips fail???


  • administrators

    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.]



  • Unfortunately, although the frame is rigidly joined together with bolts, the X and Y axes run on Delrin wheels which is a pretty good insulator. I could ground the 5 XY and Z motors to the frame fairly easily but the 5 extruder motors would be a PITA. I guess I could ground them all together, then run a single wire through the cable chain (might just have room) to the frame. The frame itself is connected to mains earth but protected by an RCD.

    I'm having a job finding continuous lengths of anti-static GT2 belts - I'd need 10 metres (and I've been modifying the printer so have just replaced all the belts about two days ago).

    It's a shame that the motors aren't fitted with earthing tags if it's such an important consideration. I guess I'll have to fit terminals to the screws.

    How about grounding the belts? I reckon I could fix some flexible braid of some such to the frame so that it will lightly touch the belts. Or I could fit a grounded steel roller where the belts run left to right at the back of the printer, like an additional idler but just touching the belts. That should discharge any static yes? Unfortunately, the idlers are all Delrin too.


  • administrators

    Grounding the belts with some braid as they pass might make things worse! See the lower electrode in this image.



  • Oh.

    It looks like I have a hell of a lot of wiring to do then. As does anyone who's steppers aren't grounded which seem to be the majority of printers out there, including the likes of Prusa, Lulzbot et al (or maybe they use anti-static belts but I somehow doubt that.



  • @dc42:

    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.



  • 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 Summary

    The 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........???



  • Are we talking about grounding the metal stepper housing to

    • mains earth, as in RCD/GFI protected neutral?

    • 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).



  • 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…



  • @resam:

    Are we talking about grounding the metal stepper housing to

    • mains earth, as in RCD/GFI protected neutral?

    • 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.



  • 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.



  • 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 quote

    If 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.........



  • @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?



  • @DjDemonD:

    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….....



  • @deckingman:

    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 quote

    The 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.



  • @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.



  • 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.



  • 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.



  • @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.



  • @resam:

    @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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