Problem with setting current for Chinese stepper...



  • Hi all!

    I have bought Chinese stepper motor 42BYGH634-4-M300 with integrated lead screw. On Amazon it was "rated" as 1.5A motor. (today on eBay I see 1.3A rating and on some strange datasheet - 0.48A rating).

    So my settings(part of the config):
    M350 X16 Y16 Z16 E16:16 I0 S2 ;
    M566 X900 Y900 Z12 E120:120 ;
    M203 X12000 Y12000 Z1200 E7200:7200 ;
    M201 X500 Y20 Z250 E250:250 ;

    M906 X680 Y680 Z1040 E714:714 I30 ;

    As you see I have set 1040mA for stepper(80% from 1.3A), before that I've tried 80% from 1.5A -- it is skipping steps!(Sometime halts at the top with whining noise, each time after homing loosing 0.2-0.3mm(checking by baby steps)). So I thought that it broken and started thinking what to do... Right now I have decided to set current to 2000mA(as I've seen in the stepper check macro) and miracle! It is not loosing steps, it is not whining/halting .

    So? Leave it 2A? Help with advise...

    Thanks.



  • 10 mins was jerking it forward/backward with baby steps, no skipping(slight whining/whistling on idle), and hot(can touch for 5 sec and then uncomfortable for fingers)


  • administrators

    You haven't said what pitch and lead your leadscrew has, so it's hard to be precise. But I suspect that your Z acceleration and maximum speed are set too high. Try Z600 in your M203 command, and Z50 in your M201 command.



  • It is T8x2, 1 lead with 2mm pitch



  • @dc42 And I want to say you BIG THANK YOU for making Duet3D so fool proof! 🙂 Today I have found that Chinese guys were using red as - and black as + for 24V power supply 🙂 But have found that after I couldn't run the motherboard 🙂



  • @dc42 Tried your settings - it won't move at all... after M906 Z2000 - all is moving perfectly.
    To add: T8x2 with Delrin anti-backlash nut + heavy enough stainless steel platform.


  • administrators

    @briskspirit said in Problem with setting current for Chinese stepper...:

    @dc42 Tried your settings - it won't move at all

    That makes no sense. If it moved using your original settings with 1040mA current set, then it must move if you use exactly the same setting except for the lower Z parameters that I suggested in M201 and M203. Maybe you had a typo in one of the lines you changed?



  • @briskspirit

    With power off, can you rotate the screw(s) by hand reasonable freely? Nothing binding? If you have a heavy(ish) bed, you don't need anti-backlash nuts - gravity will do that job for you. But as long as they aren't binding, they won't do any harm. How many screws are driving the bed
    and what is the belt arrangement?

    I'm struggling to see how you arrive at you steps per mm. T8 x 2 usually denotes a 2 start thread in which case the lead will be twice the pitch (but Chinese manufacturers do weird things with their idea of specifications). To elaborate on that, the pitch is the distance between thread peaks, but the lead is how far a nut would travel in one revolution of the screw. Many people confuse the two, mostly because on a single start thread, the lead and pitch happen to be the same. But a 2 start thread with 2mm pitch will have lead of 4mm, a 4 start screw has lead of 8mm etc.

    Assuming it is indeed a single start screw with 2mm lead, and assuming your motors are 1.8 degrees per step then 1 revolution of the screw would be 2 mm of linear movement and 200 full steps. Therefore it follows that 1mm would be 100 full steps so at 16X micro-stepping, the steps per mm should be (100x16=) 1600. If the screws are indeed 2 start, then the lead becomes 4mm so the steps per mm would be half (800). So where did 1040 in your configuration come from?



  • @dc42 Yeah, I understand... But it is what it is... 2A - all is fine(but whining noise in idle state) and with 1A it will start only with higher acceleration.

    @deckingman I had T8x8 which I could rotate freely but this one - I need to put force with two fingers so I fill a little pain because of threads... So you might be right that there is a binding somewhere. Will try to change Delrin anti-backlash for regular brass nut. And I am not wrong about steps, I set them at 1600 steps for my 1.8 stepper and single start 2mm screw. And screw is Texas made 🙂 (1040 is for current setting, not for steps)



  • Stepper is harder to turn than amy regular one(This one is with integrated screw)



  • So I assume that something is wrong with the stepper... But I have no choice as it is integrated with the screw and to redo everything I need to print parts. And I still can't understand how to convert to free floating belt driven Z screw for Replicator clone? (these machines has stepper + screw and no space to switch to stepper + coupler + screw, so only belt as an option.. but how to support that screw? )


  • administrators

    @briskspirit said in Problem with setting current for Chinese stepper...:

    Stepper is harder to turn than amy regular one(This one is with integrated screw)

    If it's harder to turn when it is disconnected from the electronics and the leadscrew is not connected to anything, then there may be some swarf in the motor, or the rotor may not be centralised within the stator. These issues can sometimes be fixed by removing the 4 screws from the back of the motor, withdrawing the rotor, blowing out any swarf, and re-assembling the motor. You may have to adjust the exact positions a little before tightening the 4 screws again.



  • @briskspirit said in Problem with setting current for Chinese stepper...:

    And I am not wrong about steps, I set them at 1600 steps for my 1.8 stepper and single start 2mm screw. And screw is Texas made 🙂 (1040 is for current setting, not for steps)

    Sorry - I thought I read M92 somewhere but checking back I can see that you didn't stipulate what micro-stepping you were using (I am overdue an eye test). ☺



  • @dc42 Tried... Will try your idea to readjust with 4 screws! How long it will "leave" on Z axis with 2A current if rated for 1.5A(or 1.3A... ) 🙂



  • @deckingman I know that you are a Master in building 3D printers ! 😉 So maybe you could throw me an idea how to convert my printer from integrated screw to stepper+coupler+screw? Replicator 2X clone, stepper is underneath and no space at all..



  • @briskspirit said in Problem with setting current for Chinese stepper...:

    @deckingman I know that you are a Master in building 3D printers ! 😉 So maybe you could throw me an idea how to convert my printer from integrated screw to stepper+coupler+screw? Replicator 2X clone, stepper is underneath and no space at all..

    Show me a picture of what you have. Better still, send me a PM with your email address. Then we can see what can be done without cluttering up this forum with non-duet related things.



  • @deckingman I can't send you PM as you have restricted who can send.



  • @dc42 Rotor is misaligned and has black marks on teeth where it has contact with stator teeth.



  • @briskspirit There is your problem then. If you can't fix it, TBH I can't think of a cheaper alternative than to replace the motor/shaft assembly. Being a cheap Chinese stepper, I don't suppose you can get your money back? It's obviously faulty.



  • @deckingman It will take too long... better imho is to convert to coupler or belt driven screw but I don't know how to do that the right way. Can you PM me your e-mail and I will send you photos of what I have got.


 

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