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  1. #21
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    can't do it tonight - company comming over maybe by this weekend.



  2. #22
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    Default The real problem and the solution

    Hello guys

    I have a similar machine (3040Z) with the same YOOCNC NT65 3X controller and I too had the missing steps problem. I hooked my oscilloscope to the controller board while in operation and I got to the bottom of it.

    The root cause of the missing steps is the violation of input timings of the Toshiba TB6560 driver chip.

    The minimum allowable pulse width depends on the oscillation frequency which is in turn set by the C39, 40, 41 capacitors. From the datasheet, 100 pF results in 400 kHz oscillation and 10 us minimum pulse width, 330 pF 130 kHz and 30 us minimum.

    The maximum pulse width Mach3 allows is 15 us. This would be fine with 100 pF capacitors, but there are two snags. Number one is, due to capacitor tolerance and stray board capacitance, the actual value seen by the chip can be higher and therefore the oscillation frequency lower. In my case, the measured frequency was about 300 kHz (measured with 10x probe, which itself adds a few pF). Number two, the TB6560 step/direction inputs are driven by optocouplers and pulled up by 5.1k resistors (R4 through R9). The rising edge of the signal (which the TB6560 is sensitive to) is very slow (about 6-7 microsecond in my case) because it is driven high by the pullup resistor only when the optoisolator is turned off.

    Now consider this: on one hand the maximum pulse width that Mach3 can be set to is in reality eroded by the slow rising edge (by approx 5 us); on the other hand, the oscillation frequency may not be optimal therefore the minimum pulse width acceptable by the chip could be even higher than 10 us. Therefore there is virtually no margin and the datasheet minimum pulse width is quite likely to be violated.

    The situation is made even less clear by the Mach3 settings suggested by the chinese geniuses in their machine manual. These settings are very short pulses (3 us) and even shorter (1 us) direction set up time. Furthermore the signal level is such that Mach3 pulses are effectively inverted at the TB6560 chip input. In this way, the step signal is inverted and therefore the ON time is very long (basically it's ON most of the time except during the Mach3 3 us pulse). The problem with this is that it violates another datasheet constraint, i.e. that the duty cycle of the input pulses should be no more than 50%). And in addition, the slow rising edge affects the direction pin too, so whenever the direction inverts from low to high at the TB6560, a step is taken in the wrong direction.

    The reason why some people have some improvement with filtering capacitors is that due to reduced noise, some margin could be recovered. However this is still not ideal. I have tested two workarounds, one software and one hardware.

    The software workaround: 1) make sure that the Mach3 signal level is such that when there is no step, pin 5 of the TB6560 (named CLK in the datasheet) is low. 2) Use 1/2 step Sherline mode, with kernel running at 25 or 35 kHz. The effect of Sherline mode is that the pulse will stay high for the entire duration of the kernel cycle, and reset on the next cycle. 3) Set the Direction pulse timing to the maximum (15 us - note the GUI indicates 1 to 5 but it will accept up to 15). The net effect is a long pulse (40 us for 25 kHz kernel, 28.5 us for 35 kHz), with the limitation that the maximum pulse rate is reduced to one half of the kernel frequency. This is not a problem given the fact that in any case the TB6560 maximum allowable step frequency is only 15 kHz.

    The hardware workaround: replace R4 to R9 with lower value (470 or 1k). This will make the rising edge sharper and gain some pulse width margin. You can't go too low with the value, otherwise the falling edge will become too slow, reducing the margin. You still need to make sure the Mach3 signal level is as in point 1 above. You can then either use Sherline mode as above, or normal mode. In the latter case, just make sure both step and direction timings are set to their maximum (15 us) and don't exceed 35 kHz (there is no point and all it will do is reduce your pulse times, this eating the margin).

    There are many more subtle and less subtle problems with the board design. It really sucks, but with either workaround it can be made to at least operate without losing steps.

    Hope this helps



  3. #23
    Registered Rakounet's Avatar
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    Hi Max,

    Thank you for this clear analysis. I will try your change proposals. By the way, did you get the schematic diagram? Could help. Otherwise let's go for reverse engineering

    Rak



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    I agree with the bulk of this. The design is severely lacking, but I traced my circuit and found out that DB25-2 goes to a 74hc14 inverter buffer, then to the opto. There are a couple resistors involved, but the one I am interested in is the 5k1 on the opto output. This resistor is the load resistor. In my opinion it should be about 1k because it in essence sets the impedance for the motor drive pulse. . Solder a 1k between pin 8 on the opto to pin 6 (the opto output) on the opto. My other concern is with the current select circuit. It appears to switch between 100pct and 20pct based on if the motor is moving or not. It may have a threshold and lose torque at low rpms. Another mod will be to integrate the e-stop ckt into the opto on pin 7. Using pin7 will immediately stop all pulses going out of each opto. So, as I get deeper into it, I wonder if it would be less work to just buy new boards for each axis.....

    Last edited by timofthedeep; 10-19-2013 at 09:32 AM. Reason: wrong info


  5. #25
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    I tried the fixes that Max put out but to no help. X is still skipping. So I put my scope to it and found noise on the oscillator capacitor as long as the motor is connected to the board, but is clean when the motor is not connected. The noise is there when the motor is connected even if it is not moving. This leads me to think it is feedback from the charge pump in the chip. I looked and foundthat there are no decoupling caps on the chips, so I put a .47uF 100v ceramic on the bottom of the board between pins 6 and 20 of each chip. The cap lays flat and fits between the board and the heatsink. Since then, no missed pulses and a much cleaner clock signal. I also made the pulse pins active low in mach3. Hope this helps.

    Tim



  6. #26
    Registered helisat's Avatar
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    Hi Tim,

    Yes, I also added these capacitors to the supply line, which completely fixed the problem (big thanks to Rak for his advice). My machine is no longer skipping steps. Even after running a machine job for 2hrs, the machine had not lost its position.

    I recommend anyone with the "YOOCNC-NT65-3X" board should check and add these capacitors if required. Users should also ensure their pulse timings are correct (no guessing values here), and take into consideration your max CPU Jitter time. I had to modify BIOS settings to optimize/minimize my CPU Jitter.

    Regards,
    Luke



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    Hi,

    I'm having the same problem but I'm not that good at PCB board design / electronics. I think I can find the components you all suggest but I'm having a bit of a hard time figuring out what the "easiest" thing to do is as I now read multiple solutions? I'd like to fix as much as I can to prevent losing steps. As I'm Dutch, some English tech info isn't all that obvious to me...

    So, i.Is my following conclusion correct? :
    1. Make some hardware adjustments:
    - Adding the 470nF capacitors (ceramic or polyester both work fine?) to the pin 15 and ground of every TB6560 as suggested in the picure uploaded by Rak.
    - Adding .47uF 100v ceramic capacitator on the bottom of the board between pins 6 and 20 of each chip: This part is not really clear to me, I haven't got a clue which pin is 6 or 20... (where to start counting and in what order?). Could you please make a picture of the adjusted board?
    2. Use a software workaround in Mach 3 as suggested by Max:
    - Select Sherline 1/2 pulse mode (kernel speed at 25kHz is fine on my system according to the Mach3 drivertest so I don't need to change that).
    - In "motor Tuning" setting "Dir Pulse" to 15
    - What to do with the step pulse? Leave it at 3 as suggested by the manual? Or also put this at 15? Luke suggests "no guessing values here" but how do I do that? I'm not really getting what's meant in the Mach3 documentation on this subject.

    If that all is done, do I need to change anything else? I have the motors now at 400 steps, velocity at 1999.8 and acceleration at 50.

    I use the router to make model railway buildings etc. that need to be cut in different layers / depths with manual toolchanges inbetween and quite good accuracy (+/- 0.1mm is ok). I use polystyrene sheets and sometimes MDF.
    Hopefully you can help me with these last bits of info so I can modify my machine and really get it to do what I've got it for!

    Thanks,

    Maykel



  8. #28
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    Hi Maykel,

    You only need to add the 470nF capacitors (ceramic or MKT) to the pin 15 and ground of every TB6560 (as shown in picture uploaded by Rak). This will fix the missing steps issue.

    I use LinuxCNC, so I'm not sure of the Mach3 config. Here are some screenshots of the Mach3 config from the manual that came with my machine. It worked for me when I first tested my machine:
    YOOCNC 3020Z-D52 losing steps-1-jpg

    YOOCNC 3020Z-D52 losing steps-2-jpg

    YOOCNC 3020Z-D52 losing steps-3-jpg

    YOOCNC 3020Z-D52 losing steps-4-jpg

    YOOCNC 3020Z-D52 losing steps-5-jpg



  9. #29
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    Hi,

    Ok, so I will try this first before buying an new controller. If it doens't help (engough), I'll let you know...

    Thanks all,

    Maykel



  10. #30
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    Hi Maykel,

    If you need any help just let me know.

    Regards,
    Luke



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    Thank you guys the solution, i also had the problem with x axis (cnc3040 machine) and now it's OK. Before the 3 470nF in a 10 minutes work i had 0,3-0,8mm position lost, now it's only 0,03mm (i can't measure 0,03mm of course but i marked the wheel and the house on the stepper motors and i have very little differences after a 10min work. i can fix it by moving 0,03mm) which is i think the general accuracy of the stepper motors. What do you think?

    Thanks again and best regards
    Thomas



  12. #32
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    Hi Thomas,

    That's good to hear. There are a few other factors that can cause missed steps.

    I'm using LinuxCNC, and in the configuration process it checks the CPU jitter time. From this you configure the Timings. From my understanding, if the timings are mis-configured, then it may miss sending some of the step pulse to the LPT, as the CPU is not ready to process the interrupt.

    I'm using an Intel P4 2.6GHz, and initially the CPU jitter was greater than 90ms (not good). I needed to disable the Intel SMI, and make a few tweaks in the BIOS, and now my CPU jitter is 12ms.

    You can still work with high jitter time, you just need to configure the timings accordingly.

    Since there is no motion feedback, the software will assume that every movement command was executed successfully. Therefore its critical that everything is configured correctly. From the PC side, the CPU and Pulse Timings are critical. In some cases is better to give yourself some buffer on the timings.


    Some people have also advised that all motor wires need to be shielded. Personally I haven't had any issues with unshielded wires.

    Hope it helps..

    Luke



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    A little update to my comment above.
    First time i used 2x 1uF MKT capacitor serial (that was at home only), now i replaced with 470nF ceramic wich is theoretically must be better.
    But no! i got a little bit more position lost in the usual 10min work (0,05mm). Then i solder a 47nF caramic cap paralell with each 470nF, now after 5 10min work i can't measure position lost at all

    Best
    Thomas



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    Default YOOCNC 3020Z-D52 losing steps

    Hello all,

    Thanks a lot for this thread. I got a CNC3040Z+D52 with the YOOCNC controller for Christmas and had exactly the same problems as described here: lost steps in the negative X-direction. Y, Z and positive X (to the right) worked fine. I couldn't believe that, I thought it must be some mechanical problem. The problem is gone after I added additional capacitors across the electrolytics as described above. I choose 1uF||0.1uF ceramics, but the precise values are probably not very important. So far I didn't change any Mach3 settings, but will probably do that later.

    I found another problem, with the board. I connected reference switches for X, Y and Z to the LIMIT socket and found that operation was highly unreliable. It turned out that the pull-up resistors for the optocouplers (R52) were much too low. They used a resistor network of 4 x 330 ohms (the fourth one is for E-Stop), which draws 15mA per channel. My parallel port input draws anther 2 mA, so that a closed switch pulled the voltage down to just a little below 1 V (which is exactly what the coupler spec says, but the designer has probably not read or understood it). That was sometimes recognized by the parallel port as low, but most of the time is was not. I removed the entire resistor network and replaced it with four single 1k resistors (size 0805). Now the reference switches work reliably.

    And finally I turned the front panel switches into their correct positions. They were mounted upside down. It is a good convention probably since Edison's days, that switches go up, right or in for “on” and down, left or out for “off”.

    And by the way, I happened to kill the IRF740 of the spindle driver just by stalling the spindle while it was powered. The fuse was blown as well, but obviously not fast enough to rescue the power MOSFET. I replaced both and now everything is back to normal. I reverse-engineered the spindle drive board and could provide the schematics, in case someone is interested.

    Cheers,

    Michael

    Attached Thumbnails Attached Thumbnails YOOCNC 3020Z-D52 losing steps-r52-jpg   YOOCNC 3020Z-D52 losing steps-switches-jpg  


  15. #35
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    Hi Michael,

    Welcome to the club

    In a different thread, I have already posted the schematic diagram and layout. May be you can check them in case I made a mistake.

    Hope it can help.

    Rakounet

    Attached Thumbnails Attached Thumbnails YOOCNC 3020Z-D52 losing steps-yoc-3024pw_diagram-jpg   YOOCNC 3020Z-D52 losing steps-yoc-pw3024-layout-jpg  
    Last edited by Rakounet; 01-05-2014 at 11:24 AM.


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    Hello Rakounet,

    >> Welcome to the club
    Thanks a lot!

    >> In a different thread, I have already posted the schematic diagam and layout. May be you can check them in case I made a mistake.
    Oh great, that would have saved me some time. Please see my version attached. Note that I did not spend the effort to enter the correct reference designators. I used DesignSpark (free PCB program, DesignSpark - Home » DesignSpark) to draw the schematics (DesignSpark file attached as well). I can see a few minor differences. My board is called PW3618 and it uses the IRF740A as power MOSFET. Also the input voltage for the spindle is 36V, not 85V and the capacitors after the rectifiers are 22uF/250V, not 220uF. Maybe one of us made a mistake or we use a different spindle. I'll verify it next time when I open the enclosure.

    Btw., do you happen to have the schematics of the stepper drivers as well? I did not spend the time yet to analyze the board.

    Michael

    Attached Thumbnails Attached Thumbnails YOOCNC 3020Z-D52 losing steps-spindle-driver-pw3618-yoocnc-pdf  
    Attached Files Attached Files


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    I also interest the stepper driver schematics if someone make it.
    Thx



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    Hi Michael,

    Thank you for your great job with DesignSpark.

    You are right, the both capacitors are 22µF/250V.

    Regarding the spindle AC voltage, it is printed on the board "AC85V-IN", but in fact, the measured voltage is 38V. You are right again.

    Unfortunately I have not the schematics of the stepper drivers.

    Rakounet



  19. #39
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    Thanks for suggestion of DesignSpark PCB, it looks quite good.

    Looks like they have a reasonable CAD software as well. Have you tried it?

    Luke



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    Quote Originally Posted by helisat View Post
    Thanks for suggestion of DesignSpark PCB, it looks quite good.

    Looks like they have a reasonable CAD software as well. Have you tried it?

    Luke
    Yes, DesignSpark Mechanical V1.0. I've installed it and it looks promising. For a beginner in 3D design like me, operation was a bit counter intuitive. I'm sure that after some training, it is a very useful tool. It was two months ago, when I was unsure whether I should buy a 3D printer or a CNC machine. After I decided that real men have CNC machines and that 3D printers are kid's stuff, I didn't use it anymore
    DesignSpark is an excellent tool and it is free. In the last two years I made about ten PCBs with it.



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