Topics created by TobiAsis

@TobiAsis said in Driver Error and MCU overheating:

You mentioned that always full current is drawn when a motor is running.
Is there any relationship between current draw, load, speed or microstepping? What could be the explanation to this?

Sorry, that's not entirely accurate, particularly as microstepping is generally used. It is accurate if you were using full stepping; at each full step, one (of the two) motor phases is at full current. However, with microstepping, between one full step of the stepper motor and the next, the voltage for a single phase varies in a sine wave from 100% to -100% and back to 100% (a transistor switches the voltage direction to reverse the polarity of the coil for the 'negative' part of the sine wave, switching magnetic direction of the coil). The voltage required for each step is set by V=I x R, where R is the coil resistance. So the current is varied to achieve the voltage required for that step, up to the maximum current limit. The stepper drivers are called 'constant current chopper drivers' because the input voltage (ie 24V) is 'chopped' (ie turned on and off very fast) to produce an averaged output voltage (for the motor coil, usually only a couple of volts), using the current as a reference, so the current remains 'constant' at that particular microstep.

Because of this, while the (maximum) current may be set to 1100mA, most of the time the stepper driver won't be drawing that much current, and averaged out over time will be drawing considerably less. Which is why the 10A fuse on V_FUSED is capable of supplying sufficient current for the 12V Regulator, 5V regulator, Stepper drivers (including external driver header), OUT 1 and OUT 2 headers, V_OUTLC1 and V_OUTLC2 selection jumpers.

Load generally doesn't matter; either the motor has the torque to overcome the load, or it doesn't and will skip steps. Speed is different, as torque reduces with speed, and there are various other complications such as back EMF, but that would require a much more complex answer, and I'm not an electrical engineer!

(Note: the above is my understanding of how a stepper driver works. I'm happy to be corrected.)

I had some previous issues with a motor stalling, and when I measured, I realized that the current draw was only about half of the current I specified in config. I experimented with increasing the current, and I only reached a full current draw when I set it to 2x the rated peak current of the motor.

I think the problem is how you're measuring the current. How are you doing that? If you're using an oscilloscope, you could see the current changing, depending on where you are measuring. If you're using a multimeter, you're probably seeing the average current over time, ie half the current. If the motor is stationary, it will depend on where in the step it is stopped.

Setting the current to double the recommended motor current is going to overheat the stepper motor and burn out the wiring, and cause a phase short error message. It may also damage the stepper driver. Don't do it!

Ian

@Dude8 we don't recommend feeding the Duet commands via USB. If you do that then when you want to pause and resume the print (or if a filament error is detected and this causes a pause), all moves that are currently queued on the Duet will be completed first, due to the serial nature of the USB interface. Whereas if you use the SPI connection and SBC mode, pausing can cancel moves that have already been queued. This is possible because the Duet can communicate to the SBC where the job file needs to be restarted from.

Also, using SBC mode means that the SBC has full access to the object model; whereas if you send commands over USB then you need to use M409 if you want to retrieve values from the object model, and the M409 command may get delayed because of other commands already in the USB buffer. So the M409 response may be delayed a little and the values will be less up to date. Similarly if you use M105, M114 etc. to retrieve other information about the state of the machine.

To tell the Duet to run in SBC mode you remove the SD card from it, so there is no SD card wear at the Duet end.

@droftarts Thanks for the note and your help. That is good news for me.

I must have confused it, and used io1.out. Or, I only turned it on and off so far, so I might not have noticed the missing PWM. But I will also need the PWM functionality in the future.

Have a good day
Tobi

@droftarts Hi Ian, thanks for your reply.

So it is what I expected. A costly learning experience, but now I know to be extra careful with the connections. I will still be able to use it in standalone mode on another project, I just need to learn now how to set everything up without SBC.

Have a good day!
Tobias