Stepper adjustment: with standard pololu stepper drivers and motors you set the pot voltage to 0.4v for 1A to the motor. However I made an assumption and everyone knows what a great idea that is. On my smaller printer I put the upgraded pololu steppers that run 1,5A and 2,2A with a heatsink and the motor is rated at 1.75A so running it at 0.4V is actually underpowering the motor. So turned up the pot to 0.7V that I worked out as 1,5A to the motor. The result my extruder used to skip every now and again and now it doesnt. The x&y never skipped but I figured that upping it to 0.6V would keep things in check and allow higher speed. Either way the calculation is in the reprap website and worth adhering too.
Do you have a link for the specific calculator?
All the specifics are on pololu’s website. Im trying to put it in a spreadsheet now. But look at http://www.pololu.com/product/1182 for the A4988
Ideally someone with a education in electronics could give a better idea of the calculation. Little sepper motors are rated a 0.4A my big one are rated at 1.75A the pololu’s are either 1A or 1,5A from experience I know that the .4 mitors with 1A drivers need a vref of 0.4V But having convinced myself I can turn up the pot on my heatsinked 8825’s with a motor that is rated at 1.75A to .88V safely I out it upto 0.7V and its running much better and not hot. Today I’m 2nd guessing my math…
Voltage references will vary from driver to driver. Some A498x drivers use 200mOhm sense resistors, others 100mOhm and the genuine Pololu ones 50mOhm - so the reference voltage to get the same current output will vary from driver to driver as well.
Pololu’s DRV8825 boards use 100mOhm and a different voltage amplification.
To sum things up:
A4988 with
50mOhm (Pololu): 2.5A per 1V (Vref)
100mOhm: 1.25A per 1V (Vref)
200mOhm: (StepStick): 0.625A per 1V (Vref)
DRV8825 with
100mOhm (Pololu): 2A per 1V (Vref)
Of course, different current settings might also influence the accuracy of your motor’s microstepping.
My understanding and experience suggests you’re not going to want to do rated current because that will generally heat the motor very hot, and risk tripping the driver thermal protection cutoff. The number on the motor is the absolute maximum rating, not a number you must hit. Run the machine for an hour, if the motor is cold, you probably have a lot of head room, dial it up, if the motor is too hot to hold onto, dial it down. I realize that’s not very methodical, but you’re trying to avoid overheating the driver at the high end and avoid skipping at the low end of the current range. The more you push your machine, the more of a balancing act it can be.
@Thomas_Sanladerer
Aaaahhhh now that makes sense. thank you its clear now, It makes sense as to why I have to run Pentium4 heat sinks with fans on my large printers axiz drivers. and with the 0.4A rated motors going to 8825 would be worse unless I drop the Pot to 0.2V And likewise if I swapped to motors from the 0.4 to the 1.75A motors I would need to increase the Pot to 0.7V for a 4988 with a 50Ohm (2,5)