innkeeper wrote:I noticed Tim has all current settings to 1.5A - seems like those were the default values and a bit high for at least the extruder.
Tim, was this intentional?
I couln't find info data or model numbers for any stepper but the extruder, maybe somone post model numbers of the steppers for X Y and Z axis?
or the specs for each if the models are unavailable.
I could find was the extruder stepper which is 42BYGH243-5
I was on vacation for a few weeks, so now I can finally get around to analyzing this. . .
It's difficult to find part numbers for these motors. One of my extruder motors (not sure if it's the original or the new one that came with the dual upgrade) has an actual label on it identifying it as Kysan P/N 1040222, which is a Kysan 42BYGH243-5 (as you pointed out). The data sheet clearly states this is a 1.0A rated motor.
But. . . I'm not a mechanical engineer, and certainly not an expert on stepper motors. The more I look into it, the more complicated it looks.
The number in the Kysan data sheet says the 1.0A rating is "current per phase". From the data sheet and other sources, I gather that because this is a
bipolar motor, there are two windings, and that the total current is therefore 2.0A. But the two phases are offset, and the stepper motor driver indicates that they are almost completely out of phase with each other, so the total current at any moment in time is still about 1.0A, and relatively constant. I checked the Vref on the Allegro A4982 stepper driver (which is set to deliver 1.5A in my as-yet-uncorrected firmware config file), and it's sitting at 0.56V. The maximum instantaneous current according to the A4982 data sheet is (Vref / (8 * Rs)), where Rs is the sense resistor, and the Smoothieboard schematic shows Rs = 0.05 ohm. So a Vref of 0.56V corresponds to a maximum current of 1.4A. That suggests that the Smoothieware may be derating the current a bit to avoid overdrive. That's all glommed together into a factor used to calculate the digipot value from the specified current in the config file. It appears to all be more or less correct. By specifying 1.5A, I'm overdriving the motor, but on the other hand, the 2.6V-rated motor is running at 0.56V, which is why 1.5A is not killing it, but only making it a bit warmer than otherwise.
My conclusion is that (1) yes, the extruder motor should be set to 1.0A; (2) Setting it to 1.5A is wrong and should be changed, but at least isn't harming the motor; (3) The smoothieware appears to be derating the current, so there is no particular need to derate the value in the config file.
Now, for the other motors. . .
I have stickers on my X and Y motors that indicate a Kysan P/N of 1124140. These are Kysan 42BYGH4804-C6 motors, and are rated at 1.5A and 2.6V. By my analysis above, they should remain configured for 1.5A.
I have no identifying marks on my Z leadscrew motor, which is kind of problematic, because Kysan offers a large number of these motors in varying current ratings. It appears, though, that (mostly) they come in two basic forms, which is 0.4A at 30 ohms winding resistance and 1.5A at 2.8 ohms winding resistance. (Note that the older model M2s used the 30 ohms motors; they were replaced a few years ago with the 2.8 ohm motors.) Although it appears to be impossible to figure out what the motor model number is, it's easy to read the resistance across the windings and so conclude that the motor is rated at 1.5A. The weird thing is that the Kysan list of motors suggests that all of the 1.5A motors are 48mm tall (the same as the X and Y motors) and that all the 34mm high motors are 0.4A/30 ohms. Of course, it may not be a Kysan.
One interesting thing I came across: The extruder motor is a 1:5.2 step-down, while all the firmware calculations assume 1:5. There is a comment on
http://makergear.wikidot.com/m2-technical-guide that notes the error. It says that the steps/mm value should be 488.547 but is set to 471.57 in the firmware (based on the simple but incorrect 1:5 ratio). In other words, the extruder is always running a little faster than the firmware thinks it is, leading to slight over-extrusion, leading to a persistent need to correct for the over-extrusion by setting the extruder multiplier less than one. I have always maintained that this was a systematic error resulting from an incorrect calculation. I'm going to try re-calibrating the extruder multiplier with the extruder motor steps/mm set to 488.55 and see what I get. . .