Hello,
I have a K8400 with two extruders which I am trying to use to play music. So far I have managed to play tetris on the z axis but need a bit more frequency range for other songs. I have set the maximum X and Y axis speed to what’s listed on the K8400’s website, but there was no information given on the max speed for the Z axis and extruders.
It was set to 10 mm/s by default, but the x and y axes were lower than the quoted max speed so I presume this is also the case for the z axis.
Can anyone tell me the maximum speed for the z axis and extruder motors in mm/s or mm/minute? Also, I would like to be able to move the extruders without heading up the hot end. How would I achieve this?
N.B. there is no load on the z axis motor apart from the print base and a sheet of aluminium, so the motor should be able to go above the max speed right? Thanks!
Also, the minimum speed and accuracy of each axis with regards to speed and distance would be very useful! Thank you!
Default max. feedrate per axis according to configuration.h in the firmware:
X/Y: 160 mm/s
Z: 10 mm/s
E: 10000 mm/s (a bit silly, isn’t it? xD)
steps per unit: 134.74 (X/Y), 4266.66 (Z), 200 (E)*
There is no real minimum speed, you could theoretically slow it to 1 microstep/day or something like that.
That said, there is an issue with the microsteps on the DRV8825 stepper driver because the lowest voltage it can produce is 12% of PSU voltage, so in standard configuration with mixed decay mode roughly the first 10 microsteps are missed because of that. So if you go to slow you get choppy movement. Workaround is either by adding 4 antiparallel diodes per motor coil or changing the driver to fast decay mode (soldering a wire between VCC input and Pin19 on the chip). Same result, but fast decay is a bit noisier than mixed decay.
Minimum accuracy of X/Y would be 0.0074mm - one microstep (see above steps per unit). Of course also afftected by the microstepping issue.
- default steps per unit of the extruder is wrong in the firmware, it should be ~149 steps/unit
Mmh, bit of a brainfart there by me … you don’t really want microsteps for making music as you’re only really interested in the full sinewaves.
All values mentioned above can be changed in the firmware. But there is also the maximum step frequency by the ATMEGA2560 itself. At 16Mhz it is at around 10kHz for single or 40kHz for quad-stepping. The firmware switches by itself between single- and quadstepping (to change that you’d have to modify stepper.cpp). The stepper driver itself is not a limiting factor here as the input goes up to ~250kHz.
So for music you might be better off switching to full steps instead of microstepping as you’d get a higher frequency from the steppers themselves.
Considering above, 10mm/s from the Z-Axis is veeery optimistic as the processor would have to got to quadstepping to achieve the necessary 40kHz and would then still be below the 42.7kHz necessary for 10mm/s. This does not even include accleration settings. With this in mind you’be hard pressed to get anything higher than 625Hz out of the steppers in 1/32nd mode, because I think you’ll actually need 2 steps to get a full sinewave.
To get the extruder motor to move without heating up the hotend you have to modify configuration.h of the firmware (default: #define EXTRUDE_MINTEMP 160)