[SOLVED] Clarification on Micro-stepping unespected effect

Hello

Currently finishing to configure a cheap milling CNC 3020, it happens that the behavior is not what I would expect while changing the micro-stepping value:

Considering my understanding of micro-stepping, changing the micro-stepping from 2 to 4 would:

• Increase frequency of pulses sent to the driver by 2
• Possibly divide the maximum speed by 2, if the pulse frequency is the limit.
• Speed of the head does not change. (if set at e.g. 10mm/s, it apply this speed)

However, on my machine, the result is totally different: The speed of the head is duplicated.

I did some tests, and it seem that the correct speed (e.g. 10mm/s) is applied with micro-stepping of 4. If applying micro-stepping 1, it run at 2.5mm/s (even if indicating 10mm/s), if I set the micro-stepping to 128... well..

My supposition is that either the steppers or the driver are not able to manage micro-stepping, or even apply already internally to simulate more steps-per-revolution.

Any experience or explanation for it?

How(or where) are you changing your micro stepping settings? You must change those settings in the drive (either with the drives configuration software, or by physical switches.) and you must make the appropriate changes to the step scale in Linuxcnc. If you are only changing the setting in on place or the other, your results will not be what you are expecting.

Step motors typically have steps/rev = 200 for full steps. If you change the micro step setting in the drive to 4x, the drive will divide the motors full steps into 4 steps giving 800 steps/rev. If you made no changes to Linuxcnc the motor will travel 1/4 as fast and as far commanded. If you reconfigured Linuxcnc to increase the microstepping by 4x but did not change the actual micro step setting on the drive, the motor would now turn 4x as fast and move 4x as far.

Make sense, and I guess my cheap drive do not allows to change this value.

Do the drives have any jumpers or dip switches or a serial configuration port? If not than yes they probably aren't adjustable.