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Z-Axis stepper motor controller testing.

Posted by Milly 
Z-Axis stepper motor controller testing.
December 29, 2010 06:23PM

I have been testing my recently built electronics now I have sourced some stepper motors. I can successfully run the X and Y axis steppers using the reprap software, stepping the motors and returning to home. Its a different story with the Z axis however as the behaviour is different and I'm not sure if this is correct or not as I am still able to step the motor. With the X and Y axis the steady state of the system is for two of the four LED's on the stepper controller board to be on, however the Z axis has no lights (other than the power light) on. When I command the Z motor to step it does rotate but for longer than the X/Y axis (with the correct LED indication). I have swapped controllers and motors around and am confident they are not defective.

Are the outputs from the motherboard (V1.2) the same irrespective of axis? I hooked up a logic probe (don't have an oscilloscope!) and compared the various pins on the axis. The X and Y axis were both the same, but the Z axis was showing a different output on pin 5 (all other pins the same). For the X/Y axis this pin was low but for the Z it was pulsing and hi. For the Z axis this pin connects to the A2 output of the ATMEGA.

I've used reprap-mendel-20100806 firmware. I was hoping to test the stepper motors using the stepper motor test sketch described in the wiki but the link to the code does not work, does anyone know where I can get this test code from?

As always, any help would really be appreciated!


Re: Z-Axis stepper motor controller testing.
December 29, 2010 07:23PM
I believe it works as intended.

As a way of speaking, Z axis takes alot more "motor action time" than the others to move a distance, because of both gear ratio and the fact it uses M8 thread. But its ok because Z is just one layer advance after another, small increments, and there is no need for actual speed on raising the carriage. The motor itself does run "longer" but because its final machine movement is much more smaller.

I think with the normal firmware, the enable pin on z axis is different than the rest. I believe the logic is that when not moving, the X&Y motors are energized to have a hold, to avoid accidental move. While for Z that is not needed and is disabled probably because of some current economy / machine efficiency reasons.

You can change Z enable to same behavior as XY in firmware. Since Z only moves a little to raise the carriage to next level, it would mean that in overall build time Z motor "duty cycle" would be significantly changed from almost nothing -> to ~100%.

Edited 1 time(s). Last edit at 12/29/2010 07:31PM by NoobMan.
Re: Z-Axis stepper motor controller testing.
January 04, 2011 03:01PM
Thanks for the reply, I've been doing some more research and I think you are spot on. The gearing for the Z axis is such that the motor does need more activation time than the X and Y axis. I'm awaiting some final parts for the mechanical side of things and then I will be able to bolt it all together and give it a good shake down!

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