Curious about how it keeps both z carriage ends at the same height.
Hello,
I'm just really curious about this and I thought I would ask here in case somebody who's familiar with the inner workings of the firmware knows the answer.
My old any cubic i3 mega had a limit switch next to each z motor. During homing it would bring both down and stop each side when it hit the limit switch. That assured that both ends of the carriage assembly were at the same height.
My MK4S doesn't have a sensor that I can tell for each z motor. And I'm trying to figure out exactly how it keeps each side of the carriage at the same height. If one was out from the other by a couple of mm, how would it correct that?
When it calibrates z, the carriage is over on the left where it touches the bed. But I can't see it do any kind of a move where it would be able to sense a relative difference in height between the two ends of the carriage rods. So there must be something very clever going on in the firmware to make sure that the carriage rods are level and the two ends of the carriage are the same height from the motors.
Can anybody explain to me how it does it?
Kevin
Best Answer by JoanTabb:
Absolute answer... there is nothing actually holding the X axis rails level...
mitigating factors
1, as far as I am aware, the Z Motors use a single stepper driver, with the Motors wired in parallel. so movement in one motor tends to energise the other motor whilst the printer is turned off. so motors tend to stay in step even when the machine is off!
2, the Z Motors remain energised when the printer is turned on maintaining X axis level (Even if the Printer is not printing!)
3, the Auto Bed levelling resolves minor variations in X level (there is probably up to one full step difference when the Z motors stall out at the top of the frame. )
4, if all else fails, X axis levelling is re established under Z axis calibration where the Z Motors, drive the X axis End pieces up to the top of the frame, where the Z Motors stall out, ensuring that the ends of the X Axis, are level again.
I think that is about it!
Joan
RE:
Absolute answer... there is nothing actually holding the X axis rails level...
mitigating factors
1, as far as I am aware, the Z Motors use a single stepper driver, with the Motors wired in parallel. so movement in one motor tends to energise the other motor whilst the printer is turned off. so motors tend to stay in step even when the machine is off!
2, the Z Motors remain energised when the printer is turned on maintaining X axis level (Even if the Printer is not printing!)
3, the Auto Bed levelling resolves minor variations in X level (there is probably up to one full step difference when the Z motors stall out at the top of the frame. )
4, if all else fails, X axis levelling is re established under Z axis calibration where the Z Motors, drive the X axis End pieces up to the top of the frame, where the Z Motors stall out, ensuring that the ends of the X Axis, are level again.
I think that is about it!
Joan
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RE: Curious about how it keeps both z carriage ends at the same height.
Ah, I see. So if something senses that it's out, it just drives them up to the top so they're both in sync again.
Thanks for the prompt answer.
RE: Curious about how it keeps both z carriage ends at the same height.
What Joan said. There's no secret sauce in firmware. It's pretty much #4 on her list. By driving the x axis up to stall out at max Z the axis gets leveled. The main problem would be if your two z rods were of significantly different lengths. Minor differences get addressed by mesh bed leveling.
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...