Wondering about CoreXY and different motor torques

Hi all
CoreXY is new to me. Heard about it only lately.
I've been wondering - how is it possible to work so good with 2 independent motors? Each motor has a tolerance about it torque. So it is very unlikely that the 2 motors will have the same exact torque.

If one motor turn more than the other - no line will ever be completely linear.

Though CoreXY works with no doubt - so how does it work?

is magic!!

sorry about the joke, but i could not hold this one..

"If one motor turn more than the other" -> the printer use stepper motors, this do not happens.

Quote
filipeCampos
is magic!!

sorry about the joke, but i could not hold this one..

"If one motor turn more than the other" -> the printer use stepper motors, this do not happens.

Can you explain why it doesn't? Surely there must be differences between motors, they cannot be made identically (especially from China)

What do you means with "Surely there must be differences between motors" ? you are making a strange question..

Maybe you are considering a steppers motor identical to the "normal" ones.
A stepper motor is build to rotate a very precise mount of degree. For example nema17 motor i know of two type of motor, the one that turn 1.8º degree and other 0.9ºdegree
That means it turn this number of degree each X steps. The X step is set in the firmware.
If the motor fail to rotate the correct amount of degree, them can be missing steps for some reason: heat, voltage, defective, etc...
But when you have two good steppers motors and correctly configured, them they never fails in the amount of rotation.

The typical step accuracy of a stepper motor is 5% non- accumulative. In the worse case scenario, one motor could be 5% low on a step and the other 5% high so the potential difference for one individual step could be 10% which equate to 0.18 degrees for a 200step/rev motor. Taking a typical 20 tooth pulley with a 2mm pitch belt, one revolution of 360 degrees would equate to 40mm belt movement. So 1 mm of belt movement takes 9 degrees or 5 steps. Assuming our worse case scenario of 0.18 degrees difference between the 2 motors, then that error translates to 0.02mm for 1mm movement. But it's a non accumulative error so it would still be 0.02 mm after 100mm or 1,000mm of travel.