serious error of position

Move what I said before:

from Y0 to Y0.5 then to Y1 then to Y0.5 again. In this point I almost bet that you will still be in Y1 and not in Y0.5

The "game mechanics" exist in all machines. Belts are not perfect at all.

however, even if it was a mechanical problem 'cause always comes back to zero in a perfect manner from any position ?

no, none of this happens, if you want to do the video, then y01 y02 y01 then, the position is performed

you are using Stepper motor correct ?
and belt , your problem is mechanical not linuxcnc software .

the divide of 1.8 deg per step , into your calculation will show this problem well , what stepper drive are you using and what microstepping ?
remember a stepper motor can only move in increments of 1.8 degrees , which is why when working to a fine resolution you need some times to use mechanical gearing to reduce this error
microstepping will not fix this problem , only mechanical gearing .

this is one type of machine where servo motors are a better solution , so you can use velocity drive and not step direction , but with some thought and gearing this can be solved

thanks for the reply.
what you say is not 'possible otherwise all machines with stepper motors would not be used, however, admit and accept your thoughts:
a ride in my car, is equivalent to 75 mm of displacement thus:
75/200 = 0.35 mm steps that should be the maximum error in accordance with your thinking logically in a single movement. according to your reasoning the error must be random, LinuxCNC the error repeats perfectly in the usual points to the usual extent. and 'to consider that the return to zero and' always perfect from any point.
tests: installed Mach3 does not have this defect.

ok thanks hal interest , positions do not correspond with the positions of axis
ypos-fb = 182.7883 axes 182 624
ypos-cmd 182.7883
xpos-fb = 366.4099 axes 366 582
xpos-cmd 366.4099

which numbers are wrong?

and 'normal that these numbers do not match the work in two different sections of the program.
thanks

I do not understand what you are saying

can you with MDI:

g0 x0
record axis DRO, xpos-cmd xpos-fb
g0 x100
record axis DRO, xpos-cmd xpos-fb
g0 x200
record axis DRO, xpos-cmd xpos-fb
g0 x100
record axis DRO, xpos-cmd xpos-fb

and post the results here?
Thanks

g0 y0 cmd -12.99443 fb -12.99443
g0 y50 cmd 37.00557 fb 37.00557
g0 y100 cmd 87.00557 fb 87.00557
g0 y150 cmd 137.0056 fb 137.0056
g0 y200 cmd 187.0056 bf 187.0056

g0 y150 cmd 137.0056 fb 137.0056
g0 y100 cmd 87.00557 fb 87.00557
g0 y50 cmd 37.00557 fb 37.00557
g0 y0 cmd -12.99443 fb -12.99443

grazie

OK so the commanded positions are correct.

so if the mechanical positions are incorrect, and its not a
mechanical problem, you are possibly losing/gaining steps somewhere

What step drives are you using?
Why is the direction change time set so long?

also what version of LinuxCNC are you using?