V - Change X - Y axis belts and steps correction in the firmware.

In recent days, I noticed that the belts of the X and Y axes were crystallized.

After looking at the local offer (in Colombia) I found that the GT2 belts - which are available here for use in robotics - were practically the same.

But after placing them, I found that they did not seem to fit precisely because as they moved a certain distance the pulleys jumped a tooth.

Looking closely I noticed that they had a small difference in tooth spacing from the original Rapman (top, original belt; lower, new belt):

Oh, problem. And they only got that way.

I then decided to replace the pulleys as well, because the salesman assured me that they fit perfectly with the new belts.

And certainly the 20-tooth pulleys fit perfectly, just that by researching a little on the internet and in the Rapman's construction manual, I found that the original pulleys only have 18 teeth.

It was then apparent that there would be an appreciable dimensional difference in the prints, because the path traveled would be different (18° of rotation of the new pulley for each tooth, vs 20° of rotation in the original pulley).

Then, I discovered the "Prusa Calculator":  www.prusaprinters.org/calculator, which allows to calculate the steps x mm in the routes of the belts in function of some already known variables of the motors and the "microstepping "of the Polulu drivers. 

Thus the result of the steps x mm is as follow:

That value of 81.22 must be changed in the Marlin firmware we edited, on line 483, so that the print is dimensionally correct:

If you are going to change belts, I suggest that they verify the measurements very well, to make the adjustments that are necessary and not to have surprises in the print.

Good luck!

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