Help with gt2 belt upgrade


I’m upgrading my t5 original belts to the GT2 belt with 16 tooth pulleys.
At the minute I need help configuring the the k8200 to run on it.

  • Where do I find the configuration.h file that I need to edit?
  • What value do I change and what do I change it to?

More questions to come…
Any help appreciated


First you need to download the firmware from Velleman web site, and after to modify the configuration.h file.

For GT2 2mm 1- tooth pulley, the value to set is 100 on this line

replace #define DEFAULT_AXIS_STEPS_PER_UNIT {64.25,64.25,2560,600} // default steps per unit for ultimaker
by #define DEFAULT_AXIS_STEPS_PER_UNIT {100,100,2560,600} // default steps per unit for ultimaker

You can also change the value via eeprom, but your firmware need to be configured to read and write on eeprom

thanks for the reply, I’m still confused as to how to change the configuration.h file. is there a step by step guide somewhere? Should i follow the steps here? (

also the 100 value is for 16 tooth pullet right?


You can use this guide to know how to update the new firmware, but to change step values, you need to edit configuration.h file to modify it.

also the 100 value is for 16 tooth pullet right?


Thanks for the help, was a lot easier to do than expected. Also I didn’t need to print any extra bits to accommodate for the new belt.
I’m printing a lego brick as a test and its a lot bigger than expected, after counting the teeth on the pulleys it turns out I was shipped with 20 tooth pulleys.
Is there a big difference between the two? I heard 16 tooth has more torque but does it make a noticable difference?

Also what values do I put in the configuration.h file for the 20 tooth pulleys?

Many thanks



just wondering what the improvement can be with a GT2 ?


More precisions and pulley with the hole in the center

After I made the GT2 -20 I recompiled Marlin2’s .h file in the Arduino compiler. It loads next to the Marlin file. I only made the X axis mod and so changed to 80 for X only.

Noticed the X and Y belts where very close so I made a bracket with an extra pulley mounted on the bolts for the belt clamp that lifted the X axis belt 5mm, clearing and possible collision with the Y belt.

Sorry about the vague description but hope you get the idea.

I changed both belts and had no problems with X and Y colliding. I did have a problem with the Y belt rubbing on the X axis rod. I made this ( to solve that problem as well as tension the belt. I recommend changing both belts as it is suprisingly easy

I’m thinking of changing my GT2 20 to GT2 36 for the X axis for clearence problems. anyone know the step value to put into the .h file??

Here is a calculator for belts and pulleys.

Looks like 44.44 is the answer.


I upgraded my x-axis some time ago. I didn’t really print anything after that because i use it for school primarily and there were the holidays. Now that i got back to printing stuff i noticed the x axis is doing less distance than it should. I changed the value in the firmware from 64.25 to 80 for the x axis (since i a have gt2 20 tooth pulley). But that didn’t seem to change anything, i tried putting it back to 64.25 and to 100 and it looks like all of these values are making it run for the same distance. Obviously i’m doing somthing wrong, but i can’t seem to figure out what exactly.

Any ideas?