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wrong DEFAULT_AXIS_STEPS_PER_UNIT in branch Marlin_UM_HeatedBedUpgrade

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Upgrading my ultimaker with a heated bed made me use branch Marlin_UM_HeatedBedUpgrade.

After some bad (z-compressed) prints i figured out the problem:

looking into Configuration.h where DEFAULT_AXIS_STEPS_PER_UNIT is defined i find the following:

#define DEFAULT_AXIS_STEPS_PER_UNIT {78.7402,78.7402,200.0,760*1.1}

steps per unit for z-axis: 200

while in branch "Marlin_v1" i find a different value for the z-axis:


which explains the "compressed" prints and my bent heated aluminium bed...

changing that value solved the problem.

The same value for the z-axis (200) is to find in branch Marlin_UM_Original_Plus.

is this intentional or just simply a mistake?



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Did you upgrade with the UM made heated bed or a custom self built one? I believe the firmware you mentioned in git is for the UM made bed which comes with a different Z stepper and screw.

If you build a custom heated bed than you should know two things... The mm per steps is 200 * 8 / 3 because the UM original without the bed upgrade has a screw with a 3 mm pitch, a stepper with 200 steps per rev and it is run in 8 microstepping mode.

The second is that the UM made bed uses a PT100 temp sensor which your bed probably doesn't use. Flashing the UM firmware for the UM made bed onto a printer with a custom built bed and a different temp sensor causes problems in the firmware with MAXTEMP or MINTEMP errors and may make updating the firmware difficult.


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Indeed i use a non UM heated bed unsing a temperature sensor with 100kOhm

Figuring out the Temperature sensor was quite straight forward and easy to find in the configuration file.

Why would a heated bed change the Z stepping resolution? Well, maybe UMs heated bed comes with a new rod... i dont know.

anyway, i think at least some comments in Configuration.h would nice to avoid that people use wrong values for the z-axis.

a wrong value there can harm the machine...


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Hello Guys!

I have a UMO and the new heated bed kit by ultimaker. I usually compile my own custom version of Marlin.

There are a few things I would like to confirm:

- the temperature sensor should be set to \\20 is the PT100 circuit found in the Ultimainboard V2.x

- the steps per unit should be 200 and the microsteps should be set to 1/8

Thanks in Advance,



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You only have to change the steps, the temperature sensor is not changed with the kit. You only get a PT100 with the UMO+.

The official firmware for the UMO+HBK is https://github.com/Ultimaker/Marlin/tree/Marlin_UM_HeatedBedUpgrade, you can compare in GitHub the changes from the https://github.com/Ultimaker/Marlin/tree/Marlin_v1.


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