Activating z-probe would lead to forbidden xy position

BasilFX · February 2018

I have a Prusa i3 printer (cartesian) with a fixed inductive z-probe mounted on the right side of my hotend. In other words:

#define Z_PROBE_X_OFFSET 32
#define Z_PROBE_Y_OFFSET 0

Reachable dimensions of my bed are 180x175mm, so I have:

#define X_MAX_LENGTH 180
#define Y_MAX_LENGTH 175
#define X_MIN_POS 0
#define Y_MIN_POS 0

The lower-left corner of my heated bed is where x=0.0 and y=0.0. After every firmware upload, I do a M502, then M500 so I am absolutely sure that I don't re-use old values. Then I run G28 to home all the axis, but this fails with the error:

Error:Activating z-probe would lead to forbidden xy position: -32.000000, 0.00

After some digging in the source code, I find this line in BedLeveling.cpp that prints this error:

if ((ZPOffsetX > 0 && Printer::currentPosition[X_AXIS] - ZPOffsetX < Printer::xMin)

This condition is true: z-probe x-offset is 32.0 and homing X/Y first yields x = 0.0, therefore 0.0 - 32.0 < X_MIN_POS.

So my question is: what are the things I have to set to make it work. The hotend can reach x=0.0 and y=0.0, but the smallest x the probe can reach is x=32.0.

I am using RADDS 1.5 with firmware v1.0.1.

MartinH · February 2018

You need to set the P1,P2,P3 probing XY positions.
To have a small margin for error i would suggest
P1 X37 Y5
P2 X175 Y5
P3 X37 Y170

Also use one of the homing options that use pre-heat and set the pre-heat temp to 0, this lets you preset the X Y coords for Z homing.

Activating z-probe would lead to forbidden xy position

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