CoreXY homing problem

[bajticzek]

Hello, I built a CoreXY laser machine and I am using Mega2560+RAMPS combo with grbl-Mega 1.1f. I have a problem with homing. Simply put after initiating homing, only one motor moves at a time. That means when machine should be homing X first, then Y, it doesn't. The gantry moves diagonally because only one of the motors moves at a time. Jogging works without an issue. I tried Repetier firmware and there homing and jogging works both flawlessly. But it isn't grbl, which I want to use.

I downloaded fresh .zip file, extracted the grbl folder to Arduino\libraries and edited following in config.h (pure minimum to get things working):

• Commented lines 37 and 38 //#define DEFAULTS_GENERIC, //#define CPU_MAP_2560_INITIAL
• Uncommented lines 41 and 42 #define DEFAULTS_RAMPS_BOARD, #define CPU_MAP_2560_RAMPS_BOARD
• Commented line 112 //#define HOMING_CYCLE_2 (1<<Z_AXIS) and left line 110 and 111 uncommented #define HOMING_CYCLE_0 (1<<X_AXIS), #define HOMING_CYCLE_1 (1<<Y_AXIS)
• Uncommented line 190 #define COREXY
• Uncommented line 208 #define INVERT_MIN_LIMIT_PIN_MASK ((1<<X_AXIS) | (1<<Y_AXIS) | (1<<Z_AXIS)) to make my limit switches work as they should

This was my second attempt in case I missed something on the first try. I tried to edit the config.h as little as possible. But still homing doesn't work. Can you guys tell me what am I missing?

Thanks for any info.

[bajticzek]

After some extensive digging in the source code I solved this issue by altering line 347 in limits.c. I changed sys.homing_axis_lock[idx] = axislock[idx]; to sys.homing_axis_lock[idx] = 65; which basically doesn't lock the movement to one motor - 65 is combined mask for step pins on RAMPS board for motor A and motor B. I consider this a bug and my workaround is really not a final solution. Can anyone who is more familiar with grbl source code look into this issue and make a bulletproof fix?

Thank you.

[chamnit]

@bajticzek : Thanks for digging and locating the bug. @docwelch Do you have time to look into this?

[docwelch]

@bajticzek and @chamnit: I don't have a CoreXY machine so have not seen this issue. I relied solely on the changes @jekhor had made here so I would defer to him. I will look a little deeper but am not sure I'll be able to quickly determine the cause. As was pointed out when RAMPS support was added, it's a temporary solution and not an ideal one.

[bajticzek]

I recently added Z-Axis to my Laser machine, so if anyone is interested in homing Z too, change sys.homing_axis_lock[idx] = 65; to sys.homing_axis_lock[idx] = 73; to allow Z homing.