Building GRBL for CoreXY

• Source: I pulled grbl from this location on the web.
  
  
• Electronics: I used the Arduino shield from Nayda Peek. The current limit resistors are now 2.5k, allowing for a motor current of about .7A. With higher currents, the motor drivers get really hot. To determine component locations, open the eagle files and look.

• Algorithm: In order to move in X or Y, both motors must move. A single motor will move the carriage on a diagonal. Ilan talks about the algorithm here.  
  

• Modified code: GRBL creates a queue of blocks as an interrupt routine executes them (spinning the motors). The CoreXY mods are inserted into planner.c where the number of steps in x, y and z are calculated. The transform then recalculates the needed movement for each motor, and modifies the block.

• I/O Mapping: The motor drivers are connected to portB instead of portD.

• Calibration: GRBL holds configuration settings in EPROM, so the system can be tuned by typing commands at the g-code prompt. To print current values, type "$" To set parameter 1 to 100 type: $1=100

Grbl 0.7d

'$' to dump current settings

$0 = 26.737 (steps/mm x)

$1 = 26.737 (steps/mm y)

$2 = 157.480 (steps/mm z)

$3 = 30 (microseconds step pulse)

$4 = 300.000 (mm/min default feed rate)

$5 = 300.000 (mm/min default seek rate)

$6 = 0.100 (mm/arc segment)

$7 = 0 (step port invert mask. binary = 0)

$8 = 20.000 (acceleration in mm/sec^2)

$9 = 0.050 (cornering junction deviation in mm)

'$x=value' to set parameter or just '$' to dump current settings

ok These values seem reasonable, but may not be perfect.

• Operation: David Mellis has a processing script to download g-code to the board. Under Linux (Ubuntu based v12 distro) the RXTX serial port driver seems to lock up at times. I replaced it with per the directions on the MTM page, but I still get some lockups.

Code Discussed in this Section:

Source
Hex