Testing of open source stepper hardware/firmware

status

x

grbl

I am starting with grbl v0.8 "edge" branch forked from https://github.com/grbl/grbl at https://github.com/chuck-h/grbl/tree/edge . ChuckH 09:19, 24 September 2012 (CEST)

grbl requires an appropriate config.h file and a patch to the stepper-enable polarity in order to work with StepperNug.

I intend to take advantage of ongoing grbl development, so I have tried to structure the fork so that merging from upstream is not too cumbersome. For example, config.h is lightly edited but largely overruled by config_ose.h .

Relevant parts of config.h (pin assignments):

// Define pin-assignments
#define STEPPING_DDR       DDRB
#define STEPPING_PORT      PORTB
#define X_STEP_BIT         5  // Uno Digital Pin 13
#define Y_STEP_BIT         3  // Uno Digital Pin 11
#define Z_STEP_BIT         1  // Uno Digital Pin 9
#define X_DIRECTION_BIT    4  // Uno Digital Pin 12
#define Y_DIRECTION_BIT    2  // Uno Digital Pin 10
#define Z_DIRECTION_BIT    0  // Uno Digital Pin 8

#define STEPPERS_DISABLE_DDR    DDRD
#define STEPPERS_DISABLE_PORT   PORTD
#define STEPPERS_DISABLE_BIT    4  // Uno Digital Pin 4
#define STEPPERS_DISABLE_INVERT    // Logic low out for disable (e.g. steppernug)

#define LIMIT_DDR     DDRD
#define LIMIT_PIN     PIND
#define X_LIMIT_BIT   7  // Uno Digital Pin 7
#define Y_LIMIT_BIT   6  // Uno Digital Pin 6
#define Z_LIMIT_BIT   5  // Uno Digital Pin 5

#define SPINDLE_ENABLE_DDR DDRD
#define SPINDLE_ENABLE_PORT PORTD
#define SPINDLE_ENABLE_BIT 3  // Uno Digital Pin 3

#define SPINDLE_DIRECTION_DDR DDRD
#define SPINDLE_DIRECTION_PORT PORTD
#define SPINDLE_DIRECTION_BIT 1  // Uno Digital Pin 13

(Note: I assigned SPINDLE_DIRECTION to an unused pin as a quick hack.)

To reverse the polarity of the stepper enable pin, I added the STEPPERS_DISABLE_INVERT flag (above) and changed stepper.c to honor it (lines 104, 124).

timing

Measured timing performance (execution time of stepper interrupt) ChuckH 21:06, 16 December 2012 (CET)

Standard interpolator, linear movement block, 3 axes moving, ~29.5 usec
Independent-axis (homing code), 3 axes moving, ~54 usec

This suggests maximum step rate in standard mode is ~30K steps/sec; homing mode ~15K steps/sec.

Measured timing performance of I2C GPIO unitary read: 148usec. (TWI_FREQ 400kHz). This is the approximate latency from a limit or home switch actuation to its becoming visible to the grbl firmware.

Test mule

I am not building a torch table but I need a breadboard "mule" to test software functionality. I purchased four of these 34-frame steppers for $10 each.