Hard Limit Triggered, Motors loose holding torque and drop Z axis. Way to avoid?

[KevinBaileyCrum]

In grbl when I have hard limits enabled and it a limit switch the machine enters alarm state. In the time it takes to send \x18 and then send $X the holding torque is dropped from the motors.
As a result my z-axis is dropped!

Is there a setting in grbl that I can tinker to maintain holding torque during alarm and reset? I tried looking over config.h, limits.c, and motion_control.c but am having trouble finding what I am looking for

-note: I understand this is less of an issue and more of a question but I cannot find the existence of a grbl question forum so I am posting here. If this is incorrect, my apologies.

[terjeio]

$1=255?

[KevinBaileyCrum]

$1 is at 255

[doppelhub]

@terjeio: Setting $1=255 isn't going to keep the steppers enabled during an alarm condition. @KevinBaileyCrum: Yes, you can change this behavior in firmware*. If you're not familiar with grbl, A simpler method might be to disconnect the stepper enable pin (pin8 on the 328p Uno)... that'll just always leave the steppers enabled.

*Search grbl source for "st_wake_up()" for the implementation.

[KevinBaileyCrum]

@doppelhub I'll take a look at st_wake_up() I am unsure when reading the source code because i certainly want to stop the steppers from moving but I dont want to disable their holding torque. I was thinking it would involve changing mc_reset() or st_go_idle but again namely want to stop the motors for moving.

in regards to disconnecting the pin from the arduino, would limit switches still work / send signals to halt motors in grbl but just not kill the signal on the duino?

[KevinBaileyCrum]

ended up changing the st_go_idle() method. it works for my implementation whereby the limit switch is hit and the motors do not drop their holding torque and therefore keeping my z axis suspended in the air. Hope this isnt too dangerous of a change and helps some else out.

// Stepper shutdown
void st_go_idle()
{
  // Disable Stepper Driver Interrupt. Allow Stepper Port Reset Interrupt to finish, if active.
  TIMSK1 &= ~(1<<OCIE1A); // Disable Timer1 interrupt
  TCCR1B = (TCCR1B & ~((1<<CS12) | (1<<CS11))) | (1<<CS10); // Reset clock to no prescaling.
  busy = false;

  // Set stepper driver idle state, disabled or enabled, depending on settings and circumstances.
  /* bool pin_state = false; // Keep enabled. */
  /* if (((settings.stepper_idle_lock_time != 0xff) || sys_rt_exec_alarm || sys.state == STATE_SLEEP) && sys.state != STATE_HOMING) { */
    // Force stepper dwell to lock axes for a defined amount of time to ensure the axes come to a complete
    // stop and not drift from residual inertial forces at the end of the last movement.
    /* delay_ms(settings.stepper_idle_lock_time); */
    /* pin_state = true; // Override. Disable steppers. */
  /* } */
  /* if (bit_istrue(settings.flags,BITFLAG_INVERT_ST_ENABLE)) { pin_state = !pin_state; } // Apply pin invert. */
  /* if (pin_state) { STEPPERS_DISABLE_PORT |= (1<<STEPPERS_DISABLE_BIT); } */
  /* else { STEPPERS_DISABLE_PORT &= ~(1<<STEPPERS_DISABLE_BIT); } */
}