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How to unlock the Z-axis stepper motor?

Posted: Wed Nov 05, 2014 4:55 pm
by aeleus
I'd like a way to unlock/release the z-axis motor before and during cuts so I can fine-tune the z height. I'm using Grbl 0.9g and have set $1=255 to keep the steppers locked at all times. This setting to applies to all steppers. I cannot unlock just one motor/axis.

I know I can put a switch in to disconnect one of the z-axis motor wires (the black one in my setup), and that gets me what I want. I was wondering if there is a way to do this through the software.

Re: How to unlock the Z-axis stepper motor?

Posted: Wed Nov 05, 2014 5:18 pm
by lildave
Shut off the power to the grbl.

Re: How to unlock the Z-axis stepper motor?

Posted: Wed Nov 05, 2014 5:50 pm
by cvoinescu
You can not unlock just one motor. The ENABLE inputs of all drivers are wired together and controlled by a single pin (D8).

If you have limit switches and use work coordinate systems, it's counter-productive to move the machine manually anyway. Jog the Z axis instead (you can set the steps and speed as small as you need).

Re: How to unlock the Z-axis stepper motor?

Posted: Wed Nov 05, 2014 5:59 pm
by aeleus
lildave wrote:Shut off the power to the grbl.
That unlocks all the motors. I just want to unlock the z axis.

Re: How to unlock the Z-axis stepper motor?

Posted: Wed Nov 05, 2014 6:21 pm
by aeleus
cvoinescu wrote:You can not unlock just one motor. The ENABLE inputs of all drivers are wired together and controlled by a single pin (D8).

If you have limit switches and use work coordinate systems, it's counter-productive to move the machine manually anyway. Jog the Z axis instead (you can set the steps and speed as small as you need).
Thanks for the insight, cvoinescu. I get what you mean about manual adjustments, but when doing a tool change or finessing the z height, I find it's simpler, quicker and less tedious to turn a knob on the shaft. I'll just use a switch on the wire to the z-motor.

Re: How to unlock the Z-axis stepper motor?

Posted: Thu Nov 06, 2014 1:53 am
by Dhpenner1
tinyG!

Re: How to unlock the Z-axis stepper motor?

Posted: Thu Nov 06, 2014 12:56 pm
by cvoinescu
DO NOT put a switch on the wire to the motor! Connecting and disconnecting the load while the power will fry the driver chip! They are well protected against shorts and over-current and overheating, but not against this.

Re: How to unlock the Z-axis stepper motor?

Posted: Thu Nov 06, 2014 1:33 pm
by fl0yd
cvoinescu wrote:DO NOT put a switch on the wire to the motor! Connecting and disconnecting the load while the power will fry the driver chip! They are well protected against shorts and over-current and overheating, but not against this.
If the goal is to fine tune the Z, wouldn't putting a switch on the "stepper enable" pin work? If you add a knob to the top of the Z motor's upper shaft, it would be easy to raise and lower it without accidentally jogging the machine in an X or Y direction.

Fl0yd

Re: How to unlock the Z-axis stepper motor?

Posted: Thu Nov 06, 2014 2:34 pm
by cvoinescu
You could do that. You need to add a pull-up resistor, though (or switch it from pin D8 to VDD -- use a break-before-make switch!), because some drivers have an internal pull-down, which keeps the driver enabled when the pin is not connected. With a gShield, there will be some PCB surgery. With a buildlog.net or GAUPS shield, you can modify the PCB, or you can de-solder the ENABLE pin of the Z axis Pololu driver module and connect the switch (and pull-up resistor) there.

What you really need is a more convenient interface for jogging, such as a jog dial.

Re: How to unlock the Z-axis stepper motor?

Posted: Thu Nov 06, 2014 4:26 pm
by aeleus
cvoinescu wrote:DO NOT put a switch on the wire to the motor! Connecting and disconnecting the load while the power will fry the driver chip! They are well protected against shorts and over-current and overheating, but not against this.
Thanks for the warning. When I tested to see which wire "released" the motor lock by disconnecting, I powered down from the power supply. It worked fine, but everything was powered down as I connected and disconnected wires.

Forgive my ignorance, but is there a danger to the driver chip even when the interruption of power is between the grbl shield and the motor?