I'd like to try to make a "z axis brake control" plugin

[patrickmcquay]

I'm in a bit of an odd situation, as I've said before I have a large heavy spindle, and its mounted to a big chunk of steel, so all in all the moving parts of my z axis are probably over 100 pounds.

This causes my spindle to sag on power off, even though I have a 5mm pitch ballscrew and a beefy stepper on it. It is a moving gantry machine so a counterbalance is not a super simple thing to engineer, and I considered some sort of constant pressure air cylinder, but space requirements exclude that, sadly.

I'd like to have a brake, and I've got one, but I want it to wait a bit to disengage when the machine is powered on, and also want to have it re-engage before the machine powers off, ideally. I'm not entirely sure I can make this work, seeing as I use the estop to power off the machine. That said my estop only stops the motors, not the controller. The controller is wired to know about the estop though.

Anyway, I figured I'd ask if it were feasible to do something like this, and also maybe for some tips on where to start. I see there is example plugin code that does something similar, but I'm not familiar enough with the system to know where else to look.

The easy way to do this of course is manually, which is what I'll fall back to. I'll just make a couple of macros that engage and disengage it. I'd just rather have it be automatic.

Sort of a middle ground is a relay that triggers on motors enabled, which might be the way to go, if there is a way to do that?

[terjeio]

If you disconnect and short the motor coils (on motor disable) will that be enough to hold the Z axis in position?

[patrickmcquay]

Probably yes, and ill admit not having to wire a brake in is attractive, but doesnt that come with the same requirement of needing an output to toggle and also potentially causing damage to the motor driver?

[patrickmcquay]

Ive done some looking around, and everywhere i can see is like "dont disconnect a motor from a driver while it has power". Technically it wouldnt, but Id be worried because there might be some residual energy left in the circuit.

That approach also eliminates the possibility of braking the motor while the drive is energised, to maintain position as precisely as possible, as well as the possibility of waiting until a certain time after the drive is enabled to release the brake, again to ensure no sagging.

Is there a way to turn on a relay when the motors are enabled/off when disabled within grblhal already?

[terjeio]

Ive done some looking around, and everywhere i can see is like "dont disconnect a motor from a driver while it has power".

Switch in resistors as load for the driver before disconnecting the motor?

Is there a way to turn on a relay when the motors are enabled/off when disabled within grblhal already?

Hook into the motor enable signal? Or driver power?
You may also add plugin code for relay control. Here is one that modifies stepper enable behaviour. You could add one that monitors driver power and brakes when lost?