Activate Z brake after every Z move

MattStu115

I am building a large format FDM printer and am using Clearpath servos with belts to move each axis. The Z motor does not have enough holding torque to keep the build plate elevated, nor does the inline brake. I recently added a piston to counterbalance the build plate weight, which allowed the motor to move and hold in place occasionally (had to keep adjusting piston force up or down).

The brake is connected via 24v mosfet to the servo's feedback circuit which is setup in "servo on" mode. The brake is always able to hold the build plate now, but only activates when the servo is disabled, which is not useful during operation.

Without spending more money on a high flow air system for the piston or buying a new motor or gearbox, how can I always activate the brake between every Z move operation?

Thanks!

o_lampe

@MattStu115 I'm sure there is a way to control the brake directly via Duet, but the timing would be critical. ( e.g. M571 would engage the brake during extrusion))
If you release the brake too early, the bed might drop. Release it too late and you might loose steps.

One way to deal with your problem is to use real counterweights. One weight would equal out the bed weight, another empty resevoir would fill up with water during extrusion and represents the filament weight by running a second "extruder" (peristaltic pump?)

MattStu115

@o_lampe

That is a smart solution, however I have a short demo in a few days and need something temporary to achieve a small print. Because the motor can typically hold its position for 5-10 seconds that should provide enough time to use M571. Will M571 send a signal even while travelling/not extruding during a layer?

jay_s_uk

@MattStu115 have you seen this? https://docs.duet3d.com/User_manual/Reference/Gcodes#m5697-configure-motor-brake-port

o_lampe

@MattStu115 said in Activate Z brake after every Z move:

the motor can typically hold its position for 5-10 seconds

Maybe you've set the idle current too low? It's the 'I' parameter in M906. Maybe your setup is different with an external servo driver?
But if M84 S0.1 is set in config.g the brake would engage after 0.1s when M569.7 is also preset for the z-motor port.