Protecting output for brakes

kuon

I am working on a printer, and I use clearpath motors with a Duet 3 Mainboard 6XD.

It is a large printer, and my z axis is heavy and it is not holding if the motors are off.

For this reason, I added a brake: https://teknic.com/products/spring-applied-power-off-brakes/NEMA-23-brake/

In the documentation, it is said that the brake has no flyback diode and can produce big voltage spike which can damage IO output.

I am wondering what is the best way wire it with the duet. I guess I need to use it with M569.7: Configure motor brake port, so it need to be on an IO port that support that.

o_lampe

@kuon
You could use a 24V relais between Duet and brake. They usually have a flyback diode.
It's surprising, that a device over 200$ comes without flyback diode, but at least they mention it...

deckingman

@kuon said in Protecting output for brakes:

..........................................
It is a large printer, and my z axis is heavy and it is not holding if the motors are off.

For this reason, I added a brake: ...............................

Autorotation with power loss is due to the steep helix angle of course lead screws. I'm guessing you have something like 4 start, 8mm lead screws (2mm pitch)? If so, a much better option, especially if you have a heavy bed, would be to use screws with (say) 2mm lead. This will both negate the need for any kind of brake, and the extra gearing effect will help reduce the motor current required to lift it.

kuon

@deckingman Yes I have 5mm lead ball screws on my Z axis, but even then it doesn't hold the Z axis weight if motor are off.

deckingman

@kuon said in Protecting output for brakes:

@deckingman Yes I have 5mm lead ball screws on my Z axis, but even then it doesn't hold the Z axis weight if motor are off.

I'm not surprised. Not only do you have a steep helix angle due to the course lead, you also have the lowest friction of any lead screw type. They are designed for high speed or prolonged movement. Is there a particular reason why you want high speed movement for you Z axis? You did say this is a printer, rather than a CNC machine, in which case apart from homing, you'll only be moving a faction of a mm at a time.

kuon

@deckingman Due to the large volume (700³), I have other plan for it, like 3d scanning, for which a decent Z speed is better.

dc42

@kuon the 6XD has built in flyback diodes on all OUT ports.

kuon

@dc42 It is actually in the doc, I don't know why I missed it. Thanks.