frequent short-to-ground on Z and extruder

dc42

We've had one or two other reports of spurious short-to-ground reports on the Duet Maestro. Please try the following:

Try using spread cycle mode on the drivers concerned. [We'll have the drivers automatically switch from stealthchop2 to spread cycle at high speeds in a firmware update soon.]
Make sure that your first move on the drivers concerned is a slow homing move. This is needed to for the drivers to tune the stealthchop2 settings. If you don't do this then stealthchop2 mode will use the wrong parameters. For this reason it is probably better to configure the extruders in spread cycle mode.
Try using the firmware binary at https://www.dropbox.com/s/m0r3ldy424mxf4v/DuetMaestroFirmware.bin?dl=0. This won't solve the problem, but if the drivers are on the verge of overheating then it will warn you. Caution: this isn't an official release yet, so use it with care. You may wish to reduce motor currents to reduce the chance of damage if something goes wrong.

HTH David

gnydick

Yeah, it exactly was stealth chop as the culprit. It's a shame, I've been tearing apart, redesigning, and replacing one part after another on my Promega for months. Turns out, all that was needed was changing the driver setting and unrelatedly, replacing the crappy Z motion system. I've spent almost 750 hours and $1000 on rebuilding this thing, only for it to be a setting.

Nothing was overheating. No voltage or current problems.

Are you also saying that the first move for every driver should be a long, slow move to tune the driver?

That could explain why I got intermittent success.

The default settings on the pmega we're not particularly slow for homing.

What's your definition of slow?

dc42

Please try the 2.02RC1 firmware. It lets you configure the speed at which the drives switch over from stealthChop to spreadCycle, to avoid the issues with stealthChop at high speeds. See the new V parameter of the M569 command.

gnydick

@dc42 said in frequent short-to-ground on Z and extruder:

Will do, thanks

gnydick

tried it, didn't even tune it, just seems to work. btw, where can i find docs on the V parameter?

dc42

https://duet3d.dozuki.com/Wiki/Gcode?revisionid=HEAD#Section_M569_Set_motor_driver_direction_enable_polarity_and_step_pulse_timing

gnydick

@dc42 It's doing it again. The only thing I can think of is that I removed the fan that was blowing on the board. Temps are averaging 42C now rather than 35C before. Is that really hot enough to cause these problems?

dc42

No, that's not too hot. If you adjusted the V parameters in the M569 commands, what values did you use?

gnydick

Well, I used Excel to plot the curve that maps the value to speed crossover.

I played with it for a bit and ultimately just set it to 1.

I'm feeling lost at this point on how to choose a value.

dc42

When the stepper drivers switch between stealthChop and spreadCycle mode, there is a motor jerk. You obviously don't want this to happen in the middle of a printing move. So I think there are two sensible settings for the V parameter:

Choose a value that corresponds to very low movement speeds. So stealthChop will be used when the motor is stationary, but it will switch to spreadCycle as soon as it starts moving.
Choose a value that corresponds to movement speeds above the highest printing speed, so that the transition will not occur during printing moves, but may occur during travel moves.

You will probably want to use the same setting for the X and Y motors, but for a Cartesian or CoreXY printer you may want a different setting, because the Z steps/mm is usually higher and because the only Z movement during printing moves is normally slow movement to do bed compensation.

To see what movement speed your chosen V value corresponds to, send M569 P# where # is the driver number.

gnydick

@dc42

Thank you so much, that makes total sense.