Runaway motor behavior w/ 3 independent z axis steppers

[jonpascoe]

Pressing the DWC (or PanelDue) "up 50mm" and "down 50mm" Z control buttons in succession several times results in a (repeatable) "runaway" condition. One or more of the 3 independent Z axis motors whines loudly for a few seconds, then spins rapidly up or down until I hit the power switch. This behavior has resulted in several violent head crashes. (My possibly ill-conceived reason for doing this in the first place, was to exercise or break-in the linear rails/carriages in hopes of reducing some minor Z banding.)

Aside from this behavior, the printer will successfully home all axis, complete bed leveling, and print fine.

I am new to 3d printing and would be grateful for help with this issue? What additional information would be helpful in troubleshooting?

Firmware Name: RepRapFirmware for Duet 2 WiFi/Ethernet
Firmware Electronics: Duet WiFi 1.02 or later + DueX5
Firmware Version: 2.02(RTOS) (2018-12-24b1)
WiFi Server Version: 1.23
Web Interface Version: 1.22.6

Thanks much in advance!!!

[Veti]

post your config and home scripts

[bot]

I suspect that there is binding in your mechanical system and one or more of the motors is stalling, but then being commanded to move again.

Try disconnecting the motor shafts from the mechanical system and try the same moves with the motor shafts spinning freely.

[jonpascoe]

Configs attached.0_1565371941476_Duet configs.txt

[jonpascoe]

@veti Done & thank you.

[Veti]

what z motors do you have?

[jonpascoe]

@bot I’ll add this to the things-to-try list.. Thank you.

[jonpascoe]

@veti I’m almost certain I have these 1.8 degree steppers on the 3 Z lead screws:

STEPPERONLINE Nema 17 Stepper Motor Bipolar 39mm Body 45Ncm (63.74oz.in) 1.5A 12V ...

https://www.amazon.com/dp/B07LF898KN/

[Veti]

@jonpascoe said in Runaway motor behavior w/ 3 independent z axis steppers:

I’m almost certain I have these 1.8 degree steppers on the 3 Z lead screws: 1.5A 12V

this is important. do double check this.
you should normally run the steppers at 70-80% of their rated current.

from the config i take it you are building a RailcoreII 300ZL

those steppers are not the ones from the BOM.

from https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors

Avoid motors with rated voltage (or product of rated current and phase resistance) > 4V or inductance > 4mH.

[dc42]

Your motor currents are all to low for those 1.5A motors. Try between 1000mA and 1300mA. The whining is almost certainly caused by binding (see the response from @bot) together with low Z motor torque.

[jonpascoe]

@dc42 & @bot & @Veti I hope to give all this a go tomorrow and will report back. Thanks so much to you each!