Motor wire shielding for a large 3-axis motion
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We've been using a Duet 3 Mainboard to drive a large 2m x 0.8m x 0.1m 3-axis motion system. At this scale, some of the wires to the head run along tracks and are ~5m long. This includes BL-touch control wires running at only 3.3V.
We had problems getting the BL-touch to actuate when the motors were powered on. The Duet outputs only 3.3V pulses on the extend wire to control the BL-touch. Using an oscilloscope showed that the signal was getting lost in high frequency noise of 2Vpp.
Our stepper motor wiring has shielding braid so we earthed this at the Duet shielding tab to get the electrical noise in control (~0.3Vpp). The shielding tab is between the ethernet and USB ports.
We noticed that connecting the shielding to the 0V input of the Duet board only reduced the electrical noise to ~1Vpp. What's the difference between the 0V input and the shielding tab? They look to be electrically connected.
Is there anything else we can do to reduce electrical noise from the Duet? I couldn't see a section in the wiki that mentioned the shielding tab.
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@wi10008 said in Motor wire shielding for a large 3-axis motion:
We noticed that connecting the shielding to the 0V input of the Duet board only reduced the electrical noise to ~1Vpp. What's the difference between the 0V input and the shielding tab? They look to be electrically connected.
The shielding tab is not connected directly to ground. It is connected to the shield of the Eternet connector. It is provided so you if the Duet is mounted against a metal pane with a cutout for the Ethernet connector, you can can connect that shield to the panel.
Is there anything else we can do to reduce electrical noise from the Duet? I couldn't see a section in the wiki that mentioned the shielding tab.
Stepper motor cables are inherently noisy. It is usually best to shield sensitive wires such as the output from BLTouch instead. If you do need to reduce interference from stepper motor cables (e.g. to meet EMC regulations), here are some techniques:
- Use two twisted pairs, one for each motor phase
- Use a ferrite core on the stepper motor cable, at the Duet end
- Optionally use shielded cable and connect the shield to Duet ground
