We have very odd problem with a DC brushed geared motor that we are driving with a classical H-bridge chopper (20kHz PWM at the moment). The motor kinda looks like a Mabuchi from an R/C car but with an epicycloidal gearbox in front of it.

We had another motor from another manufacturer that was working perfectly but with this one the CANbus keeps dropping frames as soon as it is even connected with the speed controller. Not even moving! Just connected with no current whatsoever.

We've tried various controllers and also various motors (same model) and the problem doesn't change.

We've also recently seen some problems with low voltage signals picking up noise when it's connected.

The only fix is to use a separate CANbus AND power supply. In all other cases, problems keep on piling up.

We've put different toroidal chokes and went up to dozens of turns into big ones but while that helped, definitely not enough...

Any idea or lead that we could follow?

Thank you all by advance,

  • \$\begingroup\$ How you run your power & ground lead to the motor can be critical. Make sure any current flowing through the motor does not also flow along the same copper as the digital stuff as much as possible. Generally speaking, if the motor and CPU connect at the main power supply and nowhere else that's best. However, you might try putting a capacitor, say 1-10uF non-polarized, directly across the motor terminal (in addition to your chokes). In production, we also often place a ceramic cap (0.1uF-ish) from each terminal to the motors metal case. Yes - three capacitors are needed occasionally. \$\endgroup\$
    – Kyle B
    Nov 11, 2020 at 22:26
  • \$\begingroup\$ article.murata.com/sites/default/files/static/en-global/images/… Your choke should be wound as "common mode"... meaning both these chokes are on the same toroid core. \$\endgroup\$
    – Kyle B
    Nov 11, 2020 at 22:30
  • \$\begingroup\$ To add to Kyle B's comments, you may also want to twist the motor wires together, this will keep noise from radiating from them. \$\endgroup\$
    – Aaron
    Nov 11, 2020 at 22:37
  • \$\begingroup\$ Any chance there's a shunt capacitor between the motor terminals on one motor but not the other? \$\endgroup\$
    – spuck
    Nov 11, 2020 at 22:53
  • \$\begingroup\$ Does it have the 3 capacitors on its terminals? Did the original one? (0.1 uF ceramic, in a triangle : one across the terminals, the others from each terminal to a GND point on the case.) \$\endgroup\$ Nov 11, 2020 at 23:03


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.