Interference on ground and 3.3V

A project log for BLDC motor driver for robotics

Drive BLDC as direct-drive servo motor

MishaMisha 12/09/2017 at 03:353 Comments

I'm trying to build a humanoid robot based on BLDC motors instead of steppers or servos and I'm designing my custom controller board. I'm facing this beginner problem: powerful motor de-stabilizes power supply for the controller. I will write up the project in details later, when I achieve some degree of success which can be shared, but right now I'm asking for help. Details about my design and the trouble I'm experiencing can be found here Any input on how to mitigate the problem will be highly appreciated!

Link provided explains problem in details. Here I will just give brief overview.

This is what I see between two ground points:

This is what I see instead of 3.3V


Daren Schwenke wrote 03/21/2019 at 02:56 point

You need decoupling capacitors.  Add a large value (100-1000uf) electrolytic on your power rail close to the mosfets, and then another pair of them, a 10uf and a 0.1uf, right next to the IC.  That should get you most of the way there.

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Misha wrote 03/21/2019 at 03:07 point

Daren, you are exactly right! I solved it (long ago) by adding decoupling capacitor close to mosfets. This taught me how much inductance there is in 20cm wire!

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Daren Schwenke wrote 03/21/2019 at 10:41 point

Ooops.  Looks like I'm about a year late to the party.  That is so me, you have no idea.  :) 

Glad it worked out for you and you figured it out.

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