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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 http://www.dizzy.ai/2017/12/08/interference. 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

Discussions

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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