Motor noise unintentionally driving servo - Make an Arduino-Controlled Robot

Myself and others in other forums on the web have encountered problems with our robots due to excessive noise caused by the DC motors included in the kit. My kit did come with four 0.1uF ceramic capacitors, which I soldered each between the positive & negative terminals of each motor. This one-capacitor filtering doesn't seem to cut it, as my servo turns to the right whenever the motors are running and the Arduino is behaving strangely, at times not having repeatable results when executing sketches like the HelloRobot sketch. Timeouts seem to not be followed repeatably, and sometimes the spinning just doesn't stop, like the program crashed and the power was left on the motors.

Here's some links to other's expressing motor noise problems with this DFRobot 4WD chassis kit:
http://forums.adafruit.com/viewtopic....
http://letsmakerobots.com/node/25765#...

It seems that everyone is suggesting that it would be wise to try three-capacitor filtering and add a second power supply for the motors only. At the bottom of Adafruit's Motor Shield FAQ (http://forums.adafruit.com/viewtopic....) they suggest the following:

"My program acts strange! My Arduino keeps resetting!

You are most likely seeing either power 'brownouts" or electrical noise from your DC motors. These can disrupt or even reset the Arduino processor.
*Consider a separate power supply if you are not using one already
*Add noise suppression capacitors to your motor as in the photo below. Use 0.1uF capacitors. One between the two power lugs and one from each power lug to the motor case. Soldering to the motor case can be difficult. It is best to scratch a spot on the surface first with a file or sandpaper."



I'd like to know if the author had some opinions about steps to resolve these issues, and also I'd like to encourage that there be modifications to the book's instructions and kit parts to account for those changes. Could we get a solution where the trickle charger and power switch could handle two power sources?
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  • Brian Jepson (Editor, Maker Media, Inc.) February 09, 2013 00:57
    I asked the author, and he did think that a 3-cap solution would address the EMI issues. He asked if you would feel comfortable "soldering caps to the metal shield on the motors. It requires a good soldering iron and a steady but quick hand to avoid melting the plastic motor. The caps go from each terminal to the metal shield. Short lead lengths are best."

    One of our engineers, Eric, is testing this out, and is waiting for an answer from the author as to whether his solution is OK before posting a response.

    Cheers,

    Brian
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  • I feel comfortable giving it a shot. I really see the motor terminals as the area of weakness in these motors, as they're very fragile and can move easily with too much exposure to heat. I learned that the hard way when trying to desolder my motors and prep for the 3-cap solution. I ended up having to order four new motors.



    Here you can see how the terminals are held by a small plastic part:


    Looking forward to see Eric's results. Thanks Brian!
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    Hi John,

    Attached is a photo of some caps soldered to a motor. One of the plastic pieces is held on with two bent metal tabs. You should be able to bend them out easily, and solder to them instead of the whole metal shield. They're fairly small and will heat up quickly, so you shouldn't have to keep the iron around for long.

    Good luck!

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