I have a beaglebone black that I tucked inside an rc truck. I removed the radio control chip. Everywhere it had 3.9 volt logic I put in a 3.3v gpio control from the beaglebone. It works great I'm able to control everything from the beaglebone via WiFi. The clencher is I put in a 5v regulator and power to the beaglebone and now whenever I fire the motors Linux begins shutting down, it shuts down safely and while it's shutting down I can still control it until it powers off. I tossed in a diode between ground and positive going into the beaglebone incase it was getting a voltage spike, no success. Now I'm thinking maybe it's a brief voltage drop, however I'm still unable to successfully power the beaglebone and rc car from my own custom made battery. I tried li-ion and ni-mh I went ni-mh because it seemed to do better providing the amperage the rc car needed. Do I need a cap to store energy for possible microsecond lapses in power? If anyone has an idea what's going on please let me know. Also, whatever it is it's not coming over the ground because I can share ground, it's only an issue when I add in the positive for voltage regulation.

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    \$\begingroup\$ Motors draw lots of current when they are starting to move. That can cause dips in the voltage if the supply isn't up to the task. A capacitor across the 5V input of the BBB could cure it - the bigger the better. Or it might now. Try it and see. \$\endgroup\$
    – Majenko
    Feb 11, 2015 at 23:35
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    \$\begingroup\$ +1 for Majenko. Somewhere on that board, a pin is dropping low enough to trigger voltage protection. Without actually looking at a datasheet, a diode feeding into Majenko's suggested capacitor will additionally ensure that the capacitor doesn't supply power to the motor when it starts. \$\endgroup\$
    – user39962
    Feb 12, 2015 at 0:08
  • \$\begingroup\$ Thanks Majenko and Sean Boddy. So the type of cap or size of the cap doesn't matter as long as its large enough to handle the task? And Sean the 5v regulator is powered directly from the batteries so I don't think it needs an additional diode, the motors have the driver board that came with the rc car, I saw no point in changing out a perfectly good driver board I just got out the multimeter and modded it so the Beagle bone was supplying the logic. Please correct me if I'm wrong and thanks in a programmer not an engineer I just tinker. \$\endgroup\$
    – Cfoote7
    Feb 12, 2015 at 0:19

1 Answer 1


It isn't clear from your post if you're powering the motor directly from the BBB GPIO pins. But just so you know, the BBB's GPIOs can source, at most, 1mA. You're almost certainly exceeding this if you're attempting to power any kind of motor. It's right to shut down, it would quickly overheat and destroy itself.

You need a buffer between your GPIO and motor. Connect your GPIO pins to an op amp as an emitter-follower, or a transistor configured as a follower. You'll need another line from your 5V supply to either the op amp or the collector of the transistor.

Even if you are not powering it from the BBB directly, definitely add in a bypass capacitor from 5V to ground, on the order of 10uF or higher. As has been said, the capacitor will compensate for small voltage drops from surge currents. THe drops occur because most regulators are just slow to compensate for fast line changes.

  • \$\begingroup\$ I think I may have seen in improvement with the 10uF but it's hard to tell. It still shuts itself down. I guess I'll go bigger \$\endgroup\$
    – Cfoote7
    Feb 12, 2015 at 0:42
  • \$\begingroup\$ Hmm, doesn't seem to be the problem. I started with 10 uf, went up to 47uf and finally tried 470uf. I have larger yet but I think at this point it's propably safe to say it's not the problem \$\endgroup\$
    – Cfoote7
    Feb 12, 2015 at 1:26
  • \$\begingroup\$ Nope, probably not. It would help if you post a diagram as to how you're wiring this. \$\endgroup\$
    – Paul L
    Feb 12, 2015 at 5:15
  • \$\begingroup\$ Heres little drawing imgur.com/0kBFuH7 \$\endgroup\$
    – Cfoote7
    Feb 12, 2015 at 18:54
  • \$\begingroup\$ I've tried the op-amp and transistor. I still get massive voltage drop of .5 on the 5v rail and 1v on the 7.8 line. I'm beggining to think it's just a combination of a slow regulator and high voltage drop from the motor. I don't want a seperate battery for the BBB. I added a diode to the motor with the cathode facing V+ and the anode to ground. I also tried several electrolytic caps between input voltage and ground on the regulator and output voltage and ground on the regulator. I also removed the gpio pins and fired the motor manually. Still the same issue voltage drop is killing me. thanks \$\endgroup\$
    – Cfoote7
    Feb 13, 2015 at 0:03

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