Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: saintjon on July 17, 2013, 09:42:45 AM

Title: motor causing current to sag too much
Post by: saintjon on July 17, 2013, 09:42:45 AM

Hello,
I am building a robot with the Beaglebone Black.  My voltage regulator produces 7.5 volts on output A and 5.5 volts on output B.  When I plug my Beaglebone into Output B, it boots up and runs nicely.  However, as soon as I hook a motor to Output A and induce current to the motor, the Beaglebone goes dead.  I assume that the current is dropping too low.  Do I just need to add another 7.2v battery pack or is there a more efficient solution for keeping the motor from sapping the power to the Beaglebone? :-\  Thanks for any input.

Title: Re: motor causing current to sag too much
Post by: MrWizard on July 17, 2013, 01:04:24 PM

Just test the draw (and calculate) of the motor if it isn't listed. I personally seperate the batts for the controller and the motors. But I always get commented that is not necessary. Often google is your friend on looking up the specs of the motor.

Title: Re: motor causing current to sag too much
Post by: saintjon on July 17, 2013, 01:17:45 PM

Which would work better, an additional battery or another battery of higher voltage?  In my case, I have a 7.2v battery to power the circuit but I could buy a 12v battery to replace it if it would do better....

Title: Re: motor causing current to sag too much
Post by: waltr on July 17, 2013, 07:39:05 PM

It is possible that the problem is not in the battery but the size of the wires and how the battery is wired to the motor driver and the beagle bd.
Can you draw a diagram of how these are wired. The physical layout and connections not a schematic.

Title: Re: motor causing current to sag too much
Post by: jwatte on July 17, 2013, 11:08:45 PM

If you use your 7.2V battery, and hook up the motor directly (no BeagleBone, no regulator,) what voltage does the battery show while the motor is running?

It's possible that the motor generates interference/spikes that the regulator, or the BB, doesn't like, rather than the problem being voltage sag. On the other hand, if there's substantial voltage sag when the motor runs, then that's very likely the problem.

Separate batteries for brawns and brains is always a good idea, because that keeps the noise from the motors away from the logic. You typically still need to tie the ground signals together.

Title: Re: motor causing current to sag too much
Post by: jkerns on July 18, 2013, 07:59:32 AM

How much current does your motor draw?

How much current is your voltage regulator rated for?

Above suggestions (wire size, unregulated voltage to the motor, etc.) are all good.