Power motors on batteries


#1

Hi there,
I have powered a very simple bot (only two motors) using an 8 batteries pack. When I try the motor example (loop forward and backward) the bot moves forward just one time, then starts moving backwards for a brief and then the Pi & BrickPi reboots automatically for no other reason.
When I connect the USB cable and run the same sample program the robot loops moving forward and backward as it should do.
Any ideas of what is going on?
Are the batteries weak or something?
Best and thanks,
Alex.


#2

Alex, it might be a weak battery pack. Do you have access to a voltmeter you can put on the battery pack when the motors reverse direction?

It might help to put a pause in there, even if slightly.

Also, are you running anything else on the Pi, like a USB device or the HDMI monitor while this is going?


#3

One more question Alex, are you using the Advanced or Basic?


#4

I bought was the starter bundle, so i think it is the basic, right? But my battery pack is for 8 AA batteries. and yes, i’m running a wifi dongle in one of the usb ports. nothing in the hdmi port.
yes, i have a voltimeter, what shoud i test? I mean what the batteries should mesure when i test them?
what is strange is that i’ve ran this sample program 3 ou 4 times already and the first forward move was ok every time.
Best and thanks,
Alexandre.


#5

You should then have an advanced board. So that’s good news.

If you can just test the strength of the battery pack: what does it measure while it’s running the BrickPi? If you measure the two terminals on the pack, that would be awesome.

This is strange, I think it might have something to do with the battery though. Is there a way to try out fresh AA batteries?


#6

It is measuring between 6V and 6,3V.
Can I assume it is a battery problem?

thanks!
Alex.


#7

In fact it measures close to 5.8V while the motor is running.


#8

It sounds like a battery problem. If you have 8XAAs, they should be showing between 8 and 12V, when not used. They might drop down to 7V under heavy load. The reason the Pi is resetting is that when you’re dropping down to 5.8, 5V when you run a motor, and the step-down power supply has a voltage dropout of 0.25v-1V. The voltage the Pi sees is suddenly less than the 5V needed to run it, so it restarts.

Is there a way to try with fresh AA batteries?