3pi robot acting very strange

3pi robot behaving very out-of-order

My Pololu 3pi robot had been working decently fine for about one month when it started to behave very abnormally. I do not know what the cause of this might be. Yes, I have made sure that I have a program loaded onto the robot. Every time I press the "power" button on the left of the LCD, the blue LEDs at the bottom turn on, but that's it, no sound comes out of the mini-speaker, and nothing pops up on the LCD (I have the default demo program loaded). The strange thing about this is when I connect my ISP programmer to the bot and power it on, it will only activate the very top layer of the LCD screen with a few black squares, and it only runs the program when I press the power button, and the programmer is connected and powered.

If I follow the sequence to run the code properly (connect programmer, power programmer, power bot) and then disconnect the programmer while keeping the bot on, it works fantastically, as if nothing had ever happened. Then, I turn it back off (or press the reset button), and the same strange behaviors I mentioned in the first few sentences occurs again.

Can someone please, help? I would highly appreciate it.


If you have not already done so, can you change out the current batteries with fresh batteries and see if that changes anything? Please make sure that you have the LCD plugged in correctly before powering on the 3pi and leave your ISP programmer disconnected.

If changing the batteries does not help, can you post a video showing the behavior? If you are using one of our AVR Programmers, can you try reprogramming the 3pi, run the configuration utility, and post a screenshot of it here?

- Amanda

Here you go:

Did you try replacing the batteries with fresh ones? If so, what happened?

- Amanda

Nothing, nothing at all. The “Battery” function is reading 6071 millivolts as I type this message.

Do you remember the last thing you did with the 3pi when it was working? With the 3pi powered on and your ISP programmer disconnected, can you measure the voltage on the VBAT, VBOOST, and VCC pins? Then, can you connect your programmer, get the 3pi into a good state, and measure those pins again? You can measure those pins from the expansion headers located by the LCD connector or from the pins at the front of the 3pi near the line sensors.

Can you post pictures that clearly show the components on the bottom of the 3pi so I can check for any damage?

- Amanda

No, I do not recall what I did to it last, it was many months ago, but it was working, it did this when I used it again after that time.

Measuring the voltage from the points you mention and using “GND” as a voltage reference point:

VBAT: 5.65 V
I imagine “VBST” stands for “VBOOST”?: 9.33 V
VCC: Now here’s something really strange happening here. I measured VCC at one point (The point above the LCD screen, looking at it with the “A B C” buttons at the bottom) and it read 425 millivolts (0.425 V); then, I read it at the point at the very top-right (above the topmost battery pack), and it read 5 volts. Not sure if this is supposed to happen.

3pi closeups.zip

Can you add a jumper between the VCC pin at the front of the 3pi near the sensors and the VCC pin of the expansion header and see if that fixes the problem? It sounds like one of the VCC traces on your 3pi might be damaged.

- Amanda

Amazing, this worked flawlessly!. Thank you so much, Amanda!
I’ll just solder some wire under the robot connecting these two pins. Thank you!

I’m glad that fixed the problem. If you try testing all the features in the Demo program and notice something wrong, please let me know.

- Amanda

That definitely fixed the problem. Thank you.