m3pi battery problem

Hi Guys

Recently both a 3pi robot and then a couple of m3pi robots. Love them.

I am experiencing a problem with the m3pi robots. Regardless of whether I use 4 AAA re-chargable or normal batteries it appears that the batteries are being drained very quickly even through the robot is switched off every time after use.

Example: I replace batteries with 4 new ones yesterday and played with for 10 minutes. Turned it off and came back to it just now (almost 24 hours later). The robot powers up connects to my Wii remote and then switches off (as if battery dead).

Thanks for your help with this one. I searched the forum but could not find a specific answer to my problem.




Thought it may have been the bluetooth dongle heating up and then turning off. But this is not the case.

I took a new unused robot. Added a line follower program to a new mbed. Added new batteries to m3pi and set it running. It turns on then off again.

What is the threshold value in mV that the 4 batteries supply where the m3pi will stop working?

Anyone help greatly appreciated.


It sounds like you have some kind of wireless module connected to your m3pi. What is it and how is it connected? Did you have it connected in your second test? Are you using the 3pi’s pushbutton to turn it off? Just to make sure, no LEDs are on when it is off, right? Do you have anything else connected to your 3pi besides the m3pi shield?

- Ryan

Hi Ryan

Many thanks for your response.

I am using 2 robots to test this:

Robot 1:
Has a bluetooth dongle on it and a X-Bee. Bluetooth is used to connect toa a Wii remote and X-Bee has yet to be coded. It is just sitting in the X-Bee header (would this be a cause of m3pi to loose power?)

I switch off and on using the push button always. Current battery reading for this is around 5100mV. What I will do now is remove the X-Bee and see does the m3pi loose power.

Robot 2:
This has nothing on it only an mbed. On the mbed is the code to make it follow a line. Battery reading is currently around 3000mV. It’s powering up but immediately dying. I suspect there is not enough power in the batteries left to run the m3pi. Is this the case? If so, when I put in 4 new batteries, I am wondering how long I will get out of them. Does the m3pi really use a lot of battery power and if so at waht mV battery reading should I replace the batteries.



3V is pretty low. The 3pi specifications say the minimum operating voltage is 3V, but if your battery is at 3V, it is likely already in the region where the battery is quite drained and the voltage will drop quickly with any current draw. Googling for battery discharge curves shows graphs of what I am saying. If the voltage falls below around 4.8V, I would recommend recharging your batteries.

Are you measuring the battery voltage after you turn off the m3pi and before you turn it on again later?

- Ryan