So what type of battery do you advice me to use for my arduino board based on your experience ? As for the power for the motor shield, I use the Panasonic type NCR 18650-4,2V-4200mAh battery, I use 3 batteries so I guess I have enough current capacity for the robot.
Really sorry for the inconvenience but I'm new to arduino and this community, still trying to get used to it.
Sorry, I should have elaborated further. The 5V supply you mention here would be fine:-
I use an a 5V adaptor to get power from socket to my arduino, I plug it into arduino's DC power jack
Just connect it 'directly' to the Arduino's 5V connection, not to Vin or the power jack.
I guess that apart from for testing, you won't want to use the 5V adaptor for your Arduino, since then the robot is tied to the mains power and can't travel far. For batteries, anything capable of about 7V would be fine, but you won't need as much capacity as the motor supply. Anything from about 500mAh upwards would give plenty of time between charges. Perhaps just a 7.2V NiMH, with a capacity of about 1000mAh?
Looking at the datasheet for the L293D, it requires a supply voltage of 4.5 V to 36, so the batteries for your motors aren't really suited to the purpose. Also, the L293D output saturation voltage is 1.2V, so even if the chip does function properly with 4.2V applied, the motors will only 'see' about 3V.
The battery capacity is fine, but the voltage is low enough to possibly be causing your problems.
Also, are they 'really' 4.2V, or only 4.2V when fully charged, straight off the charger?
- Well, I just took the time to read the specs on the Panasonic NCR 18650 batteries that you're using. The nominal voltage is 3.6V, not 4.2V. They would be 4.2V straight off the charger, but would fairly quickly drop to 3.6V. That's too low for an L293D, according to it's datasheet.
Anyway, here's the L293D datasheet:-
And here's the Panasonic NCR18650 battery datasheet:-
You might need to do some thinking about your design before continuing. (This is really all stuff that you should have done during the design stage, before even buying any of the parts.)
In answer to your latest post, I just read a little info on your motor shield. (The stuff I have already suggested that you read.)
There is a jumper on that shield to allow the batteries to supply the Arduino, as far as I can tell. I specifically asked you about this yesterday.
Now you need to go away and do a lot of reading on all aspects of your project, then approach it again if you want it to work properly. I've spent far too long trying to research the things that you should have already done. This is programming and electronic design, two complicated subjects. You cannot approach it half-assed.
And when looking for the info on your motor shield, don't overlook the fact that it is the old version, not the latest, which is V2. Otherwise the information will be misleading.