Power Problems on 4WD Robot - Please Help!


A newbie question so sorry if I'm being a bit slow. I have a 4WD robotbase with an Arudino, Wireless SDCard and XBee Pro as seen here.

Probably quite an ambitious project for me but it's been progressing really well until my standard 1.5v AA energiser batteries ran out of spark. I have replaced them with some 1.2v rechargeables and bought a charger but they just don't give the power the robot needs. If I power the control circuitry via the USB all is well - I can switch on the battery pack and the motors will run perfectly. But if I disconnect the USB cable and try to run on the battery pack alone the power dies as soon as the relays switch into drive the motors and everything stops working.

The battery pack splits at source to provide power to the Arduino and to the Dual HBridge Motor Driver and I have followed the instructions provided so there is a charging circuit.

Is this problem caused by the drop from 1.5v to 1.2v? Could I use a 9.6v RC model pack to power everything or am I going to need two seperate battery provisions?

Really looking forward to your best advice so huge thanks in advance


I don't know which component it is but it seems that one is a bit picky about voltages. If you power with alkaline batteries, you insert about 9V. If you use rechargeables this input voltage drops to 7.2V or even below that. That can make a huge difference. For example using a standard UNO, the voltage regulator has a minimal voltage drop of at least 1.5V plus a reverse connection protection diode that drops another 0.7V, so in best case you loose 2.2V. That's why the suggestions always tell you to use at least 7.5V on the power connector. If you provide less than that the system is possibly running at less than 5V (which is usually fine for the processor) and one component doesn't like that.

Thanks Pylon,

Just the words of wisdom and confidence I needed - thank you.

On the basis of your reply, I upgraded to a 8 x AA battery holder and stuffed 2 more 1.2v rechargeables on board and was quickly back in business.

All the best