battery powered arduino and stepper motors

here's the pitch:

following tom igoe's arduino on a breadboard i now have an atmega168 chip (programmed through arduino) that now receives data over bluetooth via a bluesmirf (which needs 5 volts). the atmega 168 chip then sends instructions to 2 stepper motors (each one a 3.15v stepper motor, rated as 1 amp per phase at 3.15 Ohms per phase - a Sanyo Denki 103H546-0440). the stepper motor instructions go through a ULN2803 Darlington Array. so typical instruction "turn motor A 10 steps anti-clockwise" and "motor b 20 steps clockwise". All good.

But how to power this set up...

I should say that I want to use rechargable batteries with long life, and physical space for this set up is limited. I am currently using the 5 volt regulator as suggested by Tom Igoe.

questions: 1. I presume I should have two separate power supplies: 1 for the ATMEGA168 and bluetooth chip, and 1 for the stepper motor. 2. For the ATMEGA and bluetooth chip, I'm thinking of either getting 6 rechargable AAs (NiMH with 2700mAh). Is this a good idea? Is there a 'smaller' solution. 6 AAs is actually quite big for this application. 3. For the stepper motors, I'm thinking of getting 4 rechargable AAs (NiMH with 2700mAh). But again is there a smaller solution (I know the stepper motor says 3.15v but i'm advised that i should give a bit more power - there's a fair bit of torque required on this thing). 4. For the stepper motors, I've used 4 ordinary (duracell) AAs and noticed that they get pretty hot quite quickly when powering the stepper motors. This is perhaps unsurprising given that each motor is rated as 1 amp per phase and is driven by exciting 2 phases at a time, and although the motors are given the instructions 1 after the other, I presume they are both 'energised' at the same time. This means that in fact there is a fairly bit 4 amps being drawn out of that battery. Is this correct? Is there a better way of doing this?

Many thanks in advance for all help / assistance. it's greatly appreciated.



A couple of thoughts:

Rechargeable AA batteries are usually only 1.2V and NOT 1.5V as ordinary AA's. So 6 rechargeable AA's is only 7.2V. The Voltage regulator on an ordinary Arduino board needs 7V to work correctly. You will probably go under 7V very quickly, this can lead to totally unpredictable behaivour.

Powering two steppermotors from 4 rechargeable AA's is probably not going to last very long, of course depending on how often / long the motors are on.

Many rechargeable batteries overstate the mAh rating.

hmm, thanks MikMo, that's exactly what i feared.

perhaps better with a 9volt pp3 for the arduino chip and then the steppers...

any ideas?

I guess that an external power supply (wall wart) is out of the question for the motors ?

Stepper motors draw a lot of current, so i guess that any (small) battery option, will have limited running time.

You could try to check some of the LiPo batteries used for RC planes. But my knowledge in that area is very limited.

wall connection is out. trying to get wireless solution. will look at LiPo batteries.



I drive my Arduino Nano + LCD + 2 Steppers + Nunchuk with a LiIon-Pack at 12V and it runs fine

max. time is 1,5h even when the steppers not running as they consume power to hold torque