# 12 volts for 12v 20 mm Metal Gearmotor

Hi,

My first project will be …

small 2 wheeled, differential drive, robot car
a third wheel (ball caster) for balance

It will just roam around the house for 15 to 30 minutes and then park for a recharge.

Controlled by a Raspberry Pi and a RoboClaw

3" diameter wheels

My approach to pick an RPM was to walk 15 feet at a speed that I thought was OK for the car.

That took 7 seconds and about 19 revolutions of the wheel.

That equates to about 163 RPM.

My thought is to pick something like this: 140 rpm 12v 20 mm diameter metal gear motor:
https://www.pololu.com/product/3490

Question #1: Because it is a 12v motor, is it appropriate to connect 2 of these 6.0 V NiMH Battery Pack in series:
https://www.pololu.com/category/106/6.0-v-nimh-battery-packs

Question #2: The motor mentioned above has a 12v stall current of 1.6 amps. With two motors, does that mean I ideally need 3.2amps to run for an hour which would mean, besides connecting two of the above batteries in series, I would have to double that and create a second pack to connect in parallel?

Thanks,
Bill

Hi, Bill.

To answer your first question, you are correct in that you can connect the two 6V batteries in series to achieve a 12V supply, but probably you should just get a 12 V battery, or you can get the 6V version of this motor.

If you actually needed to power a system that constantly draws 3.2 Amp for one hour, then you would need a power supply rated for 3.2 Amp-hours; however, I think that would be overkill for your setup. Generally, you should only load your motors with about 25% of their stall torque rating, so your average current draw should only be about 25% of the stall current (though you could use our datasheet to make a more accurate approximation). You could parallel two batteries to increase your system’s capacitance, but perhaps one of the large batteries you linked to will be sufficient on its own.

-Ryan

Hi Ryan,

re Question #1: connecting 2 6v batteries to get 12 volts.
I will go with your suggestion and get 6v motors for this first experiment.

re Question #2: picking the correct battery.
I will pick the motors and charge ahead and get one of the 6.0 V NiMH Battery Packs.

Then test the robot car.

Hook up a multimeter and have the car do it’s thing for some period of time

and measure the amperage.

Use that to tell me if I need a higher milli Amp hour battery.

Thanks for the info,
Bill