The Arduino motor shield uses a darlington driver, so giving it 7.4V input will lead
to about 5.5V out to the motor at full current due to the large voltage losses of darlington,
so its a pretty good match for a 6V motor.
The Arduino motor shield uses a darlington driver, so giving it 7.4V input will lead
to about 5.5V out to the motor at full current due to the large voltage losses of darlington,
so its a pretty good match for a 6V motor.