Hello,
I am wondering how to power my project.I am using a Seeedstudio motor shield v2 to control 2 motors. I have attached a 12v battery to the motor shield and a 15v power supply connected to the Arduino. I was so far able to control 3 Hossen TowerPro SG90 Micro 9g Servo Motor (http://www.amazon.com/HOSSEN®-10pcs-TowerPro-Torgue-Heicopter/dp/B00CCZDJX6). I need to control 2 motors (6vdc 1.8 amp each.) When I attach it and control the servos and dc motors, none of them work. Is there any extra battery or shield I can attach to power the servos and dc motors (I cannot use solar power because it will be underwater.)?
Why not use 12V for everything? 15V is not a good supply voltage to use unless there is some particular reason why 15V is available on the underwater equipment.
Can you draw a schematic to show how it's hooked up? Hand-drawn is OK.
What kind of 12V battery? 15V is too much to power an Arduino via Vin - you are likely to
have the on-board regulator cut-out from overheating at random.
If I use just a 12v supply it will not even power the servos. Here is a schematic:
12v supply
|
Arduino-------------motor shield-3 servos
| |
15v power supply 2 DC motor
I am using 8 AA batteries for the 12v power supply connected to the motor shield.
It was a software issue... I forgot to set the pins of the motor as outputs... 
I did that once. Hacking a RC car and forgot to set one of the control pins as output!