I have an input voltage of 8.5 volts (6 AA Batteries) plugged into an Arduino Uno R3 and then on that I have a Arduino Motor Shield. Then I connected a DC motor to the A+ and A- screw terminals. Then I write 255 to the right pins and the motor spins . . . slower than when I connect it directly to the battery. It's a motor rated for 9 volts but the input voltage is only 5.8 even at the screw terminals. If I increase the voltage to 12 volts (using a power plug), then I get an output of about 9 volts.
Is this because of the amp draw on the batteries? Is it documented that the motor shield has that kind of voltage loss?
I CAN just connect the 9 volts directly to the shield and power the Uno separately (but then I have to cut the vin pin on the Arduino . . . which I hope my bluetooth shield doesn't use). That's probably what I'll try while I'm waiting for an answer! Thanks.