Let's Make Robots!

transistors motors voltage

Controlling a motor with an NPN transistor

Apparently I don't yet fully understand transistors, so I'm hoping someone can explain what I'm missing. I'm using USB 5V to power my MCU (an Arduino), and I've got a 9V battery pack (6x AA) for my motors. I'm trying to switch that 9V off and on for a motor. I don't need to change directions or control speed, I just need to be able to give it either 0V or 9V.