I'm still having some issues understanding volt/amp regulation with a motor shield. I'm still a novice to a lot of electronics components. I noticed some odd behavior that I want to understand ...
I have an Arduino Uno, a Sparkfun Motor Shield (http://www.sparkfun.com/products/9815) and two 50:1 gear motors (http://www.dfrobot.com/index.php?route=product/product&product_id=354).
When the Arduino is powered off USB while I'm programming it, the motors run at speed X. After uploading my sketch, I plug in a 9v battery to the power source, and the motors then run at speed Y, which is roughly 2*X from what I can tell.
Am I overvolting those 6V motors? Or the Arduino? Or is the shield regulating the voltage back down to 6V and the USB just isn't giving enough juice to run the motors at full tilt? I just want to make sure I've set things up correctly, or if I haven't, I want to understand where I went wrong and what the consequences are!