I'm new to all this and I have an Arduino Uno plus a Seeed Motor Shield v1 and I would like to use a potentiometer to control the speed. My problem is when I attach the shield to the arduino all pins are "used" for outputs to servos and I wounder where I should connect my potentiometer, I guess that I can do it on the pins for the servos, but I cant find anywhere what I should do.
Sorry to say so, but what a crappy design.
The shield actually uses 6 pins, D8-D13.
The other pins are free to use as you like.
But those guys "designed" some "standard" of their own, and people buying any of their stuff will be forced to use that standard, like it or not.
The standard is called "grove", and for some reason only the guys at seeeeeeed can think of, it is about a 4 pin plug with 2 power wires, and 2 signal wires.
So.
Now you need to get a hold of some "grove" connector(s), and connect them to the right connector on your shield.
Tip: try to fit an old fashioned PC CD audio connector, looks like that may work.
Connectors J20-J24 offer analog pins A0 to A5 (each connector shares a pin with the adjacent connector : ).
If you look real close, you can see that on this picture from the page you linked to (click to open in a new tab): .
If your running servos why the H-bridge?
If your running a DC motor or a stepper then fine.
A servo only needs a PWM pin (and the servo library) and a power supply (unless it is a micro servo do ever try using the Arduino power supply).