detecting motion

hi, i have made a robot with some sensors on it to detect obstacle, however it can get stuck when trying to move over wires yet it doesn't know about it. It there any cheap and simple solution to this problem? What i thought of was using mouse, however it will have to be very close to the surface.

Try bigger wheels.

okay... but what i want is that the robot will know it is not moving... like a more general solution. some book suggest current sensing.. but what i want to is to detect if the body is moving, not the wheel.

ok, very simple,

you have to add a shaft encoder to a free wheel

A shaft encoder,is a device that will give you pulses when the shaft/wheel is turning, Adding a shaft encoder to a FREE wheel (not a drive wheel connected to the motor) will give you the precious answer to the question: "is the robot mooving?"

you can see a live example of this on my projects page