Hi, I want to be able to sense for the speed of a metal marble, as it travels past the orangutan perpendicular to it. i was thinking about using ultrasound ( i have a transmitter and receiver) so when the time for the ultrasound to return is less, that must mean the marble is passing. And when it is longer again that would tell you how long it took and therefore the speed. But there are problems. Ultrasound would cover an area larger than the face of the marble, so not all of the ultrasound would be broken at once. I then considered a laser beam, but it is such a narrow field that making sure it went back to the receiver would be quite difficult (also making sure it hit the marble would be difficult)
has anyone done anything like this before, and can give me advice on a good method to go about this
thanks
alex