This is an advanced robotics project, the robot arms follows a moving object, anyway that’s the idea. The arms moves a little sloppy, it surely isn’t in the final stage of development, but the author explains what problems encountered. The motion is detected using IR leds and receivers, and subtracting the ambient light from the readings to get the reflected light from the object which is tracked.
If you are interested in motion tracking this is a good place to start, my opinion is that the analog part needs to be reviewed, the IR leds should be mounted inside a tube, otherwise interferes with the reflected light and reduces the sensibility.
Object tracking robot: [Link]