7. The robot

Since the robot is a moving plateform, transporting different devices and tools together with one ore more brains from one place to another in order to execute several jobs, we have to consider its velocity and motion direction.

Suppose the robot is moving through our room at a speed, let's say 1m/sec.

The transmission protocole above needs at least 50ms for one beacon. But there will be actually three of them. We have also to add some time for calculations. So, we'll get one precise positioning every 0.5 - 1 second. During this time, the robot will travel 50 -100cm. In order not to make this a blind section, the robot must therefore be equipped with odometry-stuff.

As already picked out, through the beacons-positioning, the robot may deduce its direction and velocity. But there will always be lack of information. If the robot should create an internal map of its environment by noting, at which position it hit something, for example, the robot needs to know its actual position. Without the information of the direction and momentanous speed, this will be impossible.

Again the RCX's input limit causes a problem. But there is a way to overcome this difficulty. By the means of an intelligent gearing, the robot may control its speed and its direction with only one rotation sensor and thus observe the two independent motors of a differential drive.

Here this master-piece! It is based on the idea of a pivoting device which forces an output shaft always to turn in the same direction, whatever sense the motors may turn. Have a look at the marvelous page of Mathematical realizations.

Here our design: (Note that on the final robot, it has been slightly adapted to the medium-motion platform.)

Through the motor control, the robot has the information of the motor turning direction. So it must only interprete the rotation sensor readings correctly. Add this sub to your differential drive. You have one RCX input left, which can be used for bumpers.