Figure 1: Mechanical design of the robot (side view)

The size of a robot is limited to 7.5 x 7.5 x 7.5 cm. The robot's mechanical design (see figure 1 above). Due to the small   size,   the mechanical   design   is mainly determined by the choice of motors. They need to be powerful in order to accelerate the robot sufficiently fast while at the same time being small, energy-efficient and easy to control. Again due to size restrictions, stepper-motors are unsuitable.  That means   that   the   choice   is   limited   to   linear motors, which in turn means that a rotation sensor is needed.