When the contact 15 is actuated getting into one of the cuts in the disc 16 and when power is available in the electrical circuit, for example the magnet 1 is attracted and approaches the electrical magnet 14 as in this moment the contact is interrupted as the positioning clamp comes out of the cut in 16 and the movement of the disc continues by inertia, slowing down until 15 comes completely out of the cut when the other contact of 15 is actuated and the electrical magnet 14 reverses its magnetic field forcing the magnet 1 in the direction toward the point 121 which will cause the magnet 2 to go in the position 11 which is the start position for rotation to begin. Setting the position of the vane 23 controls the speed, the clamp-switch 15 is pressed against the disc 16 by the spring 25, which is also a means to speed movement up or down varying friction.