Self Control and Server-Supervisory Control for Multiple Mobile Robots Figure 7. Duty ratio of rotational velocity control for a motor Figure 8. Example of x-directional motion of the mobile robot with three wheels Angular Velocity Control of Wheel by Using PWM In addition to the rotational direction control, PWM (Pulse Width Modulation) control allows the robot to perform other various motions. The PWM control means the regulation of energy given to a motor by suitably varying the width of pulse. Figure 7 illustrates the duty ratio for a motor velocity control, which is the ratio of ON = - 0 . 021 - 0 . 021 0 . 042 T 1 2 3 under the assumption that undesirable slips do not occur. Omni-directional motion can be further T