Servomotor-based mobile robot control

Posted on Feb 6, 2014

Mobile robots are used in many industrial, commercial, research, and hobby applications. This project is about the control of a mobile robot using servomotors. The robot used in this project is the base of a popular mobile robot known as Boe Bot, developed by Parallax ( and The basic robot is controlled from a Basic Stamp controller (Trademark of

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Parallax Inc. ). The robot base and electronic circuit have been modified by the author so that the robot can be used with PIC microcontrollers ( Figure 1). The robot consists of two side drive wheels and a caster wheel at the back. The drive wheels are connected to servomotors. A breadboard is placed on the robot base for the electronic control circuit. The robot is driven from a 9V battery, and a 78L05-type voltage regulator is used to obtain _5V to supply power to the microcontroller circuit. In this project programs are developed to move the robot forward, backward, and to turn left and right. The circuit diagram of the project is shown in Figure 2. In this project a PIC16F84 microcontroller is used and the microcontroller is operated with a 4 MHz crystal. Operating the servomotor As described in Section 4. 7 the servomotors used in robotic applications are modified servos where the motor can rotate in either direction continuously by applying pulses to the servomotor. In a modified servomotor typically a pulse with a width of 1. 3 ms rotates the motor clockwise at full speed. A pulse with a width of 1. 7 ms rotates the motor anti-clockwise, and a pulse with a width of 1. 5 ms stops the motor. Figure 3 shows typical pulses used to drive modified servomotors. The pulse required to operate a servomotor can very easily be obtained using the PULSOUT statement of the PicBasic and PicBasic Pro compilers. When a 4 MHz crystal...

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