Design and development of control modules for robotic fish

Recent years, biomimetic approach is widely used in the development of autonomous underwater vehicles (AUVs). The robotic fish systems have wide range of applications in many areas such as marine sourcing, sea exploring, etc. Diversified and efficient swimming locomotion patterns by flapping pectoral fins and buoyancy control capability have inspired the biomimetic design of fish robot. Several hardware designs were done to improve the capability of the second version of the robot and develop a more stable and efficient robot manta ray (RoMan-III). These include the fin design, body design, tail design, waterproof design, etc. A program was written with appropriate algorithms to control 4 types of swimming patterns which include flapping, buoyancy, turning and gliding controls. Timer interrupt was used in the algorithm to control pulse width modulation to generate sinusoidal wave function for flapping motion. From the experimental results, the manta ray robot was proven to have better waterproof effect with handmade O-ring and hard joint design and was able to swim straight with extended back fin and without unsupported front fin area. Pivot turning with double-fin flapping was selected for obstacle avoidance turning mode due to its small turning radius of 0.01 m. The robot was programmed to perform turning motion in front of an obstacle at a distance of 50 cm in order to prevent its fins from hitting the obstacle. Besides that, experimental results also showed that the swimming velocity of the manta ray robot was almost in linear relationship with the flapping frequency and amplitude when the frequency was below 1 Hz. Saturation of the velocity would be reached at flapping frequency of around 1.3 Hz. In conclusion, the fastest average swimming velocity that the manta ray robot could achieve was 0.3 m/s or 0.8 BL/s with flapping amplitude and frequency of 40o and 1.5 Hz respectively.MECHANICAL ENGINEERIN