🤖Biologically Inspired Robotics Unit 8 – Flying and Swimming Robots

Key Concepts and Terminology

• Fluid dynamics studies the behavior of fluids (liquids and gases) and their interactions with objects
• Reynolds number ($Re$) represents the ratio of inertial forces to viscous forces in a fluid
  • Low $Re$ indicates laminar flow while high $Re$ suggests turbulent flow
• Lift is the upward force generated by the difference in pressure on the upper and lower surfaces of a wing or fin
• Drag is the resistive force acting on an object moving through a fluid, opposing its motion
• Thrust is the force that propels an object forward, generated by propellers, jets, or flapping wings
• Biomimicry is the design approach that takes inspiration from biological systems to solve engineering challenges
• Vortex shedding is the periodic detachment of vortices from an object in a fluid flow, often seen in fish swimming or insect flight

Biological Inspiration for Flying and Swimming Robots

• Flying and swimming animals exhibit remarkable agility, efficiency, and adaptability in their respective fluid environments
• Birds, insects, and bats inspire the design of aerial robots (ornithopters, entomopters, and bat-like robots)
  • Flapping-wing mechanisms mimic the wing motions of these animals for efficient flight
• Fish and marine mammals serve as models for underwater robots (robotic fish, dolphin-inspired robots, and turtle-like robots)
  • Undulating and oscillating fin designs replicate the swimming patterns of aquatic creatures
• Studying the morphology, kinematics, and control strategies of these animals provides valuable insights for robot design
• Bioinspired robots aim to achieve the same level of performance, maneuverability, and energy efficiency as their biological counterparts

Principles of Fluid Dynamics

• Understanding fluid dynamics is crucial for designing efficient flying and swimming robots
• Lift generation in flying robots relies on the Bernoulli principle and the shape of airfoils
  • Airfoils create a pressure difference between the upper and lower surfaces, resulting in lift
• Thrust production in aerial robots can be achieved through flapping wings, propellers, or jet propulsion
• Swimming robots generate thrust by manipulating the surrounding fluid using fins, flippers, or undulating bodies
• Streamlining the body shape reduces drag and improves the hydrodynamic efficiency of swimming robots
• Vortex shedding can be exploited to enhance propulsion in both flying and swimming robots (leading-edge vortices in insect flight, reverse Kármán street in fish swimming)

Design Challenges and Solutions

• Designing lightweight and durable structures is essential for flying robots to achieve sufficient lift-to-weight ratios
  • Carbon fiber, foam, and 3D-printed materials are commonly used for their high strength-to-weight properties
• Actuator selection plays a critical role in generating the required forces and motions for flight and swimming
  • Piezoelectric, shape memory alloy, and electromagnetic actuators are popular choices for their high power density and fast response times
• Waterproofing and pressure resistance are crucial considerations for underwater robots
  • Sealing techniques, pressure housings, and corrosion-resistant materials ensure the robot's integrity in aquatic environments
• Energy efficiency is a major challenge, as flying and swimming robots have limited onboard power storage
  • Optimizing the propulsion mechanisms, minimizing drag, and employing energy harvesting techniques (solar, wave, or flow energy) can extend the robot's operational time

Control Systems and Navigation

• Robust control systems are necessary for stable and maneuverable flight and swimming
• Feedback control loops, such as PID (Proportional-Integral-Derivative) controllers, help maintain the desired trajectory and orientation
• Bioinspired control strategies, like the Central Pattern Generators (CPGs) found in animal nervous systems, can generate coordinated and adaptive locomotion patterns
• Navigation in fluid environments requires accurate localization and mapping techniques
  • Inertial Measurement Units (IMUs), GPS, and acoustic positioning systems assist in determining the robot's position and orientation
• Path planning algorithms, such as potential field methods or rapidly-exploring random trees (RRTs), enable autonomous navigation in complex environments

Sensing and Perception in Fluid Environments

• Sensors play a vital role in providing situational awareness and enabling autonomous behavior in flying and swimming robots
• Inertial sensors (accelerometers and gyroscopes) measure the robot's motion and orientation
• Pressure sensors and flow sensors detect changes in the surrounding fluid, aiding in obstacle avoidance and flow field mapping
• Vision systems, including cameras and computer vision algorithms, enable object recognition and tracking in both aerial and underwater scenarios
• Bioinspired sensing modalities, such as the lateral line system in fish or the mechanoreceptors in insect wings, can enhance the robot's perception of fluid flow and nearby objects

Real-World Applications and Case Studies

• Flying robots find applications in aerial photography, inspection, and environmental monitoring
  • Quadrotors and fixed-wing drones are widely used for these purposes
• Bioinspired flying robots, like the Robobee developed at Harvard University, showcase the potential of insect-scale flight for search and rescue or pollination tasks
• Swimming robots are employed in marine exploration, underwater infrastructure inspection, and oceanographic research
  • The Aqua robot, inspired by sea turtles, demonstrates the capabilities of bioinspired underwater locomotion
• Robotic fish, such as the G9 developed by MIT, exhibit efficient swimming and maneuvering, with potential applications in water quality monitoring and aquaculture
• Hybrid robots, like the Aqua-MAV (Micro Aerial Vehicle) that can both fly and swim, offer versatile functionality for amphibious missions

Future Trends and Research Directions

• Miniaturization of flying and swimming robots is an ongoing trend, enabling operation in confined spaces and swarm-based applications
• Soft robotics is gaining traction, utilizing compliant materials and structures to achieve more natural and adaptive locomotion in fluid environments
• Biohybrid systems, integrating living tissues or organisms with robotic components, present new possibilities for enhanced performance and self-healing capabilities
• Swarm robotics and multi-robot coordination are active areas of research, aiming to replicate the collective behavior and intelligence observed in animal groups (bird flocks, fish schools)
• Advances in artificial intelligence and machine learning will enable more autonomous and adaptive behavior in flying and swimming robots
  • Reinforcement learning and evolutionary algorithms can optimize the robot's control strategies and morphology
• Energy harvesting and power management techniques will continue to improve, extending the operational range and duration of these robots