Design of a Shape-Memory Alloy-Based Vertical Swimming System for a Modular, Robotic Fish
Open Access
- Author:
- Wertz, Andrew
- Area of Honors:
- Engineering Science
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Bo Cheng, Thesis Supervisor
Reginald F Hamilton, Thesis Honors Advisor - Keywords:
- Soft Robotics
Biomimicry
Robotics
Shape-Memory Alloy
Prototyping
Buckling Beam - Abstract:
- The ability to maneuver in 3D has become increasingly more important for robotic fish as they approach practical applications such as non-destructively surveying aquatic life, exploring oceans and shipwrecks, and inspecting underwater infrastructure such as offshore wind turbines, oil rigs, and cargo ships. This thesis sought to design and control a vertical swimming system for the BioRob-InFL Lab’s modular, undulatory robotic fish, µBot, that would enable the robot to swim in 3D. Through a review of previous vertical swimming systems on robotic fish, a concept of soft, flexible pectoral fins actuated by shape-memory alloy wires was created to enable vertical swimming in µBot while complimenting its modularity and small size. Initially, a proof of concept was done using rigid pectoral fins to test whether µBot could achieve 3D motion and control its trajectory with its caudal fin frequency. Next, a shape-memory alloy actuator named BISMAC inspired the creation of a BISMAC pectoral fin which was found to produce large bending angles in the air but performed poorly underwater due to insulation issues. To resolve this issue, two models of the SMA actuators were made to identify the parameters that would increase the bending angles. One involved a geometric model while the other treated the actuator as a 1st-order buckling beam with an eccentric load. With the parameters identified in the models kept in mind, the tendon-based pectoral fins were designed and tested underwater in six different configurations of length and stiffness. The change in bending angle was compared for the six configurations which experimentally measured the effect of stiffness and length. Overall, this design displayed repeatability with high bending angles which provides evidence that it could serve as a vertical swimming system for µBot. Therefore, this thesis provides evidence that pectoral fins can enable small, modular robotic fish to dive, the vertical speed and pitch of a dive can be controlled by swimming at caudal fin resonant frequencies, and that shape-memory alloy-actuated pectoral fins can reliably generate high bending angles.