Session: 04-13 SS: Active Hybrid Composites

Paper Number: 167951

167951 - Swimming Characterization of a Bioinspired Robotic Fish With Hybrid Piezoelectric-Servomotor Actuation 

We present the design, fabrication, and characterization of a bioinspired robotic fish featuring a hybrid piezoelectric-servomotor actuation system to enhance underwater locomotion. Macro-fiber composite (MFC) smart materials, which are fiber-based flexible piezoelectric structures, offer a balance between deformation and actuation force that can be leveraged to generate efficient and silent hydrodynamic propulsion. Additionally, MFCs operate across a broad range of frequencies (up to kHz) and are highly scalable. This enables a low-form-factor actuator design that functions at high frequencies, potentially allowing for future energy harvesting mechanisms. Previous work has been done with an untethered proof of concept (not streamlined) and a second generation streamlined troutlike design. In these designs a pair of MFC laminates (bimorph) were driven out of phase of each other to expand and contract on either side of the substrate to stimulate bending and were utilized as a caudal fin where it acted like an artificial muscle. Our new design builds upon this previous work and now includes a servomotor in the head region which provides additional in-phase or out-of-phase motion relative to the tail. The additional degree of freedom enabled by the coupling of the servomotor with the MFC bimorph allows for more complex movements and potential enhancement of thrust and turning capabilities by combining head and tail motion, both of which have AC and DC components that can be modified to optimize different swimming behaviors.

As part of the design and fabrication process, different tail substrates were characterized to determine which of them has the lowest damping and appropriate resonant frequencies to optimize motion in water. This was done by exciting a small piece of each substrate with a shaker and applying Fast Fourier Transform (FFT) on the velocity response data, obtained via a point doppler vibrometer, to obtain their respective frequency responses. Out of the available substrates, acrylic and polyvinyl chloride material were determined to be the most suitable, with the latter being used in the final design of the fish. The tail was then fabricated by vacuum bonding a pair of MFCs to the substrate to form a bimorph and silicone was used to shape tail profile. The completed tail was characterized using the same process above, leveraging the MFCs as the excitation mechanism to better simulate the actual response of the robotic fish when swimming. A shorter tail and longer tail were tested with the shorter tail having a resonant frequency of 6.5 Hz and the longer tail of 0.8 Hz at maximum testing voltage.  The full robotic fish was fabricated largely using SLA prints and assembled along with the electronics used to actuate the MFC bimorph and servomotor. An Arduino microcontroller, a high voltage amplifier, and voltage regulators were integrated into the system to allow wireless control of the actuators. Bluetooth Low Energy (BLE) was used as the main communication protocol to send actuation commands to the fish as well as to monitor power and data.

The assembled fish was then placed in a large water tank where the swimming behaviors of the fish were characterized. Some of the tests that were performed include straight swimming, left and right turning, in-phase and out-of-phase head and tail actuation, and various experiments that involve varying the AC and DC components of the actuation signal for both the head and tail. A GoPro camera was used to record the swimming behavior of the fish in each case. The characterization process is still ongoing.

Design, fabrication, hardware/software architecture, resonant dynamics in quiescent fluid, as well as free (unconstrained) locomotion characterizations will be covered in further detail in this paper.

Presenting Author: Sonali Pradhan Georgia Institute of Technology

Presenting Author Biography: Sonali Pradhan