Multimodal biomimetic underwater robots (BURs) can conduct underwater tasks suitable for the environment. Combining the characteristics of aquatic organisms enables the swimming and leggedlocomotion required for underwater exploration. Locomotion control mechanism relies on rule-based behavior selection and the designer's discretion. This limits the robot's ability to acquire new behavioral capabilities to the predetermined range of behaviors. To address these challenges, we propose a mechanism and control system that enables the expression of multimodal locomotion capabilities from the same multi-jointed structure. A mechanism equipped with four leg-fins each having four axes is used. This controller achieves nonlinear behavior based on sensor modalities, rather than relying on predefined conditional rule-based on locomotion functions. This system was validated through both physical and simulation testing based on multiple sensor data and behavioral patterns. Utilizing a potential function in multimodal locomotion control was verified to enable transitions between two or three behaviors. Implementing the control method as a multimodal controller is expected to enhance its application in underwater exploration. Our project page is at https://tasada038.github.io/multi-jointed-bur/.
Figures & tables
Figure 1: Prototype of the manta ray robot. (a) overview of the manta ray robot, (b) CPG topological network, (c) mechanical of the leg-fins, (d) DH-parameter of the robot, (e) BVBS mechanical diagram.
Items
Characteristics
Size (L × W × H)
0.38 m × 0.85 m × 0.14 m
Total Mass
8.4 kg
Fin arrangement
fins(yaw, roll, pitch, and roll) × 4
Control mode
Wired control
Controller
Jetson Nano B01, Teensy 4.1
Power Supply
5000 mAh, 7.4V, LiPo battery × 2
Table 1: Technical specifications of the manta ray robot.
Link
θi (deg)
di (mm)
ai (mm)
αi (rad)
0
θinit
0
a0
0
1
θ1+θoffset
0
0
- 2π
2
θ2+2π
0
0
2π
3
θ3
d3
0
- 2π
4
θ4
0
0
2π
E
2π
dE
0
0
Table 2: D-H Parameters of the manta ray robot in NED frame.
Figure 2: Coordinate system of the manta ray robot in the NED frame.
Figure 3: Computational domain and CFD simulation result, (a) computational domain and boundary conditions, (b) analysis results of pitching angle 0°, (c) analysis results of pitching angle 30°, (d) forces and moments result obtained by the CFD simulation.
Figure 4: Software Architecture for the Entire System
Figure 5: Experimental pool in real and simulation environments.
Figure 6: Comparison of experimental and simulated motions in locomotion (a) swimming, (b) trot gait, (c) walk gait.
Figure 7: Comparision of locomotion velcity in experiments and simulations.
Figure 8: Crab walk ability of the optional and time variation of the position.
Figure 9: Comparison of joint angle data for the left front leg-fin, (a) swimming, (b) trot gait, (c) walk gait, (d) crab gait.
Figure 10: Multifunctional locomotion of two motion generation. (a) snapshot of the motion, (b) output signals of each joint, euler, and depth data.
Figure 11: Multifunctional locomotion of multimodal sensory feedback. (a) snapshot of the locomotion, (b) output signals of each joint.
Figure 12: Clustering Detection Results for Walls and Floors in water.
Biomimetic autonomous underwater vehicle (BAUV) with multi-link mechanism is widely used in aquatic life observation and environmental surveys due to its low power consumption and high maneuverability. An environmental survey requires a path following system that automatically follows specific points. However, the path following system of BAUV is limited, and its evaluation with multi-link mechanism robots has not yet been clarified. The path following system in BAUV requires prior simulation because the model differs depending on the type of biomimetics. In this study, we propose a path following system for BAUVs with a multi-link mechanism and evaluation in underwater simulation. In this result, it was possible to design a path following system suitable for BAUV, determine parameters using a simulator, and evaluate control methods.
Takumi Asada, Takao Oki, Hideo Furuhashi +3
Utsunomiya University, 7-1-2 Yoto, Utsunomiya, Tochigi, 321-8585, Japan · Aichi Institute of Technology, 1247 Yachigusa, Yakusa, Toyota, Aichi, Japan
Underwater robots rely on complementary sensors whose reliability changes abruptly with water visibility and vehicle motion. We introduce AquaJEPA, a sensor-configurable family of action-conditioned joint-embedding predictive models spanning full multimodal, camera-only, sonar-only, and sensor-dropout configurations. Its members share a latent objective and receding-horizon control interface that predict future representations and physical dynamics from camera, forward-looking sonar, proprioception, and thruster commands. Trained from scratch on one hour of action-labelled data, the family is evaluated in Stonefish on 120 fresh paired scenarios spanning unseen layouts, visibility changes, dynamics shifts, and scheduled DVL loss. AquaJEPA-base achieves the strongest aggregate closed-loop performance, improving success over state-only by 12.5 percentage points and reducing final error by 0.189 m; both paired 95% intervals exclude zero. In a separate three-seed evaluation, it reduces paired final error relative to AquaJEPA-S by 0.118 m, with the same direction for every seed. AquaJEPA-robust more than halves prediction error during camera and camera-DVL blackouts. These results show that full multimodal prediction improves over state-only control and the sonar-only family member in this benchmark, while sensor-dropout training provides robustness under sensor loss.
Underwater robotics has advanced significantly over recent decades. however, the development of miniaturized underwater robots remains limited by low energy densities of traditional power sources. Nature offers compelling solutions-organisms like mantis shrimps and fleas utilize latch-mediated spring actuation (LaMSA) systems that achieve rapid movements through a decoupled energy storage and release mechanism. Despite extensive studies of LaMSA, replicating such rapid, asymmetric actuation within simple, compact structures remains challenging. In this work, we introduce a bioinspired, soft bistable actuator with an integrated latch mechanism that enables asymmetric energy input and release using a single motor. Coupled with fin structures, this design facilitates efficient underwater propulsion and maneuverability. Experimental results demonstrate stable periodic flapping, precise steering, and a maximum thrust of 0.528 N, impulse of 0.147 Ns, and vertical displacement of 30 mm. By modulating fin angles, the robot achieves versatile motions, including vertical ascent, diagonal forward movement, and lateral translation. This study presents a novel, energy-efficient approach for controlling motion in compact underwater robots, paving the way for advanced biomimetic designs with potential applications in exploration, environmental monitoring, and inspection.
Chongze Bi, Wenjie Wu, Zonghao Zuo +1
School of Mechanical Engineering and Automation, Beihang University