[Paper Review] Design, Modeling and Control of A Novel Amphibious Robot with Dual-swing-legs Propulsion Mechanism

Yang Yi, Zhou Geng+3 more|arXiv (Cornell University)|Sep 21, 2015

Robotic Locomotion and Control20 references8 citations

TL;DR

This paper presents FroBot, a novel frog-inspired amphibious robot that uses a dual-swing-legs propulsion mechanism for locomotion on land and in water. It employs anti-bias universal wheels for land propulsion and flexible caudal fins for underwater thrust, achieving stable speed control via a fuzzy PID controller and demonstrating successful forward swimming and maneuverability at 0.4 m/s in underwater experiments.

ABSTRACT

This paper describes a novel amphibious robot, which adopts a dual-swing-legs propulsion mechanism, proposing a new locomotion mode. The robot is called FroBot, since its structure and locomotion are similar to frogs. Our inspiration comes from the frog scooter and breaststroke. Based on its swing leg mechanism, an unusual universal wheel structure is used to generate propulsion on land, while a pair of flexible caudal fins functions like the foot flippers of a frog to generate similar propulsion underwater. On the basis of the prototype design and the dynamic model of the robot, some locomotion control simulations and experiments were conducted for the purpose of adjusting the parameters that affect the propulsion of the robot. Finally, a series of underwater experiments were performed to verify the design feasibility of FroBot and the rationality of the control algorithm.

Motivation & Objective

• To develop a novel amphibious robot capable of efficient locomotion in both terrestrial and aquatic environments using bio-inspired propulsion.
• To address the challenge of integrating wheeled and undulatory locomotion modes in a single robotic platform with minimal actuators.
• To design a dual-swing-legs mechanism that enables stable, balanced movement on land and effective propulsion underwater.
• To validate the dynamic model and control strategy through simulation and experimental testing on land and in water.
• To improve amphibious robot mobility by combining the advantages of wheeled speed and undulatory fin propulsion.

Proposed method

• Design of a frog-inspired robot (FroBot) with a dual-swing-legs mechanism, using anti-bias universal wheels for land propulsion and flexible caudal fins for underwater thrust.
• Development of a dynamic model for forward, backward, and slope-climbing locomotion on land, based on the swing leg mechanism and wheel kinematics.
• Implementation of a two-loop control system: an inner PID loop for motor control and an outer fuzzy PID loop for velocity tracking and trajectory following.
• Use of a linear array CCD sensor for real-time position feedback during trajectory following experiments on land.
• Conduct of remote-controlled underwater experiments in a 5.5 m diameter pool with 1.0 m depth to evaluate fin-based propulsion and maneuverability.
• Offline video analysis of underwater motion to quantify speed and assess control performance, including straight swimming, descent, and S-shaped path following.

Experimental results

Research questions

• RQ1 How can a dual-swing-legs mechanism enable effective and stable locomotion on both land and in water using a single actuation system?
• RQ2 What is the optimal combination of swing amplitude, frequency, and wheel configuration to maximize land speed and stability?
• RQ3 Can a fuzzy PID controller effectively manage velocity tracking and trajectory following under varying conditions on land?
• RQ4 To what extent can flexible caudal fins replicate frog-like undulatory propulsion in an amphibious robot?
• RQ5 What are the key performance metrics (e.g., speed, maneuverability) of the robot in underwater environments, and how do they compare to theoretical expectations?

Key findings

• FroBot achieved a maximum land speed of 1 m/s and a stable underwater speed of 0.4 m/s, as confirmed by offline video analysis of underwater experiments.
• The fuzzy PID controller enabled the robot to track a target velocity of 0.47 m/s within the range of 0.40–0.55 m/s, with an average velocity of approximately 0.47 m/s during trajectory following.
• The robot successfully performed forward swimming, descent, and S-shaped path following in water, demonstrating control over yaw, pitch, and roll movements.
• The dynamic model for land locomotion was validated through simulations and experiments, confirming the influence of swing amplitude and frequency on propulsion.
• The dual-swing-legs mechanism provided stable heading control and balance during both land and underwater locomotion due to its symmetric design.
• The robot’s performance was limited on slopes exceeding 4 degrees due to passive wheel structure, indicating a need for mechanical improvements in future designs.