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AquaMILR+: Design of an untethered limbless robot for complex aquatic terrain navigation

Matthew Fernandez, Tianyu Wang, Galen Tunnicliffe, Donoven Dortilus, Peter Gunnarson, John O. Dabiri, Daniel I. Goldman

Abstract

This paper presents AquaMILR+, an untethered limbless robot designed for agile navigation in complex aquatic environments. The robot features a bilateral actuation mechanism that models musculoskeletal actuation in many anguilliform swimming organisms which propagates a moving wave from head to tail allowing open fluid undulatory swimming. This actuation mechanism employs mechanical intelligence, enhancing the robot's maneuverability when interacting with obstacles. AquaMILR+ also includes a compact depth control system inspired by the swim bladder and lung structures of eels and sea snakes. The mechanism, driven by a syringe and telescoping leadscrew, enables depth and pitch control-capabilities that are difficult for most anguilliform swimming robots to achieve. Additional structures, such as fins and a tail, further improve stability and propulsion efficiency. Our tests in both open water and indoor 2D and 3D heterogeneous aquatic environments highlight AquaMILR+'s capabilities and suggest a promising system for complex underwater tasks such as search and rescue and deep-sea exploration.

AquaMILR+: Design of an untethered limbless robot for complex aquatic terrain navigation

Abstract

This paper presents AquaMILR+, an untethered limbless robot designed for agile navigation in complex aquatic environments. The robot features a bilateral actuation mechanism that models musculoskeletal actuation in many anguilliform swimming organisms which propagates a moving wave from head to tail allowing open fluid undulatory swimming. This actuation mechanism employs mechanical intelligence, enhancing the robot's maneuverability when interacting with obstacles. AquaMILR+ also includes a compact depth control system inspired by the swim bladder and lung structures of eels and sea snakes. The mechanism, driven by a syringe and telescoping leadscrew, enables depth and pitch control-capabilities that are difficult for most anguilliform swimming robots to achieve. Additional structures, such as fins and a tail, further improve stability and propulsion efficiency. Our tests in both open water and indoor 2D and 3D heterogeneous aquatic environments highlight AquaMILR+'s capabilities and suggest a promising system for complex underwater tasks such as search and rescue and deep-sea exploration.
Paper Structure (19 sections, 3 equations, 7 figures, 1 table)

This paper contains 19 sections, 3 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Robot design
  3. Design overview
  4. Module components
  5. Waterproofing
  6. Bilateral cable actuation
  7. Power and communication
  8. Depth control system
  9. Robot control
  10. Bilateral body actuation
  11. Suggested gait
  12. Programmable body compliance
  13. Depth and pitch control
  14. Evaluation
  15. Open water locomotion
  16. ...and 4 more sections

Figures (7)

  • Figure 1: The aquatic limbless robot AquaMILR+ designed for locomotion in complex and cluttered environments. (A) Full robot assembly, featuring a modular self-contained untethered architecture. (B) AquaMILR+ navigating a laboratory obstacle-rich environment (vertical posts).
  • Figure 2: Detailed design of AquaMILR+. (A) An assembly of 4 modules with 3 joints. (B) The electronics module contained within the head module, features onboard power, a single-board computer, and a waterproof power switch. (C) An internal diagram of each module and inter-module enclosure, including the depth control and cable-driving servo motors, cable routing, and revolute joint. (D) The primary waterproofing method between modules, including a gasket seal to clamp modules with in between O-ring.
  • Figure 3: Self-contained depth control system. (A) A telescopic leadscrew design for syringe activation, granting extra stroke in a compact space. (B) The water channel used by the syringes to change AquaMILR+'s buoyancy.
  • Figure 4: Programmable body compliance through bilateral cable actuation mechanism. (A) A geometric model illustrating a single joint, used to determine the exact lengths of the left and right cables necessary to deploy a specified joint angle. (B) A schematic displaying various compliance states based on the generalized compliance variable $G$. Figures adapted from wang2023mechanical.
  • Figure 5: Demonstration of locomotion and depth control capabilities of AquaMILR+. (A)(i) Straight locomotion across a 3-m-long pool; (ii) implementation of a turning gait, where the robot can turn in place with a tight sweeping area. (B) A demonstration of a controlled, slow descent to 1.52 m deep while locomoting forward.
  • ...and 2 more figures