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Dynamic Posture Manipulation During Tumbling for Closed-Loop Heading Angle Control

Adarsh Salagame, Eric Sihite, Gunar Schirner, Alireza Ramezani

TL;DR

This work tackles active heading control for COBRA during tumbling on rough terrain by developing a cascade reduced-order model that couples posture manipulation with tumbling dynamics. A collocation-based optimization framework computes posture-controlling inputs to steer the heading, with a MATLAB-based simulation validating the approach. The results show that dynamically adjusting the elliptical ring posture can alter inertia and deflect the tumbling path, enabling targeted heading changes. The approach lays groundwork for real-time, closed-loop steering of COBRA using its multiple joints, advancing agile tumbling locomotion for challenging terrains such as lunar craters.

Abstract

Passive tumbling uses natural forces like gravity for efficient travel. But without an active means of control, passive tumblers must rely entirely on external forces. Northeastern University's COBRA is a snake robot that can morph into a ring, which employs passive tumbling to traverse down slopes. However, due to its articulated joints, it is also capable of dynamically altering its posture to manipulate the dynamics of the tumbling locomotion for active steering. This paper presents a modelling and control strategy based on collocation optimization for real-time steering of COBRA's tumbling locomotion. We validate our approach using Matlab simulations.

Dynamic Posture Manipulation During Tumbling for Closed-Loop Heading Angle Control

TL;DR

This work tackles active heading control for COBRA during tumbling on rough terrain by developing a cascade reduced-order model that couples posture manipulation with tumbling dynamics. A collocation-based optimization framework computes posture-controlling inputs to steer the heading, with a MATLAB-based simulation validating the approach. The results show that dynamically adjusting the elliptical ring posture can alter inertia and deflect the tumbling path, enabling targeted heading changes. The approach lays groundwork for real-time, closed-loop steering of COBRA using its multiple joints, advancing agile tumbling locomotion for challenging terrains such as lunar craters.

Abstract

Passive tumbling uses natural forces like gravity for efficient travel. But without an active means of control, passive tumblers must rely entirely on external forces. Northeastern University's COBRA is a snake robot that can morph into a ring, which employs passive tumbling to traverse down slopes. However, due to its articulated joints, it is also capable of dynamically altering its posture to manipulate the dynamics of the tumbling locomotion for active steering. This paper presents a modelling and control strategy based on collocation optimization for real-time steering of COBRA's tumbling locomotion. We validate our approach using Matlab simulations.
Paper Structure (11 sections, 23 equations, 8 figures)

This paper contains 11 sections, 23 equations, 8 figures.

Table of Contents

  1. Introduction
  2. Tumbling Robots
  3. Overview of COBRA Hardware
  4. Reduced-Order Model (ROM) Derivations
  5. Cascade Model
  6. Governing Dynamics for Posture Manipulation $\Sigma_{pos}$
  7. Governing dynamics for Tumbling $\Sigma_{tbl}$
  8. Controls
  9. Results and Discussions
  10. Concluding Remarks
  11. Appendix

Figures (8)

  • Figure 1: Shows transformation from snake to tumbling configuration in COBRA platform
  • Figure 2: Illustrates model parameters, coordinate frames, etc., used to derive Eqs. \ref{['eq:cascade-model']}, \ref{['eq:pos-dyn-model']}, \ref{['eq:M-tbl-dyn']}, and \ref{['eq:N-tbl-dyn']}.
  • Figure 3: Illustrates posture manipulation by considering two imaginary actuators, denoted as $u_1$ and $u_2$, which act along the principal axes of the ring to induce planar deformations.
  • Figure 4: Top figure illustrates the MATLAB simulation of the reduced order model of the robot rolling down a $5^\circ$ incline with control input applied to change the length of the principle axes of the elliptical ring. The bottom figure shows the change in the path of tumbling as an impulse is applied to the axes lengths.
  • Figure 5: Shows the change in inertia along the principle axes as the lengths of axes are manipulated.
  • ...and 3 more figures