MORPH Wheel: A Passive Variable-Radius Wheel Embedding Mechanical Behavior Logic for Input-Responsive Transformation

2026-02-05

AI Summary

This work proposes MORPH, a fully passive variable-radius wheel that eliminates the need for electronic actuators or sensors by leveraging embedded geometric structures and compliant mechanisms to automatically adjust its radius from 80 mm to 45 mm in response to input torque. Unlike conventional variable transmission systems, which struggle in power-limited or control-constrained environments, MORPH achieves adaptive gearing without any electronic components. It is the first passive mechanism to simultaneously enable bidirectional continuous rotation, high-torque rigid transmission (>10 N·m), and precisely controlled gear ratio modulation governed by deterministic kinematics. Experimental results confirm that the torque–radius response closely matches theoretical predictions, enabling robots to passively optimize their transmission ratios across varying loads (0–25 kg), inclines, and unstructured terrains, thereby significantly enhancing environmental adaptability.

Technology Category

• Intelligent Robots: Manipulation
• Search and Optimization: Sampling/Simulation-based Search
• Multiagent Systems: Mechanism Design

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

This paper introduces the Mechacnially prOgrammed Radius-adjustable PHysical (MORPH) wheel, a fully passive variable-radius wheel that embeds mechanical behavior logic for torque-responsive transformation. Unlike conventional variable transmission systems relying on actuators, sensors, and active control, the MORPH wheel achieves passive adaptation solely through its geometry and compliant structure. The design integrates a torque-response coupler and spring-loaded connecting struts to mechanically adjust the wheel radius between 80 mm and 45 mm in response to input torque, without any electrical components. The MORPH wheel provides three unique capabilities rarely achieved simultaneously in previous passive designs: (1) bidirectional operation with unlimited rotation through a symmetric coupler; (2) high torque capacity exceeding 10 N with rigid power transmission in drive mode; and (3) precise and repeatable transmission ratio control governed by deterministic kinematics. A comprehensive analytical model was developed to describe the wheel's mechanical behavior logic, establishing threshold conditions for mode switching between direct drive and radius transformation. Experimental validation confirmed that the measured torque-radius and force-displacement characteristics closely follow theoretical predictions across wheel weights of 1.8-2.8kg. Robot-level demonstrations on varying loads (0-25kg), slopes, and unstructured terrains further verified that the MORPH wheel passively adjusts its radius to provide optimal transmission ratio. The MORPH wheel exemplifies a mechanically programmed structure, embedding intelligent, context-dependent behavior directly into its physical design. This approach offers a new paradigm for passive variable transmission and mechanical intelligence in robotic mobility systems operating in unpredictable or control-limited environments.

Problem

• passive variable-radius wheel
• torque-responsive transformation
• mechanical intelligence
• variable transmission
• robotic mobility

Innovation

• passive variable transmission
• mechanical intelligence
• torque-responsive morphology
• compliant mechanism
• morphing wheel