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MiNI-Q: A Miniature, Wire-Free Quadruped with Unbounded, Independently Actuated Leg Joints

Daniel Koh, Suraj Shah, Yufeng Wu, Dennis Hong

Abstract

Physical joint limits are common in legged robots and can restrict workspace, constrain gait design, and increase the risk of hardware damage. This paper introduces MiNI-Q^2, a miniature, wire-free quadruped robot with independently actuated, mechanically unbounded 2-DOF leg joints. We present the mechanical design, kinematic analysis, and experimental validation of the proposed robot. The leg mechanism enables both oscillatory gaits and rotary locomotion while allowing the robot to fold to a minimum height of 2.5 cm. Experimentally, MiNI-Q achieves speeds up to 0.46 m/s and demonstrates low-clearance crawling, stair climbing, inverted locomotion, jumping, and backflipping. The wire-free architecture extends our previous Q8bot design, improving assembly reliability at miniature scale. All mechanical and electrical design files are released open source to support reproducibility and further research.

MiNI-Q: A Miniature, Wire-Free Quadruped with Unbounded, Independently Actuated Leg Joints

Abstract

Physical joint limits are common in legged robots and can restrict workspace, constrain gait design, and increase the risk of hardware damage. This paper introduces MiNI-Q^2, a miniature, wire-free quadruped robot with independently actuated, mechanically unbounded 2-DOF leg joints. We present the mechanical design, kinematic analysis, and experimental validation of the proposed robot. The leg mechanism enables both oscillatory gaits and rotary locomotion while allowing the robot to fold to a minimum height of 2.5 cm. Experimentally, MiNI-Q achieves speeds up to 0.46 m/s and demonstrates low-clearance crawling, stair climbing, inverted locomotion, jumping, and backflipping. The wire-free architecture extends our previous Q8bot design, improving assembly reliability at miniature scale. All mechanical and electrical design files are released open source to support reproducibility and further research.
Paper Structure (16 sections, 8 equations, 10 figures, 3 tables)

This paper contains 16 sections, 8 equations, 10 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Methodology
  3. Hardware Design
  4. Kinematic and Workspace Analysis
  5. Jacobian Analysis
  6. Software and Control
  7. Results
  8. Locomotion Performance
  9. Novel Locomotion
  10. Terrain Navigation
  11. Other Capabilities
  12. Discussion
  13. Design Choices
  14. Limitations
  15. Future Work
  16. ...and 1 more sections

Figures (10)

  • Figure 1: MiNI-Q, a miniature quadruped robot featuring a 2R leg mechanism designed to remove conventional joint limits.
  • Figure 2: Mechanical design of MiNI-Q. (a) Overall dimensions in nominal and folded configurations. (b) Exploded view of the robot assembly. (c) Detail of MiNI-Q’s 2R leg mechanism enabling unbounded joint rotation. The lower leg linkage is designed to be easily swappable using a single screw, allowing for testing with different contact geometry and materials.
  • Figure 3: Electronics system overview of MiNI-Q
  • Figure 4: Kinematic diagram of MiNI-Q leg: A 2R linkage with custom joint-to-actuator mapping. $q_1, q_2$ denote the kinematic joint angles, whereas $\theta_1, \theta_2$ represent the corresponding actuator angles.
  • Figure 5: MiNI-Q's serial linkage workspace overlay-ed on top of Q8bot's parallel linkage workspace.
  • ...and 5 more figures