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

Daniel Koh; Suraj Shah; Yufeng Wu; Dennis Hong

cs.ROMar 12, 2026

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

Authors: Daniel Koh, Suraj Shah, Yufeng Wu, Dennis Hong

Organizations: Department of Mechanical and Aerospace Engineering, UCLA, Los Angeles, CA 90095, USA.

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.

Figures & tables

Fig. 1 : MiNI-Q, a miniature quadruped robot featuring a 2R leg mechanism designed to remove conventional joint limits.

Fig. 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.

Specifications	Q8bot	MiNI-Q
Mass (g)	220	240
Nominal Dimension (cm)	14 $\times$ 7 $\times$ 7	13.8 $\times$ 9.2 $\times$ 5.7
Folded Dimension (cm)	12 $\times$ 7 $\times$ 5	13.8 $\times$ 9.2 $\times$ 2.5
Body Length (cm)	8	8.8
Maximum Clearance (cm)	5.8	5.8

TABLE I : Physical specifications of Q8bot and MiNI-Q.

Fig. 3 : Electronics system overview of MiNI-Q

Fig. 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.

Fig. 5 : MiNI-Q’s serial linkage workspace overlaid on top of Q8bot’s parallel linkage workspace.

Fig. 6 : Yoshikawa manipulability across the workspace of MiNI-Q’s 2R leg (left) and Q8bot’s parallel leg mechanism (right). Lighter color represents higher manipulability.

Panel of Figure 8 — Fig. 7 : Comparison of two trot gaits. (a) Fast trot. (b) High trot. Top: sequential snapshots of the robot over one gait cycle. Bottom: measured IMU pitch (blue) and roll (red) angles versus time.

Robot	Top Speed	Normalized Top Speed	Cost of Transport (COT)
MiNI-Q	0.46 m/s	5.22	7.1
Q8Bot [ 1 ]	0.43 m/s	5.38	6.04
Chen et al. [ 21 ]	0.52 m/s	4.4	3.2
Doggo [ 10 ]	0.8 m/s	2.14	3.2

TABLE II : Quadruped Performance Comparison

Gait Type	Steady State Velocity $V_{ss}$	Normalized Velocity	Average Current Draw	Cost of Transport (COT)	Pitch Standard Deviation	Roll Standard Deviation
Slow Trot	0.12 m/s	1.36	0.543 A	11.5	2.15	2.19
Fast Trot	0.46 m/s	5.22	1.473 A	8.1	1.57	1.25
High Trot	0.16 m/s	1.81	0.449 A	7.1	0.73	0.80
Crawl	0.03 m/s	0.32	0.220 A	19.7	0.85	1.10

TABLE III : MiNI-Q COT Table

Fig. 8 : MiNI-Q jumping where each black and white strip is 10 mm. Peak height is 220 mm.

Fig. 9 : MiNI-Q standing in upright position (Left) and inverted position (Right). Note the location of the white PCB cover.

Panel of Figure 13 — Fig. 10 : Demonstrations of MiNI-Q locomotion capabilities. (a) Stair climbing up steps $2.2\times$ the robot’s body height. (b) Low-clearance traversal through a $45\,\mathrm{mm}$ gap. (c) Locomotion on pebbled terrain using the continuous rotation gait. (d) Jumping backflip maneuver.

Legged Robotics

Legged robotics studies how robots with legs move, perceive their surroundings, and perform useful tasks across varied terrain.

See all 126 papers

High-Degree-of-Freedom Lightweight Bioinspired Leg for Enhanced Mobility in Small Robots
Jun 17, 2026Haoqi Han, Yifei Yu, Jiaming Zhang +3Legged Robotics Bioinspired Robotics
Department of Computer Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China · Department of Automation Engineering,Shanghai University of Electric Power,Shanghai,China · Department of Naval Architecture and Marine Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China +2
QLAUN: A Research-Oriented, Robust, Agile, Modular, and Affordable Torque-Controlled Quadruped Robot
Sep 3, 2026Mohamad S. Moudallal, Noel J. MaaloufLegged Robotics Modular Robotics
Department of Electrical and Computer Engineering, Lebanese American University, Byblos, Lebanon
Around the World: Unified Learned Locomotion on a 270 g Continuous-Rotation Quadruped
Oct 2, 2026Arturo Flores Alvarez, Nathan Lintu, Dennis HongLegged Robotics Quadruped Locomotion
Robotics and Mechanisms Laboratory (RoMeLa), University of California, Los Angeles (UCLA)

Jun 17, 2026J/K move · Enter open · S save

High-Degree-of-Freedom Lightweight Bioinspired Leg for Enhanced Mobility in Small Robots

Haoqi Han, Yifei Yu, Jiaming Zhang, Xinru Cui+2

Department of Computer Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China · Department of Automation Engineering,Shanghai University of Electric Power,Shanghai,China · Department of Naval Architecture and Marine Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China+2

Legged Robotics Bioinspired Robotics Robotics

Open paper AskPDF arXiv

In microrobotics, enhancing locomotion capabilities by increasing the degrees of freedom (DoF) of leg mechanisms under severe spatial constraints remains a significant challenge. Inspired by insect locomotion, this paper presents a novel micro-scale parallel leg mechanism with four degrees of freedom, and systematically analyzes its mechanical design, electrical system, and kinematics. The design incorporates two spherical five-bar linkages to achieve spatial motion within a parallel four-bar configuration. Furthermore, a concentric design strategy is employed to simplify the analytical solution of the leg kinematics. Due to the parallel system architecture, all actuators are located on the main body, substantially reducing the equivalent inertia of moving parts compared to traditional high-DOF leg structures. The total mass of the system is only 18.9 g, with an end-effector output force of approximately 0.5 N and a workspace exceeding 22255 mm3. Experimental results demonstrate that the proposed single-leg mechanism achieves excellent motion flexibility, highlighting its potential for micro bio-inspired robotics.

Abstract

Legged Robotics

Explore similar work

High-Degree-of-Freedom Lightweight Bioinspired Leg for Enhanced Mobility in Small Robots

QLAUN: A Research-Oriented, Robust, Agile, Modular, and Affordable Torque-Controlled Quadruped Robot

Around the World: Unified Learned Locomotion on a 270 g Continuous-Rotation Quadruped