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.

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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.
SpecificationsQ8botMiNI-Q
Mass (g)220240
Nominal Dimension (cm)14 ×\times 7 ×\times 713.8 ×\times 9.2 ×\times 5.7
Folded Dimension (cm)12 ×\times 7 ×\times 513.8 ×\times 9.2 ×\times 2.5
Body Length (cm)88.8
Maximum Clearance (cm)5.85.8
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. q1,q2q_{1},q_{2} denote the kinematic joint angles, whereas θ1,θ2\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.
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.
RobotTop SpeedNormalized Top SpeedCost of Transport (COT)
MiNI-Q0.46 m/s5.227.1
Q8Bot [ 1 ]0.43 m/s5.386.04
Chen et al. [ 21 ]0.52 m/s4.43.2
Doggo [ 10 ]0.8 m/s2.143.2
TABLE II : Quadruped Performance Comparison
Gait TypeSteady State Velocity VssV_{ss}Normalized VelocityAverage Current DrawCost of Transport (COT)Pitch Standard DeviationRoll Standard Deviation
Slow Trot0.12 m/s1.360.543 A11.52.152.19
Fast Trot0.46 m/s5.221.473 A8.11.571.25
High Trot0.16 m/s1.810.449 A7.10.730.80
Crawl0.03 m/s0.320.220 A19.70.851.10
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.
Fig. 10 : Demonstrations of MiNI-Q locomotion capabilities. (a) Stair climbing up steps 2.2×2.2\times the robot’s body height. (b) Low-clearance traversal through a 45 mm45\,\mathrm{mm} gap. (c) Locomotion on pebbled terrain using the continuous rotation gait. (d) Jumping backflip maneuver.
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