cs.ROMar 1, 2026

A Deployable Bio-inspired Compliant Leg Design for Enhanced Leaping in Quadruped Robots

Authors: Yiyang Chen, Yuxin Liu, Jinzheng Zhou, Fanxin Wang, Qinglei Bu, Jie Sun, Yikun Cheng

Organizations: Department of Mechatronics and Robotics, Xi’an Jiaotong-Liverpool University, Suzhou 215123, China. · Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Champaign, Illinois, United States.

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Abstract

Quadruped robots are becoming increasingly essential for various applications, including industrial inspection and catastrophe search and rescue. These scenarios require robots to possess enhanced agility and obstacle-navigation skills. Nonetheless, the performance of current platforms is often constrained by insufficient peak motor power, limiting their ability to perform explosive jumps. To address this challenge, this paper proposes a bio-inspired method that emulates the energy-storage mechanism found in froghopper legs. We designed a Deployable Compliant Leg (DCL) utilizing a specialized 3D-printed elastic material, Polyether block amide (PEBA), featuring a lightweight internal lattice structure. This structure functions analogously to biological tendons, storing elastic energy during the robot's squatting phase and rapidly releasing it to augment motor output during the leap. The proposed mechanical design significantly enhances the robot's vertical jumping capability. Through finite element analysis (FEA) and experimental validation, we demonstrate a relative performance improvement of 17.1% in vertical jumping height.

Figures & tables

Fig. 1 : Illustration of the Jumping Actuation Challenge. (Left) The baseline robot, limited by motor torque saturation, fails to reach the critical height. (Right) The proposed system, augmented with DCLs, releases extra stored elastic energy and completes the task (symbolized by the coin).
Fig. 2 : (a-e) Design workflow of the bio-inspired quadruped leaping enhancement; (b) The biological prototype [ 12 ] .
Fig. 3 : Bio-inspired design concept of the robotic leg. (a) The Philaenus spumarius, serving as the biological prototype [ 12 ] . (b) Biological mechanism highlighting the interaction between the rigid hard cuticle and the energy-storing resilin [ 12 ] . (c) The proposed quadruped robot integrated with the SSCMs. (d) Mechanical design overview.
Fig. 4 : The Gyroid lattice structure designed in nTop, shown (A) as a unit cell and (B) implemented as the internal filler of the compliant structure.
Fig. 5 : Operational states of the deployable mechanism. (a) In the Stowed State, the mechanism retracts to eliminate parasitic stiffness. (b) In the Deployed State, the module rotates 90 degrees to align with the femur for ballistic energy storage.
Fig. 6 : Exploded view of the kinematic chain. Key components: (1) SSCM Lattice, (2) Push Rod, (3) Top Cap, (4) Rotating Sleeve, (5) Return Spring, (6) Inner Fixed Post, (7) Guide Pin, (8) Sliding Block, and (9) Locking Pin. The mechanism converts linear input into a precise 90-degree rotation via a helical cam constraint.
Fig. 7 : Rigorous stiffness characterization and operating bounds. FEA raw data (blue circles) validates the structural integrity up to 45∘45^{\circ} . The Analytical Model (solid red line) is a 3rd3^{rd} -order polynomial fitted to the Operating Region ( 0∘0^{\circ} – 29∘29^{\circ} ) with maximize torque 6.8N⋅m6.8N\cdot m . The Safety Margin (blue zone) provides a ≈10∘\approx 10^{\circ} buffer before the Design Limit Line (red, 39∘39^{\circ} ), beyond which the structure enters the Densification Region (red zone).
Fig. 8 : The physical experimental setup. (A) The attached tracking balls (each rigid body circled in one color). (B) The established Unitree Go2 model in the Luster FZMotion motion capture system.
Fig. 9 : Composite time-lapse photography of the vertical jumping experiments. (Left) The Baseline group (Unitree Go2 without payload) reaching a peak height of 656.3 mm. (Middle) The Stowed group (passive mass) reaching 654.9 mm, demonstrating negligible parasitic effect (0.33% reduction) from the added mass. (Right) The Deployed group utilizing the PEBA lattice energy release, achieving a peak height of 720.3 mm, a 17.1% increase over the baseline. The white dashed reference line indicates the baseline peak height.
Fig. 10 : Effective jump height comparison from motion capture data.
Experimental GroupMax Height ( Hmax⁡H_{\max} )Eff. Jump Height ( ΔH\Delta H )Relative Change (vs. Baseline)
Baseline656.3 mm373.1 mmN/A
Stowed654.9 mm371.7 mm−- 0.4%
Deployed720.3 mm437.1 mm+17.1%
TABLE I : Vertical Jumping Experimental Results (Mean values over N=5N=5 trials)
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