cs.ROOct 19, 2026

Design and Control of a Multimodal Legged-Aerial Robot Through Separate Control Contraction Metrics

Authors: Kaushik Venkatesh Krishnamurthy, Eric Sihite, Alireza Ramezani, Morteza Gharib

Organizations: Authors are with the Silicon Synapse Labs, Department of Electrical and Computer Engineering, Northeastern University, Boston, USA. · Authors are with Center for Autonomus Systems and Technologies, Caltech, Pasadena, CA.

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Abstract

The integration of dynamic legged locomotion and aerial mobility offers versatility that is deterred by challenges in payload distribution, actuation, and the contrasting requirements of both domains. In this paper, we present the design and operation of a multimodal quadrupedal aerial-legged robot. The presence of legged aerial systems also allows for thruster-assisted legged locomotion, which we make possible with a unified control framework using Control Contraction Metrics (CCM). We search for separate domain-specific contraction metrics for walking and flight independently offline and unify them using an online energy-based Control Lyapunov Function Quadratic Program (CLF QP). This enables optimal, cross-domain control allocation, which we show using simulations. We also show experimental results that validate the mechanical viability of our hardware and the paradigm of thruster-assisted trotting. The stability of said experiments motivates the deployment of the control framework for multimodal operations.

Figures & tables

Fig. 1: The legged-aerial quadrupedal robot used in this study. The robot has three joint actuator for each leg, and four thrusters for aerial locomotion and thruster-assisted walking.
Fig. 2: Section view of actuator assembly, showing the harmonic drive, stator, and rotor embedded in the additively manufactured actuator housing.
PropertyValueUnits
Mass12kg
Height0.6m
Width1m
Length1.5m
Joint Actuator MotorT-Motor MN4004 Antigravity-
Motor KV270kV
TABLE I: Robot properties
Fig. 3: CAD model rendering of the robot, closeup view of all subsystems and components including custom-design actuators, thruster, power electronics, joints, and onboard computers.
Fig. 4: Planar VTOL and legged models used for obtaining contraction metrics. We separate the contraction metrics for the the legged and aerial systems.
Fig. 5: A. Snapshots of Matlab simulation showing thruster-assisted trotting using the min-norm controller with the unified contraction constraints. B. Zoomed in view of a couple of steps, showing the relative direction and magnitude of front and rear thruster forces and contact forces. Along with trajectories of positions, velocity, pitch, phase plots, contact forces, and constraint satisfaction.
Fig. 6: Snapshots from experimental results. The legged phase involves 2-point contact trotting while a human operator provides thruster inputs to. During the flight phase, the flight operator provides thruster inputs through the onboard CubeOrange flight controller. The robot lands again and continues trotting stably.
Fig. 7: Joint positions and velocities reference and tracking during thruster-assisted trotting experiments
Fig. 8: Euler angles in the thruster assisted trotting.
Fig. 9: Snapshots of the robot flying and landing on an obstacle.
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