Variable Aerodynamic Damping via Co-Contraction: A Dynamic Isomorphism with Variable Stiffness Actuators
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866911661659521024 |
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| author | Franchi, Antonio |
| author_facet | Franchi, Antonio |
| contents | We prove that aerodynamic co-contraction in a redundant dual-rotor actuator can tune a passive, trim-defined aero-mechanical damping while keeping the commanded net force constant. In particular, we define an incremental damping coefficient as the local sensitivity of net thrust to air-relative velocity at a trim and prove that it increases monotonically along constant-force fibers under a mild aerodynamic hardening condition. We then validate the required damping and hardening properties from a first-principles Blade Element Theory derivation, which yields a minimal thrust model affine in inflow and explicitly reveals the speed--inflow coupling driving the effect. The resulting mechanism is formalized as a Variable Aerodynamic Damping Actuator (VADA) and shown to be dynamically isomorphic to stiffness modulation in antagonistic variable-stiffness actuation (VSA), similar to the co-contraction of tendons by muscle co-activation. The same fiber-density principle also enhances the active aerodynamic promptness measure of redundant multirotors. Finally, an impedance-form representation clarifies the roles of common-mode and differential-mode actuation in the control of passive impedance and the equilibrium velocity of the VADA system. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_07292 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Variable Aerodynamic Damping via Co-Contraction: A Dynamic Isomorphism with Variable Stiffness Actuators Franchi, Antonio Robotics Systems and Control Optimization and Control We prove that aerodynamic co-contraction in a redundant dual-rotor actuator can tune a passive, trim-defined aero-mechanical damping while keeping the commanded net force constant. In particular, we define an incremental damping coefficient as the local sensitivity of net thrust to air-relative velocity at a trim and prove that it increases monotonically along constant-force fibers under a mild aerodynamic hardening condition. We then validate the required damping and hardening properties from a first-principles Blade Element Theory derivation, which yields a minimal thrust model affine in inflow and explicitly reveals the speed--inflow coupling driving the effect. The resulting mechanism is formalized as a Variable Aerodynamic Damping Actuator (VADA) and shown to be dynamically isomorphic to stiffness modulation in antagonistic variable-stiffness actuation (VSA), similar to the co-contraction of tendons by muscle co-activation. The same fiber-density principle also enhances the active aerodynamic promptness measure of redundant multirotors. Finally, an impedance-form representation clarifies the roles of common-mode and differential-mode actuation in the control of passive impedance and the equilibrium velocity of the VADA system. |
| title | Variable Aerodynamic Damping via Co-Contraction: A Dynamic Isomorphism with Variable Stiffness Actuators |
| topic | Robotics Systems and Control Optimization and Control |
| url | https://arxiv.org/abs/2605.07292 |