Non-linear resonance modeling and system design improvements for underactuated flapping-wing vehicles

Abstract

Insect-scale flying robots are currently unable to carry the power source and sensor suite required for autonomous operation. To overcome this challenge, we developed and experimentally verified a non-linear damping model of actuation-limited flapping-wing vehicles with passively rotating wing hinges. In agreement with studies on the wing dynamics of honey bees, we found that the optimal angle of the passive wing hinge in mid-stroke is about 70 • rather than 45−50 • as previously assumed. We further identified a narrow actuation force window in which the occurrence of a sharp resonance can be used to achieve both higher lift and efficiency. The findings from our model informed design changes to the Harvard Dual-Actuator Robobee, which resulted in a 130% increase in mean lift from ∼140 mg to 320 mg (with a vehicle mass increase of only 5 − 8%), along with a corresponding expected payload increase of 330 − 470% (30 − 40 mg to 170 mg). The power consumption only increased by ∼55%, making the new prototype 50% more efficient at lift production. Our model provides a greater understanding of the dynamics of this complex system, and the resulting lift and efficiency improvements are expected to bring insect-scale flying robots closer to autonomy.

Gait studies for a quadrupedal microrobot reveal contrasting running templates in two frequency regimes

“…This is similar in spirit to (Haldane et al, 2013) where high bandwidth electromagnetic motors are use to achieve stride frequencies higher than the body dynamics. In contrast to rotary motors where peak torque is produced at stall, piezoelectric actuators have force generation that is independent of actuation frequency up to actuator resonance (Jafferis et al, 2016a). We wish to leverage this property and operate in frequency regimes suited for different tasks; for example, precision quasi-static motions for orienting a vision system, using body resonance to negotiate over obstacles, or exploiting transmission resonance for high speed running.…”

A biologically inspired, flapping-wing, hybrid aerial-aquatic microrobot

“…In soapy water and tap water, the total surface forces on these components are 6.6 and 18.8 mN, respectively. This result suggests that direct liftoff from the water surface is infeasible, because a previous work (26) reports a maximum lift of 3.1 mN. In the next section, we describe energetic impulsive mechanisms that enable the water-to-air transition.…”

Hawkmoths use wingstroke-to-wingstroke frequency modulation for aerial recovery to vortex ring perturbations

“…The qualitative resonance implications in insects have been quantified in their robotic counterparts. In insectscale flapping wing vehicles, tuning wingbeat frequencies to resonance improved energy efficiency by 50% [9].…”

“…Like resonant oscillators, insects store excess kinetic energy during a wing stroke in spring-like structures and return this energy to reaccelerate the wings. This strategy effectively reduces the inertial necessary for flight 1 [3,4,5,6,7,8,9]. Recent work directly measuring resonance properties in bees suggests that wingbeat frequencies are directly tuned to match resonance frequencies [10].…”