Robotic systems that are soft or incorporate soft actuators are well suited for operation in unstructured environments and for safe interactions with fragile objects. The majority, however, are tethered or burdened with bulky payloads of pumps and compressors. In a recent article we presented a sealed, inflated actuator composed of fluidically connected membrane dielectric elastomer actuators capable of large, repeatable, and stable deformations. Each membrane could switch between two identical volumes, and maintain its shape when an applied voltage was removed. Here we extend our previous work by simulating and demonstrating asymmetric stable deformations. In an experimental two-membrane setup, the membranes experience large and significantly different area strains of >100% and >550% when transitioning between stable states. With the addition of more membranes, this asymmetry can increase the number of discrete stable membrane sizes, allowing more complex control when later implemented in a mechanism.

In this work, we examine two design modifications to a tethered motor-driven flapping-wing system. Previously, we had demonstrated a simple mechanism utilizing a linear transmission for resonant operation and direct drive of the wing flapping angle for control. The initial two-wing system had a weight of 2.7 grams and a maximum lift-to-weight ratio of 1.4. While capable of vertical takeoff, in open-loop flight it demonstrated instability and pitch oscillations at the wing flapping frequency, leading to flight times of only a few wing strokes. Here the effect of vertical wing offset as well as an alternative multi-wing layout is investigated and experimentally tested with newly constructed prototypes. With only a change in vertical wing offset, stable open-loop flight of the two-wing flapping system is shown to be theoretically possible, but difficult to achieve with our current design and operating parameters. Both of the new two and four-wing systems, however, prove capable of flying to the end of the tether, with the four-wing system prototype eliminating disruptive wing beat oscillations.

This study presents the design of a novel minimalist liftoff-capable flapping-wing microaerial vehicle. Two wings are each directly driven by a geared pager motor by utilizing an elastic element for energy recovery, resulting in a maximum lift-to-weight ratio of 1.4 at 10 Hz for the 2.7 g system. Separate directly driven wings allow the system to both resonate and control individual wing flapping angle, reducing necessary power consumption, as well as allowing the production of roll and pitch body torques. With a series of varied prototypes, system performance is examined with change in wing offset from center of rotation and elastic element stiffness. Prototype liftoff is demonstrated with open loop driving a tethered prototype without guide wires. A dynamic model of the system is adapted and compared with the prototype experimental results for later use in prototype optimization.

In previous work, a proof-of-concept artificial flapper was devised by Campolo et al. to demonstrate that DC motors, in concert with compliant mechanisms, would be able to directly flap wings at relatively high frequencies and large angles without exceeding their operational limits. The prototype makes use of a pair of relatively long elastic strings as the compliant structures. In this article, we experimentally analyze the wing kinematics and efficiency of a more compact prototype, where small helical springs are implemented instead of elastic strings. Since the proof-of-concept prototype validated the quasi-sinusoidal assumption in spite of nonlinear aerodynamic damping, incorporating instantaneous wing kinematics into the analysis is not necessary, simplifying experiments and data processing. Along with wing kinematics and system efficiency, the possibility of controlling the wing pair to flap independently is evaluated as well.

An active flexural hinge has been developed and incorporated into the transmission of a prototype flapping-wing robot. The multilayered flexure, which is constructed from a shape memory polymer and a polyimide film, showed controllable stiffness under change in temperature. At room temperature, the flexure had a bending stiffness of 572 mN·mm; when warmed to 70°C, the stiffness was 11 mN·mm. The resulting single-wing flapping system demonstrated up to an 80% change in generated lift without modification of the waveform of the main driving piezoelectric actuator. Such active stiffness tunable flexure joints could be applied to any flexural miniature mobile robot and device mechanisms.

Flapping-flight micro aerial vehicles (MAVs) pose an ongoing design problem to the scientific community, requiring careful consideration of both body structure and force production. Here, we examine a flapping MAV prototype with a passively rotating wing design. While at the current scale the lift force produced is not enough for liftoff, observing its performance under roll and pitch control can lead to insights on both the body design and the eventual free-flight implementation. As the production of roll and pitch torques are primarily uncoupled for this design, PID control is implemented in the roll and pitch directions individually on a custom designed single degree of freedom rig. By doing so, we show that the body structure is capable of sustaining independent wing amplitudes and that actuator input voltage bias shifting is successful experimentally on a dynamically driven wing. Through force compensation, the experimentally tested controller is mapped to a 1/2 scale simulated system, theoretically capable of free-flight. Though initial simulation results suggest high sensitivity to feedback noise, simulations show that decoupled roll and pitch controllers have potential as a minimal computational means for hovering and translational motion.

Flapping wing micro-aerial vehicles (MAVs) hold great potential for matching the agility of flies, their source of inspiration. At small scales, however, it becomes difficult to balance design mechanical complexity and the weight/lift ratio. Considering control in the initial stages of vehicle design can help define system feasibility and the consequences of making design simplifications. Here, four design alternatives based on a piezoelectric driven passive pitch reversal wing are modeled and compared based on their performance under an ideal linear quadratic regulator (LQR) control scheme. State error over straight line, circular, and cube trajectories are used as a means of comparison. Wing lift and reasonable control input bounds are defined for each design variation. While not nearly as maneuverable as flies, these designs show promise as feasible controllable vehicles.