A gyroscope-free visual-inertial flight control and wind sensing system for 10-mg robots

Abstract

Tiny “gnat robots,” weighing just a few milligrams, were first conjectured in the 1980s. How to stabilize one if it were to hover like a small insect has not been answered. Challenges include the requirement that sensors be both low mass and high bandwidth and that silicon-micromachined rate gyroscopes are too heavy. The smallest robot to perform controlled hovering uses a sensor suite weighing hundreds of milligrams. Here, we demonstrate that an accelerometer represents perhaps the most direct way to stabilize flight while satisfying the extreme size, speed, weight, and power constraints of a flying robot even as it scales down to just a few milligrams. As aircraft scale reduces, scaling physics dictates that the ratio of aerodynamic drag to mass increases. This results in reduced noise in an accelerometer’s airspeed measurement. We show through simulation and experiment on a 30-gram robot that a 2-milligram off-the-shelf accelerometer is able in principle to stabilize a 10-milligram robot despite high noise in the sensor itself. Inspired by wind-vision sensory fusion in the flight controller of the fruit fly Drosophila melanogaster , we then added a tiny camera and efficient, fly-inspired autocorrelation-based visual processing to allow the robot to estimate and reject wind as well as control its attitude and flight velocity using a Kalman filter. Our biology-inspired approach, validated on a small flying helicopter, has a wind gust response comparable to the fruit fly and is small and efficient enough for a 10-milligram flying vehicle (weighing less than a grain of rice).

Vector Field Aided Trajectory Tracking by a 10-gram Flapping-Wing Micro Aerial Vehicle

“…The 3-state directional command presented here enabled the Metafly to perform circular trajectory tracking and to track an 8shaped circuit while keeping a constant altitude. In future studies, we would like to (i) to increase the automation of the Metafly using micro-GPSs, gyros, magnetometers or optic flow sensors while taking into account the SSWaP (Speed Size Weight and Power) constraints of micro aerial vehicles [39,40], and (ii) to improve their vector field-based trajectory tracking performances in the presence of wind and obstacles outdoors.…”

Stabilizing Aerodynamic Dampers for Cooperative Transport of a Suspended Payload with Aerial Robots

“…For a single small rotorcraft, an inertial measurement unit (IMU) and an altitude sensor (such as time-offlight, time-of-flight [ToF], and camera) can form a minimal sensing suite for the robots to achieve sensor autonomy and realize stable flight. [47,48] Since the cooperative aerial transport task typically further demands coordination between agents to prevent a collision between agents and payload oscillations, additional sensory feedback is required for controlling the group formation on top of the flight stability at the individual level. The awareness of other robots becomes crucial, and this is conventionally provided by GPS, MoCap, or extra onboard cameras, as mentioned earlier (refer to the column "Relative positioning" in Table 1).…”

Modular and Scalable Fabrication of Insect‐Scale Aerial Robots toward Demonstrating Swarm Flights

“…We adopt the SCM method to fabricate the wing hinges, transmissions, and wings that move at 400 Hz. One challenge of the SCM fabrication approach is that a robot component consists of multiple (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) material layers, where the laser cut file of each layer must be individually generated. To simplify this design process, we implement an algorithm that automates laser cut file generation based on key kinematic parameters.…”

“…[11] They have also made substantial progress toward achieving control, sensing, and power autonomy. [12][13][14][15] However, due to limitations in robustness and fabrication scalability, these subgram MAVs have not yet demonstrated simultaneous flights. Unlike aerial insects, most subgram MAVs are fragile against in-flight collisions, which prohibit them from flying near obstacles or each other.…”