Research ArticleBIOMIMETICS

Forceful manipulation with micro air vehicles

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Science Robotics  24 Oct 2018:
Vol. 3, Issue 23, eaau6903
DOI: 10.1126/scirobotics.aau6903
  • Fig. 1 The FlyCroTug system.

    (A) FlyCroTugs’ multimodal operation allows them to combine small size, high mobility in cluttered and unstructured environments, and forceful manipulation. Several robotic systems demonstrate subsets of these attributes [e.g., MAVs (1), Salto (34), ANYmal (3), BigDog (35), and μTug (5)]. (B) A FlyCroTug with microspines for anchoring and a winch for tugging loads weighing 100 g and a 7.3-cm rotor distance from center. (C) Process of operation: Each robot (1) flies to an object and attaches a specialized end effector, (2) flies some distance away while paying out a cable, (3) lands and anchors to a surface using adhesives or microspines, and (4) pulls on the cable using a winch. Wheeled locomotion can be added in steps (1) and (3) for more precise positioning. The sequence repeats as necessary.

  • Fig. 2 Biological systems.

    (A) Like MAVs, wasps are limited by their thrust capabilities when transporting large payloads. Their solution of using attachment mechanisms to generate ground reaction forces suggests a portable approach for small fliers. Photo credit: (36). (B) Scaling trends in whole organisms/robots. Maximum forces reported for various organisms compared against small robots flying and tugging. Thrust data from (13) appendix, beetle pulling data from (19) table I, and beetle vertical force data from (20) table III. Data from diagonal lines show constant force/weight ratios.

  • Fig. 3 FlyCroTugs are a modular class of robot with end effectors specialized for a targeted task.

    Two versions shown here are tailored toward opening a door and pulling a door handle. (A) A spring-loaded hook slips underneath a door to pull, and microspines anchor the robot to an indoor carpet or other rough surface. (B) A deployable gripper is mounted to the robot’s frame to grasp a door handle. A pad of gecko-inspired adhesive anchors the robot to a smooth surface, allowing it to pull the handle down.

  • Fig. 4 Energetic efficiency.

    Efficiency of tugging, driving, and flying with different payloads, mload, across a frictional surface (stainless steel on glass, μ = 0.15) for a 100-g FlyCroTug robot equipped with a 25 mm–by–25 mm gecko adhesive pad oriented to engage with horizontal surfaces. COT−1 is plotted, the maxima indicating the most efficient load for a given mode of transportation along with the velocity, v, at which the object moves and electrical power into the system Pin. Driving involves towing the object, pulled behind the robot. Aerodynamic calculations for the flying model are described in section S2 (“Aerodynamic modeling” subsection), assuming steady level flight, and a range of drag coefficients to account for variability in the shape of payload and vehicle being transported.

  • Fig. 5 Scaling trends in actuators.

    Marden proposes two trends of scaling in maximum specific force of actuators (24). “M2/3 actuators” (e.g., molecules, muscles, winches, and linear actuators) move with slower linear motions, with force outputs limited by maximum axial stress, scaling with Fmax = 891M0.67. “M actuators” (e.g., forces from flying birds, bats and insects, swimming and running animals, piston engines, and electric motors) produce force with more rapid cycling and substantial internal forces that risk failure under low cycle fatigue, scaling with a more conservative Fmax = 55M0.99. We overlay our choices of actuators for FlyCroTug thrust and tugging as discussed in the “Scalability” section along with biological data from (13) appendix.

  • Fig. 6 Several FlyCroTug robots were specialized for different applications.

    (A) FlyCroTug robot for infrastructure inspection, as described in the “Single platform for sensor lifting” section. The 100-g robot, equipped with microspines, was guided to a suitable attachment point while paying out a cable attached to a sensor. After attachment, a human operator commanded it to lift a 200-g sensor payload, suspending it alongside a collapsed building. (B) A team of two robots opened a door with specialized end effectors, as described in the “Coordinated team for door opening” section. MAV1 attached a gripper onto the door handle and then pressed gecko-inspired adhesives onto the glass pane to pull the door handle down with 20 N of force generated via the adhesive. In tandem, MAV2 slipped a hook underneath the door, anchored onto the carpeted floor with microspines, and tugged the door open, pulling with 40 N.

  • Fig. 7 Adhesive loading angle and maximum load are dictated by the MAV’s point of attachment.

    (A) The door-handle MAV from Fig. 6 placed a patch of adhesive against the glass door, which dictated a loading angle. A force of 20 N oriented vertically downward was necessary to make the handle move. (B) Data taken from (29) show the maximum available force tangential and normal to a glass surface. The magnitude of this limit surface changed with different surfaces. Loaded at an angle of 7° from tangent, the adhesive can sustain sufficient force. (C) Because of the changing loading angle of the adhesive and door handle, the magnitude of maximum available force, Fmax, is determined by the distance the adhesive is placed below the door handle. This distance also affects the magnitude of net force vector Freq required to pull the handle with a component of 20 N downward.

  • Table 1 FlyCroTug specifications.
    Mass100 g
    Rotor diameter7.62 cm
    Rotor mount distance from center7.3 cm
    Nominal battery voltage7.4 V
    Motor max power draw at Vnominal12.2 W

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/3/23/eaau6903/DC1

    Section S1. Bioinspiration from literature on maximum thrust generation and multimodal locomotion strategies observed in wasps

    Section S2. Energetic calculations for tugging and flying of a payload using a FlyCroTug robot

    Fig. S1. Wasps are limited by their loaded flight muscle ratio (FMRo) when flying with prey.

    Fig. S2. Data and calculations for aerodynamic analysis in the “Aerodynamic modeling” section.

    Table S1. Parameters used in tugging energetic model.

    Table S2. Aerodynamic parameters used for modeling of FlyCroTug flight.

    Movie S1. Lifting a payload for building inspection.

    Movie S2. Coordinated team of two FlyCroTugs opening a door using gecko-inspired adhesive and microspines.

    Movie S3. Initial FlyCroTug prototype lifting 600 g, attaching onto a laboratory tabletop.

    Movie S4. FlyCroTug MAV flying in a cluttered environment.

    References (3743)

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Bioinspiration from literature on maximum thrust generation and multimodal locomotion strategies observed in wasps
    • Section S2. Energetic calculations for tugging and flying of a payload using a FlyCroTug robot
    • Fig. S1. Wasps are limited by their loaded flight muscle ratio (FMRo) when flying with prey.
    • Fig. S2. Data and calculations for aerodynamic analysis in the “Aerodynamic modeling” section.
    • Table S1. Parameters used in tugging energetic model.
    • Table S2. Aerodynamic parameters used for modeling of FlyCroTug flight.
    • References (3743)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Lifting a payload for building inspection.
    • Movie S2 (.mp4 format). Coordinated team of two FlyCroTugs opening a door using gecko-inspired adhesive and microspines.
    • Movie S3 (.mp4 format). Initial FlyCroTug prototype lifting 600 g, attaching onto a laboratory tabletop.
    • Movie S4 (.mp4 format). FlyCroTug MAV flying in a cluttered environment.

    Files in this Data Supplement:

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