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Research Papers

A Sarrus-Based Passive Mechanism for Rotorcraft Perching

[+] Author and Article Information
Michelle L. Burroughs

Department of Mechanical Engineering,
University of Utah,
Salt Lake City, UT 84112
e-mail: burroughs87@gmail.com

K. Beauwen Freckleton

Department of Mechanical Engineering,
University of Utah,
Salt Lake City, UT 84112
e-mail: bfreckleton@gmail.com

Jake J. Abbott

Mem. ASME
Department of Mechanical Engineering,
University of Utah,
Salt Lake City, UT 84112
e-mail: jake.abbott@utah.edu

Mark A. Minor

Mem. ASME
Department of Mechanical Engineering,
University of Utah,
50 S Central Campus Dr, RM 2110,
Salt Lake City, UT 84112
e-mail: mark.minor@utah.edu

1Corresponding author.

Manuscript received November 3, 2014; final manuscript received May 14, 2015; published online August 18, 2015. Assoc. Editor: Satyandra K. Gupta.

J. Mechanisms Robotics 8(1), 011010 (Aug 18, 2015) (11 pages) Paper No: JMR-14-1314; doi: 10.1115/1.4030672 History: Received November 03, 2014

This work examines a passive perching mechanism that enables a rotorcraft to grip branchlike perches and resist external wind disturbance using only the weight of the rotorcraft to maintain the grip. We provide an analysis of the mechanism’s kinematics, present the static force equations that describe how the weight of the rotorcraft is converted into grip force onto a cylindrical perch, and describe how grip forces relate to the ability to reject horizontal disturbance forces. The mechanism is optimized for a single perch size and then for a range of perch sizes. We conclude by constructing a prototype mechanism and demonstrate its use with a remote-controlled (RC) helicopter.

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Figures

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Fig. 1

Our mechanism, shown here attached to the skids on the bottom of an RC helicopter, uses a bilateral configuration of Sarrus-based linkages to passively grip cylindrical perches

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Fig. 2

A Sarrus linkage converts the pure translational motion between the top and bottom plates into angular motion of the plates in the connecting linkages. The two connecting linkages must be out-of-plane to keep the top and bottom plates parallel. Public domain image [3].

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Fig. 3

Kinematic description of the Sarrus-based perching mechanism considered in this paper, with the rotorcraft’s weight W causing the mechanism to grip on a cylindrical perch of a radius r. The mechanism is described by a set of constant geometric parameters: b, L, T, and Ψ. The mechanism is symmetric, and an out-of-plane linkage that is identical to the two side linkages (not shown) enforces that the top and bottom plates remain parallel as in Fig. 2. An additional set of parameters are used to describe the configuration of the mechanism on a given perch: θ, h, and Te. Pin joints are indicated with small circles. Note that a bottom-side link and a toe form a single rigid link joined to the bottom plate with a pin joint.

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Fig. 4

Right side of symmetrical Sarrus-based perching mechanism, broken into three components: (a) the top plate, (b) the top side linkage, and (c) the bottom half of the mechanism, which includes the bottom side linkage and its rigidly attached toe, attached to the bottom plate at a pin joint. Small circles represent pin joints.

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Fig. 5

Optimal design for a single perch radius, r. The link length L and grip angle θmin are set arbitrarily.

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Fig. 6

Effect of varying individual parameters on the normalized force disturbance F˜D, starting from the optimized design of Fig. 5. The parameters varied include: b˜, Ψ(rad), L˜, and θmin (rad). The optimized design is indicated with a circle (the choices of L˜ and θmin are still user-defined and arbitrary). Each parameter is varied individually while holding all other parameters at the initial values (b˜=2,L˜=1,θmin=π/18 rad, and a˜=3.255).

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Fig. 7

Normalized force disturbance F˜D versus distance to the center of pressure a˜ (with b˜=2, θmin=π/18 rad, and L˜=1)

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Fig. 8

Minimum relative perch size s versus minimum grip angle θmin (deg) with b˜=2

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Fig. 9

Normalized force disturbance versus relative perch size for four different mechanisms that have each been optimized for a specified range of perch sizes (with L˜=1,θmin=π/18 rad, and a˜=3.255 in all cases). The  “range” s=1 corresponds to the optimal design for a single perch size.

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Fig. 10

Normalized force disturbance versus normalized link length for four different mechanisms that have each been optimized for a specified range of perch sizes (with θmin=π/18 rad, and a˜=3.255 in all cases). The range s=1 corresponds to the optimal design for a single perch size.

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Fig. 11

Normalized force disturbance versus minimum grip angle (deg) for four different mechanisms that have each been optimized for a specified range of perch sizes (with L˜=1, and a˜=3.255 in all cases). The range s=1 corresponds to the optimal design for a single perch size.

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Fig. 12

Model of the prototype, optimized for the range of perch sizes of s = [0.5 1]: (a) the prototype on the smallest perch in range and (b) the prototype on the largest perch in range

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Fig. 13

Video images of the descent and ascent of helicopter with attached perching mechanism on 42 mm (top row) and 21 mm (bottom row) diameter PVC perches. The system is manually lowered onto the perch using a string in (a) and (b), the string is allowed to go completely slack in (c) to allow the complete weight of the helicopter to generate a grip and pause there, and then the string is used to lift the helicopter off the perch in (d) and (e). Top row: (a) t = 0 s, (b) t = 1 s, (c) t = 2.2 s, (d) t = 3.4 s, and (e) t = 3.7 s and bottom row: (a) t = 0 s, (b) t = 0.6 s, (c) t = 1.9 s, (d) t = 4.2 s, and (e) t = 4.5 s.

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Fig. 14

Perching on various objects: (a) toroid, (b) chair back, (c) edge of pallet, (d) square railing, (e) human fingers, (f) tree branch, (g) edge of garbage can, and (h) edge of rock

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