Landing and Perching on Vertical Surfaces with Microspines for - - PowerPoint PPT Presentation

Landing and Perching

• n Vertical Surfaces

with Microspines for Small UAVs

Alexis Lussier Desbiens and Mark Cutkosky Biomimetics and Dextrous Manipulation Laboratory Stanford University UAV’09, Reno

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Mass (g) Endurance (hour)

Dragon Eye Raven B Draganflyer WASPIII UofF Gator Black Widow Delfly II Delfly Micro Skybotic CoaX Aerosonde Rotomotion SR200 Fixedwing Rotarywing Flappingwing

Why should we perch?

• Small airplanes have limited

endurance

• Other techniques can only

provide limited benefit: – Energy extraction from gusts [Patel & Kroo 2006] – Optimization [Grasmeyer 2001]

• Perching would increase

mission duration to extended period of time (i.e. days or weeks)

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Other Advantages of Perching

• Stable vantage point while

perched vs fast dynamics of small UAVs during flight

• Possibility of landing and

physically interacting with the landing surface.

• Perching combines the best of

climbing and flying:

– Agile and fast while flying – Can cover long distances – Limited energy consumption while perched – Wait for better weather conditions – Quiet (no motor noise)

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Why Vertical Surfaces?

• Walls are common in urban

environment

• Walls are easy to detect (at least

easier than a passive wire or pole)

• Walls provide a large surface to

perch on

• Walls remain relatively free of

debris.

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Related Work

• On agile flight:

– J. How et al. (MIT) on indoor flying and hovering – P. Oh et al. (Drexel) on autonomous hovering

• On perching aerodynamics & control:

– Wickenheiser et al. (Cornell) on vehicle morphing for perching – Tedrake et al. (MIT) on controllability of fixed- wing plane for perching on a wire

• No explicit consideration of the

landing system

• Slow maneuvers sensitive to

disturbances

• Use of highly accurate motion capture

system/sensors to enable control

[Cory & Tedrake, 2008] [Wickenheiser, 2007] [Green & Oh, 2006]

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Research Goals

Allow a small airplane to perch autonomously on a variety of vertical surfaces Keep the system simple and lightweight Maintain the efficiency of conventional airplanes

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Our Approach

• Quick maneuver to minimize

disturbance effects

• Focus on the suspension

and spines to simplify sensing and control

• Everything onboard!

Sonar Spines Suspension Elevator Paparazzi Autopilot & sensors

2) Wall detection 5) Rest 1) Approach 3) Pitch up 4) Touchdown

Modified Flatana Airplane

Sticking to the wall

• Small spines (10-15 µm tip

radius) that catch and hang on asperities

• Individual spine suspensions

distribute the load

• Why spines?

– They require no power – They work on a wide range of outdoor surfaces – They are relatively unaffected by films

• f dirt and moisture

– They leave no trace of their passage – They provide directional adhesion (multiple loading cycles)

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1 2 3 4 5 Approach volume Loading Forces Volume y x

Spine Limit Surface

• Spines require a particular loading cycle

to engage asperities on the surface without slipping or failing

Loading cycle

• 1. Normal force
• 2. Pull down
• 3. Pull away

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load

Shear force Normal force

Adhesion Compression

Different angles of surface asperities Surface failure Coulomb friction

1/µ

Spine Performances

• Used on Spinybot and RISE to

climb brick, stucco, concrete and rock

• Climbing robot spine

suspensions take advantage

• f the robot's control over foot

trajectories and forces

• With UAVs, the challenge is to

provide desired forces and velocities at the instant of contact with the wall

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Suspension

• Tests reveal that vertical

rebound was the main failure mode

• Goal is to find the optimal

components (spring, damper, nonlinear elements) to:

– Minimize peak landing force – Minimize suspension travel – Prevent negative force, to stay on the wall (vertical rebound)

• Maximum energy dissipation

achieved with constant force during the impact

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Simple Model

• Vertical model of a spring,

damper and coulomb friction suspension

• Damper creates forces

dependent on initial velocity

• Coulomb friction provides

constant force

• Balance friction and

damper to get desired properties

F B K M g v0

0.05 0.1 0.15 0.2 0.03 0.02 0.01 Position Airplane (m) 0.05 0.1 0.15 0.2 20 20 40 Force on spines(N) time (sec) Fric = 33 N = 0.62 = 0.29, Fric = 11 N Spine rebound region

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Non-linear properties

• Material properties can

be used to create constant force

• Damping scaled w.r.t

position and velocity:

• Urethane foam exhibits

reduced damping at high velocity

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b = Fmax − kx(t) v(t)

0.05 0.1 0.15 0.2 0.25 0.3 5 10 15 20 25 30 35

• Max. Velocity (m/s)

Viscous Damping (Ns/m)

Rubber CONFOR foam

Suspension Designs

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k* = 780 N/m * = 0 k* = 695 N/m * = 0.15 k* = 871 N/m * = 0.38

Leg Structure

Foam hip Balsa/Carbon femur Sorbothane knee Carbon tibia Foam ankle Spines Attachment points

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Planar Model

Intermittent contact

• Simple cartesian suspension

model for now...

• Wing and control surfaces

modeled as flat plates [Cory &

Tedrake 2008]

• Equations of motion generated

using Kanes Dynamics

• Used to study the effect of:
• Incoming velocities
• Suspension parameters (foot

location, linkage non-linearity, etc.)

• Improve landing forces on the

spines

5 10 15 20 10 5 5 10 15 20 25 30

Shear Force (N) Normal Force (N)

Forces on spines during landing

= 0.1 = 0.5 = 0.8

Planar Landing Simulation

• Loading trajectory is

important

• Low damping ratio:

– Ratio Fn/Fs too high – Rebound

• High damping ratio:

– High peak force

• Moderate damping:

– Ratio Fn/Fs within adhesion limit surface

Adhesion limit surface

Rebound Steady state Initial Contact

Trajectory/Control

• Previous research focuses
• n low contact velocity:

– Low controllability at low velocity – The longer the approach, the riskier it gets (gust, etc)

• Spines need normal force to

engage, we want forward velocity!

• Use the dynamics of the

plane to reach the successful perching envelop

• f the suspension

19 Feedforward kick by the elevator Touchdown possible Pitch up maneuver Low angular velocity

Perching Strategy

• 1. Fly toward the wall at about 9 m/s
• 2. Detect the wall with ultrasonic sensor
• 20 Hz, 6 m range
• 3. Pitch up to slow down for landing (take about 2-3m)
• 4. Touchdown possible for about 1.5 to 2 m before impact
• 5. Touchdown at about 2 m/s, let the suspension absorb

the impact

20 Pitching up Successful landing Waiting for wall detection

6 5 4 3 2 1 0.8 0.6 0.4 0.2 x (m) y (m)

Simulated trajectory of the perching maneuver

Onboard Sensors

• Simple wall detection using

the LV-Maxsonar: – Range of 6 m – Update rate of 20 Hz

• Onboard accelerometer and

gyro are used for data analysis

• Combined using a second
• rder complementary filter:
• Need something better!!!

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Pitch (deg) time (sec)

Different techniques for measuring pitch

Complementary Filter Rate Gyro Integration Gravity measurement Sensitive to vibrations Drifting

τs + 1

τs + 1

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θ(s) = τ 2s (τs + 1)2 ˙ θ(s) + 2τs + 1 (τs + 1)2 θ(s)

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Touchdown possible Pitch up maneuver Elevator up Wall detection

9 m/s 2 m/s

x y

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30 successful landings (10 autonomous, 20 in manual control)... out of 40!

• Pitch = 60 to 105 deg
• Pitch rate = 0 to 200 deg/s
• vx = up to 3 m/s
• vy = up to 2.7 m/s (downward)

Landing Data

• Wall detection at 6m
• Maneuver duration
• f less than 0.7 sec
• Ready to perch

starting at t = 1.3 sec

• Lands at 1 m/s
• Most of the elevator

action happens at low angle of attack

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 50 100 time (sec) Pitch (deg) 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2 4 6 Wall Distance (m) time (sec) 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2 4 6 8 time (sec) vx (m/s) 20 40 60 80 100 120 140 160 180 0.5 0.5 1 Moment (Nm) Angle of attack (deg) Trim flight Elevator up Wall detection Throwing Autonomous flight Pitch up maneuver Touch Down

Improvement and future work

• Land on more

challenging surfaces

• Trajectory optimization

– Maximize horizontal distance travelled while ready to perch – Add propulsion

• Real conditions

landing (windy, side approach, etc.)

• Take off from the wall!!

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Conclusion

• A properly tuned mechanical

system simplifies the perching maneuver

• Suspension is essential for:

– Proper spine engagement – Maintaining controllability – Reducing control & sensor requirements

• Only 7% (28g) of total

airplane mass

• Perching is interesting for a

wide range of applications

• Perching is pretty cool!

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Questions?

http://bdml.stanford.edu - alexisld@stanford.edu

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