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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Roland Siegwart, Margarita Chli, Martin Rufli
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Locomotion Concepts
Spring 2016
Locomotion Concepts 01.03.2016
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
On ground
Locomotion Concepts 2
Locomotion Concepts: Principles Found in Nature
01.03.2016
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Nature came up with a multitude of locomotion concepts Adaptation to environmental characteristics Adaptation to the perceived environment (e.g. size)
Concepts found in nature Difficult to imitate technically Do not employ wheels Sometimes imitate wheels (bipedal walking)
Most technical systems today use wheels or caterpillars Legged locomotion is still mostly a research topic
01.03.2016Locomotion Concepts 3
Locomotion Concepts
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Biped walking mechanism not too far from real rolling rolling of a polygon with side length equal
to the length of the step the smaller the step gets, the more the
polygon tends to a circle (wheel)
But… rotating joint was not invented by nature Work against gravity is required More detailed analysis follows later in this
presentation
01.03.2016Locomotion Concepts 4
Biped Walking
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
number of actuators structural complexity control expense energy efficient terrain (flat ground, soft
ground, climbing..) movement of the involved
masses walking / running includes up
and down movement of COG some extra losses
01.03.2016Locomotion Concepts 5
Walking or rolling?
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Locomotion physical interaction between the vehicle and its environment.
Locomotion is concerned with interaction forces, and the mechanisms and actuators that generate them.
The most important issues in locomotion are:
01.03.2016Locomotion Concepts 6
Characterization of locomotion concept
stability number of contact points center of gravity static/dynamic stabilization inclination of terrain
characteristics of contact contact point or contact area angle of contact friction
type of environment structure medium (water, air, soft or hard
ground)
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Legged systems can overcome many obstacles
But it is quite hard to achieve this since many DOFs must be controlled in a coordinated way the robot must see detailed elements of the terrain
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Why legged robots?
Locomotion Concepts 01.03.2016
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Highly integrated leg design large range of leg motion
allowing for complex maneuvers “static” walking
Legged Robotics | Impressive MobilityALoF – The Quadruped Robot I
http://leggedrobotics.ethz.ch/
01.03.2016Locomotion Concepts 8
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
A minimum of two DOF is required to move a leg forward a lift and a swing motion. Sliding-free motion in more than one direction not possible
Three DOF for each leg in most cases (as pictured below) 4th DOF for the ankle joint might improve walking and stability additional joint (DOF) increases the complexity of the design and
especially of the locomotion control.
01.03.2016Locomotion Concepts 9
Number of Joints of Each Leg (DOF: degrees of freedom)
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
The gait is characterized as the distinct sequence of lift and release events of the individual legs it depends on the number of legs. the number of possible events N for a walking machine with k legs
is:
For a biped walker (k=2) the number of possible events N is:
For a robot with 6 legs (hexapod) N is already
01.03.2016Locomotion Concepts 10
The number of distinct event sequences (gaits)
! 12 kN
6123! 3! 12 kN
800'916'39! 11 N
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Statically stable
Bodyweight supported by at least three legs
Even if all joints ‘freeze’ instantaneously, the robot will not fall
Safe, slow and inefficient
Dynamic walking
The robot will fall if not continuously moving
Less than three legs can be in ground contact
fast, efficient and demanding for actuation and control
01.03.2016Locomotion Concepts 11
Dynamic Walking vs. Static Walking
CoGCoG
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Most prominent example: Boston Dynamics
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Legged Robotics Today | Finally, a breakthrough?
Locomotion Concepts 01.03.2016
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Forward falling combined with passive leg swing Storage of energy: potential kinetic in combination with low
friction
01.03.2016Locomotion Concepts 13
Case Study: Passive Dynamic Walker
C y
outu
bem
ater
ial
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Efficiency = cmt = |mech. energy| / (weight x dist. traveled)
Locomotion Concepts 14
Efficiency Comparison
C J. Braun, University of Edinburgh, UK
01.03.2016
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Most prominent example: Boston Dynamics 2.2016
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Legged Robotics TodayFinally, a breakthrough?
Locomotion Concepts 01.03.2016
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli 01.03.2016Locomotion Concepts 16
Towards Efficient Dynamic Walking: Optimizing Gaits
C Structure and motion laboratory University of London
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli Locomotion Concepts 17
Efficient Walking and Running | serial elastic actuation
01.03.2016
https://www.youtube.com/watch?v=6igNZiVtbxU
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli 01.03.2016Locomotion Concepts 18
StarlETH – ein Laufroboter mit “elastischen Gelenken” https://www.youtube.com/watch?v=Tj1wreifYhU
https://www.youtube.com/watch?v=IO_sZ6FBAwQ
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
High mobility “to go where today only humans can go”
10 kg of payload 2 h of continuous operations
01.03.2016Locomotion Concepts 19
ANYmalan electrically actuated dog for real-world scenarios
Prof. Marco Hutter
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Wheels are the most appropriate solution for most applications
Three wheels are sufficient to guarantee stability
With more than three wheels an appropriate suspension is required
Selection of wheels depends on the application
01.03.2016Locomotion Concepts 20
Mobile Robots with Wheels
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
a) Standard wheel: Two degrees of freedom; rotation around the (motorized) wheel axle and the contact point
b) Castor wheel: Three degrees of freedom; rotation around the wheel axle, the contact point and the castor axle
01.03.2016Locomotion Concepts 21
The Four Basic Wheels Types
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
c) Swedish wheel: Three degrees of freedom; rotation around the (motorized) wheel axle, around the rollers and around the contact point
d) Ball or spherical wheel: Suspension technically not solved
01.03.2016Locomotion Concepts 22
The Four Basic Wheels Types
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Stability of a vehicle is be guaranteed with 3 wheels If center of gravity is within the triangle which is formed by the
ground contact point of the wheels. Stability is improved by 4 and more wheel however, this arrangements are hyper static and require a flexible
suspension system. Bigger wheels allow to overcome higher obstacles but they require higher torque or reductions in the gear box.
Most arrangements are non-holonomic (see chapter 3) require high control effort
Combining actuation and steering on one wheel makes the design complex and adds additional errors for odometry.
01.03.2016Locomotion Concepts 23
Characteristics of Wheeled Robots and Vehicles
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli 01.03.2016Locomotion Concepts 24
Different Arrangements of Wheels I
Two wheels
Three wheels
Omnidirectional Drive Synchro Drive
COG below axle
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
All wheels are actuated synchronously by one motor defines the speed of the vehicle
All wheels steered synchronously by a second motor sets the heading of the vehicle
The orientation in spaceof the robot frame will always remain the same It is therefore not possible
to control the orientation of the robot frame.
01.03.2016Locomotion Concepts 25
Synchro Drive
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Four wheels
Six wheels
01.03.2016Locomotion Concepts 26
Different Arrangements of Wheels II
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Four powered castor wheels with active steering Results in omni-drive-like behaviour Results in simplified high-level planning (see chapter 6)
01.03.2016Locomotion Concepts2
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Case Study: Willow Garage‘s PR2
C W
illow
Gar
age
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Movement in the plane has 3 DOF thus only three wheels can be independently
controlled It might be better to
arrange three swedishwheels in a triangle
01.03.2016Locomotion Concepts 28
CMU Uranus: Omnidirectional Drive with 4 Wheels
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Purely friction based
01.03.2016Locomotion Concepts 29
Wheeled Rovers: Concepts for Object Climbing
Change of center of gravity(CoG)
Adapted suspension mechanism with
passive or active joints
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Passive locomotion concept 6 wheels two boogies on each side fixed wheel in the rear front wheel with spring
suspension Dimensions length: 60 cm height: 20 cm
Characteristics highly stable in rough terrain overcomes obstacles up to
2 times its wheel diameter
01.03.2016Locomotion Concepts 30
Climbing with Legs: Shrimp (ASL EPFL/ETH)
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Forces acting on a profile with relative wind speed
Lift force Drag force Moment
01.03.2016Locomotion Concepts 33
Flying « Locomotion »
Leading edge
RelativeWind
Trailing edge
Chord
Chord length
25 % Chord
Angle of attack
Thickness
Fl
FdM
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Helicopters: < 20 minutes Highly dynamic and agility
Fixed Wing Airplanes: > some hours; continuous flights possible Non-holonomic constraints
Blimp: lighter-than-air > some hours (dependent on wind conditions); Sensitive to wind Large size (dependent on payload)
Flapping wings < 20 minutes; gliding mode possible Non-holonomic constraints Very complex mechanics
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UAV (Unmanned Aerial Vehicles) | flight concepts
Festo BionicOpter01.03.2016Locomotion Concepts
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
Naro (2009)| the tuna robot
Taratuga (2012)| the turtle robot
Nanins (2013)| the modular underwater robot
Sepios (2014, with Disney)| the Kalmar robot
01.03.2016 35
AUV (Autonomous Underwater Vehicles)
– designed by students
Locomotion Concepts
https://www.youtube.com/watch?v=GeCLL2RWV1c
https://www.youtube.com/watch?v=L61O2CmZCc4
https://www.youtube.com/watch?v=pqy_NSHcGLs
https://www.youtube.com/watch?v=r5uGmWRZKGU
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ASL Autonomous Systems Lab
Autonomous Mobile RobotsRoland Siegwart, Margarita Chli, Martin Rufli
The end
36Locomotion Concepts 01.03.2016