Machine and behaviour co-design of a powerful minimally actuated hopping robot

127 Pages·2015·6.77 MB·English

Machine and behaviour co-
design of a powerful minimally
actuated hopping robot
J.J.M. Driessen
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BioMechanical Engineering (BMechE)

Machine and behaviour co-design of a
powerful minimally actuated hopping
robot
Master of Science Thesis
For the degree of Master of Science in Mechanical Engineering at Delft
University of Technology
J.J.M. Driessen
Friday 30th October, 2015
Faculty of Mechanical, Maritime and Materials Engineering (3mE) · Delft University of
Technology
The work in this thesis was supported by Istituto Italiano di Tecnologia (IIT). Their cooper-
ation is hereby gratefully acknowledged.
Copyright (cid:13)c BioMechanical Engineering (BMechE)
All rights reserved.
Cover Art: Gattoni, Ugo. Panic. 2012. Caravan Palace album poster.
Delft University of Technology
Department of
BioMechanical Engineering (BMechE)
The undersigned hereby certify that they have read and recommend to the Faculty of
Mechanical, Maritime and Materials Engineering (3mE) for acceptance a thesis
entitled
Machine and behaviour co-design of a powerful minimally actuated
hopping robot
by
J.J.M. Driessen
in partial fulfillment of the requirements for the degree of
Master of Science Mechanical Engineering
Dated: Friday 30th October, 2015
Supervisor(s):
Prof.Dr. R. Featherstone
Dr.ir. H. Vallery
Reader(s):
Prof.Dr.ir. M. Wisse
Dr. S.H. Hossein Nia Kani

Abstract
This thesis presents the first steps of a design study on the robust hopping and balancing
robot Skippy. The purpose of the overall design study is to challenge a new design approach
for robots with high physical performance. This approach comprises an iterative study of
machine (physical system) and behaviour (action strategy) co-design. Skippy is maximally
simple in that it has only two actuators to control itself in 3D, and it is to be made from
COTS components. It should be able to hop up to heights of 4m and in addition be able to
balance, do acrobatic manoeuvres and survive its crashes.
The goal of this thesis is to design a realistic action strategy and mechanism for Skippy in 2D
to hop up to 4m that is compliant with Skippy’s required additional abilities and physical
limitations. In 2D, Skippy only requires one actuator.
A study that uses the new design approach is presented in this thesis. The initial model of
Skippy assumes a perfect actuator and simplified transmissions. The thesis proceeds step-
by-step to a more realistic model. The physical system is designed to consist of linkage
mechanisms and two non-linear passive elastic elements. The action strategy is designed such
that Skippy acts in saturation. Saturation is determined by various physical limits such as
the limited nut velocity of the driveline’s ball screw and electrical limitations of the motor’s
armature. The system’s behaviour is improved by a redesign of the physical system that
moves the cause of the saturation, which increases the mechanical power output of the motor.
This redesign includes tuning of inertial, dimensional and stiffness parameters. It is shown
that Skippy is able to reach its target height while having basic control over lift-off momenta,
which is required for performing acrobatic manoeuvres. In addition, Skippy’s balancing per-
formance has been investigated. By adjusting the inertial and dimensional parameters that
favour balance, the jumping height is reduced to 3.8m. This suggests that it is important
to take additional abilities, like balancing, at an early stage into consideration for design
decisions of the iterative design process.
Step-by-step introduction and alteration of parts and their parameters in alternation with
restrictions and secondary requirements have allowed for well-understood system behaviour
and have built towards a more realistic system that works.
Master of Science Thesis J.J.M. Driessen
ii
J.J.M. Driessen Master of Science Thesis
Table of Contents
Acknowledgements vii
1 Introduction 1
1-1 Problems in legged robotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1-2 Introducing Skippy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1-3 Goal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1-4 Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1-5 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 From idea to model 7
2-1 Setting the research scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2-1-1 Morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2-1-2 Energy and dimension calculations . . . . . . . . . . . . . . . . . . . . . 9
2-1-3 Transmission: mechanisms and components . . . . . . . . . . . . . . . . 10
2-1-4 Passive ankle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2-1-5 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2-2 A first 2D model of Skippy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2-2-1 Dynamic model description . . . . . . . . . . . . . . . . . . . . . . . . . 16
2-2-2 Thrust conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2-2-3 Interim results: locked ankle . . . . . . . . . . . . . . . . . . . . . . . . 19
2-2-4 Ankle spring profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2-2-5 Knee torque profile: thrust and steering . . . . . . . . . . . . . . . . . . 20
2-2-6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Master of Science Thesis J.J.M. Driessen
iv Table of Contents
3 Inverse dynamics approach 25
3-1 Knee torque profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3-1-1 Parabolic thrust profile . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3-1-2 Continuous fuzzy transition . . . . . . . . . . . . . . . . . . . . . . . . . 29
3-1-3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3-2 Driveline modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3-2-1 Linear actuation kinematics . . . . . . . . . . . . . . . . . . . . . . . . . 31
3-2-2 Spring and driveline inertia . . . . . . . . . . . . . . . . . . . . . . . . . 36
3-2-3 Inverse dynamics control . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3-2-4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4 Feedforward approach 45
4-1 Applying rotor torques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4-2 Electrical limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4-2-1 Electric circuit modelling . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4-2-2 Current saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4-2-3 Voltage saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4-2-4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4-3 Velocity limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4-3-1 Nut velocity saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4-3-2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4-4 Energy analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4-4-1 Ball screw friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4-4-2 Energy flow analysis and results . . . . . . . . . . . . . . . . . . . . . . 56
4-5 Steering analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4-5-1 Simplified steering strategy . . . . . . . . . . . . . . . . . . . . . . . . . 57
4-5-2 Interim steering results . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4-5-3 Bilinear spring profile parameters . . . . . . . . . . . . . . . . . . . . . . 58
4-5-4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4-6 Energy-based model improvements . . . . . . . . . . . . . . . . . . . . . . . . . 61
4-6-1 Increase mechanical work . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4-6-2 Improving energy conversion . . . . . . . . . . . . . . . . . . . . . . . . 66
4-6-3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
J.J.M. Driessen Master of Science Thesis