Development of Servo-Units for a Compliantly Actuated Quadruped Prototype

117 Pages·2016·26.04 MB·English

MASTER'S THESIS
Development of Servo-Units for a
Compliantly Actuated Quadruped
Prototype
Florian Fischer
2016
Master of Science (120 credits)
Space Engineering - Space Master
Luleå University of Technology
Department of Computer Science, Electrical and Space Engineering
Master Thesis
Development of Servo-Units for
a Compliantly Actuated
Quadruped Prototype
by
Florian Christoph Fischer
Wu¨rzburg February 2, 2016
Abstract
This master thesis deals with the development of servo-motor-units as part of the quadruped
project at the Institute of Robotics and Mechatronics, German Aerospace Center (DLR). To be
able to perform highly dynamic motions such as jumping, the servo-motor-units of a quadruped
robot require to produce high torque and velocity peaks on the one hand while being of compact
sizeandlightweightontheotherhand. Thisisachievedbymeansoftakinganofftheshelfservo-
motor-unit and replacing the electronics by a custom electronics which requests the maximum
power of the motors. The developed servo-motor-unit provides a compact powerful motor with
a good position sensor and a real-time USB link. The firmware enables to command the motor
with a frequency of 1 kHz. The frequency of control loop and the communication can be set
independently from each other. In a second part the development of an automated test system
for motors is described. The measurements showed that performance factors and the efficiency
of the developed servo-motor-unit are almost on the same level of a high-end motor, specially
designed for application in robotic systems.
It is interesting that the servo-motor-unit is almost as efficient as a high-end robot motor, but
is about factor 10 cheaper.
I
Table of Contents
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 State of the art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 The Quadruped project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Detailed problem description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Theory of electric motors 8
2.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Different motor types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.1 AC Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 DC Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Comparison of DC motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4 Brushed DC Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Selection of a brushed DC motor . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.5.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.5.2 BlueBird BMS-2514 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.5.3 SAVOX SV-1270TG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3 Controlling of a DC motor 18
3.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2 Control strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3 System identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.4 Implemented control loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4 Development of the electronics 26
4.1 Requirements concerning the electronics . . . . . . . . . . . . . . . . . . . . . . . 26
4.2 SuperModified V3.0 for servo motors . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.3 Electronics development on the basis of an ATmega328 . . . . . . . . . . . . . . 27
4.4 Electronics development on the basis of an ATmega32u4 . . . . . . . . . . . . . . 29
4.4.1 Short introduction to USB . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.4.2 USB for real time communication . . . . . . . . . . . . . . . . . . . . . . . 31
II
4.4.3 Main components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.4.4 ATmega32u4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.4.5 Functioning of the AS5048A . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.4.6 Functioning of the H-bridge 34931 . . . . . . . . . . . . . . . . . . . . . . 33
4.4.7 Prototype Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.5 Mechanical parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.6 Board development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.6.1 Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.6.2 General PC board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.7 Circuit diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.7.1 Sensor circuit board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.7.2 Micro-controller circuit board . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.7.3 Motor driver circuit board . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.8 Layout of the PCBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.9 Manufacturing and assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.9.1 Populating of the boards. . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.9.2 Assembly of a motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.10 Firmware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.11 The quadruped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5 Performance test of the motor 60
5.1 Reasons for the measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.2 Goals of the measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3 Measuring objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.4 Development of a testbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.4.1 Measuring shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.4.2 Load motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.4.3 Test objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.4.4 Data acquisition system . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.4.5 Fastening system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.4.6 Final test system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.5 Measurements and results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
III
5.5.1 Performance measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.5.2 Stall torque measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.5.3 Application test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.6 Evaluation of the results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
6 Conclusion and outlook 79
A Appendix 89
A.1 Matlab scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
A.2 PC boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
A.3 Testbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
B Eidesstattliche Erkl¨arung 108
IV
List of Figures
1 Illustration of Spirit with the rocker bogie suspension [11] . . . . . . . . . . . . . 1
2 Mount Sharp [12] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3 MIT Cheetah v.2 outdoors[23]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4 BigDog[28] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5 Series elastic actuator[78] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6 CAD sketch of a single leg of the quadruped[78] . . . . . . . . . . . . . . . . . . . 6
7 Overviews of different motor types . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8 Structure of an AC motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9 Circuit of a DC motor[40] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
10 Velocity-torque characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11 SAVOX SV-1270TG[43] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12 Performance test of a SAVOX SV-1270TG motor and the results . . . . . . . . . 17
13 Block diagram of the transfer function for a DC motor . . . . . . . . . . . . . . . 19
14 Current control loop block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 20
15 Velocity control loop block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 21
16 Cascading control loop block diagram for a DC motor . . . . . . . . . . . . . . . 21
17 System identification of a SAVOX SV-1270TG motor . . . . . . . . . . . . . . . . 23
18 SuperModified V3.0 [48] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
19 Prototype board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
20 Hall effect element and sketch of position sensor. . . . . . . . . . . . . . . . . . . 33
21 Circuit of H-bridge and diagram of motor driver . . . . . . . . . . . . . . . . . . 34
22 Prototype board for two motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
23 Picture of the motor as well as CAD drawings of the motor and the magnet holder 36
24 AS5048A sensor circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
25 SAMTEC plug and used pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
26 Pinout of external connector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
27 Different USB ports [63] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
28 Power supply circuit of the micro-controller . . . . . . . . . . . . . . . . . . . . . 42
29 ESD and EMI protection circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
30 Oscillatory circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
V
31 LED HSMF-C114 circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
32 SAMTEC socket and used pinouts . . . . . . . . . . . . . . . . . . . . . . . . . . 45
33 Power supply circuit of the H-bridge . . . . . . . . . . . . . . . . . . . . . . . . . 46
34 Motor terminal and voltage divider . . . . . . . . . . . . . . . . . . . . . . . . . . 46
35 Feedback circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
36 GUI of PADS Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
37 Both sides of the sensor board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
38 CAD drawing of the stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
39 Final production of the PC boards . . . . . . . . . . . . . . . . . . . . . . . . . . 52
40 Ready populated PC boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
41 Final asembled motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
42 Quadruped during jumping test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
43 GUI of the Elmo Application Studio II . . . . . . . . . . . . . . . . . . . . . . . 64
44 Simulink model of the test system . . . . . . . . . . . . . . . . . . . . . . . . . . 67
45 State machine of the testbed logic . . . . . . . . . . . . . . . . . . . . . . . . . . 68
46 CAD drawing of the holding system . . . . . . . . . . . . . . . . . . . . . . . . . 69
47 Final test system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
48 Performance diagrams of the tested motors . . . . . . . . . . . . . . . . . . . . . 72
49 Stall torque diagrams of the tested motors . . . . . . . . . . . . . . . . . . . . . . 75
50 Diagrams of the application tests . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
51 Further diagrams of the application tests. . . . . . . . . . . . . . . . . . . . . . . 107
VI
List of Tables
1 Estimated values of the system identification . . . . . . . . . . . . . . . . . . . . 23
2 Different USB data transfer modes . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3 Structure of a PC board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4 Technical data of TMHS 306 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5 Technical data of SENSO-Wheel SD-LC . . . . . . . . . . . . . . . . . . . . . . . 63
6 Peak efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
7 Maximal mechanical power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
8 Different efficiency due to different supply voltage for the SAVOX SB-2231SG
motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
9 Efficiency without and with logic power consumption . . . . . . . . . . . . . . . 74
10 Power consumption of the logic unit . . . . . . . . . . . . . . . . . . . . . . . . . 74
11 Electrical Work during different jumping sequences . . . . . . . . . . . . . . . . . 78
VII
1 Introduction
1.1 Motivation
A three-stage Delta II rocket was launched from Cape Canaveral Air Force Station on 10th
of June 2003. This rocket transported Spirit to the Mars where it landed on 4th January 2004.
ItwasoneoftworoversoftheMars Exploration Rover Mission whichweredevelopedbyNASA.
The mission goals were the exploration of the climate, nature and geology of the surface of Mars
and the search for water [8]. The terrain on Mars has a rough, rocky surface and presents a
special challenge for mobile robots. To manage these conditions each rover have six wheels each
with an integrated motor mounted on a rocker-bogie suspension.
Classical four wheeled vehicles are able to get
over vertical obstacles with a height equal to the
height of the axis of their wheels. The rocker-
bogie system ensures that in rough, uneven ter-
rain all six wheels stay on the ground which can
be seen in figure 1. The height of the obstacles
whichcanbeovercomewiththisconstructionde-
pends on the lengths of the suspension, the pos-
Figure1: IllustrationofSpiritwiththerocker
sible angle and the diameter of the wheels. In
bogie suspension [11]
case of the mars rover it is more than the diam-
eter (250mm) of the wheels [9]. The mobility of the the rovers was highly increased with this
construction. Figure 2 was taken by Curiosity, another rover on Mars on 9th September 2015
[8] [12]. It shows the higher regions of Mount Sharp. The possibility to reach the top of such a
mountain with a rover even with its improved mobility is without question very small. Finding
an appropriate path to the top through this rough and steep area is a challenging task with
uncertain success for a wheeled vehicle. To explore such terrain, different locomotion ideas and
systems have to be developed.
In 1990, the NASA already thought about using legged robots for the exploration of Mars [1].
At the moment they are working on a humanoid robot called Valkyrie which should land on
Mars before humans do and prepare the landing side [13] [14].
Not only on distant planets but also on earth there is a broad field of operating range for legged
1