1. SNAKELIKE ROBOTS LOCOMOTIONS CONTROL
R U S S I A N S T A T E S C I N T I F I C C E N T R E
C E N T R A L R E S E A R C H A N D D E S I G N I N S T I T U T E O F
R O B O T I C S A N D T E C H N I C A L C Y B E R N E T I C S
SNAKELIKE ROBOTS
LOCOMOTIONS CONTROL
Oleg Shmakov
CRDI RTC DEPARTMENT OF SPbSPU
Joint Advanced Student School 2006
Saint Petersburg
Course 5: Mechatronics – Foundations and Applications
5th APRIL 2006

2. Introduction Why snakelike robots? Biomechanics of snakes Review
Mechanic model of snakelike robots
Mathematical model of snakelike robots
Hardware realization control
Snakelike robot CRDI RTC
Conclusion
Nowadays snakelike robots are an actively upcoming area in robotics. Frequently the term snake like robot is applied to all hyper redundant robots; those are consisted from modules connected by active or passive joints. Among these devices the real snakelike robots are those that use the wave movements of the successive module chains for locomotion on hard surfaces and in liquids. At most attention of specialist's serpentine designs is explained by their desire to use the unique possibilities of the limblesses to adapt to surfaces and environments. These possibilities are relatively harmonize with the simple anatomy.
The initial developments of the snakelike robots were executed in 70-s by Hirose's group of investigators. He made the analysis of limblesses motions experimental data and suggested mathematical description of the snake's instant form. The curve was called "serpenoid" and is used for the snakelike robot's control assignment. The first designs of Hirose's snakelike robots had modules with small passive wheels. The same design was used in projects of Gavin Miller.
Robot that has no wheeled supports for its motion is more close to the biological analogs. The first successful developments of this type of robot appeared at the end of the 90-ies at Carnegie Mellon University. At the same time active development of algorithms of snakelike robot locomotion control was carried on. In the articles by Ostrovskiy, Chirikian, Choset, Dowling and other scientists various decisions for control generating that could provide some locomotion modes in the snakelike robots have been rendered.
It is necessary to point out that for a long time a rational model of the snake's movement has not been presented. Such model would be very helpful to develop effective algorithms to control movements of the snakelike robots that have no wheels. One of quoted movement models has been offered in by A.I. Dobroluybov. The mechanical moving model of running waves of the deformation having local motionless contact, has allowed to give qualitatively true description of factors influencing on moving of a flexible body with use various locomotion modes. Unfortunately, it did not contain the proved mathematical description.
In A.A. Ivanov suggested some mathematical models of the flexible body dynamics and kinematics. These mathematical models allow to describe experimental data on snakes' kinematics within the limits of biological experiment precision. Having mathematical models let us make right constructive decisions not only on mechanical structure of the snakelike robot but also on the purposeful movement system control with the use of different modes of locomotion.
I am going to take a review of the snakelike robot constructions as well as to report on biometrical requisites for development of such devices and to give a description of mechanical and mathematical models of the reptiles' movement. I would like to inform you about the real hardware of the snakelike robot movement control and to give a detailed description of the snakelike robot developed in our Scientific Research & Design Institute of Robotics and Technical Cybernetics. This model have already performed showing different modes of locomotion.
Oleg A. Shmakov
Snakelike robots locomotions control

3. Why snakelike robots? Advantages
Stability
Terrainability is the ability of a vehicle to traverse rough terrain
Traction is the force that can be applied to propel a vehicle
Redundant
Simple anatomy
Oleg A. Shmakov
Snakelike robots locomotions control

4. Why snakelike robots? Applications
Search and Rescue
Examination blockages after earthquake
Planet’s exploration
Medical applications
Examination hard-to-reach areas
Tube inspection
Bio Terrorist
Remote sampling
Military inspection …

5. Biomechanics of snakes Vertebrate
Snake vertebral articulation is one of the most complex of all vertebrates.
Real snakes have vertebrae
Oleg A. Shmakov
Snakelike robots locomotions control

6. Biomechanics of snakes Locomotion modes
Lateral undulation
Sidewinding
Propulsion (with creeping)
Concertina
Rectilinear movement
Oleg A. Shmakov
Snakelike robots locomotions control

7. Review Design snakelike robots
Non-modular
Modular
WITH WHEELS
WITHOUT WHEELS
Oleg A. Shmakov
Snakelike robots locomotions control

8. Review Hirose & Umetami - SERPENOID
the waveform that the snake assumes during creeping movement is a curve which changes sinusoidally along the curvature of the body, and a formula for this, called a serpenoid curve.
Oleg A. Shmakov
Snakelike robots locomotions control

9. Review Hirose & Umetami – ACM III
Active Cord Mechanisms – ACM
Wheeled robots
Robots that could perform lateral undulation
Hirose’s development of modeling and control first derived expressions of force and power as functions of distance and torque along the curve described by the snake.
Comparisons with natural snakes across constant friction surfaces showed close agreement between the serpenoid curve and the empirical data.
Snakes quickly adapt locally to variations in terrain and environment.
The control took the form of angle commands at each joint
Oleg A. Shmakov
Snakelike robots locomotions control

10. Review Hirose & Umetami – ACM R3
Oleg A. Shmakov
Snakelike robots locomotions control

11. Review Carnegie Mellon University – Kevin Dowling
Oleg A. Shmakov
Snakelike robots locomotions control

12. Review Carnegie Mellon University – Biorobotics Lab
Oleg A. Shmakov
Snakelike robots locomotions control

13. Mechanic model of snakelike robots Dobroluybov A.I.
«genetic relationship» wheels and waves and
Snakes are using rolling motion ”
Some points of a moving body or set of bodies during movement should vary periodically roles: mobile points become motionless and on the contrary. On character of this procedure of locomotion can be divided into two big classes: pacing when reference points of a body only during some moments of time pass from motionless in a mobile condition and back, and rolling when these transitions are carried out continuously. Snakes can move by pacing and rolling. Carry of points of a support of the essences, moving in the way rolling, can be various.
Oleg A. Shmakov
Snakelike robots locomotions control

14. Mechanic model of snakelike robots Ivanov A.A.
Oleg A. Shmakov
Snakelike robots locomotions control

15. Mechanic model of snakelike robots Ivanov A.A.
Shank movement
Lateral bending
Rectilinear movement curving (without creeping)
Concertina
Propulsion (with creeping)
Side winding
Oleg A. Shmakov
Snakelike robots locomotions control

16. Mathematical model of snakelike robots How to control?
Random Search
Hill climbing
Simulated
Annealing
Neural Nets
Response Surface Methods
Genetic Algorithms
Trigonometric forms
Fourier
Parametric curves
Bayesian optimization algorithms
DOWLING
CONRO
TANEV CMU – Biorobotics Lab
Oleg A. Shmakov
Snakelike robots locomotions control

17. Genetic algorithms for locomotions control
Category
Value
Function set
{sin, cos, +, -, *, /}
Terminal set
{time, segment_ID, Pi, random constant, ADF}
Population size
200 individuals
Selection
Binary tournament, ratio 0.1
Elitism
Best 4 individuals
Mutation
Random subtree mutation, ratio 0.01
Fitness
Velocity of simulated Snakebot during the trial
Trial interval
180 time steps, each time step account for 50ms of “real” time
Termination criterion
(Fitness >100) or (Generations>30)
or (no improvement of fitness for 16 generations)
Fitness convergence characteristics of 10 independent runs of GP for cases where fitness is measured as velocity in any direction (a) and snapshots of sample evolved best-ofrun sidewinding locomotion gaits of simulated Snakebot (b, c), viewed from above. The dark trailing circles depict the trajectory of the center of the mass of Snakebot. Timestamp interval between each of these circles is fixed and it is the same (10 time steps) for both snapshots.
Trajectory of the central segment (cs) around the center of mass (cm) of Snakebot for a sample evolved best-of-run sidewinding locomotion (a) and traces of ground contacts (b).
Oleg A. Shmakov
Snakelike robots locomotions control

18. The determined approach of Ivanov A.A.
Oleg A. Shmakov
Snakelike robots locomotions control

19. Hardware realization controlС0 С1 С2
18 19
16 17
14 15
12 13
10 11
8 9
6 7
4 5
2 3
0 1
RS232
Microcontrollers
Oleg A. Shmakov
Snakelike robots locomotions control

20. Hardware realization control
microcontroller
Control & power
DC motors
Feedback from sensing
JOINT
Power supply
Sensors
MAIN
Microcontroller
For all joints
(CMU)
Oleg A. Shmakov
Snakelike robots locomotions control

21. Snakelike robot CRDI RTC
Total mass
3 kg
Length
1120 mm
Width
65 mm
Maximal course torque
0,3 Nm
Maximal pitch torque
1,2 Nm
Number of the links 16
Number of the joints 15
Number of the servos 30
Voltage
4,8 – 6 V
Oleg A. Shmakov
Snakelike robots locomotions control

22. System of snakelike robot control
RS232
USB 1.1
Power supply
Microcontrollers PC
volt
Power supply servo
6 volt
Camera
Coding - MAX 232
“SnakeWheel -1”
Oleg A. Shmakov
Snakelike robots locomotions control

23. Structural control scheme
63 byte AA F1 1 CS 59 60
63 byte*
Oleg A. Shmakov
Snakelike robots locomotions control

24. Low level control fsend ≤ 50 Гц fbase = 1,5 Гц 60°/0,11 с T ≥ 2/3
1 channel
2 channel
t, мс
10 мс
20 мс
0,9
1,5
2,1
fsend ≤ 50 Гц
fsend = 30 – 60 Гц
fbase = 1,5 Гц
T ≥ 2/3
fsend ≤ 50 Гц
60°/0,11 с t φ T
20 – 40 main points
Oleg A. Shmakov
Snakelike robots locomotions control

25. Software scheme Entering parameters Forming Send Visualization Bloc Of
Protection
Forming
Bloc
Camera control
Blok
Changing
movement
Send
RS-232
Oleg A. Shmakov
Snakelike robots locomotions control

26. Software – snake-charmer5 3 2 1 4
COURSE
PITCH
Oleg A. Shmakov
Snakelike robots locomotions control

27. EXPERIMENT Lateral bending
Amplitude corner by course 35
Amplitude corner by pitch 18
Quantity link which are using in course wave 8 4
Phase
SPEED (max) (cm/sec)
2.5
SPEED (min) (cm/sec) 1
Oleg A. Shmakov
Snakelike robots locomotions control

28. EXPERIMENT Lateral bending
Oleg A. Shmakov
Snakelike robots locomotions control

29. EXPERIMENT Side winding
Amplitude corner by course 35
Amplitude corner by pitch 20
Quantity link which are using in course wave 8
Phase
π/2
SPEED (max) (cm/sec)
4,3
SPEED (min) (cm/sec) 3
Oleg A. Shmakov
Snakelike robots locomotions control

30. EXPERIMENT Side winding
Oleg A. Shmakov
Snakelike robots locomotions control

31. EXPERIMENT Motion on the given curve
Oleg A. Shmakov
Snakelike robots locomotions control

32. EXPERIMENT Motion on the given curve
Oleg A. Shmakov
Snakelike robots locomotions control

33. Conclusion
Oleg A. Shmakov
Snakelike robots locomotions control

34. ? Thank you for your attention
Oleg A. Shmakov
Snakelike robots locomotions control