1. The Hexapod Walking Robot
FOBOT
The Hexapod Walking Robot
Authors:
Balázs András
Pécskai Balázs
Supola Balázs
Vámossy Zoltán
Molnár András
Budapest Polytechnic, John von Neumann Faculty of Informatics, Hungary
23 March 2004

2. Contents The main purposes of the robot Similar development
Common features
Particular purposes
Construction of the system
Mechanical structure
Electric structure
Movement of the legs
Communication
PC side control
Planning of the walking strategies
Walking strategies
Global Positioning System
Global positioning
Eye-based navigation
Processing of the PAL-optic picture
Position determination step by step
Results I
Results II
Further information

3. The main purposes of the robot
The robot is able to:
Move quickly (apart from the quality of the terrain)
Have duplex communication channel with the controlling PC
Have remote control option
Partially explore its environment
Avoid obstacles
Reach a designated target by self-navigation

4. Similar development Autonomous hexapod robot Only one actuator per leg
Speed: 2.25 m/s
3700 m distance on one set of batteries
Swims, and climbs stairs
Onboard control of the robot and wireless access to the command interface is supported by RHexLib
Rhex
Source:

5. Common features Has got six legs Similar movement Structure
Six legs can be controlled independently from each other
Curved legs

6. Particular purposes
Development of the construction (number of the legs)
Solution of the problem of the motor control:
Turn direction, speed, setting feet options
Programming of the central process unit:
Duplex communication between CPU and PC
The execution of the various walking strategies
Joining of the GPS module to CPU:
Data pre-testing and pass it on to PC
Developing the PC-side software:
User interface
Communication module and test environment alternatives
Map manager module
Virtual environment building module*
Avoiding obstacles, route-planning and navigation module*
* optional modules

7. Construction of the system* * * *
* optional modules

8. Mechanical structure Dimensions: Evolution of the legs: Length: 420 mm
Width: 265 mm
Height (standing): 175 mm
Leg height: 115 mm
Aluminum skeleton
Evolution of the legs:
Early
stage
Curved
spiral
Plan-parallel
Straight

9. Electrical structure Printed electric circuit: Main parts:
6 pcs. DC motor (12 Watt)
6 pcs. PIC 16F873 microcontroller
6 pcs. L6203 motor controlling IC
Interfaces on the robot:
2 pcs. serial port socket (communication + GPS)
Programmer interface for PICs
Sockets for GPS and camera
Interfaces for optional sensor and structure

10. Movement of the legs Leg movement: Speed: Regulation:
Determination of velocity and direction (automatic and/or by PC) setting to position
Speed:
PWM modulation is created by PIC
Regulation:
Speed of the obtaining of the desired position is in direct proportion to square of distance
Speed’s derivative is similar to the aforesaid
Advantage: regulation time is short, increased burden is easier solved

11. Communication
FOBOT communicates on the serial port(RS232) with own protocol.
All PICs have different address.
1th. byte: address + instruction’s type
2nd. byte: desired position or velocity
PICs send back two bytes:
Actual speed
Actual position
Advantage of serial communication:
Easy programmable
Single transmission
Wireless communication is realizable by two one-channel transceiver-receiver pairs

12. PC side control Control & test:
The test of the communication and errata continuously
Test of the leg-control:
Simple leg-control
Walking description
Option of the succession control
Simulation:
Simulated motion of the robot and position-diagram of the legs

13. Planning of the walking strategies
Position plotted
against time
Items of
target points
Speed
Tripod walking:

14. Walking strategies Turning: Tripod: Quattro: Worm: (the slowest)
the legs move just like at the tripod strategy, but the two sides move in different direction
Quattro:
Worm: (the slowest)

15. Global Positioning System
GPS signals: NMEA sentences (National Marina Electronics Association)
- GPGGA, GPRMC, GPGSA, GPGSV
Example:
$GPGGA,123519, ,N, ,E,1,08,0.9,545.4,M,46.9,M,,*42
Degree of latitude
Degree of longitude
Height above sea-level.
Measuring controlled by the software:
Minimum number of the used satellites
Applied filters: average, median
Displaying the properties of the satellites

16. Global positioning Planning route: Route following:
Placing sub-targets
Route following:
Filtering input signals
Actual position on the map
Calculating of the direction of the sub- targets
Properties of the satellites:
Positions
Range of the input signals

17. Eye-based navigation Step of the real-time image processing:
Digitalization (Video for Windows)
Modified input image by filters:
Dilatation
Erosion
Edge detection
SUSAN algorithm
Skeleton
Binarization
Position and orientation
determination based on edge detection

18. Processing of the PAL-optic picture
PAL = Panoramic Annular Lens (invented by Prof. Pal Greguss)
Real-time mapping and effect of filters:
Centric-minded imaging

19. Position determination step by step
Add filters
Selection of the followed points manually
Layout of the PAL-image
Edge detection
Schoolyard
Here is FOBOT
PAL-image
3D transformation, mapping the points
Determination of the spatial vectors from the PAL-image
Determination of the vertical position of the FOBOT

20. Results I. Movement: In progress: Speed: 5,8 meters / min
Turning around: 36 sec
Simple walking development possibility
Several walking strategies are developed
In progress:
Eye-based navigation
Obstacles avoidance
Wireless communication and local power-supply

21. Results II. Tested GPS receiver:
GNV12 (Lowrance), Summit (Garmin), PS1 (µblocks), Navistar (BAE Systems), Jupiter (Connexant)
Test of the navigation on road and the court of the college (football pitch)
Football pitch

22. Further information
project homepage:
fobot.bmfnik.org