1. Behavior Control for Robotic Exploration of Planetary Surfaces Written by Erann Gat, Rajiv Desai, Robert Ivlev, John Loch and David P Miller Presented By Tony Morelli 9/30/2004

2. Abstract ● Describes robots developed at JPL (Jet Propulsion Laboratory) ● Demonstrate using behavior-control approach to control small robots on planetary surfaces ● Behavior-Control uses very little computation.

3. Introduction ● Cannot remote control robots from Earth because of the delay ● Size is limited by power, not physical size ● 3 ways to power a robot – Radioisotope Thermal Generators (decay of Plutonium) – Photovoltaic cells – Require heavy batteries – Non-Rechargable batteries – Short life

4. Behavior control ● (Rod) Brooks – Decompose the problem by task rather than function – Subsumption ● Advantages of Behavior Based Control – Fast behaviors are not slowed down by slow behaviors (act independent of each other) – Task Specific so designers can simplify the behavior

5. ALFA – A Language For Action ● Programming Language to describe reactive behavior-control mechanisms for autonomous robots ● Consists of Modules connected by Channels – Module – Converts inputs to a set of outputs – Channel – Dataflow – Data from Modules or sensors ● Similar to Subsumption – No Wires – Easier to add modules – Provide layers of computational abstraction rather than layers of functionality

6. ALFA – Code Sample

7. Tooth - Overview ● 30 cm X 20 cm – Indoor Robot ● 1 Bit Sensors – Grippers and rear bumper – Infrared Proximity Sensors ● Analog Sensors – Photo Cells (Find Light Beacon) – Tachometer on the drive motors ● Used 3.5kBytes of EEPROM and 100 bytes of RAM

8. Tooth – Control Structure ● Drive Processor/Grasp Processor ● Bottom Up Design – Cooridinating the Drive and Steering Motors – Backing up and getting out of endless loops – Picking up/Dropping objects – Head to beacon

9. Tooth Control Structure

10. Tooth – Getting Out of Loops and Dead Ends ● Unthrash Module – Lower priority than obstacle avoidance – Counts the number of times the robot changes direction in a certain amount of time and tunrs at a random direction if it thinks it's stuck ● Dead ends – If the Robot hits a dead end it will back up, then try to go forward. If it hits a wall again, it will back up more the next time. ● Grasp Module – If it tries too many times to pick up something, it will give up ● Forward turning radius is different than backwards

11. Tooth - Results ● No way of searching out objects, just finds them while wandering around ● Very Robust ● Could not handle wires, holes or bright lights

12. Rocky III - Overview ● Demonstrate behavior control could be used in a realistic planetary mission ● Infrared beacon detector ● 10 kBytes of RAM ● Weighs 18kg

13. Rocky III – Control Structure ● 3 Layers nearly identical to Tooth – Speed and Direction – Obstacle Avoidance – Sequencer

14. Rocky III - Results ● Very Reliable – 90% of the time completes its mission ● First example of an autonomous that operates in outdoor natural terrain that performs both navigation and manipulation

15. Rocky IV - Overview ● Chasis is virtually identical to Rocky III ● Weighs 7.5kg ● Construction Materials were modified to work in the climate on mars. ● 1 Master Processor and 3 slave processors

16. Rocky IV - Status ● Not yet complete ● Every aspect of a Mars mission has been demonstrated ● Hardware Issues – Activating the rock chipper caused the computer to crash (Obviously not software related)

17. Discussion ● Behavior control succeeds because action selection is not a difficult problem. ● ALFA code is easy to write, debug, and re- use ● Other robots were larger because they were required to scale a 1 meter tall objects ● Few simple sensors work as well as a lot of complex sensors

18. Summary and Conclusion ● Low power consumption is a necessity ● Low CPU usage to save power ● Used a modified version of subsumption ● ALFA seperates data flow computations from state machine computations ● As complex as other State of the Art robots

19. Questions?