Tetherbot by Scott Preston

General Description
Tetherbot is a technology demonstrator, like his predecessor 
Followbot. The main technologies that he demonstrated were: IR
Object Avoidance. Servo Control from the PC (Windows NT 4.0). 
and Algorithm Testbed. All were very successful and Tetherbot 
will continue to be used in Genetic Algorithm Research.

Subsystems Description
Chassis - consist of a Radio Shack 6"x4" Project Box. The tether 
is a 25' RJ-45 cable connected to my PC's Parallel Port.

Power - since it's tethered I was able to use an old PC power 
supply. It supplies +5VDC and ground via two unused wires in the

Locomotion - x2 "Hacked" Futaba 3003 DC Servo Motors. The hack 
I used was to replace the potentiometer with a voltage divider
consisting of two 1/4 watt 2.2k resistors.

Sensors - 2 Hi-Output IR LED's from Radio Shack and 1 Sharp 40 
kHz IR receiver Module. A schematic of the circuit can be found

Control - PC Parallel Port. Because this is under Windows NT and 
the OS does not have direct access to the I/O. I am using
DriverLINX by Scientific Software Tools, Inc. I also used a bit 
of code that allows me to measure how long my PC takes to
perform For-Next operations. This was very helpful in sending 
the correct Microsecond pulse to the servo motors, mainly since
VB's timer is only Millisecond resolution.

Genetic Algorithms
So far I have only tested one genetic algorithm. It's goal is to 
teach Tetherbot how to get out of it's playpen in a certain
amount of time. If I turn on the "avoid object" algorithm it will 
eventually be able to escape but I wanted the robot to be able
to repeat what it has learned.

To do this I have employed a genetic algorithm that consist of one 
gene. That gene contains a sequence of directions that
tetherbot needs to move. The genes are tested for fitness by the 
whether Tetherbot realizes he has espaped or the directions from
the gene have been exausted.

You can find out more at my web site: http://preston.dyndns.com.

Email: scott@preston.dyndns.com

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