3-wheel robot by Gaston Klares

3-wheel robot for outdoors

Another variation on the mechanics. Most of the electronics again recycled from previous robots. One
large battery and one smaller one in series (25 Ah and 7 Ah); the big one for the main supply, the
second to get the needed 24 Volts for some circuits, those i didn't want to modify (important
modifications would have been necessary).
Concept: One wheel in front of the robot, this one is orientable (car wiper motor with bicycle
chain) to run a curve, only this one is driven by a wheel chair motor (bicycle chain too) running
just at the half of its nominal voltage (it's still strong enough!). The two rear wheels are running
free and are both equipped with a perforated disk and photocouplers to measure the way the robot is
running.
The processor is a new concept: Atmel AVR AT90S8535 with 8255 port expansion. the AVR has 8 analog
input ports. A very interesting chip for building robots because of its FLASH-memory, EEPROM and
in-circuit-programming. Two infrared pulsed diodes and one IR-receiver on the front side, Ultrasonic
on the rear, 2 x 2 bumper microswitches on each corner, two more switches to detect the end of range
of the direction motor. LCD-Display and some LEDs to indicate its actual status and for observing
some parameters. Programming via a four-wire-printer cable from a pentium laptop using BASCOM AVR.
This robots is rolling much faster than previous models, but another problem appears: the wheel
chair motor is driving the front wheel via a bicycle chain with not too well-centered wheels; the
chain is often jumping off the wheel. After that i decided to use standard motor belts like in
automobile motors.
Next step is to set a "tower" with detectors on the top of the robot, a small platform with more
analogues sensors on it, the platform makes a scanning movement from left to right and back, it
scans about 300 degrees of a circle. The sensors to be mounted are two microphones, two LDRs an
infrared receiver and two high brightness white LEDs to light the robot's path and environment. The
platform is driven by a DC motor with a gearbox, a potentiometer and two switches detect the ends of
scanning range to inverse the scan direction, and to get the precise position (angle) of the
scanning sensors. This should allow the processor to calculate the way to the detected signal source
and drive in that direction.

http://webplaza.pt.lu/gklares/Robot/dreirad.html

Email: gklares@ara.lu


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