Welcome
to Pam and Chris Lewis's WEB Page
Shown
above is my first really successful robot. After many attempts with the suspended
BI-core BEAM robot circuitry the synchronization of the legs became an issue
so I designed the two motor walking robot shown above. Built from scavenged
parts the frame supports two cheap geared motorised assemblies bought from the
States. Potentiometers attached to a rear stub-shaft of the gearbox provide
feedback for the position of each motor. The casing from an old biro pen was
utilised to create a coupling between the stub shaft and the potentiometer.
A hole drilled through the shaft of the potentiometer prevented slipping.
Whilst
this robot cannot be described as a BEAM robot the motors are controlled by a
PICAXE processor. This affordable solution comprises of a standard Microchip
Technology PIC loaded with a bootstrap routine allowing code to be written is
basic and downloaded as many times during the development phase .Two analogue
input channels are utilised to monitor the position of both of the motors whilst
a single buffer chip allows both motors to be driven in both directions and
halted. The software development was carried out on the development board
purchased from revoloution whilst the final version minus PC interface, reset
circuitry and high power FET drivers was wire wrapped on stripboard.
The project is based on an 18 pin
microcontroller project board with 4 FET buffered digital outputs (not used for
this project). Addition of a LDL293D chip provides two reversible motor
outputs.Code is written in BASIC and downloaded via a serial port. Software is
free and can be downloaded from the following site. Revolution Education Ltd.
This 143:1 gearmotor goes 70RPM at 5V,
drawing 670mA at stall while providng 43 in-oz torque. Free running current is
57.6mA at 5 volts. With a 7mm double-flat output shaft (avoid using the green
double flat output - it's not meant to take rotational load), and a built-in
clutch and built-in mounting screw holes. The motors are sequenced as
follows:-
1.Rear CCW front off
2.Rear off front CCW
3.Rear CW
front off
4.Rear off front CW
The software
main: readadc 0,b0
readadc 1,b1
raise_front: readadc 0,b0
readadc 1,b1
if b1 > 90 then goto raise_rear
pause 5
debug b1
pause 5
high 5
low 4
pause 40
low 5
low 4
goto raise_front raise_rear: readadc 0,b0
readadc 1,b1
if b0 > 90 then goto lower_front
pause 5
debug b0
pause 5
high 7
low 6
pause 40
low 7
low 6
goto raise_rear lower_front:readadc 0,b0
readadc 1,b1
if b1 < 80 then goto lower_rear
pause 5
debug b0
pause 5
high 4
low 5
pause 40
low 4
low 5
goto lower_front lower_rear: readadc 0,b0
readadc 1,b1
if b0 < 80 then goto main
pause 5
debug b0
pause 5
high 6
low 7
pause 40
low 6
low 7
goto lower_rear
