Introduciton
A robot must have a possibility to move. One of the simplest solutions is to use a tracked chassis propelled by two engines. Two DC motors working allows for forward movement, one motor or two in differnet directions - turn left/right.We need
- L298N coontroller
- Arduino with firmata library
- Raspberry Pi with python and firmata package
- two DC motors for test (probably we will use other engines to drive the robot)
Motor drive controller with L298N module
L298N DC motors controller specification:
- operating voltage <48V
- 2A per channel
- the maximum 20W power at 75 °C
- supply current 36mA circuit
- operating temperature:-20C +135 C
- dimensions 44mm x 44mm x 27mm
and my test connections:
my application to control motors (motor_test.py):
from pyfirmata import ArduinoMega
board = ArduinoMega('/dev/ttyUSB0')
__copyright__ = "Copyright 2014, http://letsmakearobot.blogspot.com/"
__version__ = "0.2.0"
__license__ = "GPL"
__email___ = "sebastian.dziak@gmail.com"
pin_motor_A_L = board.get_pin('d:4:p')
pin_motor_A_R = board.get_pin('d:5:p')
pin_motor_B_R = board.get_pin('d:6:p')
pin_motor_B_L = board.get_pin('d:7:p')
cmd_motor = ('A','B')
cmd_direction = ('L','R','S')
invalid_number_parameters = "Invalid number of parameters!"
invalid_parameter = "Invalid parameter: "
def set_motor(motor, cmd, speed):
if args[0]=='A':
if cmd=='S':
pin_motor_A_L.write(0)
pin_motor_A_R.write(0)
elif cmd=='L':
pin_motor_A_R.write(0)
pin_motor_A_L.write(speed)
elif cmd=='R':
pin_motor_A_L.write(0)
pin_motor_A_R.write(speed)
if args[0]=='B':
if cmd=='S':
pin_motor_B_L.write(0)
pin_motor_B_R.write(0)
elif cmd=='L':
pin_motor_B_R.write(0)
pin_motor_B_L.write(speed)
elif cmd=='R':
pin_motor_B_L.write(0)
pin_motor_B_R.write(speed)
def info():
print "------------------------------------------------"
print "Command parameters:"
print " A,B - motor id"
print " L,R,S - L - left rotation, R - right rotation, S - motor stop"
print " 0.0-1.0 - velocity (should be given only with the option of L or R)"
print " ...and exit from app: exit"
print "Examples:"
print " A R 0.4"
print " A S"
print "------------------------------------------------"
def validate(engine, cmd, speed):
if engine not in cmd_motor:
return invalid_parameter+engine
elif cmd not in cmd_direction:
return invalid_parameter+cmd
elif cmd=='S' and not speed is None:
return invalid_number_parameters
elif (cmd=='L' or cmd=='R') and speed is None:
return invalid_number_parameters
elif not speed is None and (float(speed)<0.0 or float(speed)>1.0):
return invalid_parameter+speed
info()
while True:
cmdLine = raw_input('CMD (A/B L/R/S 0.0-1.0):')
if cmdLine == 'exit': break
args = cmdLine.split()
if len(args)>0:
engine = args[0]
else:
engine = None
if len(args)>1:
cmd = args[1]
else:
cmd = None
if len(args)>2:
speed = float(args[2])
else:
speed = None
resp = validate(engine, cmd, speed)
if resp is None:
set_motor(engine, cmd, speed)
else:
print resp
print "goodbye"
links:
http://arduino-info.wikispaces.com/MotorDrivers
http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000240.pdf
http://www.funnyrobotics.com/2011/03/arduino-with-l298n-based-dual-motor.html
http://en.wikipedia.org/wiki/Phase-locked_loop
