#contents

Motors

Speed Control

To control motor speed, you must write "on" to the following device file.

echo on > /sys/class/tacho-motor/motor0/speed_regulation

Speed control is disabled by default at startup because it is set to off.

When it is off, you can set the duty cycle using duty_cycle_sp.

Then write the target speed to the following file.

echo 50 > /sys/class/tacho-motor/motor0/speed_sp

The value specified here represents the number of counts per second. Therefore, convert angular velocity using the value obtained from the following device file.

For Motor M and Motor L, the value returned by count_per_rot is 360, so conversion is not necessary.

cat /sys/class/tacho-motor/motor0/count_per_rot

After that, enter the following command to start rotation.

echo run-forever > /sys/class/tacho-motor/motor0/command

To obtain the current angular velocity, use the following device file.

cat /sys/class/tacho-motor/motor0/speed

The above procedure using ev3dev-lang-cpp is as follows.

ev3dev::large_motor lm = ev3dev::large_motor();
lm.set_speed_regulation_enabled("on");
lm.set_speed_sp(50*lm.count_per_rot());
lm.run_forever();
std::cout << lm.speed()/lm.count_per_rot() << std::endl;

Using ev3dev-lang-python, it can be written as follows.

lm = ev3.LargeMotor()
lm.set_attr_string("speed_regulation", "on")
lm.speed_sp = 50*lm.count_per_rot
lm.run_forever()
print lm.speed/lm.count_per_rot

Running for a Fixed Time

To run a motor for a specified amount of time, first set the duration using the following device file.

echo 2000 > /sys/class/tacho-motor/motor0/time_sp

Then start operation with the following command.

echo run-timed > /sys/class/tacho-motor/motor0/command

Position Control

To perform position control, you must first set duty_cycle_sp (or speed_sp if speed_regulation is enabled).

echo 50 > /sys/class/tacho-motor/motor0/speed_sp

Next, set the target position using the following device file.

echo 100 > /sys/class/tacho-motor/motor1/position_sp

Since this position is also specified as a count value, convert it using count_per_rot.

Start operation with the following command.

echo run-to-abs-pos > /sys/class/tacho-motor/motor1/command

To specify an angle relative to the current position, use the following command.

echo run-to-rel-pos > /sys/class/tacho-motor/motor1/command

The current position can be obtained from the following device file.

cat /sys/class/tacho-motor/motor1/position

The above procedure using ev3dev-lang-cpp is as follows.

ev3dev::large_motor lm = ev3dev::large_motor();
lm.set_speed_regulation_enabled("on");
lm.set_speed_sp(50*lm.count_per_rot());
lm.set_position_sp(100*lm.count_per_rot());
lm.run_to_abs_pos(100*lm.count_per_rot());
#lm.run_to_rel_pos(100*lm.count_per_rot());

Using ev3dev-lang-python, it can be written as follows.

lm = ev3.LargeMotor()
lm.set_attr_string(None, "speed_regulation", "on")
lm.speed_sp = 50*lm.count_per_rot
lm.run_to_abs_pos()
#lm.run_to_rel_pos()

Operating Sensors with C++ and Python

Obtaining Reflected Light Intensity from the Color Sensor

• C++

ev3dev::color_sensor cs = ev3dev::color_sensor();
std::cout << cs.reflected_light_intensity() << std::endl;

• Python

cs = ev3.ColorSensor()
print cs.reflected_light_intensity()

Obtaining the ON/OFF State of the Touch Sensor

• C++

ev3dev::touch_sensor ts = ev3dev::touch_sensor();
std::cout << ts.is_pressed() << std::endl;

• Python

cs = ev3.ColorSensor()
print cs.reflected_light_intensity()

Obtaining the Angle from the Gyro Sensor

• C++

ev3dev::gyro_sensor gs = ev3dev::gyro_sensor();
std::cout << gs.angle() << std::endl;

• Python

gs = ev3.GyroSensor()
print gs.angle()

Operating the LCD

• C++

ev3dev::lcd lcd = ev3dev::lcd();
unsigned char *fb = lcd.frame_buffer();
for(int i=0;i < 3072;i++)
{
if(i%24 < 12)fb[i] = 0x00;
else fb[i] = 0xff;
}

• Python

lcd = ev3.Screen()
lcd.mmap.seek(os.SEEK_SET)
lcd.mmap.write(chr(0xff)*3072)
for i in range(lcd.fix_info.smem_len):
if i%24 < 12:
lcd.mmap.seek(os.SEEK_SET)
lcd.mmap.seek(i)
lcd.mmap.write_byte(chr(0xff))