Robot Code

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//Terms of use

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//THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

//IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

//FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

//AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

//LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

//OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

//THE SOFTWARE.

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#include <SoftwareSerial.h>

#include <Wire.h> //Include the Wire.h library so we can communicate with the gyro

SoftwareSerial SoftSerial(6, 7); // RX, TX

int gyro_address = 0x68; //MPU-6050 I2C address (0x68 or 0x69)

int acc_calibration_value = 450; //Enter the accelerometer calibration value

//Various settings

float pid_p_gain = 60; //Gain setting for the P-controller (15)

float pid_i_gain = 0.0; //Gain setting for the I-controller (1.5)

float pid_d_gain = 5; //Gain setting for the D-controller (30)

float turning_speed = 30; //Turning speed (20)

float max_target_speed = 50; //Max target speed (100)

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Declaring global variables

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

// bit encoding [0, 0, 0, joySW, joyY-, joyY+, joyX-, joyX+]

byte start, received_byte, low_bat;

int left_motor, throttle_left_motor, throttle_counter_left_motor, throttle_left_motor_memory;

int right_motor, throttle_right_motor, throttle_counter_right_motor, throttle_right_motor_memory;

int battery_voltage;

int receive_counter;

int gyro_pitch_data_raw, gyro_yaw_data_raw, accelerometer_data_raw;

long gyro_yaw_calibration_value, gyro_pitch_calibration_value;

unsigned long loop_timer;

float angle_gyro, angle_acc, angle, self_balance_pid_setpoint;

float pid_error_temp, pid_i_mem, pid_setpoint, gyro_input, pid_output, pid_last_d_error;

float pid_output_left, pid_output_right;

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Setup basic functions

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void setup(){

SoftSerial.begin(9600);

Serial.begin(9600); //Start the serial port at 9600 kbps

Wire.begin(); //Start the I2C bus as master

TWBR = 12; //Set the I2C clock speed to 400kHz

//To create a variable pulse for controlling the stepper motors a timer is created that will execute a piece of code (subroutine) every 20us

//This subroutine is called TIMER2_COMPA_vect

TCCR2A = 0; //Make sure that the TCCR2A register is set to zero

TCCR2B = 0; //Make sure that the TCCR2A register is set to zero

TIMSK2 |= (1 << OCIE2A); //Set the interupt enable bit OCIE2A in the TIMSK2 register

TCCR2B |= (1 << CS21); //Set the CS21 bit in the TCCRB register to set the prescaler to 8

OCR2A = 39; //The compare register is set to 39 => 20us / (1s / (16.000.000MHz / 8)) - 1

TCCR2A |= (1 << WGM21); //Set counter 2 to CTC (clear timer on compare) mode

//By default the MPU-6050 sleeps. So we have to wake it up.

Wire.beginTransmission(gyro_address); //Start communication with the address found during search.

Wire.write(0x6B); //We want to write to the PWR_MGMT_1 register (6B hex)

Wire.write(0x00); //Set the register bits as 00000000 to activate the gyro

Wire.endTransmission(); //End the transmission with the gyro.

//Set the full scale of the gyro to +/- 250 degrees per second

Wire.beginTransmission(gyro_address); //Start communication with the address found during search.

Wire.write(0x1B); //We want to write to the GYRO_CONFIG register (1B hex)

Wire.write(0x00); //Set the register bits as 00000000 (250dps full scale)

Wire.endTransmission(); //End the transmission with the gyro

//Set the full scale of the accelerometer to +/- 4g.

Wire.beginTransmission(gyro_address); //Start communication with the address found during search.

Wire.write(0x1C); //We want to write to the ACCEL_CONFIG register (1A hex)

Wire.write(0x08); //Set the register bits as 00001000 (+/- 4g full scale range)

Wire.endTransmission(); //End the transmission with the gyro

//Set some filtering to improve the raw data.

Wire.beginTransmission(gyro_address); //Start communication with the address found during search

Wire.write(0x1A); //We want to write to the CONFIG register (1A hex)

Wire.write(0x03); //Set the register bits as 00000011 (Set Digital Low Pass Filter to ~43Hz)

Wire.endTransmission(); //End the transmission with the gyro

pinMode(2, OUTPUT); //Configure digital poort 2 as output

pinMode(3, OUTPUT); //Configure digital poort 3 as output

pinMode(4, OUTPUT); //Configure digital poort 4 as output

pinMode(5, OUTPUT); //Configure digital poort 5 as output

pinMode(13, OUTPUT); //Configure digital poort 6 as output

for(receive_counter = 0; receive_counter < 500; receive_counter++){ //Create 500 loops

if(receive_counter % 15 == 0)digitalWrite(13, !digitalRead(13)); //Change the state of the LED every 15 loops to make the LED blink fast

Wire.beginTransmission(gyro_address); //Start communication with the gyro

Wire.write(0x43); //Start reading the Who_am_I register 75h

Wire.endTransmission(); //End the transmission

Wire.requestFrom(gyro_address, 4); //Request 2 bytes from the gyro

gyro_yaw_calibration_value += Wire.read()<<8|Wire.read(); //Combine the two bytes to make one integer

gyro_pitch_calibration_value += Wire.read()<<8|Wire.read(); //Combine the two bytes to make one integer

delayMicroseconds(3700); //Wait for 3700 microseconds to simulate the main program loop time

}

gyro_pitch_calibration_value /= 500; //Divide the total value by 500 to get the avarage gyro offset

gyro_yaw_calibration_value /= 500; //Divide the total value by 500 to get the avarage gyro offset

loop_timer = micros() + 4000; //Set the loop_timer variable at the next end loop time

}

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Main program loop

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void loop(){

if(SoftSerial.available()){ //If there is serial data available

received_byte = SoftSerial.read(); //Load the received serial data in the received_byte variable

receive_counter = 0; //Reset the receive_counter variable

}

if(receive_counter <= 25)receive_counter ++; //The received byte will be valid for 25 program loops (100 milliseconds)

else received_byte = 0x00; //After 100 milliseconds the received byte is deleted

//Load the battery voltage to the battery_voltage variable.

//85 is the voltage compensation for the diode.

//Resistor voltage divider => (3.3k + 3.3k)/2.2k = 2.5

//12.5V equals ~5V @ Analog 0.

//12.5V equals 1023 analogRead(0).

//1250 / 1023 = 1.222.

//The variable battery_voltage holds 1050 if the battery voltage is 10.5V.

battery_voltage = (analogRead(0) * 1.222) + 85;

if(battery_voltage < 1050 && battery_voltage > 800){ //If batteryvoltage is below 10.5V and higher than 8.0V

digitalWrite(13, HIGH); //Turn on the led if battery voltage is to low

low_bat = 1; //Set the low_bat variable to 1

}

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Angle calculations

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

Wire.beginTransmission(gyro_address); //Start communication with the gyro

Wire.write(0x3F); //Start reading at register 3F

Wire.endTransmission(); //End the transmission

Wire.requestFrom(gyro_address, 2); //Request 2 bytes from the gyro

accelerometer_data_raw = Wire.read()<<8|Wire.read(); //Combine the two bytes to make one integer

accelerometer_data_raw += acc_calibration_value; //Add the accelerometer calibration value

Serial.println(accelerometer_data_raw);

if(accelerometer_data_raw > 8200)accelerometer_data_raw = 8200; //Prevent division by zero by limiting the acc data to +/-8200;

if(accelerometer_data_raw < -8200)accelerometer_data_raw = -8200; //Prevent division by zero by limiting the acc data to +/-8200;

angle_acc = asin((float)accelerometer_data_raw/8200.0)* 57.296; //Calculate the current angle according to the accelerometer

if(start == 0 && angle_acc > -0.5&& angle_acc < 0.5){ //If the accelerometer angle is almost 0

angle_gyro = angle_acc; //Load the accelerometer angle in the angle_gyro variable

start = 1; //Set the start variable to start the PID controller

}

Wire.beginTransmission(gyro_address); //Start communication with the gyro

Wire.write(0x43); //Start reading at register 43

Wire.endTransmission(); //End the transmission

Wire.requestFrom(gyro_address, 4); //Request 4 bytes from the gyro

gyro_yaw_data_raw = Wire.read()<<8|Wire.read(); //Combine the two bytes to make one integer

gyro_pitch_data_raw = Wire.read()<<8|Wire.read(); //Combine the two bytes to make one integer

gyro_pitch_data_raw -= gyro_pitch_calibration_value; //Add the gyro calibration value

angle_gyro += gyro_pitch_data_raw * 0.000031; //Calculate the traveled during this loop angle and add this to the angle_gyro variable

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//MPU-6050 offset compensation

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Not every gyro is mounted 100% level with the axis of the robot. This can be cause by misalignments during manufacturing of the breakout board.

//As a result the robot will not rotate at the exact same spot and start to make larger and larger circles.

//To compensate for this behavior a VERY SMALL angle compensation is needed when the robot is rotating.

//Try 0.0000003 or -0.0000003 first to see if there is any improvement.

gyro_yaw_data_raw -= gyro_yaw_calibration_value; //Add the gyro calibration value

//Uncomment the following line to make the compensation active

//angle_gyro -= gyro_yaw_data_raw * 0.0000003; //Compensate the gyro offset when the robot is rotating

angle_gyro = angle_gyro * 0.9996 + angle_acc * 0.0004; //Correct the drift of the gyro angle with the accelerometer angle

static float last_angle_gyro;

const int ratio = 1;

angle_gyro = (angle_gyro + last_angle_gyro * ratio) / (ratio + 1);

last_angle_gyro = angle_gyro;

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//PID controller calculations

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//The balancing robot is angle driven. First the difference between the desired angel (setpoint) and actual angle (process value)

//is calculated. The self_balance_pid_setpoint variable is automatically changed to make sure that the robot stays balanced all the time.

//The (pid_setpoint - pid_output * 0.015) part functions as a brake function.

pid_error_temp = angle_gyro - self_balance_pid_setpoint - pid_setpoint;

if(pid_output > 10 || pid_output < -10)pid_error_temp += pid_output * 0.015 ;

pid_i_mem += pid_i_gain * pid_error_temp; //Calculate the I-controller value and add it to the pid_i_mem variable

if(pid_i_mem > 400)pid_i_mem = 400; //Limit the I-controller to the maximum controller output

else if(pid_i_mem < -400)pid_i_mem = -400;

//Calculate the PID output value

pid_output = pid_p_gain * pid_error_temp + pid_i_mem + pid_d_gain * (pid_error_temp - pid_last_d_error);

if(pid_output > 400)pid_output = 400; //Limit the PI-controller to the maximum controller output

else if(pid_output < -400)pid_output = -400;

pid_last_d_error = pid_error_temp; //Store the error for the next loop

if(pid_output < 5 && pid_output > -5)pid_output = 0; //Create a dead-band to stop the motors when the robot is balanced

if(angle_gyro > 30 || angle_gyro < -30 || start == 0 || low_bat == 1){ //If the robot tips over or the start variable is zero or the battery is empty

pid_output = 0; //Set the PID controller output to 0 so the motors stop moving

pid_i_mem = 0; //Reset the I-controller memory

start = 0; //Set the start variable to 0

self_balance_pid_setpoint = 0; //Reset the self_balance_pid_setpoint variable

}

//Serial.print(0);

//Serial.print(" ");

//Serial.print(angle_gyro);

//Serial.print(" ");

//Serial.print(pid_output);

//Serial.println();

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Control calculations

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

pid_output_left = pid_output; //Copy the controller output to the pid_output_left variable for the left motor

pid_output_right = pid_output; //Copy the controller output to the pid_output_right variable for the right motor

if(received_byte & B00000001){ //If the first bit of the receive byte is set change the left and right variable to turn the robot to the left

pid_output_left += turning_speed; //Increase the left motor speed

pid_output_right -= turning_speed; //Decrease the right motor speed

}

if(received_byte & B00000010){ //If the second bit of the receive byte is set change the left and right variable to turn the robot to the right

pid_output_left -= turning_speed; //Decrease the left motor speed

pid_output_right += turning_speed; //Increase the right motor speed

}

const float maxSetpoint = 0.1;

if(received_byte & B00000100){ //If the third bit of the receive byte is set change the left and right variable to turn the robot to the right

if(pid_setpoint > -maxSetpoint)pid_setpoint -= 0.01; //Slowly change the setpoint angle so the robot starts leaning forewards

if(pid_output > max_target_speed * -1)pid_setpoint -= 0.001; //Slowly change the setpoint angle so the robot starts leaning forewards

}

if(received_byte & B00001000){ //If the forth bit of the receive byte is set change the left and right variable to turn the robot to the right

if(pid_setpoint < maxSetpoint)pid_setpoint += 0.01; //Slowly change the setpoint angle so the robot starts leaning backwards

if(pid_output < max_target_speed)pid_setpoint += 0.001; //Slowly change the setpoint angle so the robot starts leaning backwards

}

if(!(received_byte & B00001100)){ //Slowly reduce the setpoint to zero if no foreward or backward command is given

if(pid_setpoint > 0.1)pid_setpoint -=0.01; //If the PID setpoint is larger then 0.5 reduce the setpoint with 0.05 every loop

else if(pid_setpoint < -0.1)pid_setpoint +=0.01; //If the PID setpoint is smaller then -0.5 increase the setpoint with 0.05 every loop

else pid_setpoint = 0; //If the PID setpoint is smaller then 0.5 or larger then -0.5 set the setpoint to 0

}

//The self balancing point is adjusted when there is not forward or backwards movement from the transmitter. This way the robot will always find it's balancing point

if(pid_setpoint == 0){ //If the setpoint is zero degrees

if(pid_output < 0)self_balance_pid_setpoint += 0.0015; //Increase the self_balance_pid_setpoint if the robot is still moving forewards

if(pid_output > 0)self_balance_pid_setpoint -= 0.0015; //Decrease the self_balance_pid_setpoint if the robot is still moving backwards

}

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Motor pulse calculations

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//To compensate for the non-linear behaviour of the stepper motors the folowing calculations are needed to get a linear speed behaviour.

if(pid_output_left > 0)pid_output_left = 405 - (1/(pid_output_left + 9)) * 5500;

else if(pid_output_left < 0)pid_output_left = -405 - (1/(pid_output_left - 9)) * 5500;

if(pid_output_right > 0)pid_output_right = 405 - (1/(pid_output_right + 9)) * 5500;

else if(pid_output_right < 0)pid_output_right = -405 - (1/(pid_output_right - 9)) * 5500;

//Calculate the needed pulse time for the left and right stepper motor controllers

if(pid_output_left > 0)left_motor = 400 - pid_output_left;

else if(pid_output_left < 0)left_motor = -400 - pid_output_left;

else left_motor = 0;

if(pid_output_right > 0)right_motor = 400 - pid_output_right;

else if(pid_output_right < 0)right_motor = -400 - pid_output_right;

else right_motor = 0;

//Copy the pulse time to the throttle variables so the interrupt subroutine can use them

throttle_left_motor = left_motor;

throttle_right_motor = right_motor;

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Loop time timer

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//The angle calculations are tuned for a loop time of 4 milliseconds. To make sure every loop is exactly 4 milliseconds a wait loop

//is created by setting the loop_timer variable to +4000 microseconds every loop.

while(loop_timer > micros());

loop_timer += 4000;

}

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//Interrupt routine TIMER2_COMPA_vect

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

ISR(TIMER2_COMPA_vect){

//Left motor pulse calculations

throttle_counter_left_motor ++; //Increase the throttle_counter_left_motor variable by 1 every time this routine is executed

if(throttle_counter_left_motor > throttle_left_motor_memory){ //If the number of loops is larger then the throttle_left_motor_memory variable

throttle_counter_left_motor = 0; //Reset the throttle_counter_left_motor variable

throttle_left_motor_memory = throttle_left_motor; //Load the next throttle_left_motor variable

if(throttle_left_motor_memory < 0){ //If the throttle_left_motor_memory is negative

PORTD &= 0b11110111; //Set output 3 low to reverse the direction of the stepper controller

throttle_left_motor_memory *= -1; //Invert the throttle_left_motor_memory variable

}

else PORTD |= 0b00001000; //Set output 3 high for a forward direction of the stepper motor

}

else if(throttle_counter_left_motor == 1)PORTD |= 0b00000100; //Set output 2 high to create a pulse for the stepper controller

else if(throttle_counter_left_motor == 2)PORTD &= 0b11111011; //Set output 2 low because the pulse only has to last for 20us

//right motor pulse calculations

throttle_counter_right_motor ++; //Increase the throttle_counter_right_motor variable by 1 every time the routine is executed

if(throttle_counter_right_motor > throttle_right_motor_memory){ //If the number of loops is larger then the throttle_right_motor_memory variable

throttle_counter_right_motor = 0; //Reset the throttle_counter_right_motor variable

throttle_right_motor_memory = throttle_right_motor; //Load the next throttle_right_motor variable

if(throttle_right_motor_memory < 0){ //If the throttle_right_motor_memory is negative

PORTD |= 0b00100000; //Set output 5 low to reverse the direction of the stepper controller

throttle_right_motor_memory *= -1; //Invert the throttle_right_motor_memory variable

}

else PORTD &= 0b11011111; //Set output 5 high for a forward direction of the stepper motor

}

else if(throttle_counter_right_motor == 1)PORTD |= 0b00010000; //Set output 4 high to create a pulse for the stepper controller

else if(throttle_counter_right_motor == 2)PORTD &= 0b11101111; //Set output 4 low because the pulse only has to last for 20us

}