Difference between revisions of "S22: Firebolt"

Hardware Schematic Diagram

ESC & DC Motor

The DC motor is controlled by ESC using PWM signals provided by the motor controller for forward and reverse movements. We used the 9v NiMH battery to power up the ESC. The DC motor is powered by the ESC which has a dc-to-dc converter which converts 9v to 6v. The output from the ESC is used to power the Servo motor. ESC has an ease set button which is used for calibration and setting different modes for the car.

The car can be operated in the following 3 modes:
Sport mode(100% Forward, 100% Brakes, 100% Reverse)
Racing mode(100% Forward, 100% Brakes, No Reverse)
Training mode(50% Forward, 100% Brakes, 50% Reverse)

As we needed more than 50% speed for steep ramps, we used Sport mode. The frequency of the PWM signal fed to the servo motor is 100Hz. Based on the duty cycle set by the user, the car will go forward, reverse, or neutral. 10% - 20% duty cycle for reverse. 15% duty cycle for neutral. 15%-20% duty cycle for the forward motion.

Traxxas ESC

Traxxas Brushless DC Motor

Servo Motor

The servo motor we used is Traxxas 2075 which was provided with the car and it is responsible for steering the car. It takes the 6V power directly from ESC. The servo motor is controlled directly from the SJ2 micro-controller board. The PWM signal fed to the servo motor is of frequency 100Hz. Based on the duty cycle of the signal sent to the servo, it rotates in the left / right direction. 10% - 20% duty cycle for left. 15% duty cycle for straight. 15%-20% duty cycle for right.

Traxass Servo Motor

RPM Sensor

There are two parts to the RPM sensor - one is the trigger magnet and the other is the sensor. The RPM sensor is used as an input to maintain a constant speed of the vehicle. The sensor mounts on the inside of the gear cover, the trigger magnet mounts on the DC motor shaft. The gear cover and motor shaft need to be removed using the toolkit provided along with the RC car. The procedure is similar to this video, but note that the car used in the video is a 4WD RC car by Traxxas. We made use of the trigger magnet attached to the spur gear to trigger a pulse on the sensor for every rotation of the spur gear. These pulses are then read by the SJ2 board to calculate rotations in a second and later convert it to RPM and MPH. The RPM sensor has 3 wires, the white wire is the output wire that provides the pulses to the SJ2 Board, and the other wires are Supply(6V) and GND. We also used a Pull Down 1K Resistor between Supply and RPM output wires.

Traxxas RPM Sensor

Trigger Magnet

Software Design

The motor node acts based on the speed and direction received over CAN bus from the Driver Node. The positive speed values are treated as forward motion and the negative speed values are considered to be the reverse motion of the RC car.

The steering angles are divided into 5-degree segments and the motor node sends the pre-defined pwm duty cycle of the particular segment to the servo motor depending on the angle value received from the driver node.

Speed Control Flowchart

Technical Challenges

Geographical And Bridge Controller

Hardware Design

Software Design

The GEO controller consisted of 4 main parts which are: 1. GPS Module 2. Compass 3.Waypoints Algorithm 4. Geo Logic

The Geo logic takes data from GPS module processes it to get current coordinates, takes data from compass for raw heading. After acquiring data from compass and GPS, it calculates heading , bearing and distance and sends it on CAN bus.

1. GPS Processing

The GPS module uses UART1 to communicate with our SJ2 board. The API call for the GPS driver requires setting up the gps registers to only allow GPGGA data to improve processing. The main API function is called gps__run_once() which digests data from the physical GPS hardware. Inside gps__run_once(), we call two functions that help with parsing the gps coordinates. The first is taking using a line buffer for the UART characters that are digested during operation and checking if they are in fact a full GPGGA string. The second function parses those coordinates from the line buffer and converts them from GPGGA minutes data to polar coordinates. Once the function is called, global static variables located in geo_gps.c are used while a gps__get_coorindate() function is called whenever the API's data wants to be used outside of the gps.c file. In order to check if there is a gps fix, we created a function that checks if certain GPGGA bits are set or not.

2.

Technical Challenges

Driver Node

Driver Node is the master controller. It receives input from sensor and bridge node, processes it to make right decision for controlling the speed and steering direction of the car and then commands the motor node to drive accordingly. This node is also interfaced to the LCD, which acts as dashboard of the car and displays information such as car speed and distance to destination on the screen.

Hardware

LCD is interfaced with the SJ2 board and it communicates over UART. P4.28 and P4.29 which is UART3 on board is used. Headlights and Tailights are also connected to the driver node using four GPIOs.

Sjtwo-board

LCD Display

Software Architecture Driver Logic

Obstacle Avoidance Logic

if (obstacle_on_all_front_sides()) {
          stop_the_car();
          reverse_car_and_steer();
        } else if (obstacle_on_left() && obstacle_in_right() && (!obstacle_on_front())) {
          drive_forward();
        } else if (obstacle_on_left() && (!obstacle_in_right())) {
          obstacle_on_right = false;
          get_steering_range(obstacle_on_right); // right steer
        } else if (obstacle_in_right() && (!obstacle_on_left())) {
          obstacle_on_right = true;
          get_steering_range(obstacle_on_right); // left steer
        } else if (obstacle_on_front() && (!obstacle_on_left() && !obstacle_in_right())) {
          stop_the_car();
          reverse_car_and_steer();
          obstacle_on_right =
              (internal_sensor_data.SENSOR_SONARS_right < internal_sensor_data.SENSOR_SONARS_left) ? true : false;
          get_steering_range(obstacle_on_right);

        } else if (obstacle_on_rear() && (!obstacle_on_all_front_sides())) {
          obstacle_on_right =
              (internal_sensor_data.SENSOR_SONARS_right < internal_sensor_data.SENSOR_SONARS_left) ? true : false;
          get_steering_range(obstacle_on_right);
          debug_values.car_driving_status = FORWARD;
          debug_values.car_steering_status = STRAIGHT;
        } else {
          stop_the_car();

          debug_values.car_driving_status = STOPPED;
          debug_values.car_steering_status = STRAIGHT;
        }

Steer Left and Right

  if (obstactle_on_right == true) {
    //steer left
    motor_signal.DRIVER_TO_MOTOR_direction = (motor_signal.DRIVER_TO_MOTOR_direction <= 40)
                                                 ? motor_signal.DRIVER_TO_MOTOR_direction + offset_to_angle
                                                 : max_angle_threshold;
    motor_signal.DRIVER_TO_MOTOR_speed = slow_speed;
    update_lights(10, headlight_left);

  } else {
    //steer right
    motor_signal.DRIVER_TO_MOTOR_direction = (motor_signal.DRIVER_TO_MOTOR_direction >= -40)
                                                 ? motor_signal.DRIVER_TO_MOTOR_direction - offset_to_angle
                                                 : -max_angle_threshold;

    motor_signal.DRIVER_TO_MOTOR_speed = slow_speed;
    update_lights(10, headlight_right);
  }

Reverse and Steer

  if (!obstacle_on_rear()) {
    motor_signal.DRIVER_TO_MOTOR_direction = 0;
    motor_signal.DRIVER_TO_MOTOR_speed = reverse_speed;
    update_lights(10, taillight_left);
    update_lights(10, taillight_right);
  } else {
    stop_the_car();
  }

Navigation to Destination

Driver receives raw heading and bearing from the Geo node and in order to calculate the turning direction, it first computes the difference between heading and bearing. Then based on which quadrant the difference lies and where the destination lies, take navigation decisions to steer left, right or straight.

if (heading_difference >= 350 && heading_difference <= 10) {
    gps_navigation_direction = straight;
    heading_difference = fabs(heading_difference);

    debug_values.car_driving_status = FORWARD;
    debug_values.car_steering_status = STRAIGHT;
  } else if (heading_difference > 180) {
    gps_navigation_direction = left;
    heading_difference = 360 - heading_difference;

    debug_values.car_driving_status = FORWARD;
    debug_values.car_steering_status = LEFT;

  } else if (heading_difference < 0 && heading_difference > -180) {
    gps_navigation_direction = left;
    heading_difference = fabs(heading_difference);

    debug_values.car_driving_status = FORWARD;
    debug_values.car_steering_status = LEFT;
  }

  else if (heading_difference < -180) {
    gps_navigation_direction = right;
    heading_difference = fabs(heading_difference + 360);

    debug_values.car_driving_status = FORWARD;
    debug_values.car_steering_status = RIGHT;
  } else if (heading_difference > 0 && heading_difference <= 180) {
    gps_navigation_direction = right;

    debug_values.car_driving_status = FORWARD;
    debug_values.car_steering_status = RIGHT;
  }

Technical Challenges

• Driver receives data from sensor and geo node, so mainly the issue was sometimes not getting data accurate data from sensors or receiving late. This has made the obstacle avoidance quite slow. Make sure the sensor is transmitting data fast enough and driver is also receiving fast.
• Driver Node has the least hardware interfacing compared to other nodes, so there were not many challenges on hardware front. If the LCD communicates over UART, remember to connect the gnd of both lcd and board otherwise the data printed on LCD could be gibberish.
• High speed of car can also cause to problem for sensors, we noticed that they cannot accurately detect obstacles on high speed.
• Compass calibration was also issue sometimes, if not properly calibrated the car will have trouble navigating to gps location.

Mobile Application

User Interface

Software Design

Maps Activity

Bluetooth/WIFI

Technical Challenges

Conclusion

Project Video

Project Source Code

Advise for Future Students

• Get started early and make your hardware stable as early as possible so that you have enough time for extensive testing of the software. Because without on field testing corner cases and potential problems in the code can't be determined.
• We took references from previous projects and ran into problems due to lack of information. Ensure that you fully understand both software and hardware you are taking reference from before implementing on the car.
• First of all make your motor run smoothly only then you will be able to do on field testing. So even if you have to use initial week to get the motor part ready. Buy new hardware for that to---- to be continued (Ritika)

Acknowledgement

References

http://socialledge.com/sjsu/index.php/Industrial_Application_using_CAN_Bus