F15: ThunderBird

Abstract

ThunderBird is a 1/10 2 WD electric short self-driving truck. The truck is equipped with sensors to detect obstacles, GPS for getting directions, Compass for the truck's orientation, Bluetooth for communicating with the android device and LCD for displaying the sensor values on screen. The modules are interfaced using 5 SJ One boards which features a Cortex-M3 LPC1758. CAN bus is used for communicating between the modules. Android device is used to enter the destination coordinates through bluetooth. When the sensors detect obstacles, it signals the motors to drive the car accordingly.

Objectives & Introduction

Team Members & Responsibilities

• Master Controller and Android application
  • Sravani Aitha
  • Vishnu Vardhana Reddy Mandalapu
  • James Sushanth Anandraj
  • Athavan Kanagasabapathy
• Motors and I/O
  • Dheeraj Dake
  • Akhil Bhargav Josyabhatla
• Sensors
  • Nitesh Jain
  • Rajashree Kambli
• GPS
  • Rishit Borad
  • Ravi Vanjara

Schedule

Motor and I/O Schedule

Sl. No	Start Date	End Date	Task	Status	Actual Completion Date
1	10/6/2015	10/13/2015	Determining the ESC initialization sequence	Completed	10/11/15
2	10/13/2015	10/20/2015	Testing the Servo and DC motor using SJ One board PWM's	Completed	10/16/2015
3	10/20/2015	10/27/2015	Design motor control using messages from the CAN bus
4	10/27/2015	11/3/2015	Implement code to accept messages from other modules over CAN bus and display it on the LCD
5	11/3/2015	11/10/2015	Update motor speeds on the LCD in real time
6	11/10/2015	11/17/2015	Interface I/O and motor modules with master controller and establish communication
7	11/17/2015	11/24/2015	Fine turning motors for precise control
8	11/24/2015	12/01/2015	Fine tuning (buffer)
9	12/01/2015	12/08/2015	Testing and debugging

Geographical Position Controller Schedule

Sl. No	Start Date	End Date	Task	Status	Actual Completion Date
1	10/6/2015	10/13/2015	Research & order GPS module	Completed	10/8/2015
2	10/13/2015	10/20/2015	Interface GPS using I2C with SJOne board	Ongoing
3	10/20/2015	10/27/2015	Interface Compass with SJOne board
4	10/27/2015	11/3/2015	Calibrate Compass and GPS
5	11/3/2015	11/10/2015	Parse raw data and create meaningful data
6	11/10/2015	11/17/2015	Implement CAN communication with SJOne board
7	11/17/2015	11/24/2015	Test and debug GPS & Compass locally
8	11/24/2015	12/01/2015	Integrate GPS/Compass module with Master board
9	12/01/2015	12/08/2015	Implement routing algorithm for Car
10	12/08/2015	12/15/2015	Test and Debug GPS/Compass integration with master

Sensor Controller Schedule

Sl. No	Start Date	End Date	Task	Status	Actual Completion Date
1	10/5/2015	10/11/2015	Finalize and order the sensors	Completed	10/11/2015
2	10/12/2015	10/18/2015	Wire the sensors and write a sample test code to check the sensors.	Ongoing
3	10/19/2015	11/01/2015	Transfer the sensor data to master controller via can bus.
4	11/2/2015	11/9/2015	Implement and integrate the code for all the sensors.
5	11/2/2015	11/15/2015	Test and Debug the integrated module.
6	11/16/2015	11/29/2015	Collaborate with the other module teams to make sure that the sensors are in working condition.
7	11/30/2015	12/06/2015	Test for stability of sensors and report.
8	12/07/2015	12/13/2015	Prepare for Demo.

Master controller and android controller Schedule

Sl. No	Start Date	End Date	Task	Status	Actual Completion Date
1	10/6/2015	10/13/2015	Car purchase ,dismantle and setup for project	Completed	10/8/2015
2	10/13/2015	10/20/2015	Can setup components purchase, Can bus design and soldering	Ongoing
3	10/20/2015	10/27/2015	Basic Can communication testing by sending and receiving data and can msg specification for all controllers and messages.
4	10/27/2015	11/3/2015	Development and implementation of Algorithm for driving car and obstacle avoidance.
5	11/3/2015	11/10/2015	Interface bt dongle with sjone board and android device and test with commands
6	11/10/2015	11/17/2015	Develop Android GUI and application to interact with car using bluetooth. Implement all necessary commands on sjone board for communication with android device. Interface with Motor and IO Controller.
7	11/17/2015	11/24/2015	Test and debug Master algorithm and Android interface locally and with Motor controller interfaced by providing predetermined directional commands.
8	11/24/2015	12/01/2015	Integrate Master Board with all boards and implement heartbeat protocol.
9	12/01/2015	12/08/2015	Test run 1 with all boards integrated and with all planned features developed.
10	12/08/2015	12/15/2015	Test run 2 after solving issues found in test run 1.

Parts List & Cost

S.R.	Description	Manufacturer	Part Number	Qty	Total Cost
1	SJOne Board	-	-	5	$400.00
2	RC Car	Furry Arrma - 2 Wheel Drive - 1/10	-	1	$185.00
3	Ultrasonic Sensor	LV-MaxSonar - EZ1	MB1010	5	$140.00
4	1.8 Color TFT LCD display with MicroSD Card Breakout	Adafruit	ST7735R	1	$19.95
5	SparkFun Venus GPS with SMA Connector	Sparkfun	GPS-11058	1	$49.95
6	Triple-axis Magnetometer (Compass) Board	Adafruit	HMC5883L	1	$9.95
7	CAN Transceiver (Free Samples)	Microchip	MCP2551	6	$0.00
	Total (Including Shipping and Taxes				----

Design & Implementation

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Hardware Design

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Hardware Interface

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Software Design

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Implementation

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Motor and I/O Controllers

ThunderBird is a 2 WD truck. It is equipped with a ARRMA BLX brushless DC motor connected to an BLX80 ESC(Electronic Speed Control). The ESC drives the DC motor according to the PWM(Pulse Width Modulation) signal. The truck's front wheels are connected to a waterproof ADS-7M Metal Geared Steering Servo. The servo and the DC motor are controlled using the PWM pins of the SJOne board.

Pulse Width Modulation - Controlling DC and Servo motors

Fig 1. Initializing pwm signal

Fig 2. Forward pwm signal

Fig 3. Reverse pwm signal

Fig 4. Servo pwm signal

Pulse width modulation is a technique which is used to encode the analog signal into a pulsating signal. The signal is represented as a series of pulses. This signal can be easily generated using the pwm pins of the SJOne board. The ESC is initialized upon passing a PWM signal which is sent by the RF module on the truck. The type of signal is observed by hooking the PWM pin to the digital oscilloscope. The initialization signal is shown in figure 1. A resolution of 1ms is set on the oscilloscope. The PWM signal has a width of 1.5 ms. This signal initializes the ESC. Once the ESC's are initialized, the motors require a signal to accelerate and decelerate. The type of signals for moving the motor forward and backward are realized by hooking the output pin of the RF module to the digital oscilloscope. The forward and backward pwm signals at full throttle are shown in figures 2 and 3 respectively. The respective pwm signal pulses for moving the motors forward and backward are shown below.

• Acceleration PWM signal
  • Forward full throttle - 2 ms
  • Forward medium throttle - 1.8 ms
  • Neutral - 1.5 ms

• Reverse PWM signal
  • Reverse full throttle - 1 ms
  • Reverse medium throttle - 1.2 ms
  • Neutral - 1.5 ms

The PWM value to be set is determined from these calculations:

• PWM is a percentage of the signal frequency
• The signal is of 50 Hz i.e. 20 ms duration
• A 10% of the signal value gives a duration of 2 ms - 10/100 * 20 = 2 ms

The respective percentages for all the signal were calculated and the PWM signals were generated using the PWM.set function. The generated pulses from the SJOne PWM pin is passed to the ESC for initialization and controlling the DC motor. The ESC has 3 connections - Vcc, GND and PWM. SJOne board's GND and PWM are connected to the ESC. The Vcc is supplied from the battery pack.

A sample code demonstrating the PWM signals is written and the motors were controlled using the on-board SJOne switches. Click here for the demo.

The servo motor channel in the RF module is hooked to the digital oscilloscope to determine the initial sequence. It is observed that when the RF transmitter is switched on, the RC remote sends a pwm signal which resets the servo to its starting position. This PWM signal re-centers the truck's wheels. The signal is realized by hooking the data pin from the first channel of the RF module to the digital oscilloscope. The PWM signal is shown in figure 4. The signal is having a pulse of 1.6 ms. The steering on the RC is moved left and right to determine the PWM signals. The signal values were noted from the oscilloscope. The values are tabulated below.

• Steering PWM signal
  • Steer full right - 2 ms
  • Steer full left - 1 ms
  • Steer center - 1.6 ms

A PWM signal having a pulse width between 1.6 ms to 2 ms is used to control the steering towards right precisely. Similarly, a PWM signal having a pulse width between 1 ms to 1.6 ms is used to control the steering towards left precisely. The servo has 3 connections - Vcc, GND and PWM. The servo motor is not connected to a ESC. It doesn't get any voltage if it is not connected to the RF module. The servo motor operates at 6V. For testing, the Vcc of the servo motor is connected to the RF module. The GND from the RF module is made common with the GND from SJOne board. The PWN signal is given as an input from the SJOne board. The PWM signal values were calculated using the procedure shown above. The respective PWM signals were then sent to the servo motor using the PWM pin on the SJOne board for steering the truck.

The on-board switches on the SJOne board are used to steer the truck left and right. A sample code demonstrating this functionality is written and tested. Click here for the demo.

Testing & Technical Challenges

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My Issue #1

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Conclusion

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Project Video

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Project Source Code

• Sourceforge Source Code Link

References

Acknowledgement

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References Used

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Appendix

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