2002 Intelligent Ground Vehicle Competition Design Report. Grizzly Oakland University

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1 2002 Intelligent Ground Vehicle Competition Design Report Grizzly Oakland University June 21, 2002 Submitted By: Matt Rizzo Brian Clark Brian Yurconis Jelena Nikolic

2 I. ABSTRACT Grizzly is the product of just under a year of work conducted by undergraduate engineering students that had never before designed or built an autonomous vehicle. The main focus of the team was to learn and understand new technologies and attempt to make them work in a real-world project. The ground vehicle that is entered in this year s competition has a Global Positioning System (GPS), an omni-directional self-stabilizing camera system for vision, a pair of LIDAR distance sensors to measure distances to hard objects, and wheels speeds sensors to help control the vehicle. A laptop is used to combine all sensors and control the vehicle. In addition to the design and construction of the vehicle our team attempted to use this project to help other students, both college and high school, in their understanding of engineering principles. In addition, this year s team was pleased to bring back to life Oakland Universities AUVS student chapter, and we hope that it will remain active for many years to come.

3 Table of Contents I. ABSTACT II. Grizzly Subsystems a. Electrical i. NovAtel GPS ii. Omni-Directional Self Stabilizing Camera iii. Mitsubishi LIDAR iv. Innovation First Robot Controller 1. Victor H Bridges 2. Spike Relay 3. Hall Effect Wheel Speed Sensors v. Power system 1. Battery 2. Fuse setup 3. 5v Converter 4. RS422 to RS232 converter b. Mechanical i. Mabuchi RS550 PF-6534 ii. Step down gearbox, 147 to 1 ratio c. Navigation/Control i. A* Path Planning / Obstacle Avoidance Program ii. Sensor Fusion with Kalman Filter iii. Software PI Controllers iv. C++ Dynamic Link Libraries III. System Integration IV. Costs V. Conclusion

4 II. Grizzly Subsystems Electrical Subsystem The electrical subsystem of Grizzly consists of the necessary components that are required for autonomous navigation. The NovAtel Pro-Pak4E GPS unit contains the Euro4 that is capable of tracking 12 satellites and has accuracy below 2 meters in both latitude and longitude. The Pro-Pak4E is further enhanced with the GPS-600L1 antenna with NovAtel s Pinwheel (patent pending) aperture couple slot array technology. The Pro-Pak4E also has the ability to output the vehicles forward velocity and current heading. All communication with the device is done using a standard PC serial line and custom-built C++ program to read in the GPS data packets. It is also important to note that NovAtel was gracious enough to give us an educational discount on the price of the unit. Without this discount we probably would have not been able to purchase this device. The Omni-Directional Self-Stabilizing Camera system is the main sensor on the vehicle. It is responsible for detection white lines painted on the ground, and finding any other obstacles that are in front of the vehicle. The camera system uses a simple and cheap USB web cam, and a convex mirror that is designed for trucks. The advantage of this system is its field-of-view (FOV) is greatly enhanced with the use of a convex mirror. The only drawback is the decrease in resolution. In order to determine distances on the ground, the camera is calibrated and a map of the mirror is built using Sugano- Type Fuzzy Logic. The Self-Stabilizing platform, which was designed by Ruben de Schipper, is used to maintain a vertical positioning of the camera. The camera is calibrated while vertical to the ground so any deviation from this will cause errors in the positioning calculations. The Self-Stabilizing platform uses 2 angular rate sensors (gyros) and 2 linear accelerometers to maintain the platform s position. The system also uses sensor fusing to estimate the angle of the platform.

5 Self-Stabilizing platform Omni-Direction Camera The Mitsubishi LIDAR s where donated to our team by Mitsubishi Electric and have the ability to measure distances using an infrared laser. Grizzly uses 2 of these units, where each unit has a FOV of 12 degrees wide by 4 degrees tall. Within the 12 degree span the unit takes 80 measurements that can measure as far as meters. The major disadvantage to these units is their narrow FOV. To fix this problem a rotating platform with the two LIDAR s fixed 90 degrees to each other was looked into; the prototype platform did not provide the results we wanted and with time running out, we abandoned the idea for this year. The major problem encountered in the prototype was that lack of smooth free action and scanning time. Communication with the LIDAR s is accomplished using a Hitachi SH2 micro-controller and a standard PC serial port to connect the SH2 to the laptop. Each LIDAR uses a serial port from communications, so the SH2 was used to compress the 2 serial ports down to 1. To control the motors on the vehicle an Innovation FIRST Robot Controller was used to act as an interface/relay between the laptop and the H-Bridges. The Innovation First Controller is designed for the FIRST high school robotics competition. A C++

6 program was developed to communicate with the controller using a serial port line. The program allows the computer to have complete control over the commands being sent to the H-Bridges. The wheel speed calculations are fed into the FIRST Controller s digital I/O lines, which are then sent back to the PC. Included with the FIRST Controller are the Victor H Bridges and the Spike Relay. These all connect to control pins that are controlled by the FIRST Controller. The final piece of the electrical system is the power system. Grizzly s power system consists of fuse/circuit breaker distribution blocks that allow independent protection for all electrical components, and a 12V to 5V output DC-DC converter. A single sealed lead-acid 12V 18Ah battery is used to power the entire system with an estimated run time of 3 hours. Mechanical Subsystem Grizzly was constructed using only the simplest of framing materials. This choice has two major advantages, one, the overall cost of construction is low, and two, the vehicle is simple and requires limited resources. The underlining frame is a child s Power Wheels toy build by Fisher Price. This frame was chosen because of its ability to handle rough terrain, its light weight, its already had a built in motor and gear box and it was easy to add on to. Two Mabuchi RS550 PF-6534 motors with accompanying 147:1 gearboxes are used to power the 18-inch plastic wheels; these motors are connected directly to the H- Bridges previously mentioned. During field tests a safe vehicle speeds was found to be much lower than the max speed, so during normal operations the motors are not running at their maximum speeds.

7 Navigation/Control Subsystem The overall control of the vehicle is governed by a navigation program that used the A* path planning method. The A* method consisted of a grid being laid out around the vehicle and each cell within the grid can either be passable or impassable. The A* program is given the target cell position and its starting position and it searches the grid for the target. Once the target is found it traces its steps back to find the path. The A* program utilizes a heuristic, of the distance from its current position to the target, in its calculations. This ensures that the path found would be the optimal path given the particular grid. The A* method is very flexible because it does not differentiate between types of obstacles; they can be white or yellow lanes, construction barrels, or white 5 gallon jugs. It takes into account the value of the cells it interacts with, being either passable or impassable. This feature makes it much easier for the programmers because the same program, with only limited changes, can be used for both the Autonomous and Navigation Challenges. A* example #1 A* example #2 The navigation program starts by taking in all current sensor and target data. It then builds the grid and marks all cells near calculated obstacle positions as impassable. Once the grid is built, the A* program finds the path to the target. The path known, a heading error is calculated by looking out on the path a fixed distance on the path. A PI (Proportional/Integral) Controller is used to minimize the heading error. This process is repeated until the target is reached or the vehicle is stopped.

8 The navigation programs construction is unique in the fact that C++ Dynamic Linked Libraries (DLLs) where used to separate individual components of the software. For example, all serial port communication run on its own thread or process. This allows constant communications with a device and ensures a constant steady stream of sensor data and motor commands to be received and sent. The code separation that is required when using DLLs helped tremendously because as the sophistication of our vehicle grew, so did the amount of code that was being written. Without the use of DLLs, the amount of code in a single program would have been so large that debugging would be very difficult. Also included in the navigation program is a Kalman Filter that is used to combine wheel speed sensors with the GPS positioning data to calculate a more accurate position. The Kalman Filer code was written in C++ and uses a free matrix algebra C++ library for the matrix calculations. The filter estimates the position of the vehicle using both the raw GPS data along with dead-reckoning calculations that are done using the Hall Effect sensors that measure the RPM of each wheel. This has proven very useful and has enhanced our already accurate GPS. III. System Integration Grizzly is made up of many subsystems but without a core center nothing would happen. The core of Grizzly is the laptop which reads in all sensor data, makes a decision on what the next actions should be, and then commands the motors to manipulate the vehicle. As mentioned before all communication to and from the laptop is made through RS-232 serial ports. The exceptions are the joystick and the camera, which are USB. The laptop being used is a Dell Latitude CPt 400MHz, and the backup laptop is a Sony Vaio, 800 MHz Athlon

9 IV. Costs Equipment NovAtel GPS + Antenna $ Intel USB WebCam ~$100 Frame/Motors/Gearbox ~$200 Innovation FIRST Controller $800 (donated) Microsoft Sidewinder Joystick $25 Batteries $100 12v to 5v DC-DC converter $80 Hitachi SH2 $300 Stamp micro-controller $100 PCMCIA-to-quad serial port card $360 Convex Mirror $10 Self-Stabilizing platform? (custom made) Cost V. Conclusion Grizzly is a capable autonomous vehicle that can navigate itself to pre-determined GPS positions while avoiding obstacles along its traverse. Grizzly is also able to compete in the Autonomous Challenge where it will stay within the lanes throughout the course while avoiding any and all obstacles. Grizzly was an excellent learning experience and has open all of the participating students to many new fields and topics that where unknown a year ago. The chance to work with today s cutting-edge technologies, such as GPS, is an experience more engineering students should have.