Electromechanical Systems

Prospect Eleven’s mechanical systems replace the arms and legs of a human driver, allowing the vehicle to manipulate the steering wheel, brake pedal, and throttle.

Steering control is accomplished via direct gear connection with the steering column. An optical rotary encoder provides precise position feedback. The vehicle’s throttle is controlled electronically. The brake pedal is mechanically controlled by a custom-built linear ball-screw actuator used for autonomous operation, and a pneumatic piston for emergency braking. These are connected to the brake pedal with steel cable. The cable connection allows a human operator to use the brake pedal even during autonomous operation. A potentiometer monitors the position of the actuator shuttle in its track. Prospect Eleven also has the ability to shift the transmission, although the necessary actuators were disabled for the Grand Challenge competition.

Computing, Infrastructure, and Electronics

Prospect Eleven uses only two computers for the entirety of its processing. One computer is dedicated to on-board stereo image processing and obstacle detection, while the other computer handles the main command decisions and interfaces with the vehicle’s sensors and actuators. Both computers were custom assembled from off-the-shelf parts, and are comparable to high-end consumer PC’s. Each computer is housed in 4U rack cases, mounted in a shock-isolated rack. The vision computer, known as Prospero, contains an AMD Athlon 64 3200+ with 2GB of RAM. The command computer, called Santiago, runs an Intel Pentium 4 at 3.0GHz with 2GB of RAM. Communication between the two computers is over local ethernet through a gigabit switch. The stereo camera uses an IEEE 1394 connection, while most other devices connect via Serial ports. Two wireless routers, one configured as a client and the other as an access point, allow both computers to connect to the internet and developers to connect remotely to the computers.

A LabJack data acquisition unit handles analog and digital I/O to allow for computer interfacing with on-board electronics and sensors such as indicator lights, wheel odometry data, transmission position, brake lights and engine conditions. Power to the steering and braking motors is interfaced with a RoboteQ motor controller.

A deep-cycle battery bank and a 1500 Watt inverter/charger unit provide a steady power supply to Prospect Eleven’s onboard electronics. The system charges using the vehicle’s stock alternator while the engine is on. While parked in the garage, Prospect Eleven charges from a standard power outlet.

Software

All of the code for Prospect Eleven was written using Microsoft’s Visual Studio development environment. The C# programming language was used exclusively due to its ease of debugging and convenient component interfacing. The only exception is in the vision processing algorithms, whose speed requirements necessitated the extra optimizations of C++.