MARTY: Measurement and Compute
Measurement of Vehicle States
To perform precision automated drifting, it is important to accurately measure the position, pose, and velocity of the vehicle. MARTY uses an off-the-shelf GPS/Inertial Navigation System solution, namely the Oxford Technical Instruments RT4003. This system can use readings from a nearby fixed GPS basestation to enhance its measurements using the popular Real-Time Kinematic technique, resulting in accuracies of about 2 centimeters in practice.
The angle of the car's body relative to the direction of the car's velocity vector is the sideslip, or drift angle. The central challenge of drifting is controlling large values of sideslip with precision, and so it is critical to measure this angle accurately. On MARTY, this is done by comparing the relative positions of two GPS antennas located on each side of the roof, yielding an absolute estimate of the angle of the car body.
The RT4003 provides measurements of the vehicle's absolute position, velocity, and acceleration states at a rate of 250Hz.
Two GPS antennas are installed on either side of the roof. By measuring the angle between these antenna locations, the GPS/INS system is able to accuracy estimate the angle of the vehicle, which is critical for drifting.
Close-up view of the driver's side GPS antenna.
Computer Systems
Due to their physics-based reasoning, the controllers described in Automated Vehicle Control Beyond the Stability Limits are computationally efficient, and are implemented on a (relatively slow) 900MHz dSpace MicroAutoBoxII automotive-grade, hard-real-time computer. The DS1401 is configured run at 250Hz, and interfaces with the steering, throttle, and navigation subsystems. Although not used in this thesis, a faster auxiliary Linux-based PC is available on an internal network for heavier run-time computation.
The computers are installed behind the seats.
Close-up view of the computer systems, showing LTE modem, router, hard real-time computer, and auxiliary Linux computer. The red box is the Oxford Technical Instruments RT4003 GPS/INS receiver.