CDS 110b: Control Implementation

This page contains the material for a sequence of lectures on control law implementation. Each lecture is its own section, with an outline and links to handouts and other reference material. This page is focused on the course project for Winter 2006: steering control for Alice.

• Course Project Information

Alice Architecture

This introductory lecture will provide information on the course project requirements and some background on the system that we are going to use.

Lecture Outline

1. Course Project Structure
2. Brief Introduction to Alice
   • High level architecture
   • Control structure
3. Alice operations (video): desert testing, site visit

Lecture Materials

• Lecture presentation
• JFR05 paper - this is an overview paper written by the students that built Alice. Recommended reading for understanding the high level architecture.
• Alice documentation - this is part of the DGC wiki; feel free to look around since not everything is yet linked to the documetnation page

Dynamics and Control Specification

This lecture will introduce the dynamics and control of Alice.

The dynamics of Alice can be represented at several different levels. The simplest model, the bicycle model, is a kinematic model that can be used for simple path planning and control when no sliding is present. More complicated models include tire friction models and allow slip forces to be included. A significant complication is the presence of magnitude and rate constraints in the steering controller. Results from DGC05 NQE testing and the site visit will be used to illustrate the level of performance achievable on the system.

The control specification for the project to solve the following design problem:

• Given a set of waypoints (xy coordinates), find a feasible path for the system through the waypoints and create a trajectory file that will be used by your controller.
• Design a controller that follows the trajectory you have specified with errors of no more than 50 cm transient error and 20 cm steady state error in the lateral direction
• Analyze the performance and robustness of your system assuming 10% variation in the wheel length and sensor noise corresponding to 50 cm "jumps" in position (from the GPS).

Lecture Outline

1. Video of Alice follower performance
   • External view
   • Internal (planner) view
2. Alice dynamics
   • Bicycle model
   • Nonlinear effects: magnitude and rate limits
3. Controller specification (from DGC05)

Lecture Materials

• Lateral Slip Prevention, Detection and Recovery for High-Speed Autonomous Off-Road Driving, H. Huang, Senior Thesis, 2005 - this paper provides a fairly detailed description of the bicycle model, including frictional forces. This is the model that is implement in the asim program.

Control Implementation

Lecture Outline

1. Interface hardware
   • Actuation: steering, (throttle, brake)
   • Sensing: GPS, IMU, steering angle
   • Serial interface summary
2. Interface software (follow)
   • Quick overview of sparrow
   • Description of the control architecture (handout)
   • Overview of the user interface
3. Implementing controllers on Alice
   • Example: PI control of steering