Waypoint Navigation for a Skid Steer UGV

Introduction

This page describes autonomous waypoint navigation of a small skid steer unmanned ground vehicle. A description of the vehicle kinematics, feedback sensors, and control loops will be presented. In addition, experimental test data will be presented that demonstrates the effectiveness of the SmartIMU as a feedback sensor as well as the UGV's path.

Background

Feedback Sensors

The SmartIMU sensor was used for Global Position (Latitude, Longitude), yaw angle, and Yaw angular rate feedback. These measurements were used to navigate the vehicle to the various predefined waypoints.

Control Loops

A simulation model was created to demonstrate the control loop structure and compare the modeled and experimental results. The controller consists of a yaw rate inner loop which tracks the desired yaw rate input using a PD controller. The innerloop is feed by the desired yaw outer loop which tracks the yaw toward the waypoint. Similar to the implementation, sateration limits were added to limit the commanded yaw rate and actuator commands. The testing controller was designed with the same inner and outter control loops, using the SmartIMU sensor data as feedback for the control system.

Testing Results

The model results show a slightly damped second order response to a step input:

The actual testing results show similar results as shown:

Although the simulation and testing results are similar, there exists several factors that interfere with the control of this type of platform. The friction between the wheels and the ground varies significantly with terrain. Also motor inertia and wheel slippage has not been considered for modeling this vehicle. This effort has demonstrated the integration of the SmartIMU sensor into a small unmanned ground vehicle for waypoint navigation. IATech will continue to provide testing results for various unmanned platforms to demonstrate the versatility of IATech's product line for many real world problems.