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differentialDriveKinematics

Differential-drive vehicle model

Description

differentialDriveKinematics creates a differential-drive vehicle model to simulate simplified vehicle dynamics. This model approximates a vehicle with a single fixed axle and wheels separated by a specified track width. The wheels can be driven independently. Vehicle speed and heading is defined from the axle center. The state of the vehicle is defined as a three-element vector, [x y theta], with a global xy-position, specified in meters, and a vehicle heading, theta, specified in radians. To compute the time derivative states for the model, use the derivative function with input commands and the current robot state.

Creation

Description

example

kinematicModel = differentialDriveKinematics creates a differential drive kinematic model object with default property values.

kinematicModel = differentialDriveKinematics(Name,Value) sets properties on the object to the specified value. You can specify multiple properties in any order.

Properties

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The wheel radius of the vehicle, specified in meters.

The vehicle speed range is a two-element vector that provides the minimum and maximum vehicle speeds, [MinSpeed MaxSpeed], specified in meters per second.

The vehicle track width refers to the distance between the wheels, or the axle length, specified in meters.

The VehicleInputs property specifies the format of the model input commands when using the derivative function. Options are specified as one of the following strings:

  • "WheelSpeeds" — Angular speeds for each of the wheels, specified in radians per second.

  • "VehicleSpeedHeadingRate" — Vehicle speed and heading angular velocity,specified in meters per second and radians per second respectively.

Object Functions

derivativeTime derivative of vehicle state

Examples

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Create a Robot

Define a robot and set the initial starting position and orientation.

kinematicModel = differentialDriveKinematics;
initialState = [0 0 0];

Simulate Robot Motion

Set the timespan of the simulation to 1 s with 0.05 s timesteps and the input commands to 2 m/s and left turn. Simulate the motion of the robot by using the ode45 solver on the derivative function.

tspan = 0:0.05:1;
inputs = [50 40]; %Left wheel is spinning faster
[t,y] = ode45(@(t,y)derivative(kinematicModel,y,inputs),tspan,initialState);

Plot Path

figure
plot(y(:,1),y(:,2))

Figure contains an axes. The axes contains an object of type line.

References

[1] Lynch, Kevin M., and Frank C. Park. Modern Robotics: Mechanics, Planning, and Control 1st ed. Cambridge, MA: Cambridge University Press, 2017.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Introduced in R2019b