drive with pid control

8/10/2019 Drive With PID Control

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Drive with PID Control

This example shows how to simulate a simple closed-loop control algorithm in Simulink and

how to run it on an Arduino board.

Supported Hardware:

Arduino Leonardo

Arduino Mega 2560

Arduino Mega ADK

Arduino Pro

Arduino Uno

Available versions of this example:

Arduino Mega 2560 board:

Arduino Mega2560 Drive Open-loop

Arduino Mega2560 Drive Closed-loopOn this page

Introduction

Prerequisites

Required Hardware

Task 1 - Build the Vehicle

Task 2 - Build the Motor Controller

Task 3 - Simulate Open-Loop Control Model

Task 4 - Run Open-Loop Control Model on the Arduino Mega 2560 Board

Task 5 - Simulate Closed-Loop Control Model

Task 6 - Run Closed-Loop Control Model on the Arduino Mega 2560 Board

Other Things to Try

Summary

Introduction

In a vehicle using independent wheel control, applying the same power to each wheel

generally does not result in the vehicle moving straight. This is caused by mechanical and

surface differences experienced by each of the wheels. To reduce deviation in the vehicle

heading, a better approach is to use a closed-loop controller which adjusts the power applied

to two motors based on the difference in their rates of rotation. One such controller is a well-

known proportional-integral-derivative (PID) controller.

PID control is a basic control loop feedback mechanism. The controller minimizes the

difference between the measured and the desired value of a chosen system variable by

adjusting the system control inputs.

This example shows you how to simulate the controller using a simple plant model, first with no

feedback control (Open-Loop Control), and then with feedback control (Closed-Loop Control).
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This example also illustrates how to switch between simulating the PID controller and running it

on hardware in the same model.

Prerequisites

We recommend completingGetting Started with Arduino Hardware.

Required Hardware

To run this example you will need the following hardware:

Controller board:

Supported Arduino board

USB cable

Motor controller parts:

Texas Instruments SN754410 quadruple high-current half-H driver

Two 10 kOhm resistors

Small breadboard

Breadboard wires

A four-wheel vehicle:

A mobile platform with four wheels powered by four DC motors

Two optical encoders wired to front DC motors

A battery pack consisting of five AA 1.5V batteries

A single pole, single throw (SPST) switch

Notes:

This example was tested with the four-wheel vehicle built using DFRobot 4WD Arduino-

Compatible Platform w/Encoders.

Other vehicle kits can be used as long as they have the same mechanical characteristics (four

wheels, four DC motors and two encoders).

With a minor modification to the controller connections, a vehicle with only two DC motors can

be used as well.

Encoders used in this example are ten-step encoders. Different encoders can be used with

minor modifications to the example models.
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Task 1 - Build the Vehicle

1.Assemble the mobile platform. Attach the two DC motors with encoders to the front wheels.

2.Attach the other two DC motors to the rear wheels. If your platform has only two DC motors,

let the rear wheels rotate freely.

3.Assemble the battery pack and attach it to the mobile platform using suitable fasteners.

4.Connect the positive end of the battery pack to the switch using the breadboard wires.

Note: If you are using DFRobot 4WD Arduino-Compatible Platform w/Encoders kit, follow the

vendor's instructions.

Task 2 - Build the Motor Controller

The Arduino board alone cannot provide high enough current to power DC motors. For that

purpose, you will build the motor controller based on the Texas Instruments SN754410

quadruple high-current half-H driver.

1.Assemble the motor controller using the following circuit diagram. This example shows how

to assemble on Arduino Mega2560 board.


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2.Connect the controller to the vehicle battery pack following the same circuit diagram.

Task 3 - Simulate Open-Loop Control Model

This step illustrates that independently powered wheels cause deviations in vehicle heading.

1.Open themodel.Observe two subsystems in the model.

2.Open the Open-Loop Controllersubsystem. This subsystem controls the vehicle driving.

Observe that the controller does not use the difference between two encoder outputs to control

the motors.

3.Notice the Motorssubsystem. The subsystem contains both simulated and actual motors.

The Environment Controller block takes the outputs of the simulated or actual motors,

depending on the current environment. This allows you to represent both simulated and actual

motors in one model. As an alternative, you may create two models, one for simulation, and

the other one for running on actual hardware.

4.Click Runbutton in the Simulink toolbar. Click the Scopeblock and observe that

theEncoder Output Mismatchincreases over time. This indicates that the vehicle will not

move straight.
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Task 4 - Run Open-Loop Control Model on the Arduino Mega 2560 Board

1.Disconnect the battery power wire leading to the Vin terminal on the Arduino Mega 2560

board since the board will get powered via a USB cable.

2.Connect the Arduino Mega 2560 board to your host computer using USB cable.

3.In the model, click the Deploy To Hardwarebutton on the toolbar.

4.After the model is downloaded, disconnect the USB cable from your Arduino Mega 2560

board.

5.Connect back the battery power wire leading to the Vin terminal on your Arduino Mega 2560

board.

6.Place the vehicle on the ground and turn the vehicle switch on. The model runs on the boardand the vehicle starts moving.

7.Notice that the path of the vehicle is not straight, as predicted by the simulation.

8.Turn the vehicle switch off.

Task 5 - Simulate Closed-Loop Control Model

1.Open themodel.Observe two subsystems in the model.

2.Double-click PID Controllersubsystem. Notice that the proportional (P) control is used to

synchronize two motors when the vehicle runs straight. Also, notice that during a turn, no

synchronization is applied.

3.Click Runbutton in the Simulink toolbar. Click the Scopeblock and observe that

theEncoder Output Mismatchremains close to zero. This indicates that the vehicle will skewless compared to the Open Loop Controlmodel.
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Task 6 - Run Closed-Loop Control Model on the Arduino Mega 2560 Board

1.Disconnect the battery power wire leading to the Vin terminal on the Arduino Mega 2560

board since the board will get powered via a USB cable.

2.Connect the Arduino Mega 2560 board to your host computer using USB cable.

3.In the model, click the Deploy To Hardwarebutton on the toolbar.


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4.After the model is downloaded, disconnect the USB cable from your Arduino Mega 2560

board.

5.Connect back the battery power wire leading to the Vin terminal on your Arduino Mega 2560

board.

6.Place the vehicle on the ground and turn the vehicle switch on. The model runs on the board

and the vehicle starts moving.7.Observe that the path of the vehicle is straighter, as predicted by the simulation.

8.Turn the vehicle switch off.

Other Things to Try

Adjust the PID Controllersettings. Improve the vehicle's ability to move straight on a rough or

tilted surface.

Summary

This example showed how to simulate and implement a basic closed-loop controller on an

Arduino Mega 2560 board. In the example you learned that:

Open-Loop Control does not ensure straight driving in a vehicle with independently powered

wheels.

Closed-Loop Control uses the difference between two encoder outputs to calculate the power

that should be applied to each wheel individually.

Both simulated and actual hardware may be used in the same model, provided that a

mechanism for switching between them exists.

drive with pid control

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