Day 2 slides UNO summer 2010 robotics workshop

Robotics: Designing and Building

Multi-robot Systems

Day 2

UNO Summer 2010 High School UNO Summer 2010 High School

Workshop

Raj Dasupta

Associate Professor

Computer Science Department

University of Nebraska, Omaha

College of Information Science and Technology

Plan for Day 2

• Designing autonomous intelligence in robots...controller– MyBot: Simple Obstacle Avoidance

– Blinking LEDs

– Controlling motors– Controlling motors

– Camera-based object following

– Finte State machine: Lawn mower like pattern

– Obstacle Avoidance: Code review

– Line Follower: Code review

– Odometry: Simulation only

– Braitenberg: Code review

Designing the Robot’s Controller

• Controller contains the ‘brain’ of the robot

Controller

Read input from

sensors

Send output

to actuators

Designing the Robot’s Controller

• Controller contains the ‘brain’ of the robot

Controller

Read input from

sensors

Send output

to actuators

Reading the Input from the sensors

#include <webots/robot.h>#include <webots/distance_sensor.h>#include <stdio.h>

#define TIME_STEP 32

int main() {wb_robot_init();

WbDeviceTag ds = wb_robot_get_device("my_distance_sensor");wb_distance_sensor_enable(ds, TIME_STEP);

while (1) {wb_robot_step(TIME_STEP);double dist = wb_distance_sensor_get_value(ds);printf("sensor value is %f\n", dist);

}

return 0;}

Reading the Input from the sensors

#include <webots/robot.h>#include <webots/distance_sensor.h>#include <stdio.h>

#define TIME_STEP 32

int main() {wb_robot_init();

This is the “name”

field of the robot’s

sensor from the

scene tree

1. Get a handle to

the sensor device

WbDeviceTag ds = wb_robot_get_device("my_distance_sensor");wb_distance_sensor_enable(ds, TIME_STEP);

while (1) {wb_robot_step(TIME_STEP);double dist = wb_distance_sensor_get_value(ds);printf("sensor value is %f\n", dist);

}

return 0;}

2. Enable the sensor device...the general format of this step is

wb_<sensor_name>_enable (sensor_handle, poll_time)

How often to get

the data from the

sensor

3. Get the sensor data...the general format of this step is

wb_<sensor_name>_get_value (sensor_handle)

Designing the Robot’s Controller

• Controller contains the ‘brain’ of the robot

Controller

Read input from

sensors

Send output

to actuators

Sending the output to actuators

#include <webots/robot.h>#include <webots/servo.h>#include <math.h>

#define TIME_STEP 32

int main() {wb_robot_init();

WbDeviceTag servo = wb_robot_get_device("my_servo");WbDeviceTag servo = wb_robot_get_device("my_servo");

double F = 2.0; // frequency 2 Hzdouble t = 0.0; // elapsed simulation time

while (1) {double pos = sin(t * 2.0 * M_PI * F);wb_servo_set_position(servo, pos);wb_robot_step(TIME_STEP);t += (double)TIME_STEP / 1000.0;

}

return 0;}

Designing the Robot’s Controller

• Controller contains the ‘brain’ of the robot

Controller

Read input from

sensors

Send output

to actuators

A simple example#include <webots/robot.h>#include <webots/differential_wheels.h>#include <webots/distance_sensor.h>

#define TIME_STEP 32

int main() {wb_robot_init();

WbDeviceTag left_sensor = wb_robot_get_device("left_sensor");WbDeviceTag right_sensor = wb_robot_get_device("right_sensor");wb_distance_sensor_enable(left_sensor, TIME_STEP);wb_distance_sensor_enable(right_sensor, TIME_STEP);

while (1) {wb_robot_step(TIME_STEP);

// read sensorsdouble left_dist = wb_distance_sensor_get_value(left_sensor);double right_dist = wb_distance_sensor_get_value(right_sensor);

// compute behaviordouble left = compute_left_speed(left_dist, right_dist);double right = compute_right_speed(left_dist, right_dist);

// actuate wheel motorswb_differential_wheels_set_speed(left, right);

}

return 0;}

A simple example#include <webots/robot.h>#include <webots/differential_wheels.h>#include <webots/distance_sensor.h>

#define TIME_STEP 32

int main() {wb_robot_init();

WbDeviceTag left_sensor = wb_robot_get_device("left_sensor");WbDeviceTag right_sensor = wb_robot_get_device("right_sensor");wb_distance_sensor_enable(left_sensor, TIME_STEP);wb_distance_sensor_enable(right_sensor, TIME_STEP);

while (1) {wb_robot_step(TIME_STEP);

// read sensorsdouble left_dist = wb_distance_sensor_get_value(left_sensor);double right_dist = wb_distance_sensor_get_value(right_sensor);

// compute behaviordouble left = compute_left_speed(left_dist, right_dist);double right = compute_right_speed(left_dist, right_dist);

// actuate wheel motorswb_differential_wheels_set_speed(left, right);

}

return 0;}

Get input from sensor data

Send output to actuator

A very simple controller

A few other points#include <webots/robot.h>#include <webots/differential_wheels.h>#include <webots/distance_sensor.h>

#define TIME_STEP 32

int main() {wb_robot_init();

WbDeviceTag left_sensor = wb_robot_get_device("left_sensor");WbDeviceTag right_sensor = wb_robot_get_device("right_sensor");wb_distance_sensor_enable(left_sensor, TIME_STEP);wb_distance_sensor_enable(right_sensor, TIME_STEP);

Keep doing this as long as

the simulation (and the

robot) runs

Mandatory initialization

step...only used in C language

while (1) {wb_robot_step(TIME_STEP);

// read sensorsdouble left_dist = wb_distance_sensor_get_value(left_sensor);double right_dist = wb_distance_sensor_get_value(right_sensor);

// compute behaviordouble left = compute_left_speed(left_dist, right_dist);double right = compute_right_speed(left_dist, right_dist);

// actuate wheel motorswb_differential_wheels_set_speed(left, right);

}

return 0;}

• How often to get data

from simulated robot into

the controller program

• Every controller must

have it

• Must be called at regular

intervals

• Placed inside main()

MyBot Controller

• Simple obstacle avoidance behavior

– Get IR distance sensor inputs (both L and R)

– If both of these readings are > 500... its an

emergency, back up fastemergency, back up fast

– If only one of these readings is > 500...turn

proportionately to the sensor values

– If both readings are < 500...nothing wrong, keep

moving straight

• Let’s program this in Webots

E-puck: Spinning

• Start spinning left

• If left wheel speed > 1234, stop

E-puck: LED blinking

• Blink the 8 LEDs of the e-puck one after another

– Turn all LEDs off

– Count repeatedly from 1...8– Count repeatedly from 1...8

• Turn LED<count> on

• Note that in this example, we are not using any sensor inputs...the LEDS just start blinking in a circle when we start running the simulation

Camera Controller

• Objective: Follow a white ball

• How to do it...

– Get the image from the camera

– Calculate the brightest spot on the camera’s – Calculate the brightest spot on the camera’s

image...the portion of the image that has the

highest intensity (white color of ball will have

highest intensity)

– Set the direction and speed of the wheels of the

robot to move towards the brightest spot

State-based controller for object

following with camera

Analyze

image to

find the

brightest

spot

Do some math

to calculate the

direction and

speed of the

wheels to get to

the brightest spo

Get image

from

camera

the brightest spo

Set wheel

speed to

the

calculated

values

State Machine

• Controller is usually implemented as a finite

state machine

State i

State j

State k

Transition (i,j) Transition (J,k)

A finite state-based controller for

avoiding obstacles

Stop

One of L or R front

sensors recording

obstacles

40 steps complete

Moving

forward

Make a

U-turn

Both L and R front

sensors not recording

any obstacles

40 steps not complete

Angle turned >= 180

degrees

E-puck Webots Review

• Obstacle Avoidance: Code review

• Line Follower: Code review

• Odometry: Simulation only

• Braitenberg: Code review• Braitenberg: Code review

Summary of Day 2 Activities

• Today we learned about the controller of a robot

• The controller is the autonomous, intelligent part of the robotpart of the robot

• The controller processes the inputs from the robot’s sensors and tells the robot’s actuator what to do

• We wrote the code for different controllers and reviewed some complex controllers

Plan for Day 3

• We will learn how to program some basic

behaviors on the e-puck robot

– Zachary will be teaching this section