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iRobot Create Robot
This is a simple project that shows how to interface mbed to control the iRobot Create robot. The Create is basically a Roomba without the vac parts designed for educational users. The Create has an internal microcontroller and a serial port. Over the serial port you can send motor commands and read back sensor packets. The Create comes with a serial cable, but it uses RS-232 signal levels so that it can plug into a PC serial port. To control it using mbed you need to connect to the serial port with TTL levels and provide power for the mbed module.
mbed Hardware Interface¶
Inside the Create robot cargo area is a DB25 connector that has all of these connections. With only four jumper wires you can connect everything needed. This is not a standard pinout for a serial connector, all of the pins have special uses for the Create. Pin assignments can be found in the Create User Manual.
Here are the four connections to the Create:
| mbed | Create DB25 Pin | Description |
|---|---|---|
| p9 | 1 - RXD (0 – 5V) | Serial input to iRobot Create |
| p10 | 2 - TXD (0 – 5V) | Serial output from iRobot Create |
| Vin | 8 - Switched 5V | Provides a regulated 5V supply (low current) |
| GND | 16 - GND | iRobot Create battery ground |
mbed Create Demo Code¶
The demo code sends out serial commands to the Create. Serial commands can be found in the Create Open Interface Manual. Sensor values are also reported back over the serial port, but are not used in the short demo code. Here is a short video of the demo code running on the Create:
The demo code is shown below. Basically it waits for the Create to power up, and then starts sending a sequence of commands over the serial port with time delays between commands.
Create_Demo
#include "mbed.h"
Serial device(p9, p10); // tx, rx
// Definitions of iRobot Create OpenInterface Command Numbers
// See the Create OpenInterface manual for a complete list
// Create Command // Arguments
const char Start = 128;
const char SafeMode = 131;
const char FullMode = 132;
const char Drive = 137; // 4: [Vel. Hi] [Vel Low] [Rad. Hi] [Rad. Low]
const char DriveDirect = 145; // 4: [Right Hi] [Right Low] [Left Hi] [Left Low]
const char Demo = 136; // 2: Run Demo x
const char Sensors = 142; // 1: Sensor Packet ID
const char CoverandDock = 143; // 1: Return to Charger
const char SensorStream = 148; // x+1: [# of packets requested] IDs of requested packets to stream
const char QueryList = 149; // x+1: [# of packets requested] IDs of requested packets to stream
const char StreamPause = 150; // 1: 0 = stop stream, 1 = start stream
const char PlaySong = 141;
const char Song = 140;
/* iRobot Create Sensor IDs */
const char BumpsandDrops = 7;
const char Distance = 19;
const char Angle = 20;
int speed_left = 200;
int speed_right = 200;
void start();
void forward();
void reverse();
void left();
void right();
void stop();
void playsong();
void charger();
// Demo to move around using basic commands
int main() {
// wait for Create to power up to accept serial commands
wait(5);
// set baud rate for Create factory default
device.baud(57600);
// Start command mode and select sensor data to send back
start();
wait(.5);
forward();
wait(.5);
stop();
wait(.1);
reverse();
wait(.5);
left();
wait(1);
stop();
wait(.1);
right();
wait(1);
stop();
wait(.5);
// Play a song
playsong();
wait(10);
// Search for battery charger IR beacon
charger();
}
// Start - send start and safe mode, start streaming sensor data
void start() {
// device.printf("%c%c", Start, SafeMode);
device.putc(Start);
device.putc(SafeMode);
wait(.5);
// device.printf("%c%c%c", SensorStream, char(1), BumpsandDrops);
device.putc(SensorStream);
device.putc(1);
device.putc(BumpsandDrops);
wait(.5);
}
// Stop - turn off drive motors
void stop() {
device.printf("%c%c%c%c%c", DriveDirect, char(0), char(0), char(0), char(0));
}
// Forward - turn on drive motors
void forward() {
device.printf("%c%c%c%c%c", DriveDirect, char((speed_right>>8)&0xFF), char(speed_right&0xFF),
char((speed_left>>8)&0xFF), char(speed_left&0xFF));
}
// Reverse - reverse drive motors
void reverse() {
device.printf("%c%c%c%c%c", DriveDirect, char(((-speed_right)>>8)&0xFF), char((-speed_right)&0xFF),
char(((-speed_left)>>8)&0xFF), char((-speed_left)&0xFF));
}
// Left - drive motors set to rotate to left
void left() {
device.printf("%c%c%c%c%c", DriveDirect, char((speed_right>>8)&0xFF), char(speed_right&0xFF),
char(((-speed_left)>>8)&0xFF), char((-speed_left)&0xFF));
}
// Right - drive motors set to rotate to right
void right() {
device.printf("%c%c%c%c%c", DriveDirect, char(((-speed_right)>>8)&0xFF), char((-speed_right)&0xFF),
char((speed_left>>8)&0xFF), char(speed_left&0xFF));
}
// Charger - search and return to charger using IR beacons (if found)
void charger() {
device.printf("%c%c", Demo, char(1));
}
// Play Song - define and play a song
void playsong() { // Send out notes & duration to define song and then play song
device.printf("%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c",
Song, char(0), char(16), char(91), char(24), char(89), char(12), char(87), char(36), char(87),
char(24), char(89), char(12), char(91), char(24), char(91), char(12), char(91), char(12), char(89),
char(12),char(87), char(12), char(89), char(12), char(91), char(12), char(89), char(12), char(87),
char(24), char(86), char(12), char(87), char(48));
wait(.2);
device.printf("%c%c", PlaySong, char(0));
}
Once you have the demo running, you can get started on more complex robotics projects. First, you would want to read the incoming serial sensor packets to use sensor data to modify the commands sent. Additional sensors could be added to the robot such as IR and Sonar to detect objects without hitting them. With additional sensors, it is likely that you will need to provide a 5V regulated supply since the current is very limited on the internal 5V supply being used for mbed. This is possible without an additional battery by using the 18V battery voltage from the Create's battery. It is also available on the DB25 connector pins. Make sure that the 5V voltage regulator chip used can tolerate that high of an input voltage. A special 5V 3A switching regulator board designed just for this purpose is available from Robotics Connection. It is common to mount a sheet of plastic over the cargo bay area using the 6-32 screw holes provided. Additional sensors and hardware can then be attached to the plastic sheet. One such project using a clear plastic sheet to mount a robot arm is seen below.
