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m3pi

Table of Contents

  1. Hello World!
  2. Hardware
  3. Library and API
  4. Resources
  5. Useful numbers
  6. m3pi with Remote Procedure Call (RPC) Interface
  7. Related Pages
  8. Resources

The m3pi robot consists of an mbed connected to the Pololu 3pi robot

The 3pi contains a low level MCU that takes care of motor control, optical sensors and other hardware oriented functions. When the 3pi is programmed with the stock "slave" firmware, will make this functionality available through an API over a serial port.

The m3pi consists of an mbed Microcontroller running the high level functions and control algorithms, implemented by API calls to 3pi hardware. The mbed Microcontroller is then free run protocol stacks and communications interfaces (bluetooth, Zigbee, Wifi and so on) as well as control algorithms, mass storage for preprogrammed routines and so on.

m3pi

Hello World!

This simple program will drive the m3pi forward, spin it left, reverse it and spin it right.

Import program
m3pi_HelloWorld - main.cpp

00001 #include "mbed.h"
00002 #include "m3pi.h"
00003 
00004 m3pi m3pi;
00005 
00006 int main() {
00007 
00008     m3pi.locate(0,1);
00009     m3pi.printf("LO World");
00010 
00011     wait (2.0);
00012 
00013     m3pi.forward(0.5); // Forward half speed
00014     wait (0.5);        // wait half a second
00015     m3pi.left(0.5);    // Turn left at half speed
00016     wait (0.5);        // wait half a second
00017     m3pi.backward(0.5);// Backward at half speed 
00018     wait (0.5);        // wait half a second
00019     m3pi.right(0.5);   // Turn right at half speed
00020     wait (0.5);        // wait half a second
00021 
00022     m3pi.stop();       
00023 }
You Tube Clip

Hardware

There is very little connectivity required between the mbed 3pi work

mbed3pi
GroundGround
VinVcc
p8nRST to the 3pi
p9 (from mbed)RXD (to the 3pi)
p10 (to the 3pi)TXD (from the 3pi)

Library and API

Import library
m3pi - m3pi Class Reference

Public Member Functions

m3pi ()
Create the m3pi object connected to the default pins.
m3pi (PinName nrst, PinName tx, PinName rx)
Create the m3pi object connected to specific pins.
void reset (void)
Force a hardware reset of the 3pi.
void left_motor (float speed)
Directly control the speed and direction of the left motor.
void right_motor (float speed)
Directly control the speed and direction of the right motor.
void forward (float speed)
Drive both motors forward as the same speed.
void backward (float speed)
Drive both motors backward as the same speed.
void left (float speed)
Drive left motor backwards and right motor forwards at the same speed to turn on the spot.
void right (float speed)
Drive left motor forward and right motor backwards at the same speed to turn on the spot.
void stop (void)
Stop both motors.
float pot_voltage (void)
Read the voltage of the potentiometer on the 3pi.
float battery (void)
Read the battery voltage on the 3pi.
float line_position (void)
Read the position of the detected line.
char sensor_auto_calibrate (void)
Calibrate the sensors.
void calibrate (void)
Set calibration manually to the current settings.
void reset_calibration (void)
Clear the current calibration settings.
void leds (int val)
Write to the 8 LEDs.
void locate (int x, int y)
Locate the cursor on the 8x2 LCD.
void cls (void)
Clear the LCD.
int putc (int c)
Send a character directly to the 3pi serial interface.
int getc ()
Receive a character directly to the 3pi serial interface.
int print (char *text, int length)
Send a string buffer to the 3pi serial interface.

Resources

Useful numbers

  • Speed of rotation: 720 degrees per second at half speed
  • Forward/Backward: 470mm per second at half speed

m3pi with Remote Procedure Call (RPC) Interface

The RPC interface is a very powerful way to remotely execute functions. Michael Walker did some excellent work on the RPC interface, and wrote the RPC Interface cookbook page.

The main initial interest for m3pi is to execute RPC calls over a serial interface. This could be directly from USB serial, or using any one of many serial-cable-replacement techniques, including Bluetooth and Zigbee.

Import program
m3pi_USBSerialRPC - main.cpp

00001 #include "mbed.h"
00002 #include "m3pi.h"
00003 #include "SerialRPCInterface.h"
00004 
00005 SerialRPCInterface Interface(USBTX, USBRX); // defaults to 9600
00006 m3pi m3pi;
00007 
00008 int main() {
00009 
00010     m3pi.locate(0,1);
00011     m3pi.printf("USB RPC");
00012 
00013     // do nothing, just wait for RPC comands over USB
00014     while (1) {}
00015 }

To keep things simple initially, the first experiment will be to use the mbed USB Serial port. If this is your first encounter with mbed, you can read more about the USB Serial port mbed provides on the Serial PC page in the handbook.

If you are using Windows, you will need to install a driver to have access to the mbed USB Serial port. You can find more information on the Windows Serial Configuration page.

To get this example working:

  • Build the USB RPC example, and program it into your mbed
  • If you are using Windows, run the Windows Serial Configuration
  • Open a serial terminal, if you are not sure which to use, see the Serial Terminals page in the handbook.
  • Connect to your mbeds Serial port using standard/default "9600 8-N-1" settings
  • Ensure that your serial terminal sends "CR+LF" on transmission
  • Start typing commands to control your m3pi

/media/uploads/chris/m3piusbrpcteraterm.png

Typing /m3pi into the terminal will display the list of commands possible. For reference they are:

A subset of the function in the m3pi class can be called over RPC, they are:

  • forward - both motors forward at the same speed (0.0 to 1.0)
  • backward - both motors backwards at the same speed (0.0 to 1.0)
  • left - Rotate, left motor backwards, right motor forwards (0.0 to 1.0)
  • right - Rotate, right motor backwards, left motor forwards (0.0 to 1.0)
  • left_motor - Direct control of direction and speed (-1.0 to 0.0)
  • right_motor - Direct control of direction and speed (-1.0 to 0.0)
  • stop - As it says :-)
  • battery - Read the battery voltage as a float
  • line_position - Where the line is detected, from left to right (-1.0 to 1.0)
  • sensor_auto_calibrate - Run the auto calibration routine

Bluetooth Interface

Import programm3pi_BluetoothRPC

Accepts RPC commands over bluetooth (RN42)

Last commit 12 May 2011 by Chris Styles

Resources

All wikipages