LEGO Mindstorms NXT Carnegie Mellon Dacta Lego Timothy Friez Miha Štajdohar SOURCES:

Principles of Robotics Integrity. Robots hold together throughout the competition (no small task when you are talking about robots built out of Legos). Accuracy. The robot's mechanical outputs and its location acquisition and feedback to the RCX and subsequent programming provide the intelligence for precise performance. Execution. The robot performs the tasks it was designed to accomplish. Repeatability. The robot can perform the exact routine time and time again. Ergonomics. The robot is easy to handle, reconfigure, and change batteries or reprogram if necessary. Efficiency. The robot's design makes optimal use of its parts to execute tasks, minimize friction, and use power.

Why students learn more when they participate in a real challenge?

Sophisticated robots can be build Accuracy of mapping program and NXTAccuracy of mapping program and NXT –Draw letter “E” –Circle Program –Light Following on simulation More videos at ce191nxtMore videos at ce191nxt

Examples of mobile and humanoid robots MotivationMotivation Project OverviewProject Overview Hardware SpecificationHardware Specification –Lego Robot Programming EnvironmentsProgramming Environments –NXC –RobotC Method and ApproachMethod and Approach IdeasIdeas DesignDesign

Mindstorms NXT mindstorms.lego.com

Mindstorms NXT mindstorms.lego.com

Ideas youtube.com...

Brick 4 sensor inputs 3 sensor inputs / motor outputs Programmable

Purchasing NXT Kits Two options (same price; $250/kit) –Standard commercial kit –Lego Education kit education kitAdvantages of education kit –Includes rechargeable battery ($50 value) –Plastic box superior to cardboard –Extra touch sensor (2 total) commercial kitStandard commercial kit –Includes NXT-G visual language

From Idea to Pseudo-Code to software to robot behavior

Thinking about Programming Creating a successful robot takes a team effort between humans and machines. Role of the Robot The robot follows the instructions it is given, thereby carrying out the plan.

Human/Machine Communication 1.Because humans and robots don’t normally speak the same language, a special language must be used to translate the necessary instructions from human to robot. 2.These human-to-robot languages are called programming languages. 3.Instructions written in them are called programs. 4.ROBOTC is just one of many such programming languages that humans use to talk to machines.

Think about “Behaviors” Behaviors are a convenient way to talk about what a robot is doing and what it must do. Moving forward, stopping, turning, looking for an obstacle… these are all behaviors. Complex Behavior Some behaviors are big, like “solve the maze.” Basic or Simple Behavior 1.Some behaviors are small, like “go forward for 3 seconds.” 2.Big behaviors are actually made up of these smaller ones.

Planning the Behaviors

The main principle is braking large behaviors into hierarchies of smaller and smaller behaviors. You have to understand every piece of input-output behavior of a robot

PSEUDOCODE programming language itself, like if-else statements and loops 1.As the programmer becomes more experienced, the organization of the behaviors in English will start to include important techniques from the programming language itself, like if-else statements and loops. hybrid language 2.This hybrid language, halfway between English and the programming language, is called pseudocode. larger programs understandable 3.It is an important tool in helping to keep larger programs understandable.

ROBOTC is text based! 1.Commands to the robot are first written as text on the screen. 2.They are then processed by the ROBOTC compiler into a machine language file that the robot can understand. 3.Finally, they are loaded onto the robot, where they can be run.

Software development options Onboard programs –RobotC –leJOS –NXC/NBC Remote control –iCommand –NXT_Python

NXT Brick Features 64K RAM, 256K Flash 32-bit ARM7 microcontroller 100 x 64 pixel LCD graphical display Sound channel with 8-bit resolution Bluetooth radio Stores multiple programs –Programs selectable using buttons

Programming languages NBC, NXC NXT Python,.NET IDE – interactive development environment

Programming Environments NXC –A High-level language –Similar to C –Stand-alone language (No plug-ins or add-ons) –The program runs in the robot itself. NXC On Bot More Robust language Takes and uses values Robust language can Graphically represent Desired input and results

NXT Python demo bluetooth remote control

Python IDE Python Programming Environments Python 2.4.4Python –Scripted Programming Language –Plug ins PyGame: “Simulated World”PyGame: “Simulated World” PyODE: Shapes, vectorsPyODE: Shapes, vectors PyBluez: Bluetooth communicationPyBluez: Bluetooth communication Python NXT: Python Libraries for NXTPython NXT: Python Libraries for NXT –Programs Light SensorLight Sensor Ultrasound SonarUltrasound Sonar Sound SensorSound Sensor Python NXT PyBluez PyODE PyGame

Mapping ProgramMapping Program –Generate movement on NXT robot, record movement and plot robot’s path in real time in a simulated world. Python + SimulatorPython + Simulator –Thread function, lock on global objects NXC + SimulatorNXC + Simulator –Separate program activates robot, simulator polls output values Moves Robot Method and Approach Sends motor readings Starts Pygames Draws readings on Pygames

ROBOTC firmware tasks, program loop Sensors, motors data bluetooth, messages

RobotC Commercially supported – Not entirely free of bugs Poor static type checking Nice IDE Custom firmware Costly –$50 single license –$250/12 classroom computers

Bluetooth PyBluez

Motors Configured in terms of percentage of available power Built-in rotation sensors –360 counts/rotation –No rotation sensors in old Lego

Working with Motors Selecting Your Hardware Platform 1.RobotC supports a variety of different hardware platforms. Tetrix/FTC robots pure LEGO robots 2.For these exercises we will configure RobotC to include support for the Tetrix/FTC robots as well as pure LEGO robots. 3.The “FIRST Tech Challenge (NXT)” platform is a superset of the “NXT” platform. 4.Whether your robot is using LEGO motors or the Tetrix 12V motors, you can control them with nearly identical code.

On the Robot / Platform Type menu make sure that you have “FIRST Tech Challenge (NXT)” selected. Click on the New icon on the RobotC toolbar to start a new program.

Configuring your Motors You need to tell RobotC how your motors are attached to your NXT. On the Robot menu, open the Motors and Sensors Setup wizard and select the FTC Servo/Motor Ctrl tab. A. Using LEGO NXT Motors –If your robot is using LEGO NXT motors for the drive wheels, select “No controllers configured”:

Using pragmas #pragmaTwo #pragma statements and a comment line should have been inserted into your program looking something like this: #pragma config(Motor, motorA, motorLeft, tmotorNormal, PIDControl) #pragma config(Motor, motorB, motorRight, tmotorNormal, PIDControl) //*!!Code automatically generated by 'ROBOTC' configuration wizard !!*// #pragmaA #pragma is an instruction to the RobotC compiler to change something about how your program gets compiled. config()necessary prefix code to configure your programThe config() pragma tells RobotC to automatically include the necessary prefix code to configure your program to use the motor and sensor ports you specified in the wizard.

Important recommendations to Robot C programmer should not modify 1.You should not modify these lines of code by hand. 2.If the configuration of your robot changes 2.If the configuration of your robot changes, go back into the Motor and Sensor Setup wizard and change the values there. 3.When you exit the wizard it will update the #pragmas to reflect the changes you made. 4.Comment lines in RobotC begin with “//”. 5.Everything that follows a double-slash to the end of the line is ingored by the compiler. 6.The comment inserted by the wizard is a reminder that the #pragmas preceeding it were automatically created for you.

Using Tetrix 12 Volt Motors

Three #pragma statements and a comment line should have been inserted into your program looking something like this: #pragma config(Hubs, S1, HTMotor, HTServo, none, none) #pragma config(Motor, mtr_S1_C1_1, motorRight, tmotorNormal, PIDControl, reversed) #pragma config(Motor, mtr_S1_C1_2, motorLeft, tmotorNormal, PIDControl) //*!!Code automatically generated by 'ROBOTC' configuration wizard !!*// A #pragma is an instruction to the RobotC compiler to change something about how your program gets compiled. tells RobotC to automatically include the necessary prefix codeThe config() pragma tells RobotC to automatically include the necessary prefix code to configure your program to use the motor and sensor ports you specified in the wizard. Using Tetrix 12 Volt Motors

1.You should not modify these lines of code by hand. 2.If the configuration of your robot changes, go back into the Motor and Sensor Setup wizard and change the values there. 3.When you exit the wizard it will update the #pragmas to reflect the changes you made. Using Tetrix 12 Volt Motors

1.Comment lines in RobotC begin with “//”. 2.Everything that follows a double-slash to the end of the line is ingored by the compiler. 3.The comment inserted by the wizard is a reminder that the #pragmas preceeding it were automatically created for you. Using Tetrix 12 Volt Motors

First example of Programming Motors