The LEGO Mindstorms and LEGO NXT robot prototyping systems
Whilst the Microsoft Robotics Studio/Visual Programming Language can be used to program a wide variety of 'full size' commercial, research and domestic robotics, it can also be used to programme hobbyist and educational robotics systems such as the original LEGO Mindstorms Robot prototyping system (with the RCX controller brick) and the LEGO NXT robotics system.
We have put together a series of educational robotics activities based on an Open University "TXR174" residential school activity that can be completed using LEGO NXT and LEGO RCX/Mindstorms robots.
To complete the activities you will need a working RCX or NXT robot.
If you are using the Lego NXT Robot System, we recommend using the Tribot model, plans for which can be found on the official Lego NXT construction guides webpage.
If you are using an original LEGO Mindstorms kit, (the one with the big yellow RCX brick!) we recommend using the TXR174 buggy, the plans for which are shown below.
Architecture of a Robot System
The robot you will be using has several different identifiable subsystems:
1) mobility subsystem: the mobility subsystem is based around two wheels just off centre on the robot that are independently driven from two electric motors and a skid at the front of the robot.
2) control subsystem: the control subsystem is based around the RCX brick or the NXT controller brick. Both bricks contain a microcontroller, which is made up from a microprocessor and a limited amount of computer memory, as well as providing an interface to both sensor inputs and effector outputs, such as motors.
3) sensory subsystem: the sensory subsystem uses a switch (also called a touch sensor) to detect when the robot has come into contact with an obstacle, light sensors that measure light levels and a rotation sensor that measure how far the wheels have turned round. The NXT robot will also work with an unltrasonic ("sonar") sensor;
4) power subsystem: the power is supplied to the brick by a set of batteries in its base.
5) mechanical assembly: the LEGO that holds the robot together.
Similarites and Differences Between the RCX and NXT Based Robots
The RCX brick has three sensor inputs and three motor outputs (Handout describing the RCX Brick).
The NXT brick has four sensor inputs and three motor outputs.
- Sensors connected to the inputs provide sensory data that may be used by the program running on the brick to make decisions about what to do next.
- Effectors connected to the motor outputs can be switched on and off independently. For example, motors that are connected to wheels, tracks or legs to move the robot about.
The controller brick can be used to control the robot in several ways:
- it can be instructed directly to turn the motors on and off using a remote control handset, or a remote control signal sent from a PC, using infra-red (RCX - LEGO Mindstorms RCX Tower handout), Bluetooth wireless (NXT) or umbilical USB cable (NXT);
- it can be autonomously controlled with a computer program that runs on the brick itself. The program is written on a PC, compiled into a form that can be run on the operating system running on the controller brick, and then downloaded to the brick through an infra-red link (RCX) or Bluetooth/USB cable (NXT).
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