© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 Tree Surveying Existing Design See Teacher Guide for printing instructions

© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 Opening Activity Find something to replace the wheel. Your idea must be: Cheap Easy to manufacture Easy to use Durable Energy-efficient in use Scalable to many sizes, large and small Able to do something the wheel can’t

© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 Opening Activity Legs are difficult to manufacture and operate Treads are more expensive and less energy- efficient than wheels (and they use wheels inside them anyway) Flying is very energy-inefficient, expensive, and hard to do Hovercraft are also energy-inefficient Crawling like a slug is slow and expensive A ball is basically a 3D wheel, but has trouble moving in a straight line Replace the wheel.

© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 Opening Activity WHY??? “Reinventing the wheel” means wasting effort on trying to develop a new solution when a perfectly good one already exists Don’t reinvent the wheel! Use it! Side note: “Reinventing the square wheel” is a related idiom that means wasting effort on trying to develop a new solution when a perfectly good one already exists… and coming up with something even worse Replace the wheel.

© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 Auto-Caliper A measuring tool that takes and displays measurements of tree size already exists –Instead of inventing a new one, build and improve on the existing design –How does it work? –Build and analyze one The proverbial “wheel”? –Probably not, but good enough for us Existing Tree Caliper Design This measuring device already exists, why spend time building a different one?

© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 Existing Design: Technical Review Data Hubs & Wires Display Block

© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 Data Hubs & Wires Many blocks have data hubs which can be opened by clicking the notch in the lower-left corner of the block. A data hub contains many data plugs, which allow information to flow in and out of the block. Data wires control the flow of data between blocks. Output plugs typically send out a sensor value, or the result of a computation. Such information usually goes into another block’s input plug, allowing the reading or result to be used as a value inside the block. Speed Controlled by Sensor Ultrasonic Sensor distance output plug controls the value of the Move Block’s power setting

© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 Display Block: Number The Display Block displays images or text on the NXT’s LCD display. The Display Block does not have built-in support for displaying Numbers. In order to display a Number, you must first convert it to Text using the Number to Text Block. The Display Block must also be configured to display Text, or it will ignore the wired-in value. Display Ultrasonic Sensor Value Ultrasonic Sensor reading is converted to Text then displayed on the NXT’s LCD screen

© 2006 Carnegie Mellon Robotics Academy Designed for use with the LEGO MINDSTORMS ® Education NXT Software and Base Set #9797 It’s inefficient to reinvent solutions that already exist and work Instead, build and adapt existing solutions to meet your new needs Summary You will study an existing caliper measuring device to understand how it works You will build the device You will write the default program