Every year, the students in my middle-school Physics by Design class at the Shady Hill School in Cambridge, MA build “meet and greet” robots after they learn Robolab programming. The robot must respond to a wave or a handshake with some sort of enthusiastic display—lights, motion, music, etc. This year, for the first time, we built the robots using the NXT instead of the RCX. To my delight (and somewhat to my surprise), this year’s robots were the best ever. In the past, most of the RCX robots had waved back and flashed lights. This year, the NXT robots picked up their feet and danced, rocked back and forth, even high-fived the hand-shaker. The sturdiness and flexibility of NXT beam-and-peg building allowed my students to express their creativity in ways that were difficult with the RCX.

Resources A Simple NXT Car Ultrasonic Pendulum Lesson Gallery

Initially, I had been worried that building with pegs and bricks would be harder for students to master and more intimidating for beginners than the brick-based RCX system. While the students did find the NXT frustrating at first, especially as they tried to build simple cars, they soon became adept builders. In fact, when we built geared-down “snail” cars—the last car across the finish line wins—their comfort in building with beams resulted in some extremely slow cars. The motor of this year’s slowest car must turn 5.3 x 1044 times in order for the wheels to turn once. The gear trains this year were so elaborate that I had to borrow extra 40-tooth gears from another school, which had never happened in my previous eight years of teaching with the RCX.

Switching to the NXT gave us additional sensors to explore. With the ultrasonic distance sensor, we built burglar alarms that detected when people approached, pendulums that logged the distance to the ground in order to measure period and frequency, and trombone-like musical instruments that changed pitch as the slide moved in and out. With the sound sensor, we made clap-on/clap-off machines to control lights and applause meters to measure audience reaction. I elected to use ROBOLAB 2.9 with the NXT to retain the data logging activities that were important to the course learning goals.

So, clearly the quality of the creations and the range of possible projects have improved. What else has my class gained by switching to the NXT? There are a host of small improvements—the ease of downloading programs, the adjustable volume on the NXT, the more sensitive light sensor, the ability to synchronize the motors. Inevitably, there are also some losses. I miss the simplicity of the RCX motors and the ability to switch their polarity by reversing a lead. I miss the ease with which one could build a sturdy two-motor car.

Unfortunately, the biggest problem I found in switching from the RCX to the NXT occurred right at the beginning—the loss of the RCX’s appealing simplicity. Suddenly, I had a class of beginning builders and a not-so-intuitive piece of equipment. With the RCX, I had often had the students start the year by designing simple cars by themselves. With just a brief explanation of how to wire the motors, they could build functional, if not exactly elegant, vehicles. With the NXT, this activity became impossible. The students could not build an NXT vehicle with no instructions—and the building plans that came with the set were complicated and time-consuming. Instead, I have the students start with a non-motorized building project—such as a chair for a small teddy bear, using the NXT as the seat. This less-daunting project lets the students get used to beam-and-peg building without having to worry about the motors. From there, I move to building cars. I provide plans for a simple two-motor car; the students may build an exact replica of my car, a variation of it, or a car of their own design. After completing these two projects, I find that the students are comfortable enough with NXT building to tackle more complicated projects with confidence.

When I decided to use the NXT this year, I was not sure if I was making the right decision. After seven months in the classroom, I am happy I decided to switch—and I can hardly wait to see what my students invent next!

by Barbara Bratzel

Barbara Bratzel is a science teacher at the Shady Hill School in Cambridge, MA. She is also the author of Physics by Design (for the RCX and NXT) book from College House Press.