Servo - August 2010

The LEGO MINDSTORMS NXT is an amazing piece of technology in more ways than one. With the combination of the power of the NXT and the ability to rapidly prototype mechanisms with LEGO elements, the MINDSTORMS NXT kit really brings together all the components you need to learn the basics of robotics which would otherwise seem like a daunting task. First, we’ll look at what exactly the NXT is good for; where it falls short; and just how far we can push the software. Then, we'll build a driving chassis, learn some basic programming, and talk about gear ratios.

What exactly is the NXT good for?

One of the most common responses I get when I tell people I teach LEGO robotics is "Wait — you can build real LEGO robots? I always thought the LEGO Star Wars kits were cool but I had no idea that there was a kit for building real robots!" The fact is, most people think of LEGO as the brick and have no concept of just how far LEGO has come over the years. The LEGO MINDSTORMS NXT is in every way more advanced than LEGO Star Wars, and it's important that people make a distinction between a 'model' and a 'robot.' The NXT is a robotics development kit — not a static model kit — so if you're looking to build the next big movie re-enactment in LEGO, look elsewhere.

Because the LEGO TECHNIC pieces included in the MINDSTORMS kit are made of plastic and the snap-in connections are relatively weak compared to screws or bolts, the NXT is primarily useful for learning about robotics and prototyping — rather than building the next big ComBot. In the kit, you get a set of three motors, several sensors, a brain, and a bin full of LEGO pieces to build your robot with — as well as software with which to program it.

Where does the NXT fall short?

The biggest shortcoming of the NXT is its inability to deal with extra weight. The pieces are not designed to handle much stress beyond their own weight. So, as soon as you add a few pounds of cargo to your bot, you'll probably notice sagging and strain on the motors. For this reason, it's important to try to keep your LEGO robots lightweight; even then, make sure to use reinforced connections wherever feasible. Scale is another issue that sometimes comes into play with LEGO. LEGO pieces are only so big and only so small. So, your dreams of building a life-sized robotic LEGO car or a miniature 500 g Sumo robot out of LEGO are sadly ill-founded. Besides that, the NXT is capable of some very impressive things.

Just how far can you push the software?

The awesome thing about the NXT is that it's open-source, and there are many languages and programming environments you can choose from to up the performance of your robot. For this reason, the NXT software is capable of some extremely impressive things. Notably, software has been created for NXT robots that balance on a ball, solve a Rubik's Cube, and even draw digital pictures on paper automatically!

For those looking to go beyond using the included software, you might check out Lejos — a Java-based programming language for the NXT — or Robot C — a C-based programming language also compatible with the NXT.

Building Eddie

Now that we've seen some of what's possible with the NXT, let's get on to our project: building a basic, expandable driving platform. The robotic driving platform we're building today is named Eddie 1.0 (the "ED"ucational robot). Eddie has two drive wheels and uses a plastic ball as a caster in the rear. Eddie is very expandable with lots of points to affix attachments, and some other great mechanical features that we'll talk more about later! So, let's get building!