Have you ever gone somewhere on a bike, a school bus, a train, or in a car? Your answer is most likely yes — you might even ride more than one of them every day. All of these vehicles have one important thing in common — wheels. Around for thousands of years, wheels make vehicles very good at traveling on flat surfaces like paved roads. Some all-terrain vehicles (like tanks or dirt bikes) are even designed to be driven off-road through fields, rocks, and dirt. But when it really comes down to it, legs are sometimes better for getting around. For example, you might be able to ride your bike through mud and gravel, but chances are you probably would not ride it completely off-trail in the middle of the woods, or up a flight of stairs (we know some professional bike riders do this — but it is difficult and very dangerous).

Many different types of robots use wheels, legs, or something in between. The NASA Curiosity rover uses large wheels to help it handle the rough Martian terrain. Back here on Earth, Boston Dynamics has developed robots that can walk on four legs like a dog or even two legs like a human. In between these two. we have robots like RHex from the University of Pennsylvania and Whegs™ from Case Western Reserve University. These robots use attachments that spin continuously in one direction (like wheels), but they are not circular — they have at least one distinct point that comes in contact with the ground, like a leg (you might have figured out by now that the "Whegs" robot takes its name after a combination of the words "wheel" and "leg"). This gives the robots some of the advantages of wheels, like good balance and speed on flat ground, along with some of the advantages of legs, like climbing stairs and traveling over rough ground.

In this project, you will use a LEGO® Mindstorms® kit to build the body of a basic robot car, along with a series of different attachments to replace the wheels. You will then test the performance of the different attachments in three different ways — their ability to climb "stairs" (made from a pile of textbooks), speed on flat ground (like a wooden floor), and speed on rough ground (through grass or gravel outdoors). You will use these tests to determine if some attachments work better than others in different situations.

The video shows you how the robot we built at Science Buddies handled climbing a staircase made of textbooks with different motor attachments. We will provide some basic directions for building a robot similar to this one in the Procedure section, but remember that this is an engineering design project — you do not have to follow our directions exactly. The size, shape, and nature of your robot and its attachments are up to you — limited only by your imagination (and the size of your LEGO collection)!