Tanks are fun to build and have the added advantage of easily climbing over obstacles. You will notice that a lot of tank designs will have larger center wheels. Having a larger center wheel can be particularly useful if you want to climb up ramps or go over bumps. Without the center wheel, if you are climbing over a bump, there is a chance of getting stuck. However, when you have a larger center wheel, your robot will often be tilted. Your robot will not be constantly parallel to the ground, which can be a problem with calibrating any sensors you might be using for navigation. I encourage you to play around with larger center wheels on your tanks, but the models I provide here have smaller center wheels. You will need the parts shown in the following screenshot in the Bill of Materials to assemble the tread-bot:

Start with your chassis:

You will now make two of the following submodels, which are the tread assemblies. You will start out by attaching pins, axles, and bushings to a 13-mod beam as shown in the following screenshot:

Next, attach the spoked black wheel hubs to the axles. You will secure the spoked wheel hubs onto the axles with the yellow half bushings. The gray tire hub is centered on the treads using the red bushings. If you were to add the rubber tire onto the tire hub, this would easily make the center of the tread slightly bigger. As it is, the bare tire hub lends just enough support so that the treads do not collapse.

To finish the tread assembly, add the tread belt to each assembly:

Now, add one tread assembly onto the right-hand side of the robot with the long axle inserted into the larger motor. You will notice that the black friction pins in the beam will insert into the side of the large motor:

Now, add the other tread assembly onto the left-hand side of the robot with the axle into the large motor and the friction pins again into the side holes in the motor:

Finally, to prevent the treads from sliding, add two yellow half bushings onto the end of the axles that are sticking through the large motors.

Although both the Retail Edition and the Educational Editions of the EV3 kit come with treads, you will find that the Retail Edition tread is a simple belt. This limits what you can do with the tread, but it does make it easy to use. The rubber does have more friction than a plastic tread, but only comes in one size.