Tutorial: Connect LEGO wheels an gears to a RoboBuilder servo

Among the biggest nuisances in the hobby robotics world is finding good wheels, and finding a way to connect them to whatever motor you want to use.

LEGO makes the largest variety of high-quality wheels and tires in the world (as well as a decent selection of gears and other mechanical parts). RoboBuilder makes smart, modern servos that also act as great continuous-rotation gearmotors with built-in encoders and other feedback. This led me to wonder: how can I use them together?

You will need:

Here are the parts listed above. The servo is at the top; that Technic knob wheel is on the lower left, and the RoboBuilder servo horn is at right.
Use the four screws to attach the knob wheel to the servo horn. I did this with the servo horn pushed into the servo (where it will hold quite tightly just by friction, though you can secure it with another screw if you want).

Note that the 15 mm (long) screws I used are really about 5 mm too long for this job, so they stick out quite a bit. The RoboBuilder kit doesn't appear to come with 1 x 10 mm screws, but if you could find some, I think they would work perfectly. The screws sticking out like this is why I chose a LEGO wheel with a deep well on one side.

Next, insert the LEGO axle into the knob wheel.
Finally, push your wheel onto the LEGO axle. That's it! It's a very secure connection, with no wobble I can perceive. Of course the wheel is only held on by friction, in the standard LEGO manner — but I've never found this to be a problem. (The tolerances on LEGO parts are extremely tight.)

Last Updated: 08/06/09 . . . . . . webmaster@strout.net