This lesson combines LEGO®’s capability for building powered machines having gears with PocketLab Voyager’s ability to make detailed measurements of the resulting motion. This lesson uses parts from LEGO®’s Simple & Powered Machines Set. Students will construct a powered car with two interlocked gears—the input drive gear on the motor and the output driven gear on the rear wheel axle. By using Voyager’s range finder to determine the translation speed of the car, students will calculate the gear ratio and compare this ratio to that determined from the ratio of the number of teeth on the gears. Using the car’s translational speed along with measurement of wheel diameter, students will determine the angular velocity of the wheels as well as the RPM of the motor. Finally, students will replace the wheels with a set of wheels having a larger diameter, predict the translational speed of the car with the larger wheels, and then compare their prediction with Voyager range finder measurements of speed. Detailed student instructions are included.