Activity 15: Gearing in Vehicles

Activity Presenter: Deryn Martin, Engineering student at Robert Morris University, former FLL team member, and FLL Mentor

Duration: Three 15-minute periods

Content Areas: Science, Engineering

Grade Level: Middle School Science – Simple Machines and Engineering Design (though it's been used successfully with grades 3-5 and adults in informal settings – NO robotics experience required)

Materials

4 wheels
8 axles (2 long for reaching between the wheels)
8 bushings
2 long beams

Background

Using gears in vehicles is extremely important. Gears are used in the steering column as well as the motor. The combination of gear types varies depending on the function of a particular part of the vehicle. In a sports car, which is light and fast, some of the torque can be sacrificed for speed. In semi-truck, which has to haul heavy loads, the gear combination has to provide a lot of torque or the truck won’t move.

Vehicles can increase speed or torque by gearing up or gearing down. Gearing up means that a larger gear is attached to the motor and is driving a smaller gear. As you learned in Activity 14, gearing up from a bigger to a smaller gear at the point of action – in this case the wheel - increases the speed but decreases the torque. Gearing down means that a smaller gear is driving a larger gear, which increases the torque but decreases the vehicle’s speed. Gearing up allows you to go faster usually on a level road, and gearing down helps when driving up hill or hauling a heavy load.

On a bicycle or when you drive a car, you’ll “shift up” for a higher cruising speed on level roads, but “downshift” to go down a steep hill at a safe speed or to get the power you need to make it up a mountain road. Shifting up and shifting down are the same as gearing up and gearing down.

Task

1. Play around with the gear ratios on the wheels on your robot and try to maximize the speed while maintaining enough torque for the robot to move.

2. Describe the gear combination that would make one vehicle better at hauling cement, and the other better at racing.