Gears: What are Gears and Gear Ratios

Gears are fundamental components in LEGO® Technic models, enabling the transfer of rotational motion between different parts. They are particularly useful for adjusting the speed and torque of a mechanism, like an RC car or robotic arm.

When gears of different sizes are paired, they can either increase or decrease the rotational speed. This alteration comes with a trade-off: as speed increases, torque decreases, and vice versa. This inverse relationship is crucial to understand when designing gear-driven systems.

For instance, if you double the speed of a gear, the torque output will be halved. By carefully selecting gear ratios, you can optimize the performance of your LEGO® Technic models.

Gear Ratios: The Heart of LEGO® Technic Mechanisms

A gear-set typically consists of two or more gears, which can be identical or different in size. The relationship between these gears, known as the gear ratio, determines how they interact to transmit motion and torque.

Let’s explore a few examples to better understand gear ratios.

Input Gear

16 Tooth Gear

Output Gear

16 Tooth Gear

Ratio

1:1 ratio

Input shaft speed and output shaft speed are the same. Torque remains the same.

Input Gear

8 Tooth Gear

Output Gear

24 Tooth Gear

Ratio

3:1 Ratio

Input gear spins 3 times for every 1 turn of the output.

We can calculate this ratio by dividing 24 by 8 which gives us 3. Therefore our output speed is 3 times slower than the input shaft but the torque of the output shaft is 3 times higher than the input. In this case, our input shaft has to spin 3 times for every 1 rotation of the output shaft.

Input Gear

24 Tooth Gear

Output Gear

8 Tooth Gear

Ratio

1:3 Ratio

Input gear spins once for every 3 turn of the output.

We can calculate this ratio the same way as above but because we are increasing the speed of the output, we write the ratio as 1:3 instead of 3:1. Therefore our output speed is 3 times faster than the input shaft but the torque of the output shaft is 3 times lower than the input. In this case, our input shaft spins once for every 3 rotations of the output shaft.

Exercise

Below is a Technic panel with various gear sets, can you calculate the ratio for each gear set?

Hint: Gears featured in the photo above and below include 8, 12, 16, 20, 24, 28, 36 and 40 tooth gears

The next lesson will teach you how to use what you’ve learned here in practical ways and show you different types of gearboxes