GearRatios

Gear Ratios

Motors are powerful, but they do not always spin at exactly the right speed or with exactly the right strength for every task. That is where gears come in!

A gear ratio describes the relationship between two or more gears that are connected together. Mastering gear ratios is the secret to building fast drivetrains, powerful lifting arms, and reliable intakes without burning out your motors.

Why does this matter?

A robot that drives fast might not be able to lift heavy objects, and a robot that lifts heavy objects might not drive very fast. Gear ratios are how you tune that balance for whatever your robot needs to do.

Speed vs. Torque

Every motor has a fixed amount of total power. You can think of it like a budget — you can spend it on speed or on strength, but not both at the same time.

• Speed: How fast the gear or wheel spins, measured in RPM (Rotations Per Minute).
• Torque: The twisting force of the gear — essentially how much weight it can push or lift.

The Golden Rule: If you want more speed, you lose torque. If you want more torque, you lose speed. You cannot have both at once.

When two gears connect, each plays a role:

• Driving Gear (input): Connected directly to the motor. This gear provides the power.
• Driven Gear (output): Connected to the wheel, arm, or mechanism. This gear receives the power.

Calculating a Gear Ratio

To find the gear ratio, divide the number of teeth on the driven (output) gear by the number of teeth on the driving (input) gear:

Examples

1. Gearing Up for Speed (1:X)

Imagine two gears: one with 42 teeth (on the motor) and one with 14 teeth (on the wheel).

• What happens: For every full spin of the motor gear, the wheel gear spins 3 times. The robot moves 3x faster!
• The cost: The wheel gear only has 1/3 of the motor’s original strength. If the robot is too heavy, the motor might stall.

2. Gearing Down for Torque (X:1)

Now swap the roles — the 14-tooth gear is on the motor and the 42-tooth gear is on the mechanism:

• What happens: The motor spins 3 times to make the output move once. The output moves slowly, but with 3x the lifting strength!
• The cost: The mechanism only moves at 1/3 the motor’s original speed.

Idler Gears

An idler gear is a third gear placed in between the driving and driven gears.

Surprisingly, idler gears do NOT change the gear ratio at all. So why use them?

• To bridge a gap: If your driving and driven gears are too far apart to touch, an idler gear fills the space.
• To flip direction: Two gears spin in opposite directions. Adding an idler gear flips the output direction so both gears spin the same way.

Compound Gear Trains

Sometimes a simple two-gear system cannot give you enough of a ratio without needing enormous gears. The solution is a compound gear train — a chain of multiple gear pairs stacked together, each adding more mechanical advantage.

A compound gear train works by locking pairs of gears on the same axle. The first pair gives you one ratio, and the second pair multiplies on top of that.

To calculate a compound gear ratio:

1. Break the system into individual gear pairs (stages).
2. Calculate the ratio of each stage separately.
3. Multiply all the individual ratios together.

Connection to Code

Here is an important detail: your Motor Encoders only measure how much the motor shaft spins — not how much the actual mechanism moves. If you have a 5:1 gear reduction on a lifting arm and you want the arm to raise 90 degrees, you need to tell the motor to spin 5 times as much:

Always account for your gear ratio in your code, or your movements will be way off!