Gear Train Lab
Change the number of teeth and watch what happens. Bigger gears turn slower but push harder. Drag any gear to turn it by hand, or press play and let the motor run.
Theory of Machines · Diploma / B.TechBrass bar is the motor, teal bar is the output. Power stays at 20.9 W on both sides: gears trade speed for torque, they never create energy.
Try this
0 of 4 doneMake the output turn exactly 3 times slower than the driver.Hint: output teeth = 3 × driver teeth
Gear up: make the output spin faster than the motor.Hint: what if the output gear is the small one?
Make the output turn the same way as the driver.Hint: look at the checkbox
Get at least 100 N·m out of the output shaft.Hint: combine motor torque with a big ratio
What's happening
Teeth set the ratio
Meshing teeth move past each other one for one. A 24-tooth gear driven by a 12-tooth gear needs two turns of the small gear to complete one turn.
Slower means stronger
When the output turns slower, its torque goes up by the same factor. That's why a bicycle's low gear makes hills easier but your legs spin faster.
Idlers flip direction
Every pair of meshing gears reverses rotation. An idler adds one more flip, so the output turns the same way as the driver, while the ratio stays unchanged.
Who figured this out?
Antikythera mechanism
About 2nd century BCE, GreeceAn ancient Greek bronze calculator with dozens of meshing gears, used to predict the positions of the Sun and Moon and the dates of eclipses.
Ismail al-Jazari
1206, MesopotamiaDescribed water clocks and machines driven by gears in his Book of Knowledge of Ingenious Mechanical Devices.
Leonardo da Vinci
Around 1500, ItalyFilled his notebooks with drawings of gear trains that change the speed and direction of turning.
Learn more
- Gear train · Wikipedia
- Antikythera mechanism · Wikipedia
Check yourself
1. A 12-tooth driver turns a 36-tooth output at 30 rpm. How fast does the output turn?
2. You add an idler gear between the driver and the output. What changes?
3. The output gear is smaller than the driver. Its torque is…
Common questions
How do you calculate a gear ratio?
Divide the number of teeth on the output (driven) gear by the number of teeth on the driver gear. A 12-tooth driver turning a 36-tooth output gives 36 ÷ 12 = 3, written 3:1. The output turns 3 times slower and, ignoring friction, with 3 times the torque.
How do gears work?
The teeth of two gears lock together, so when one gear turns it pushes the other round. Because the teeth pass one for one, a bigger gear turns more slowly than a smaller one. The slower gear pushes harder: it trades speed for torque.
What is a gear train?
A gear train is two or more gears meshed together to pass rotation from one shaft to another. A simple gear train has one gear per shaft. A compound gear train has two gears fixed on the same shaft, which multiplies the ratios of each stage.
What does an idler gear do?
An idler gear sits between the driver and the output. It doesn't change the overall gear ratio, because its teeth cancel out. It reverses the direction once more, so the output turns the same way as the driver, and it can bridge a gap between two shafts.
Does a bigger gear ratio give more torque?
Yes. Output torque equals input torque multiplied by the gear ratio, and output speed equals input speed divided by the ratio. Power stays the same apart from friction losses, which are typically 2–5% per pair of gears.
Where are gear trains used in real life?
Bicycles, car gearboxes, clocks and watches, mixer grinders, wind turbines and robots all use gear trains to change speed, torque or direction of rotation.
Ideal gears, no friction losses. Real gearboxes lose roughly 2–5% of power per mesh as heat.
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