Technology and Engineering · High school

A three-speed gearbox

Change gear: as the gear ratio grows, the output slows down but the torque rises; the power stays the same.

In the learning section below the figure, predict, try, complete the tasks and check yourself with short questions.

Fig. 1A three-speed gearbox

Tap the gear knob, pick a gear below or take the box apart

Neutral

Parts and inside

Apart0%

With the box apart, hover over a part, tap it or pick it from the list.

The cutaway removes the upper half of the case and the top of the front wall: you see the gears, the collars and the oil. Purple gears are the pairs carrying the power right now; the gears turn in the ratio of their numbers of teeth.

Pick a part to see what it does and what it is made of in a real gearbox.

Gear

Motor speed

Load

Numbers of teeth

Try your own gears: type a whole number from 12 to 48 in each box (press Enter or leave the box). If the two gears of a pair differ too much, the larger one does not fit in the case; the figure takes the nearest value that fits and says why.

Fixed pair (input → countershaft)

Input gear

Countershaft, fixed pair

Gear 2 pair (countershaft → output)

Countershaft, gear 2

Output, gear 2

Gear 1 pair (countershaft → output)

Countershaft, gear 1

Output, gear 1

Load · 6 kg

–

Gear ratio–
Output speed–
Most torque at the output–
Torque the load needs2.94 N·m
Most in this gear–
Rope speed–

Power balance0 W

Neutral: the output shaft is disconnected from the motor and the drum brake holds the load. The gears still turn.

Learn

Progress is kept on this page only; no points are given.

1Predict
2Try
3Explain

A 6 kg load lifts easily in gear 1. If you shift to gear 3 without changing the motor speed, what happens?

Purple gears: the path the power takes right nowGold knob: gear leverThe numbers come from one model: an adjustable-speed electric motor that gives at most 2 N·m of torque, a drum of radius 5 cm for the rope, and no friction. With the default gears the fixed pair has a ratio of 2; gear 1 is 4 : 1, gear 2 is 2 : 1 and gear 3 (the input shaft locked straight to the output) is 1 : 1. Each disc is 2 kg (at most 10 discs are drawn) and the hanger’s own mass is ignored. The turning is slowed down in the drawing.

How does a gearbox work? The trade between speed and torqueRead the article