Gears

What is a gear and how does it work?

• A gear is a Wheel with teeth that is connected to an axle.• Gears are used to transmit power

from one part of a machine to another part.• For example: A bicycle uses a gear

and chain to take the power from the pedals to the back wheel.

In a car, gears transmit the power from engine to the driveshaft that ultimately powers the wheels.

Compounded gear system

• A compounded gear system is when TWO or MORE gears are used together to power a system.

• When two gears are used together, the input rotation and output rotation will be in opposite directions

• That is why we use a idler gear to set the input rotation and output rotation to the same direction.

4 Different ways to use gears

• Gears for speed• Gears for force• Worm gears • Rack and pinion gears

Diagram

Gears for speed

• In this simple gearsbox, there are 3 wheels.• Large gear with 40 teeth, medium gear with

20 teeth and small gear with 10 teeth.• When the Large gear is turned around ONE

time, the medium gear will turn TWO times as much and the small gear will turn FOUR times as much as the Large gear.

• Thus when we use a BIGGER DRIVER gear the system will be FASTER

Diagram 2

Gear for Force

• The same simple gear system is used in the next diagram.

• But now we use the smaller gear(10 teeth) as the DRIVER gear.

• Now the driver gear has to be turned FOUR times to let the large gear turn ONE time

• The DRIVEN gear will turn SLOWER but will turn much stronger.

Worm gears • This gear system uses a screw-like gear to

drive a bigger gear.• This gear can change one rotation direction

into another rotation direction with a different angle.

Rack and pinion

Rack and pinion gear

• This gear takes the rotation movement and turn it into a side-to-side movement.

• The Pinion(gear wheel) has teeth and it goes into the holes of the rack(flat ridged bar) and when the wheel is turned the flat bar will move to one side.

• Example: when a steering wheel of a car is turned it is hooked to a pinion that makes the rack moves side to side that swivel the wheels.

Different types of gears• Spur gears• Bevel gears• Rack and spur gears• Rack and worm gears• Worm and spur gears

Spur gear

Rack and spur gear

Worm and spur gear

Worm and rack gear

Bevel gear

Speedratio

• Speedratio is when we want to determine how fast the one gear will turn against the other one.

• Formula: Speedratio = Teeth on the DRIVEN gear ÷ Teeth on the DRIVER gear.

Example

• Driver gear has 20 teeth• Driven gear has 100 teeth

• Speedratio = Teeth on the DRIVEN gear ÷ Teeth on the DRIVER gear.

• Speedratio = 100 ÷ 20• Speedratio = 5:1

• This means that when the Driver gear rotate FIVE times, the Driven gear will rotate ONE time

• This system will be used for FORCE