Gears

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Contents

Types of Gears

Spur Gears

Spur gears.png
Gear-spurgearhead.jpg
Inside the Globe motor gearhead.
A closeup of the gearhead, clearly showing 5 stages of spur gear reduction (the gearhead output shaft is disconnected) resulting in a 187.68:1 gear ratio.



Rack and Pinion

Rack and pinion.png


Bevel Gears

Bevel gears.png


Helical Gears

Helical gears.png
Gear-helical2.jpg


Worm Drives

Worm drive.png


Planetary Gears

Gear-planetary-anim.gif
Gear-planetarystage.jpg
Gear-planetary.jpg


Ball Screw/Lead Screw

Gear-ballscrew-small.gif
Gear-ballscrew2-small.jpg


Harmonic Drive Gears

Harmonic gears.jpg
Gear-harmonicdrive.gif
Gear-harmonicdrive2aligned.jpg
Gear-harmonic-drive-anim.gif


Spur Gear Geometry

For external spur gears (most common), the gear geometry is as shown in the figure below. The line of action is the line that passes through the intersection of the pitch circles and also tangent to the base circles.

Gear-spurdetails.jpg
Gear circle geometry.png


Spur Gear Meshing and Forces

Gear meshing results in contacts with normals along the line of action, so the resultant force, W is along this line. This results in both tangential and radial forces, Wt and Wr, on the gear pair. When these gears are mounted on a shaft, the radial force causes a bending moment while the tangent force causes both a bending moment and a torque.

Gear triangles.png

References

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