Chapters

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01 Why a robot joint needs a gearbox
An electric motor is a device that is good at spinning fast and bad at pushing hard.…
02 Module, teeth and the involute
Two numbers describe almost everything about a gear: the module m, which is the size of a tooth, and the number of teeth z, which is the size of the w…
03 Profile shift: rescuing a small pinion
A robot joint wants the biggest ratio it can get from one stage, which means the smallest pinion it can get away with.…
04 Contact ratio: why gears are quiet or loud
The transverse contact ratio ε α is the average number of tooth pairs carrying load at any instant.…
05 Tooth forces and flank pressure
The force between two involute teeth acts along the line of action, at the working pressure angle.…
06 Planetary trains
A planetary — sun, planets, ring, carrier — is how you get a large ratio in a short, coaxial package that shares the load between several meshes.…
07 Harmonic and cycloidal drives
These two dominate robot joints, and both work on the same trick: mesh two toothed rings that differ by a tiny number of teeth, and the difference — n…
08 How the calculator works, and what it does not do
Where every number comes from What Source Standard and shifted spur geometry, inv α w KHK Gears, Calculation of Gear Dimensions σ H0 , Z H , Z E , Z ε…