Yellow input wave generator of oval shape always contacts with all rollers of a closed chain. A link of the chain has an elongated pin to create a revolution joint with orange conrod. The latter has revolution joint with blue output crank. The input, the output and the gear are coaxial. The chain performs a complicated motion forming “waves”.
Tooth number of grey fixed gear Zg = 30
Link number of the chain Zc = 28
Transmission ratio: i = Zc / (Zg – Zc)
If (Zg – Zc) small and Zc large, i can be very large.
The input and output rotate in opposite directions.
For this case 14 revolutions of the generator correspond 1 rev. of the blue output crank. Velocity of the latter is not constant.
For comparison: if chain, conrod and crank of this mechanism are merged into a flexible part, it becomes a familiar harmonic drive of flexible gear.
Replacement of revolution joint (the orange conrod) with a prismatic one (a slider sliding in a runway on the output crank) is possible.