The drive gear meshes with a larger driven gear whose radius ratio
sets the speed reduction (and torque multiplication). That output
shaft cranks a four-bar linkage, converting rotation into the coupler
point's characteristic looping path.
RPM_out = RPM_in / gear_ratio
T_out = T_in · gear_ratio · η
η = 1 − friction_loss
- Input torque — torque applied to the drive gear's shaft.
- Gear ratio — teeth ratio between driven and drive gears; higher ratio trades speed for torque.
- Joint friction — mechanical losses at gear mesh and linkage pins, reducing overall efficiency.
This is the same trade-off every gearbox designer balances: a
higher ratio gives more torque at the output shaft but always at
the cost of rotational speed, since power (torque × RPM) is roughly
conserved minus friction losses.