 By simply adding a small idler gear between each larger gear, the result is a series of rollers, all being powered in the same direction.Idler gears can also transmit rotation among distant shafts in situations where it would be impractical to simply make the distant gears larger to bring them together.Not only do larger gears occupy more space, but the mass and rotational inertia (moment of inertia) of a gear is quadratic in proportion to its radius.