Planetary Gear Box

A planetary gearbox is a gearbox with the input shaft and the output shaft aligned. A planetary gearbox is used to transfer the largest torque in the most compact form (known as torque density). The bicycle’s acceleration hub is a great example of a planet-wheel mechanism: Have you ever wondered...

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Product Description

A planetary gearbox is a gearbox with the input shaft and the output shaft aligned. A planetary gearbox is used to transfer the largest torque in the most compact form (known as torque density).

The bicycle’s acceleration hub is a great example of a planet-wheel mechanism: Have you ever wondered how you can get so much power and capabilities in such a little hub? For a three-speed hub, a one-stage planetary gear system is used, for a five-speed hub a 2-stage. Each planet gear system has a reduction state, a direct coupling and an acceleration mode.

In mathematical terms, the smallest reduction ratio is 3: 1, the largest is 10: 1. At a ratio of less than 3, the sun gear becomes too big against the planet gears. At a ratio greater than 10 the sun wheel becomes too small and the torque will drop. The ratios are usually absolute i.e. an integer number.

The planetary gearbox design is fairly simple, consisting of a central sun gear, an outer ring (also referred to as an internal gear, because its tooth face inward), planetary gears, and a carrier. Input power to the sun gear causes it to spin. The planetary gears mesh with the sun gear, and as the sun gear spins, the planetary gears rotate on their axes. The planetary gears also mesh with the ring gear, which is stationary, causing the planetary gears to revolve around the sun gear. The carrier holds the planetary gears together and sets their spacing. It rotates with the planetary gears and incorporates the output shaft.

Single speed planetary gearbox, with the same mounting and output interface as a 2.5" CIM motor. Each planet gear has its own bearing to spin freely on the carrier plate pins. A 2.5" CIM Motor may also be used as the motor input, but requires this pinion gear ( am-0556) and a CIM Spacer (am-0555).

Motor Input:

9015 motor fits on this gearbox

550 motor fits on this gearbox

2.5" CIM Motor can be mounted, with a bored-out sun gear and a spacer

Included Hardware:

Two - 8mm id ball bearings, (19mm od, 22mm od) supporting output shaft

One - Steel planet and sun gears, 32 dp, 20 degree p.a.

Five - Planet gears (12 tooth)

One - 15 tooth sun gear, with 0.125 inch bore

One - 40 tooth ring gear

Performance Data:

(with the input being a 9015 Fisher-Price motor)