# Principle of operation of the hub.

#### Principle of operation of the hub.

The operation of all gear hubs, is based on the planetary gear wheel system.
The planetary system ( Figure 1 ) consists of the following components:

• sun gear, a gear with external teeth.
• The planetary gear, a gear having external teeth which should pass over the sun gear. The system is typically equipped with three or four planet gears.
• The planet carrier, which connects all planetary gears with each other and can run as a whole.
• The ring gear, a gear with internal teeth which the planet gears rotate in.

In order to be able to step up a gear, the sun wheel is or will be connected to the shaft. The planet wheels are with their axle pivotally connected with the planet wheel holder.

The simplest 3-speed hubs use a single planetary epicyclic gearset. The sun gear is mounted solidly to the axle and is thus fixed relative to the bicycle frame.

In low gear, the sprocket drives the annulus and the planet carrier drives the hub, giving a gear reduction.
In middle gear, the sprocket drives the hub directly.
In high gear, the sprocket drives the planet carrier and the annulus drives the hub, resulting in a gear increase.

The delay of the planet wheel holder relative to the ring wheel is dependent on the number of teeth in the ring gear and the number of teeth on the sun wheel. The delay of the planet wheel holder can be calculated using the following formula:

Number of ring gear teeth
number of teeth ring gear + sun gear

The acceleration of the ring gear can be calculated using the following formula:

1 + number of theeth sungear
number of teeth ring gear

If the sun gear has 20 teeth and the ring gear 60 teeth, then the ring gear to one complete revolution of the planet gears about the ring gear will make 1.33 revolutions.
(V = 1 + 20:60 = 1.33). the ring wheel rotates 33% faster than the planet carrier.

Between the first and third gear, of course, the second gear. This is at the 3-gear hub a 1: 1 transmission ratio. That is, the chain wheel directly drives the hub shell through the ring wheel. Thus, there occurs no delay or gear.

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