Planetary gearing

A planetary gear set consists of a centrally mounted sun gear, an outer ring gear and planet gears rolling between the two. The name comes from the way the planets orbit the sun gear, like planets around the Sun.

Its advantage is that the load is shared between several planets. That lets it carry high torque in a compact size — exactly what a bicycle hub needs, as it has to take your legs’ power, and even an e-bike motor’s, in very little space.

Stepped planets, two sun gears

In the SPEEDHUB’s first two planetary sets — (1) and (2) below — two shiftable sun gears work in each. The stepped planets’ first gear stage meshes with sun gear 1 and the ring gear, the second gear stage with sun gear 2.

Three ways of shifting are possible:

• sun gear 1 is coupled to the ring gear — direct drive;
• sun gear 1 is locked to the axle;
• sun gear 2 is locked to the axle.

So each of the two sets gives three different ratios. The third planetary set gets its own direct drive on the same principle: there, sun gear 3 and ring gear 3 are coupled. The 14 gears come from combining the ratios of the three sets.

The ratios

Set (1) is driven by the ring gear and passes the rotation on through the planet carrier — a reduction. In set (2) it is the other way round: the carrier drives and the ring gear is the output — an overdrive.

Shift state	(1) ring gear → carrier	(2) carrier → ring gear
Sun gear 1 coupled to the ring gear	1 : 1	1 : 1
Sun gear 2 locked	1 : 0.774	0.774 : 1
Sun gear 1 locked	1 : 0.682	0.682 : 1

In direct drive, sun and ring gear turn together at the same speed, the planets do not roll, and the set passes the rotation on 1:1.

With sun gear 1 locked, the stepped planets roll with their first gear stage between the turning ring gear and the stationary sun gear: one turn of the ring gear gives 0.682 turns of the carrier.

With sun gear 2 locked, the planets roll with their second stage on the stationary sun gear 2 and with their first stage on the ring gear: the ratio is 0.774. Sun gear 1 then turns forwards freely, without a function.

The full construction, part by part, is shown in Construction: exploded view.