May 05, 2023

The technology in the igus:bike – the planetary gear

A so-called planetary gear is used as the gearbox for the igus:bike. However, this is not a special gearbox that is only used by us, but is a widespread solution, far beyond the bicycle sector. The big difference between our bike gearbox and the competition’s is that ours is made of high-performance plastics, does not rust and does not need lubrication or maintenance. It is also very sustainable thanks to the plastics used, which can be easily recycled. Incidentally, a buy-back is planned for the igus:bike if the bicycle should reach the end of its life at some point. We already do the same with energy chains, which can be returned to us to be recycled and reprocessed into new products.

The prototype of the one-speed gearbox system

Layout of the planetary gear from inside to outside

Diagram of a planetary gear with three planets

But why does the planetary gear have such a strange name? It’s not like it comes from another star. Or maybe it is? E.T. also flew over the earth on a bicycle … well, a little joke to lighten the mood before the facts, which hopefully won’t be too dry. The planetary gear was neither brought to earth by an extraterrestrial life form nor does it have other extraterrestrial influences. The naming is simply based on the construction of the gearbox, which bears a certain resemblance to our solar system.

In principle, the structure of our planetary gear is very simple. It consists of several gears whose teeth mesh with each other. In the middle of the gearbox is the sun (the so-called sun gear), which in our case does not move. Around the sun gear revolve four planets (the planet gears). These are connected to the planet carrier, so they always keep the same distance from each other. Unlike in our solar system, there is also a fourth component in the gearbox besides the carrier: the ring gear. This encloses the complete construct.

Frontal view into the gearbox: in the centre the sun gear, the four planets spread out all around it

Oblique view of the gearbox. The front sprocket is nice to see.

The drive then works as follows: the planet carrier is connected to the bicycle crank and is moved by it. The planet gears rotate around the fixed sun gear and thus move the outer ring gear to which the sprocket is attached. The sprocket is connected to a smaller pinion on the rear axle via a belt. This way, the rear wheel is driven with a larger gear ratio and you can cruise leisurely through the city with the igus:bike.

Ah, wait, go back again. There was something about the gear ratio. It is precisely because of this that all the gearbox work is being done in the first place! This is because the planetary gears translate the power you put in with the crank via the pedal into a higher rotation. When you turn the crank one turn, the ring gear including the sprocket does not only move one turn further, but a little bit more. Your power is converted into a higher speed. And that’s really practical! Well, now you can really cruise through the city with the igus:bike!

The planetary gear in action

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