3 speed bicycle hub

How does a 3 speed gear hub work?

I made this one a short time ago, to see what could be achieved with Eevee, the new realtime viewport render engine in Blender 2.8 – though I ended up using the LookDev mode instead, which acts somewhat like an “Eevee preview”. Even that looked quite impressive! 

It’s no replacement for raytracing rendering (like with cycles) but it looks acceptable enough for this sort of work. This makes it possible to quickly create technical animations such as this without the need to render the job on an external render farm. 

Regarding the subject: in my teens I used to cycle 30 kms per day, to school and back. After two years of that, the third gear on my bike started slipping, and using my dad’s vise, I managed to open the hub and found that the problem was caused by worn, rounded-off axes of the planetary gears causing the clutch to slip. I got some spare part from the local bike shop and it was like new again. 

It was also fun to learn how that thing actually worked – the funny thing is that while a planetary gear seems pretty simple, at the time I was completely fazed by how it achieved that particular gear ratio 0.75 – 1 – 1.33! Looking at the thing, I would have sworn that in third gear, the ratio would be 2 instead of 1.33 – it’s quite counter-intuitive until you work out the math. 

Another reason to make this particular animation is that there isn’t one yet that clearly explains how it works. There’s one from Sturmey Archer, made in the 1970’s, but I didn’t find it very clear. However, there is a live video here of someone taking it apart and explaining it quite well. 

Below are some examples of the different viewport render methods now available in Blender 2.8. Besides Eevee (which even does volumetric fog in realtime!) and LookDev, there is a really good MatCap renderer. It can show the object as having a uniform material, or having all different colours, or semi-transparent, or cartoon-shaded as in a drawn illustration. Again, I am very much impressed by Blender 2.8.