The fixed distance between hub and bracket made it possible to enclose the whole traction-system with a chain-box.
Variation number 2: chain-box.
At first, I had a standard type chain-box made of ABS, that I had broadened slightly in the middle,
and shortened in length.
When I replaced my 3-speed gear-hub by a somewhat thicker 5-speed hub (Torpedo Pentasport),
a bigger gear-wheel was needed on the hub (to prevent the chain to touch the hub),
and - to keep the same transmission rate - the front-wheel had to be enlarged, too.
This didn't fit in my first chain-box anymore. So I had to build myself a new one.
I wanted it transparent (more beautiful), and as ABS cannot be made transparent, I used polymethylmethacrylate (Perspex).
You can see this new chain-box on the picture.
It looked beautiful, but the material turned out to be too brittle. Soon, it broke into pieces.
At this moment, I still don't have a chain-box, but I am intending to make one again with stronger materials.