There were two good reasons for converting my "luxury" mountain bike (BTWIN RockRider 540) into an e-bike: Not wanting to study for my A-levels. And living in a village in the Allgäu, which is 100 metres above and six kilometres from Kempten - which is why my daily commute to school by bike is only fun in one direction. So I put my German things away, watched lots of tutorials and then ordered some nice components from AliExpress. It was clear relatively early on that I would use a brushless hub motor (36V, 300W) for the rear axle. It is controlled by an ordinary Arduino board, a cheap, indestructible Nokia display and a 500W motor controller. The pedal sensor never worked properly - which is why I decided to switch the motor on and off with buttons on the handlebars. It's perhaps more like a moped than an e-bike. But it's definitely more comfortable. Without pedalling, my bike goes at 22 km/h - with pedalling, it is theoretically open at the top, because I accidentally forgot to throttle the motor to 25 km/h.
Translated with DeepL.com (free version)
I wanted to DIY the battery (36V / 10Ah) too, I thought. There are 30 cells (type 18650) in a downpipe from the hardware store. Unfortunately, I only later realised that you need a special spot welder for this. So I went to the rubbish depot, got an old microwave and removed the transformer. The control unit for my self-build spot-welder, like almost everything else, comes from China. Voilà, there's my 5€ welding machine. To make it easy to remove the battery block, I came up with a holder like a drinking bottle. To be absolutely sure that the batteries don't fly out while driving, the holder is welded from solid steel, which has unfortunately increased the weight considerably.
One of the many unexpected problems was the conversion of the rear disc brake. Because of the hub motor, it had to be repositioned, of course. Today I would simply use shoe brakes. But the two-month project paid off: One charge gets me over 40 kilometres - that's about 3 times to school and back. And I also somehow managed to pass my A-levels.
