Since a few years bicycles with electrical drive have been gaining popularity. However, these bicyles are very expensive and so a young mechanical engineer developed a cheaper DIY kit. All parts together cost less than 300 Dollars and an instruction is available via instructables.
Since a few years the instructables-creator and mechanical engineer “MechEngineerMike” has wanted to own a bike with electrical drive, but these bikes cost over 4.000 Dollar and kits to adapt conventional bikes cost about 1.500 Dollar. The self-created kit that Mike had developed costs less than 300 Dollar.
From a mechanical perspective, any reliable home FDM 3D printer will get the job done. Some of the parts need support structures and a lot of infill is suggested (30 to 50 %). The infill will give the parts higher mechanical stability and of course it will raise your printing times. The required files for 3D printing can be bought through Pinshape for 10 Dollar or alternatively you may consider buying the complete hardware kit (without 3D printed parts) for 75 Dollar on eBay.
On the electrical side a battery pack, motor and a controller are used. These parts have to be bought by yourself and build together, but a detailed instruction of all steps is available on Instructables. The finished Booster Pack can be mounted on different positions of the bicycle – easy and fast mounting as well as unmounting is possible. However, there are also some limits to this self-build solution, for example you can’t drive when it’s raining because the electrical unit is not water resistant. Nevertheless you can reach up to 25 mph with pedal assist and the pack has a decent range of 5 miles, when driving unassisted.