How an old garage find moped received an electric power train.
As the two stroke engine was due for a complete restauration a plan was made to fit the bike with an electric power train.
Primary goal was to keep as many parts original.
The first concept was a steel chain drive where I only had to attach the motor and regroup the sprockets. It was a working prototype with a very high noise level.
Also chain tension was hard to set, even with the existing chain tensioner.
chain-drive 
chain drive
So a new concept had to be made.
At that time I came across a mountainbike with a belt drive system. Being more elastic, tension was easier to keep and also the noise level was by magnitudes smaller.
For a belt drive I had to design two belt pulleys. One would be attached to the motor and the other would be free spinning on the mid axle to power the rear wheel.
As the pulleys were no standard parts I had to develop them from scratch. The 3D prints were made out of PETG, a high strength thermoplast, with medium infill and a gyroid infill-pattern for uniform strength characteristics.
First test with the motor-pulley showed that the form fitting slotted hole could not take up the forces of the motor shaft. So I added a metal core, wich would be surrounded by the PETG pulley.
To this date the hybrid pulley works just fine.
As the pulleys were no standard parts I had to develop them from scratch. The 3D prints were made out of PETG, a high strength thermoplast, with medium infill and a gyroid infill-pattern for uniform strength characteristics.
First test with the motor-pulley showed that the form fitting slotted hole could not take up the forces of the motor shaft. So I added a metal core, wich would be surrounded by the PETG pulley.
To this date the hybrid pulley works just fine.
The pulley on the mid axle took more effort, as it was a hybrid metal-PETG pulley and had to be free spinning.
Prototype 1 had not enough infill to make the metal-PETG connection strong enough. So after increasing the infill at highly stressed regions, it was ready for field testing.
The electric machine is a 750W DC motor rated at 36 V.
It is attached at the same mounting points as the gasoline enginge. Two multiplex plates, one attached to the frame and one attached to the motor are screwed together for ease of assembly.
For a 750 W motor and a nominal voltage of 36V the battery should provide round about 25A of continuous discharge. Adding a safety factor, the battery should have a 30 A rating. I settled for a lithium ion battery with a 10S4P configuration and Samsung SDI INR18650-35E high discharge current cells ( 3,6 V & 3450 mAh) This results in a battery pack with 36V and 14Ah with a continuous discharge rate of 30A, limited by the battery management system (BMS).
I bought the battery already assembled on eBay. For future projects I plan to build a spot-welder and manufacture the battery packs at home.
