Being a freshmen in high school I was too young to have my license. However, I still desired the ability to get around town in an efficient manner. After being passed by someone going at what seemed like Mach One on a bikem, I knew that my vehicle of choice would be an electric bike. It was the right blend of speed and power and I knew it would be perfect to get around town with.
The Idea
When I began this project, during the summer after my freshman year, I knew I wanted something unique. So rather than mount the motor on the rear wheel I decided I would mount the motor in the center of the frame. The motor would then power the front chainrings which in turn would power the rear cassette.
From this idea I created a rough cad in Solidworks. In the model I sketched out the frame, motor and motor mount. This allowed me to ensure a proper fit while also ensuring clearance for chain. The design consisted of six individual parts which all bolted together using L Brackets.
The Design
Motor Mount
To create the motor mount I utilized my high school robotics machine shop. In the shop, I used the CNC Router in order to machine the two larger side plates. However, for the two smaller plates I was able to fit them on the bed of the CNC milling machine. I then finished my machining by milling to size four L brackets.
Electronics
For the power train I decided on a 48 volt 1000 watt hub motor. I then paired this with a standard 48 volt brushless motor controller and two 24 volt lithium ion battery packs However, for this set up to work I would need to run the packs in series. This forced me to modify the batteries so the BMS (Battery Management System) was bypassed.
Controller and Battery Mount
After the modification I mounted batteries via a set of small camera cases in order to protect them from the elements. These cases were bolted to a set of 3d printed clamps. This set up also allowed for the speed controller to be mounted in the same area.
Final Thoughts
Ultimately this first design resulted in a fun ride. The bike had a top speed of 28 mph and a range of 15 miles. On top of being an cool mode of transportation, this project gave me an introduction into motors, batteries, and Solidworks. The bike also taught me how to machine accurately to a thousandth of an inch, and the basics of operating a CNC machine. This project was instrumental in cementing my love for designing and creating.
