A solution to urban transportation
Some day in 2016, I saw a video of a guy making his electric skateboard. It immediately caught my eyes and I then decided to make one by myself. At first, I improvised the design without even knowing how skateboard works. The goal is to make a skateboard without a steering bar.
Design and the product
Skateboard is basically a wood plate with wheels. Therefore, I have bought a wood plate and some casters and decided to use the 775 motors because I have some in my home and they seemed to be powerful. The wheels are of a diameter of 100mm and with calculations, I found the gear ratio to be about 1:25 to achieve a top speed of 30kph. To power the motor, I have purchased a 12V10Ah battery and an ESC.
The first problem that came is how to steer, and my first idea is differential steering since it is simple. To brake the wheels, the easiest way is to buy fixed casters with brake and use a mechanism to press the brake lever installed on the casters. My idea is to drill holes on the wood plate and design a pedal with a rod on it, and the rod goes through the hole and reaches the brake lever on the casters.
However, if I had any knowledge, I would know that differential steering is impossible due to the large wheelbase-track ratio.
My next idea is to use a parallelogram arm that connects the front casters to steer. To control steering, my idea is to use a pedal that connects the parallelogram steering bar and use the foot to move the pedal. However, this does not work well. At the same time, I found that the 775 motor requires a really high current which causes the battery to cut power, so I bought a huge 12V30Ah battery in order to make it work. As you can probably tell, I was already going off-track.
I finally realized I need a steering handle to complete this project based on the progress so far. I bought a cheap scooter and took its steering handle and its support off. I installed it on my skateboard plate and now the whole thing finally worked. However, the project looked like a disaster - heavy, loud and unstable, but I could not just finish there. Then, my uncle suggested me to buy a good-quality scooter and modify it instead.
As instructed by my uncle, I bought a nice scooter, a hub motor and some standardized electronics for an e-bike. The idea is to install another plate on the aluminum deck and put the battery and controller in between, replace the rear wheel with a hub motor for customized scooters and replace the right-side handlebar with the control bar with brake. This would be the easiest and most achievable solution according to my uncle.
Finally, in September 2016, I have finished the e-scooter with a lot of help from my uncle. It became my very first mechatronic project.
This e-scooter uses a 350W in-hub motor and a 36V12AH LiPo battery. It can run up to 35km/h with a distance per charge of 30km, which is sufficient for urban traveling. It is controlled just like most commercial e-bikes in China - rotating the grip to accelerate, and using a mechanical brake.