How I Built My Own 'lectric Longboard
One day I woke up with an idea in my head, several months later, I was riding on a self-designed and assembled, fully functioning work of engineering. The idea of turning the hilly roads of my neighborhood into an endless downhill slope, was possible by creating an electric skateboard. With my experience with remote control cars, boats, helicopters and drones, I knew it was the next project for me. After weeks of research and persuasion of my parents to give me the go ahead, I began my project.
In the initial stage of my project, I used a computerized design program to create a 3D model of the board I was going to build. When designing and building the board it was important for me to consider safety, durability, ease of use, appearance, top speed and maximum distance. I personally designed the custom deck as well as the motor mount on the board in a computer design program.
To cut out the deck I printed out a full size image of the deck to tape to the wood for cutting lines. The length and width of the deck was designed to provide stability when riding at high speeds. I also added a protective sealant of polyurethane to keep the wood in good shape and bring out the natural color of the wood.
At first, I had designed a 3D printed motor mount that would clamp onto the trucks of the skateboard. After a few test rides it was apparent that the plastic 3D printed part was not strong enough to remain in the same place during a ride. After this failure, I designed a motor mount to be cut out of a sheet of aluminum and welded to the trucks. I had the mount cut out and then had it welded to the trucks. During this process I searched for and found a welder and machinist to provide the necessary assistance and they were all impressed and delighted to see a young student pursuing something as complicated as this project.
Choosing the right motor and gearing were important in that I needed to have enough torque and acceleration to propel a rider up hills as well as generating enough speed to make it an efficient mode of transportation. The motor is a brushless motor, and can spin at a maximum of 6,370 rpm with the batteries I used. The batteries I used were lithium-polymer batteries which are a lightweight, but powerful option. I wired two 3S lipo batteries in series to create a 6S battery and when fully charged I had a voltage of 25.2 volts. I then had to use a smaller gear on the motor and a larger gear on the wheel in order to keep the speeds of the board safe, not overheat the motor, and provide enough torque.
The board was controlled by a handheld remote. The remote controls the speed of the board and can also control the brake. The motor was used as a brake, which slowed down the board and also used regenerative braking to recharge the battery powering the board.
Finally, I thought it would be beneficial if I could charge my phone while riding the skateboard so I created a charging system which used the motor as a generator. This required changing the AC current coming from the motor into DC current to charge a phone. To do this, I used a three phase rectifier which converted the AC current into DC current. In order to charge my iPhone I needed only 5 volts. I was generating anywhere from 12 to 24 volts from my motor so I used a transformer that converted 12-24 volts back down to 5 volts.
During a number of test rides around a high school track, I registered a top speed of 25 miles per hour and found that the board has a maximum distance of about 4 miles. If more distance was necessary, I could use batteries with a higher capacity or add two more batteries wired in parallel to double the maximum distance. During one full ride the board can boost an iPhone's battery level by 40%. Riding the board is an exhilarating experience where I can carve up hills, on flat ground and down hills.
I entered this project in a local Science and Engineering Fair and received many awards from this project. I won 1st place by the United States Air Force for Outstanding Engineering Fair Project, 1st place by the Achievers League for Most Creative Project, and 3rd place by The American Society of Mechanical Engineers for Excellence in Engineering.
Looking back on this project I can think about how much I learned about mechanics, electricity and so much more. I am so grateful for the assistance and wisdom from the people I met along the way. The board is a blast to ride and every time I hit the throttle and zoom uphill on my board I put one more person in awe.
By Ryan Needle
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