Three-Wheel Electric SkateboardFollow article
With the recent buzz around electric cars and the engineering challenges surrounding their development, I thought I would take a look at the feasibility of creating my own form of alternative electric transport using my own unique set of design values. I thought it would also be nice to prove that electric vehicles need not be heavy, complicated, expensive things but rather super simple, fun to run and built with basic materials.
Bill of Materials
- Hardwood plank
- Electric scooter rear wheel assembly with sprocket
- 300w 24v DC motor with sprocket
- 12v lead-acid batteries
- Momentary-on push button
- Electrical tape
- 4mm steel plate and strips
- Mountain board trucks
- Mountain board wheels
- M6 screws, washers and locking nuts
- M8 screws, washers and locking nuts
- Countersunk wood screws
- Two core, multistrand power cable
- Single core, multistrand power cable
- Cable ties
For this project, I decided to build an electric skateboard using salvaged parts I found at the back of my shed. I started with a 300w DC motor from an old electric scooter which was driving a large pneumatic wheel via a chain and sprocket. I have a fascination with three-wheeled vehicle design so I decided to use the entire rear-assembly of the scooter in single rear-wheel drive design.
Stability is vitally important in three-wheel vehicle design, anyone that is familiar with the Reliant Robin or Regal will know that despite the badge name their vehicles had a tenancy to be unstable due to their centre of mass being biased on top of one pivoting wheel. It is therefore important to bias the centre of mass of any three-wheel vehicle over the main axle, much like the motor-tricycles that Reliant ironically derived their designs from.
Credit BBC TV: Left, the iconic Regal. Right, the Robin as driven by Jeremy Clarkson.
My design aimed to feature the main two-wheel steering axle at the front of the board and a single chain-driven wheel at the back for simplicity. Positioning my bodyweight across the front axle pushes the centre of gravity towards the front of the board leaving room for the batteries and motor to be secured at the back while also ensuring a stable weight distribution.
I designed the main chassis around a single piece of hardwood, much like a normal skateboard or longboard deck however the addition of the bulky electric drivetrain extended the board’s overall length which required the chassis to be strengthened. To do this I cut some strips of steel and fixed them to the edges of the board with countersunk self-tapping screws. These strips were also used to mount the rear wheel to the chassis using a hole drilled at the end for the rear wheel fixing bolt.
Front Axle and Steering
With the chassis finished, the next step was to add the steering axle, otherwise known as the truck. I decided to use a mountainboard truck and matching wheels to ensure a consistent ride height alongside the large diameter of the rear wheel. The truck was chosen due to its large wheel-track spacing which allowed the board to spread my bodyweight over a wider area, combined with the long wheel-base between the front and rear wheels made the board extremely stable.
In order to drive the rear wheel, I needed to mount the motor to the board, taking care to align the sprockets on the motor and rear wheel and leaving the right amount of spacing to attach the chain from the old scooter. Using DesignSpark Mechanical I modelled the dimensions of the bracket, taken from the motor’s mounting feet which were conveniently tapped for M6 screws. I then exported a DXF file in order to cut the bracket on a CNC machine out of 4mm mild-steel plate to be angled in a hydraulic folding machine. I then attached the motor to the bracket with M6 screws and fixed the bracket to the board with M8 screws and washers. I could then attach the chain to finish the rear wheel assembly.
With the motor mounted I could then focus on the power supply, for simplicity I used two 12v lead-acid batteries in series to create the 24v DC supply required for the motor. The batteries were strapped next to the motor bracket with cable ties for easy removal and charging. The motor was then connected to the battery pack using a single-core cable with spade-crimp terminations, ensuring good vibration resistance.
A two-core power cable was used to connect an old push-button to the battery pack with spade-crimps and electrical tape, this flying cable allows the motor to be controlled by the user as they are standing on the board. The control system is very crude as it currently stands, when the button is toggled, power is either completely applied or removed from the motor making acceleration very aggressive, in later iterations of the skateboard a PWM control system will be added in order to control the rate of acceleration.
The DC motor proved to be a brilliant actuator with a colossal starting torque, the magnitude force it applies to the chain from rest has been enough to pull it off the motor sprocket during testing. To counter this effect, I fabricated a crude chain tensioner out of two steel strips, M10 threaded bar, 10mm spacer and M10 plain nuts which were clamped against the steel chassis which fixed the problem, allowing me to finally test my board properly.
This is a classic example of a project you start for use in the summer and finish much later into the winter, despite the apparent simplicity of the design there were a few hidden complexities in the chassis and drivetrain that took a bit longer to realise. However, the project was successful in the end and a proved great example of how alternative electric transport can be available to everyone. If anything, I hope this article has been thought-provoking and inspires people to develop their own ideas in pursuit of a greener future.