The electric skateboard project started out when my cycle got stolen. I needed a means of transportation around the huge campus, and this time I wanted it to be portable so I could take it to my room and lab. A skateboard seemed like the ideal option. I mean why not, they’re fun to ride, easy to carry around and look cool. Except, when you have to go uphill. So going electric seemed like the best option. Electric skateboards are better than hoverboards or unicycles because they are self balancing and you can ride them even when the battery is dead.
I used this project to teach myself 2D sketching and woodworking. I drew up dozens of board designs, learning to use SketchUp for 2D modelling. I wanted to use a CNC to cut the board and route channels for the wire inlays and the electronics. But ended up having to hand cut the deck.
I wanted to make the prefect board for Indian road conditions. Potholes and speedbumps abound. So I opted for 10 inch axle and 90mm wheels. I generally work late nights and go home through an unlighted road, so strong headlights were a must as well. After riding for a bit I realized the need for a horn as well, and added a motorcycle horn. Since I had no experience skateboarding before this, I first made the bare board and got used to riding. I opted for a solid wood deck because the low flex would protect the batteries and it is much easier to make.
After much research and thinking I decided on the electronics as well, here is an excerpt from my tutorial explaining the choice of electronics.
” All right, lets get down to the electronics. There’s four main choices to make here: battery, motor and motor driver(aka electronic speed controller or ESC) and remote control. Now, you want a low rpm motor, something under 300KV lower the better. Another factor to consider is the max power draw, you want something over 1KW for good startup acceleration. I got a 270KV motor for real cheap. The motor was rated for max 90 amps and six lithium cells(22V) giving peak power of about 2KW. I got two 5AH 20C three cell batteries to match(5*20=100 amps max safe current draw). Put in series they make a six cell 5AH battery pack. Since the ESC is the weakest link in the current chain, you want it to be rated for much higher current. Car ESC’s are rated for much higher peak current than airplane ESC’s and have support braking and reverse. So, I chose a 150amp car ESC capable of handling 6 lithium cells. For remote control, you can choose any one channel remote control. Anything cheap and low range would be fine, since you are going to be right on top of the receiver at all times(hopefully). You’ll probably want to add a deadman switch in case you’re not. And don’t forget to program the ESC to brake upon loss of radio input. You’ll want to encase the electronics the electronics in some durable casing. Avoid anything that cracks easily or doesn’t fare well under repeated stress like acrylic(won’t be making that mistake again!). I custom molded transparent polycarbonate and it looks great. “
I designed the drive chain to be based on timing belt instead of a chain to make it low maintenance and quiet. I chose the gear ratio at 1:2.5 to get a top speed around 35Kmph. I designed the motor mount and wheel hub in sketchup and machined them out of aluminium myself. I didn’t realize that the aluminium axle and motor mount can’t be welded using a normal stick welder. So, I had to persuade a mechanic to teach me MIG welding.
The skateboard remote itself was a huge project. I went through several iterations, using various radio chips and experimenting with ergonomics. I even made a gesture control remote. Some of the lessons learned:
1) Epoxying sand on joysticks gives them much better grip(especially if you have hyperhydrosis, like I do)
2) Don’t reinvent the wheel. Modify existing designs and products.
3) Always include a battery meter in anything critical
4) Best way to waterproof electronics is epoxy.
5) If you have a mechanical switch on something and you keep it in your bag, it will switch on and drain the battery completely.
I finally settled on the body of Wii nunchuck and a HC05 bluetooth serial module.
I also experimented with some unconventional means of remote control. I really liked the idea of emulating Iron Man’s palm thrusters, point back to go forward, point to the front to stop and reverse. The angle would vary the speed. So, I made a simple gesture based controller. Turns out it takes a toll on the wrist. Oh well.. I also tried a pressure sensitive foot pedal on the board itself, cellphone app based approaches.. But none were very successful.
Now for the performance.. I get a 15 km real world range and haven’t come across a speedbump I can’t ride over. Get around 35kmph top speed on flat concrete. Going over flyovers is no problem, but startup on an upward slope requires a push.