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Prototype Version 5 Wins Gold at Regional Science Fair!

Following the end of the construction of the fifth prototype electric skateboard, I decided to enter my project into the Greater Vancouver Regional Science Fair. The experience was absolutely astonishing! Not only did I meet hard-working, dedicated students and their innovative projects, but I also met experts in the field of engineering, who offered creative criticism. And all of this couldn’t be possible without the committed judges and voulenteers, who took time out of their daily lives to set up and monitor this event. Way to go!

In order to make my project more scientific, I decided to run an experimental trial to see how the gear ratio effects the power consumption on the fourth prototype of the electric skateboard. I did this with several gear ratios and weights, and I used the results to improve the skateboard, by choosing the best gear ratio for my weight. I also determined the speed at which the skateboard has the maximum range, which turned out to be 19km at 9km/h. This is just an estimate; I still need to test that.

Bluetooth Logging System:

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I also decided to run an experimental trial on the maximum current and power consumption under different loads. Both of these trials were recorded with a custom-made, Bluetooth Logging Module that I designed, programmed and built. It uses a GPS to track location and velocity, a hall effect current sensor (for current), and the standard voltage divider/reference diode for voltage detection. More on the module in a further post.

Introducing Prototype Version 5:

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Prototype version 5 is the best, most complex prototype I have built so far. I had to learn how to work with carbon-fiber for this board, as I wanted to reduce the weight of the board even further. The deck has a foam-core, and I used wooden supports around the trucks. There were a couple of differences with the gear drive as well; I 3D printed two PLA spacers so that they could more easily hold the gear in place. Additionally, I used a 25 tooth gear that I modified. It used the least amount of power out of all the gear ratios tested.

The electronics side was a bit different as well. The largest change was the addition of a lithium-ion BMS board. I found one on eBay for about $15 for the 6 cell configuration I was using. The major advantage: safe and fast balance charging. I can charge from dead to full in under 60 minutes! I also picked up an inexpensive 24v power supply, which I modified to become a constant current/constant voltage source through the “33R Mod”. More on that in a later post.

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These were some of the major changes that I changed from the fourth prototype skateboard. Currently, I am working on alternative methods of controlling the board; everything from Wii-Nunchucks to Bluetooth Low Energy and Gamepad Controllers.

The development of this board, as well as the write-up and experiments that I did helped me win gold at the Greater Vancouver Regional Science Fair! I also recieved an award from the Canadian Institute of Energy, and I will be travelling to Montreal for the nationals in mid-May!

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Recent advancements and ideas on the autopilot

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The autopilot is well on its way to controlling a real boat. I am now testing the autopilot on land and on water. One of my most recent modifications was the addition of LED indicators:

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The LED’s (from left to right) show when the rudder is being turned, when the autopilot is at the next way-point, and when the Arduino does not receive any data from the GPS. These LED’s have reduced the need for a laptop when testing. I strongly suggest the adding these to anyone building their own autopilot.

I also upgraded the airboat that I use to test the autopilot on water:

I sent this new boat out onto the water with the line attached. I also used orange juice bottled as floats to keep the line from touching the bottom. They also helped rip the lily pads which got stuck on the line at one point; more on that later.

Since the motor was more powerful now, the boat tilted downwards whenever the motor was on. Not a good sign. I am planning to rebuild the bottom section of the boat. I’ll make it wider, longer, slightly taller, and I will change the tips of the hulls (they won’t be a v shape from the top, but will be a < shape from the side). I’m hoping this larger deck will allow the boat to have a better center of gravity.

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I launch the boat from the waterline and I have tested it go to point 1 and back and also point 3 and back. Going to point 1 caused the boat to get stuck in lily pads which were ripped out by the bottle floats when I pulled on the line. Point 3 avoided those lily pads. Both times however, the boat did not stop when it got to those points. It just went on going past. I have no idea what is causing this, but I will investigate.

I also wanted to make the rudder smoother. Right now the rudder reacts way too fast. I plan on smoothing it and have the rest of the program run in the background. That way, the rudder is smoothed, but won’t slow down the reaction time.

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An arduino “case”: Part 2

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A new Arduino/autopilot “case” was needed if I were to flip the container upside-down. This case is slightly larger than the old one, but it is more solid, durable, will work if flipped, and it also leaves plenty of space for a battery or two.

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The lid (the one in the middle) has a hole in it for wires/cables to go in and out of the case. The opening is then sealed with hot glue. Hopefully I can power the motor through this.

One thing I also calculated was the power consumption and max battery time.

Part Power Consumption Time on 1.8 Ah Time on 2.2 Ah
Arduino 50mA 25.2h 30h
GPS 41mA 30.73h 37.56h
Compass 0.1mA 12600h 15400h
Total 91.1mA 13.83h 16.9h

As you can see, the compass has an extremely low power usage. I also found out that by taking out the power regulators out of the Arduino board, I can save up to 15mA.

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