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Increasing the range of an electric skateboard by analyzing power consumption

My entry for the regional and Canada-wide science fair was my electric skateboard, but it was more of an engineering project than a science fair experiment. Since the judges were tasked with analyzing the scientific thought/method of the contestants, I decided to run experimental trials on my latest prototype in order to determine how the speed, load, and gear ratio effects power consumption. From that, I found the optimal speed for maximizing the range of the skateboard, the optimal gear ratio, and I also provided proof that my particular ESC had substantial regenerative braking capabilities.

The trials:

In total, I did an absurd amount of trials (absurd = 48). I had two different groups; a group that accelerated uniformly, and a group that rode however they wanted. I would log the power consumption, location and speed of the electric skateboard during the trial with my Bluetooth data logger, which would conveniently place an .xml file in a folder on my phone.

I also had two different groups with two different gear ratios, as I wanted to see which one would perform better. All of these groups had four different rider loads. Here are all of the trials and the data I have collected for my experiment.

The hardware:

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In order to log the data for analysis, I had to build a piece of hardware similar to an RC logger. Above is the schematic I came up with, which I etched using my dad’s CNC machine. I put a stronger emphasis on accuracy, so I included a tunable voltage reference for the microcontroller. The Bluetooth logging system would log the voltage of the batteries, current, temperature, throttle, location, speed, and position, and send them over Bluetooth to an Android device. The Android device would be running BlueTerm during a trial, and would be set to record the data.

The data:

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The most interesting data that I collected from this experiment was the effect of gear ratios on power consumption. I tested two very different gear ratios. I hypothesized that the larger gear ratio would consume less power, since it exerted a lower torque load on the motor, and that lined up with a higher efficiency on a BLDC efficiency vs torque-load graph. My results were the opposite, and they were statistically significant enough to prove the opposite. After a bit of communication with my mentor (who provided an unbelievable amount of help over email), I realized that the max load had not been achieved on the motor, and thus, I was sampling the wrong part of the graph.

range graph

From a similar data set as the data above, I was able to estimate the speed at which the skateboard should get the farthest range. I derived a formula which worked off the best fit line for the previous chart, and turned it into a range vs. speed graph. The result showed that the absolute maximum range is about 19km, and that could be achieved by a 140lbs rider at a speed of 8.9km/h. This has yet to been tested.

RiderInterval

Another thing was proven as a result of my experiment was the regenerative braking of the ESC. A lot of people doubted that the ESC I was using could put power back into the battery pack, but no-one could explain where the energy would go, other than the battery. I was able to prove that regenerative braking exists, and provides a significant amount of power into the battery. I was also able to determine the peak current, average current, preferred riding speed and more. For more information and data regarding my experiments on the electric skateboard, check out this link.

 

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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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Bluetooth Skateboard Controller Update!


I have successfully produced 4 prototype electric skateboard controllers. Here are the specs:

  • Modes: Car/Boat and Electric Skateboard
  • Sensitivity: 1000 degrees
  • Input Voltage: 4.5~6.5 VDC
  • Max Voltage Measurement: 55 volts
  • Failsafe: Slowly turns off the motor
  • Dimensions: 50.0 x 38 x 12mm

These controllers are almost ready to ship. All that’s left is to waterproof each circuit using epoxy resin, and ensure compatibility across all Android devices.

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