Intro: Wireless Glove-Controlled Electric Mountainboard: an Analysis
Hey guys! So I finally decided to make a page that has everything you could possibly know about my project. Even though I had previously answered everyone's questions, they were usually through a message. Because of that, I was usually asked the same questions and I figure making this instructable will mitigate that. So without further adieu, here's the source! If you still have any questions that weren't already answered, just let me know so I can add it!
Disclaimer: I would NEVER EVER recommend that anyone use a motorized mountainboard with straps. If you're wondering why I am saying this, it's because it was only after riding it for a while that I realized why everyone feared so much for my safety. You'd have to be insane to want to build this and ride it! I felt comfortable knowing I have years of experience in skateboarding, snowboarding, skimboarding, and surfing to really give me control of the board, but I never underestimated what I built nor did I ever forget about Murphy's Law. Heck, even all my board experience wasn't enough for the 4 second delay that came from the PlayStation 2 controller when I was trying to stop the board. I ended up cleaning the pavement a few feet with my leg, as you can see in the picture below. In anything you do, always be careful, be willing to accept the consequences for whatever you do and when something happens, you have no one to blame but yourself. So let me repeat this: I am not and will never be liable for anything that happens to you.
Now that we have that out of the way, let my project show you that when you follow your dreams, ignore the naysayers, and push yourself to your full potential, you achieve things that you had never imagined. People far too often underestimate their own strengths and skills, and many brilliant ideas end up just being an idea and nothing more. I want my project to show everyone that they can make anything a reality if they go for it. When I first started the project, I didn't really know about motors and I had to refresh my memory on some of the topics I learned in my classes. If you have the motivation, you can learn everything about a certain topic, as well as master it, and make it your own. Don't ever let anyone tell you that you can't do something if you truly believe in what you are shooting for. All that being said, I'll leave you with what renowned Irish playwright George Bernard Shaw once said: "You see things; and you say, 'Why?' But I dream things that never were; and I say, 'Why not?'"
By the way, here is a link to a video of my board in action just in case you're interested: http://www.youtube.com/watch?v=686oJ7bNFIU
Step 1: Materials
Disclaimer: this is most likely what I used. Now that I'm looking at the motor specs, I can't remember if I got a 1.2 or 1.6 since I remember the wattage that I got, but don't remember seeing the maximum voltage rating ever being lower than 26 volts. But anyway, this was meant to be a guideline, not a step-by-step tutorial. This project is dangerous from the start, and providing steps to a project I even had bugs on could give you a false sense of security, a belief that if it's online and everything is drawn out so nicely for you to follow along, that the finished product will be safe since that couldn't be further from the truth. I wouldn't want you to get injured, and I definitely don't want to deal with lawsuits. So I'll repeat this again: I am not and will never be liable for anything that happens to you.
Brushless Outrunner Motor
-RimFire 1.2: http://www.electrifly.com/motors/gpmg4505.html
Brushless Motor Controller
+Can't find the exact one that I used, but I'm pretty sure this should do
Lithium Iron Phosphate Battery
SparkFun Flex Sensors
SparkFun NRF2401A Transceiver
I bought my board on eBay, and I think it's an MBX mountainboard. The rest of the materials were either purchased at Home Depot (thick gauge wires), made from the ECE Machine Shop (casing for my battery, casing for the motor, and gears), or given to me from the ECE Service Shop (buttons, small wires, LEDs, op-amp). Some of the board was also built in the ECE Machine Shop.
Step 2: Pictures That Show Details
When I was looking up how to create something like this online, one of the problems was trying to see exactly what they did. So I took many pictures to give you different angles to see exactly how I did it. I hope they help you immensely! Just in case you were puzzled by what the blue thing on the battery was, it is a PlayStation 2 controller because at one point, I controlled the board with it (http://www.youtube.com/watch?v=AkhjeEDaagQ).
Step 3: Frequently Asked Questions
(Picture Attached: Courtesy of XKCD)
What makes your idea unique?
Well, I love to surf and skimboard; there's a sheer joy I get from riding a wave, but riding a skateboard with loose trucks has been the closest I have gone to it living up in Illinois. It's a bummer to be landlocked in the midwest and that method just isn't the same as riding a wave. While having a board run by itself is a start, other electric boards out there are stiff, straight skateboards while mine is a bendable, strong mountainboard. Mountainboards are meant to be abused and absorb lots of the movement you get from a bumpy terrain, so it really feels like I'm gliding on the street. The way the trucks are attached to the board also allow me to have a lower center of gravity, which really gives me the opportunity to carve the street and really give me the feeling that I get when I surf. My idea is also unique because of the technology that it utilizes. All the boards I came across used technology of the last century, from brush motors to lead batteries. Lead batteries can be about 15 pounds per battery and a brush motor can weigh around 10 pounds. I used a lithium iron phosphate battery, a battery technology leading the way in the hybrid car industry. The battery I picked is only 6 pounds, has around 240 watt hours, and I also used a brushless motor that weighs about 3 pounds, and has around 2 horsepower. My project is also unique because it uses a wireless glove control that I built. I just bend a flexible sensor with my fingers and the board changes the speed based on how far I bend the sensor.
What was your goal in making this project?
When I first started it, my goal was to design a trick board where I could do 180's and jump down stairs. After realizing how heavy the board would be and the risks involved with attempting those tricks, I went with a different approach: design the board for solely getting around. My goal then was to just have a board run on electricity and use cutting-edge technology to make it the strongest and lightest board out there.
When did you start making the project and how long did it take you to complete?
Well I came up with the idea late November 2009 but started actually building the project in the beginning of February 2010. I knew what I wanted the board to do, but I didn't know exactly how to go about with regards to design. I spent weeks researching what is currently on the market, what is and isn't currently being utilized, different designs, and then after a while I just decided to start building the thing. It took a month and a half to get the board working, from construction to debugging the electronics. It first was controlled with a PlayStation 2 controller, but I decided in Spring 2010 to make it work with a glove. It took a few weeks to research, design, build, and debug the glove and get it working with the board.
How did you go about starting choosing the materials you needed?
Well, it was difficult. There were many dependent variables that determined the speed of the board: gear ratios, voltage of the battery, maximum board speed, torque of the motor, weight of the board, and the maximum speed of the motor. This was the main reason it took me a long while to even start building the board. I constantly had questions floating around in my head: if I want to go a slower than desired speed, should I make the gear ratio larger? I could have the same effect by just buying a battery with a smaller voltage, or I could even buy a motor that has a lower RPM. If I get a battery with less voltage, would the new weight make it accelerate faster? My lack of experience made deciding what to get a bit overwhelming and perhaps led me to overanalyze everything. After researching and planning for 2 months (November 2009 to January 2010), I just said "Enough planning. I'm going to take action or this idea will only stay as an idea." It was hard for me to accept the fact that the prototype wouldn't be the perfect one, but it was a great lesson to learn in retrospect. All you need is a model to work with and from there, you'll know how your 2.0 should look! After all, I may have done all the perfect calculations on paper, but that doesn't represent how the project would actually behave. I'm glad I didn't overanalyze for too long because it turned out that it didn't matter as much as I thought.
How did you choose the motor?
When I was originally doing the research over how I was going to get my board moving, I looked up the different motors that are out there. Turns out there was something called brushless motors, motors much more efficient and lighter than brush motors. Brush motors don't have a linear relationship between RPM and input voltage and end up not spinning as much for every extra volt that you send through it. However, brushless motors even have a Kv rating that means voltage per RPM. I then chose an outrunner brushless motor because it has more torque. Outrunners vs inrunners have different attributes because of the locations of the permanent magnets: http://en.wikipedia.org/wiki/Outrunner
Now that I know what kind of motor I wanted, I had to figure out what Kv rating I wanted. I had to use some rudimentary Newtonian physics to figure out how much energy I would need to accelerate at a certain speed and how fast I wanted to be at a certain time. I remember going to an empty parking lot, putting tape on the ground to measure 10 foot intervals, and I would then push myself as fast I could on my skateboard and would look at my watch to record the times I passed through the pieces of tape to figure out exactly how fast I was accelerating and how fast a person on a skateboard usually goes. Comparing my results with the acceleration and maximum velocity of the electric skateboards currently on the market, I had an idea of how fast I wanted to accelerate.
Only thing I needed to figure out was the gear ratio. After finally picking the battery that I wanted, I had some motors I could choose from, and after figuring out the maximum gears that I could use, I chose the motor and gear ratio (which ended up being I believe 1:9). A few months later, my board stopped functioning and I thought my motor wasn't working. It turned out it was my motor controller, but either way I wanted a motor with more torque and with half the Kv rating since the max speed of the first motor was insane. I ended up buying a brushless outrunner motor from Slot & Wing Hobbies, a very helpful hobby store in Champaign right by State Road 84 (http://www.slotandwing.net/). Yes, the motor is definitely overkill, but I would rather pay more and not have to worry about a motor getting damaged in the long run.
I'm working on a similar project. Would you recommend that I get a 25.6V battery pack or a 36V one?
I had to try and figure that out too and it all depends on the kind of motor that you use, how fast you want to go, the gear ratios, how much you want to spend, etc. Because the RPM of brushless motors is linearly related to voltage, there is a sort of relationship between them that makes choosing the battery not that big of a deal, although it is nicer for your motor to depend on voltage to speed up as opposed to the current. So for instance the Kv rating was 10 Kv and we used a battery with 10 volts, then we'll get 100 RPM. It'll still spin 100 RPM if the battery was 20 volts but the rating was 5 Kv.
After working on my project, I found 25.6V to be the best for me. Motors can get to a low Kv, but those generally are much more expensive because they are very heavy duty. Those motors are generally bought when the person needs a motor with lots of torque. Also, you don't want too high of a gear ratio either since your project could get all cluttered up. Because of that, I did some calculations and found that with my given Kv, the gear ratios I had to use, and I didn't want to exceed the 12-15 mph range, I went with the 25.6V battery pack.
So I know I didn't give a definitive recommendation, but it just depends on many other factors. Usually go with the battery with a higher voltage, but depending on what it is you want to do, the highest battery voltage you want could just be the 25.6V pack.
How did you choose the motor controller?
Well this was easier to do because I knew the maximum voltage my battery could output was 26 volts, and I saw that the circuitbreaker attached to the board would shut off if there was ever more than 50 amperes going through, so I had an idea of the kind of motor controller that I needed.
Where did you get that switch for your board?
I went to the ECE service shop in Everitt Lab to look for a switch that could handle high amps. Well, they found one!
How did you choose which battery you used?
I researched many different types of batteries, how they are used, when they are used, energy density, cycle life, value, etc. I read how lithium batteries had great potential, but found that lithium polymer batteries are very unsafe and I sure wouldn't want something like this to happen while I am riding (http://www.youtube.com/watch?v=-DcpANRFrI4&t=0m42s). I then read how the hybrid car industry accepted using lithium iron phosphate for their cars, and that to me was a clear indication that those batteries were safe and the way to go. They are more expensive, but they have an excellent energy density ratio and are very light for the energy that they contain. The one I bought was only about 6 pounds and has a 2,000 cycle life.
How long does the battery last?
Well I think it could go about 45 minutes to an hour non-stop. I remember using it to get to my classes and I went a full two days without charging it (although when I was heading to my apartment, I made it there at the exact moment that my battery died).
Do you have a problem with it being one-wheel drive?
Not at all! I know it sounds weird, but my board doesn't end up turning one way because of the one-wheel drive.
Did you consider making it anything other than one-wheel drive?
Yes, but the thing is that making it two-wheel drive would involve using a differential to keep the wheels from sliding. If you're wondering what I am talking about, the wheels have different angular speeds. Here's a great tutorial on how differential gears work: http://www.youtube.com/watch?v=K4JhruinbWc.
How fast does your board go?
Well it used to be able to go about 25 miles per hour, but I've only gone that fast twice in an empty parking lot. I remember holding on to my controller for life and kneeling to keep my center of gravity, and that was enough to say "Okay I got to enjoy that experience. Won't be doing that anytime soon." With a mountainboard having trucks as loose as that, you could end up seriously injured at best going that speed. I did change my motor because I thought the other one broke, but it turned out it was the motor controller giving me problems the whole time. It was good though because the new motor has half of the Kv rating, so the maximum speed is now safe to ride anywhere, which is around 12 miles per hour.
How can I get started on making a project like this?
Well to start, don't feel like you will create something like this in a day or two. In fact, most cool projects take many long hours of hard work and persistence. However, you can make awesome incremental progress and that's what I'm going to explain right now. First, I think working with an Arduino Duemilanove is a great way to start. You can find many awesome projects at www.hackaday.com, www.hacknmod.com, etc. that use microcontrollers. To learn how to program, you should definitely visit www.thenewboston.com because there are so many free tutorials on programming languages. If you want to learn a bit about electricity, www.khanacademy.com has free video lectures that could benefit you. Google is your friend (in this case), and so is Wikipedia. Really, all the information is out there and if you look hard enough, you could teach yourself all this stuff.
Andres, you still haven't answered the question! How do I get started on this project?
I feel I'd be doing you a disservice by telling you step-by-step how to do the project. I think all the tools are at your disposal and you even have an advantage of really having sites like www.khanacademy.com and www.thenewboston.com that can help you out on your quest to work on really exciting projects! But if you really want me to give you a sort of guide, here it is.
Step 1: Get comfortable with working on a microcontroller and being able to program it.
Step 2: Have the microcontroller interface with the outside world. These are what sensors are for, and www.sparkfun.com is definitely a place you should know about. Oh, and www.digikey.com is great too!
Step 3: Build a wired controller. All you need to do for this is just have a circuit with a battery, a potentiometer, resistors to bring down the voltage for the LED so it doesn't burn out, and small wires. You'd send the variable voltage to the microcontroller.
Step 4: Use the Arduino's A/D converter library to take in the variable voltage and output a PWM signal. This is what controls the speed of a brushless motor controller (and RC's in general, or at least to my knowledge).
Step 5: Be able to spin a motor with it
Is that it?
Yep! I hope all your questions have been answered and that this has inspired you to really try and make your ideas a reality. I can understand what Nikolas Tesla meant when he said: "I do not think there is any thrill that can go through the human heart like that felt by the inventor as he sees some creation of the brain unfolding to success... Such emotions make a man forget food, sleep, friends, love, everything."
So I wish you the best of luck, and remember that you have everything you need at your disposal. The world is your oyster and you can change the world as you see fit if you have the drive to do so. Good luck on your future endeavors, and keep in touch too! I'd like to see what kind of awesome projects you guys end up working on. You got my info: www.agballen.com/contact. Later!