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Thesis: It is feasible to construct a very powerful, efficient, and lightweight personal mobility device using hobby-grade equipment for under $400. This amount can be drastically less depending on the individual requirements of the builder. This is possible only through the extremely high power density of modern battery, motor, and controller technologies and the extremely low cost thereof in the radio control model hobbies. The advantages of constructing your own personal electric vehicle include educational experience, the ability to self-service, and the ability to customize to your own preferences at will.
I'm a builder and tinkerer by nature, and am always on the lookout for cool parts, devices which can be made better with cool parts, or some times both. During the summer months of 2007, I happened upon a chance to work with both.
As a bit of backstory, I build and compete fighting robots - as in Battlebots and Robot Wars - and as other builders of robots and non-robots may know, the search for the perfect motor is neverending. In June of 2007, I went on a trip to China to visit my aging grandparents... and hunt for parts. As RC hobbyists may know, China is the prime source of the vast majority of model equipment these days - big-branded or not.
So it was in a small hobby shop in a neighborhood of Beijing that I spotted this large outrunner motor. The only word to describe it was "assnormous" - according to the info card, it was a "7050/6" type motor. Translation: 70mm diameter stator, 50mm stator length, 6 turns per stator pole. Real translation: Massive power. It claimed 6 kilowatts maximum, but as overrrated as many hobby parts tend to be, I didn't trust the rating. Many high-quality BLDC motors of this size range can produce up to 10-11 kilowatts of power. They also cost a cool grand or two, not the $100 I ended up getting this motor for. Here's one example.
However, that didn't prevent me from impulsively buying it, since it's bigger than every other brushless motor I had at the time anyway.
Back in the US, I had to figure out what on earth to do with such a gigantic motor. I had no controller for it, no battery system that could possibly feed it, and no application. My personal hovercraft project was ditched a year before. I could not shove this motor into a 12-pound class combat 'bot.
It took a lucky trip to a local flea market to get this project going. On that day, I passed by the usual vendors selling toys when I noticed one had a small electric scooter, about the size of a large Razor scooter.
And it all went downhill from there.
(Update 15 January 2009) Hey guys, I have 31,000 views and 21 rates? Please rate whether you liked it or not, because that provides me with feedback! As always, comments and questions are welcome. Also, I am preparing a writeup on the wheelmotor scooter, but want to get my motor theory a bit more inline before I finish it.
I'm a builder and tinkerer by nature, and am always on the lookout for cool parts, devices which can be made better with cool parts, or some times both. During the summer months of 2007, I happened upon a chance to work with both.
As a bit of backstory, I build and compete fighting robots - as in Battlebots and Robot Wars - and as other builders of robots and non-robots may know, the search for the perfect motor is neverending. In June of 2007, I went on a trip to China to visit my aging grandparents... and hunt for parts. As RC hobbyists may know, China is the prime source of the vast majority of model equipment these days - big-branded or not.
So it was in a small hobby shop in a neighborhood of Beijing that I spotted this large outrunner motor. The only word to describe it was "assnormous" - according to the info card, it was a "7050/6" type motor. Translation: 70mm diameter stator, 50mm stator length, 6 turns per stator pole. Real translation: Massive power. It claimed 6 kilowatts maximum, but as overrrated as many hobby parts tend to be, I didn't trust the rating. Many high-quality BLDC motors of this size range can produce up to 10-11 kilowatts of power. They also cost a cool grand or two, not the $100 I ended up getting this motor for. Here's one example.
However, that didn't prevent me from impulsively buying it, since it's bigger than every other brushless motor I had at the time anyway.
Back in the US, I had to figure out what on earth to do with such a gigantic motor. I had no controller for it, no battery system that could possibly feed it, and no application. My personal hovercraft project was ditched a year before. I could not shove this motor into a 12-pound class combat 'bot.
It took a lucky trip to a local flea market to get this project going. On that day, I passed by the usual vendors selling toys when I noticed one had a small electric scooter, about the size of a large Razor scooter.
And it all went downhill from there.
(Update 15 January 2009) Hey guys, I have 31,000 views and 21 rates? Please rate whether you liked it or not, because that provides me with feedback! As always, comments and questions are welcome. Also, I am preparing a writeup on the wheelmotor scooter, but want to get my motor theory a bit more inline before I finish it.
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General considerations Just about any wheeled object you pick up these days can be hacked, modded, or boosted to yield a higher power-to-weight ratio. What is particularly exciting about electric vehicles is that this process is comparatively easy, part of the reason why I am eagerly awaiting mainstream electric cars, having reached the age of unlimited desire in vehicular performance.
The basic technology of almost all small EVs - scooter, bike, or car - these days is lead-acid batteries and large DC motors. While the heavy build of these parts increases their relative durability compared to a lighter but more powerful part, performance is often left to be desired.
Hence, most small EVs you may find are amenable to power mods. I focused specifically on an electric scooter since.. well, I had one, but also because they tend to be small and extremely portable. One example of a commercial "mini-electric scooter" is the Roth Motorboard 2000XR, which, while extremely compact, has the performance of much larger vehicles.
Larger electric scooters such as the steel tube-framed pneumatic-wheel types can stand a more massive power system than what you can fit on a Razor-size scooter, but weigh comparatively more. Bicycles, electric or not, are another common conversion base. Conversions aside, you can build an electric powertrain into whatever you please.
Conceptually, however different the physical manifestation, the operation of the vehicles are the same, as shown in the diagram. EVs are relatively simple things at their very basic level.
In the end, the kind of power system and performance you will get is a function of how much money you want to spend and what your goal is. Something to move you around campus or town won't cost as much as the next Killacycle.
My personal conversion was an electric scooter whose primary intended application was as a campusmobile for college. It is a Sharper Image Electric X2 model scooter I bought nth-hand for $10, with leaking batteries, no charger, and a slipping belt drive. It was pretty much perfect.
The basic technology of almost all small EVs - scooter, bike, or car - these days is lead-acid batteries and large DC motors. While the heavy build of these parts increases their relative durability compared to a lighter but more powerful part, performance is often left to be desired.
Hence, most small EVs you may find are amenable to power mods. I focused specifically on an electric scooter since.. well, I had one, but also because they tend to be small and extremely portable. One example of a commercial "mini-electric scooter" is the Roth Motorboard 2000XR, which, while extremely compact, has the performance of much larger vehicles.
Larger electric scooters such as the steel tube-framed pneumatic-wheel types can stand a more massive power system than what you can fit on a Razor-size scooter, but weigh comparatively more. Bicycles, electric or not, are another common conversion base. Conversions aside, you can build an electric powertrain into whatever you please.
Conceptually, however different the physical manifestation, the operation of the vehicles are the same, as shown in the diagram. EVs are relatively simple things at their very basic level.
In the end, the kind of power system and performance you will get is a function of how much money you want to spend and what your goal is. Something to move you around campus or town won't cost as much as the next Killacycle.
My personal conversion was an electric scooter whose primary intended application was as a campusmobile for college. It is a Sharper Image Electric X2 model scooter I bought nth-hand for $10, with leaking batteries, no charger, and a slipping belt drive. It was pretty much perfect.
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http://www.razor.com/us/products/scooters/specs.html?name=A5+Lux
The motors hes using draw far far far much more power. are brushless requiring a 3 phase AC speed controller.
It just wont work.
Question though, what is the run time of your system? I am going to be running a 24V with the battery capacity being around 6-9AH. Reason is I have a scooter I am converting to an electric skateboard, but I want to make something thats lighter than 40 lbs (due to the Lead-Acid Batteries, capacity at 13AH I think) that I can haul around school.
Thanks,
Nick
Here is my scooter! I can go up to 25mph ( 40.3km/h)!!
I got a 1480W brushless motor with 33.3V lithium battery.
Here is a picture of the scooter with GPS showing 40.3km/h
www.jeromedemers.com/blog/wp-content/uploads/2009/10/scooter_speed_record_-002-545x409.jpg
Here is the post on ES
http://endless-sphere.com/forums/viewtopic.php?f=12&t=13315
I also have my own website that is dedicated to the scooter.
www.JeromeDemers.com
I will be making a new video of the scooter going 25mph. Really fun and dangerous!
I also notice that you will be modifying a Xootr Street push scooter. I am really jalous!
I will be working on a new version of that scooter using 5 to 6 inch pneumatic wheels.
Keep up the great work! Can't wait to see you next projects!
ps- I can got faster then 25mph, since I am driving a 37V motor with 33V! :)
Also, the batteries, custom circuitry and controller are in a back-pack. This keeps the expensive electronics relatively more secure, the scooter lighter(It currently weighs about 20 pounds) and "smaller" and helps shield the electronics from the weather.
Predictions -
Range: 10+ miles. Likely around 12 or so, but I'll need to measure it.
Top Speed: 27 according to my simulator, but I'll be limiting it to 20 since anything faster doesn't really feel safe. Top speed up a 7% hill? 15 mph.
When I get my battery repaired either tomorrow or the day after, I'll be sure to report actual information.
BTW, I think MIT's computer-science/electrical engineering program is so much better than University of Washington's(The university I'm currently attending). Most of the theory I learned from OCW's 6.002 seems to be at least "that's 300/400 level!" according to my current "intro to electrical engineering" professor(i.e., 3+ sequenced classes away) and these classes learn in 5 weeks what took MIT 1.5.
An 18650 Li-ion cell is 2300mah/3.7volts, they can sustain 5c (6.6AH * 5 = 33 amps continuous) discharge rates with some air cooling. If you have a 12s/2p (44.4 volts/6.6 AH) pack it would be about the same size as 28 Sub-C cells but at about 1/2 the weight. And would give you triple the range.
It also depends on what you're going for... A pack made of 18650s will give you further range provided you can keep the current draw very low. But they will not be able to give you as much kick when you want to accelerate.