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.
Step 1: Select your vehicle
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.