Picture of Advanced Brushless Power Systems for Small Electric Scooters
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.

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wilgubeast1 year ago

Any chance you could refresh the links in step 6?

Why not try to replicate (or just swipe) the throttle system on a corded power drill? (or similar device) Unless your insanely trigger happy you'll get a much smoother ride. (take a look at one of the more quality committed brands, some of the lesser admired brands simply use really sadly wired mosfets and lead heatsinks. :( Needless to say removing that nice stageless motor control.)
i think the throttle he has is pretty similar...
Drill motor throttles are only capable of a 15 maybe 20 amps at around 12 volts. and that is a half bridge DC brushed motor controller.

The motors hes using draw far far far much more power. are brushless requiring a 3 phase AC speed controller.

It just wont work.
but he can use a rely wich in turn will allow 4 more( WAY MOOORE POWER) to be put to use.
The problem with relays for speed control is they are either all, or nothing. What his throttle needs is either some high current pots, or a digital system linking some form of analog control (probably pots...) To an h-bridge. The only way for relays to work for this in any sort of controlled manner would be multiple relays each with some percentage of the total allowable current, and do it in steps, but that would still probably land him on his ass, and/or wreck the device. As the motor would go from off, to a decent percentage of the power curve milliseconds. (By relays, could use opto-isolators as well, but relays should be cheaper, and probably a bit more robust for this... Opto's as I remember are a bit more fragile... And precise, not good things for this...)
uill want to protect yr circut boards big tyme unless u like. see big sperks a fire come from them. when they get wet?
theres a bug in step 3. the first link cannot be found.
this is my new fav EV instructable. I'd gotten close to a design uisng some huge kW brushless motors but was having trouble with transmission parts. Yours had the link to where I can get pulleys and belts able to handle the load. Now I just gotta find a big motor like that for the price you paid. Probably not gonna find it on this side of the Pacific without significant markup, huh?
try vacum motors yes they have brushes. but if u do the mods on them u too can convert them to brushless.
try vacum motors yes they have brushes. but if u do the mods on them u too can convert them to brushless.
teamtestbot (author)  phugedaboudet6 years ago
Have you tried United Hobbies/HobbyCity? They have great deals on obnoxiously large motors... Or, you could roll your own.
swbluto6 years ago
Thanks partially to this inspiration, I finally built the electric scooter of my dreams! Its build page (with warts and all) is at http://endless-sphere.com/forums/viewtopic.php?f=12&t=7638&p=131721#p131721 . A few things I did differently - I ended up going with one with pneumatic tires in a common size so there'd be more suspension which I know from experience becomes more critical the faster you go. I also created my own signal board which converts the signal from a regular e-bike throttle to a servo pulse the Phoenix-85 understands. I also added capacitors on the input to ensure the controller won't fail, current limiting so that I could use my existing lower-C-rate LiFePO4 (I want to use it until it dies! Which, by my calculation, will be in 2-4 years.), customized current ramping and also temperature sensing on the motor and controller to protect them from thermal damage. I also ended up doing a battery mod to drop the battery voltage of the nominally 48 volt battery. I plan to add a customized LCD and I'm currently on the look-out for cheap, available serial LCDs(the black on green kind. Apparently, SparkFun is always out.).

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.
try checking out dx.com and alibaba.com yes uill have to wait up to a full month to get them in but. happy parts hunting
teamtestbot (author)  swbluto6 years ago
Wow, that's some pretty sophisticated stuff. I bet the current limiting also helps prevent Funny Car Syndrome. I always want to put additional electronics on my stuff past the bare minimum to get it moving, but the whole "it works, don't touch it..." always gets me. FWIW, I see you-ve been to my site - I never fixed that ball of wire that was the signal driver on RazEr. Totally am not cut out for EECS :')
markiscool6 years ago
how do you build the circuit for the different power outputs??? please help me
just look up charge controllers there a insturctable 4 those as well. im pretty shure of it.
UbuntuNinja6 years ago
Does anyone know anything about using super capacitors (electrolytic double layer) instead of batteries?
uill have to use a double out put stylle to power and charge yr caps tho
drhoff6 years ago
Great Instructable! Very informative and well written. What was the cost of the battery pack? I didn't see it in the cost breakdown. Also, as a fellow combat robot builder (just antweights, but they count too ; D), I would love to check out your bots. Do you have a link?
why not go 4 the stadium crusher. turn a full sized exacavator into aah battle
bot !!!!!!!!!!!!
leowhite drhoff5 years ago
I'd like to know this aswell
drhoff drhoff6 years ago
I have another question i forgot to ask earlier. How many rpm / v is that motor supposed to put out?
Pale_Flyer5 years ago
that looks like you said to be a very brute force... but it also looks like you know what you are doing with components and a soldiering iron. I am thinking about doing something similar, and using a parallax BS2 system for control. i just haven't found a motor that would have enough torque. i want to find it somewhere that it comes to me from a store i can physically walk into. I might try the local home center...
try alibaba.com even if u have to wiat up to a month to get it.(stupid homeland security red tape).
verdict264 years ago
Given your comments about the size of the scooter and the concern about the center of gravity (basically you're getting thrown off)....Have you thought about the Razor A5 Lux. I have two of them and work great for adults. I weigh 180 lbs and it works flawlessly. I imagine there will still be some handling issues, but given the larger wheels....I speculate it will improve.

dang yr a light wieght. try my 310+lbs of weigth. i'd most of them upon getting on.
ebikegp2 years ago
Hi I'm a complete newbie to this site so was wondering if anyone knows if & how you can contact the Author of this paper?
4 this write up every tyme some one makea a post or replys to another post they get the post in form of an email.
KDan2 years ago
Good idea for the efficient scooter. HTD belt is a good choice. Stock Drive Products also offer Fairloc pulley for the HTD belt far better than set screw pulley. http://sdp-si.com/ss/pdf/81002121.pdf. Fairloc pulley tightly grip the shaft without contacting shaft like set screws.
MustangGuy2 years ago
Can you please tell me what model that scooter is? It seems like the perfect platform for a carry on electric scooter.
LOL! I loved your instructables. I want to build one! Maybe with max 6miles/hr, not 25! I have a 30 mm outrunner (gearing down 10-30:1) , but maybe it's too small? For 3-4 month ago somebody threw away a similar scooter as yours, but the backweel was ruined. Then I found a nice round wheel for a month ago... And then I saw this article... AAARGH!
jweirs4 years ago
where did you acquire your motor and batteries?
Pale_Flyer5 years ago
you might be able to run the wires up the handle and across the t-bar for some protection...
Very Nice!! I'm considering doing something similar (which is how I re-discovered this 'ible) with some sort of scooter - either the kind with the little bike tires, a Razor style with larger wheels, or using a broken electric scooter as a base. Anyway, I will use a 245Kv 63mm x 64mm BL outrunner and 70A 10S LiPo ESC (both from HobbyPartz, a good US-based chinese stuff distributor), although I will probably end up using 3 12V SLAs to save money at the cost of efficiency... Not sure what capacity I will need, though, what sorts of runtimes do you get with your 3000mAh cells? Thanks and great instructable!
KT Gadget5 years ago
 Great instructable, I am now researching what would be a good substitute for the batteries (looking at lighter LiFePO4 or high capacity NiCads).

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.
This is easily the best-written instructible I've ever read.  VERY WELL DONE.  Is the scooter still running?
i was digging through my garage and found my old razor electric scooter, i remember getting it new for a hundred dollars and it goes 15mph and the front wheel has an innertube, so you can go over large cracks.
Antleredguy5 years ago
 Does anyone know of an instructable that gives a total introduction to motors, controllers, batteries, and the like? It would be so helpful!
ElvenChild5 years ago
 did you by any chance call it the bwd scooter shown on the mittech website
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