In 2008, I put together a guide on Instructables about upgrading the power system of your small personal electric vehicle . It was a primer on the basics of an electric vehicle power system and offered resources and tips specific to compact electric scooter conversion. As of right now, it has a solid 5 rating - I didn't know you could write that much on Instructables without telling anyone how to build anything and still receive perfect reviews.

I am delighted to report that in 2011, three years after the fact, that putting together a compact, powerful, and efficient electric vehicle drivetrain for local commutes (such as your campus, neighborhood, or urban area) using both R/C hobby hardware and specialized EV components is now cheaper and easier than ever. Price competition, new technologies, and just plain increased availability of fabrication and material resources means that building an electric personal transport device is now within the capabilities of just about everyone.

I will assume that you already know the fundamental parts of an EV or have built them before. If not, you're welcome to refer to my previous Instructable on this topic (linked above), or check out one of the many great Instructables on EV systems. This Instructable is intended as a conglomeration of resources, and so will discuss the pros and cons of component choices, specific vendors, design strategies, and other high-level considerations. It will also offer tips and tricks that I've found or had passed on to me pertaining to building small electric scooters. The guide will be overtly calibrated towards said scooters, since I favor them over electric bicycles, though much of the advice is just as pertinent to e-bikes. It should also be helpful for the occasional odd electric skateboard or other unconventional vehicle.

The format of the Instructable will primarily be a page or two on each primary component of an EV - such as the motor, controller, battery, and drivetrain (and associated mechanics).Then I'll present some designs that have emerged as being relatively easy to execute and fabrication advice for fully custom vehicles (i.e. not conversions).

Step 1: R/C Hobby Parts: The Pros and Cons

The focus of my previous instructable was on repurposing R/C hobby, namely model aircraft, parts for vehicle propulsion. It will also make up a substantial portion of this one. Why on earth would you use parts designed for things which aren't technically supposed to be touching said earth when they're working correctly?

R/C aircraft components are the highest power-to-weight electric power systems easily available to the average consumer.

In the quest for ever-increasing flight durations, model sizes, and acrobatic performance, the R/C aircraft world has seen most components such as motors and motor controllers pushed to the limit of realizable power densities. The performance of the average brushless airplane motor greatly exceeds that of an average ferrite-magnet, DC brush scooter or bike motor - typically by three or four times. In the size and weight of a 500 watt electric scooter motor (about 3 inches diameter, 4 inches long, and weighing about 4 pounds), the example motor shown at the bottom can handle 2 - 3000 watts (i.e. 3 to 4 horsepower) of power throughput, and up to 6,000W peak.

The advent of mass produced, high performance lithium ion batteries is another factor. A modern lithium polymer (more on the distinction between different lithium flavors later!) battery the size of a U.S. house brick (about 1.3 liters) can store up to 300 watt hours, at the usual lithium polymer energy density of 240 Wh/L, and discharge at several kilowatts for a few minutes. No traditional lead-acid, or even nickel-chemistry battery system can come close to that. Granted, there are downsides to having such a dense energy source, and those will be addressed, but the truth is there in the numbers.

Part of my engineering interest is taking advantage of these increased power densities to create ever more compact but still practical vehicles. For instance, only with brushless technology is the miniature hub motor I've been working on a possibility...much less electric inline skates using them . Electric scooters are still imagined by most people to be large, low-performance, lead-acid battery powered monstrosities that are reserved for kids with back yards too big to run around efficiently in. While this may be true for most commercially sold ones due to cost reasons, if you're building one yourself, there's no reason to not expect better.

R/C aircraft components are the best power-to-price electric power systems, period .

You'd notice I left the fine print "commonly available" up there, because there are things which are more hardcore than a cheap brushless motor in terms of power density. The problem is, you can't buy them. Not easily, and definitely not cheaply. However, because R/C aeromodelling has become so prolific, parts are readily available over the internet and extremely cheap. Most R/C parts these days are manufactured in China and other East Asian countries and sold by dealers directly from those areas.

Even three years ago when I wrote my previous piece, this was not as true as it is now. The electric flight market, for the better part of the last decade, was dominated by high-market European manufacturers, and so was extremely expensive and also exclusive. The American market had two major motor manufacturers in this era which were well established: Astroflight and Aveox (which seems to have left the hobby market), and probably also Neu Motors . While the most hardcore of aeromodellers still stick with the highest performance European and American brands and companies, the majority run some inexpensive East Asian power system. 

For a custom small vehicle, it's hard to find parts which have better price numbers. Depending on your power needs, a motor that has enough wattage to propel a vehicle will run between $40 to $100. A controller that can run the motor will be around $50 to $150. Batteries are the big cost breaker for EVs, still, but typical model aircraft lithium polymer packs price out to between $0.40 to $0.70 per watt-hour . A scooter may have around 150 to 200 watt hours of battery onboard, so expect about $70-100 in commonly available batteries. As I will show in more detail, you can assembly a roughly 1500 watt electric power system for something like $200 to $300 - and that is for everything , even including batteries, and a charger if you're good at shopping.

All of this might seem like cheap airplane parts are the way of the future. However, they also have their downsides.

Unfortunately, R/C aircraft components are usually very rudimentary and somewhat fragile .

Let's face it - airplanes are, in the purely mechanical sense, pretty easy loads to handle. The torque and power required increase directly with speed, so there's no static or locked-rotor (stall) conditions to worry about, unlike in vehicles where maximum torque is required at zero speed in order to accelerate from standstill. Airplanes are never supposed to hit things, bound over rocks and sidewalk cracks, or be jostled by suspension movements. What matters more in aeromodelling is light weight.

As a result, model motors are usually made as lightweight as possible, using thin metals and plastics, and undersized bearings and shafts. Substantard metal alloys (such as soft architectural aluminum) are common in "cheap" motor construction. R/C power controllers are usually single-PCB affairs which pack power semiconductors and logic right next to eachother using the minimum amount of support components possible by design, and only capable of reaching their ratings when placed in a constant airflow (such as, you know, the draft of a propeller), and are rated to just under the peak power handling capabilities of the semiconductors.  One of the major themes I'll hit on later is that you must derate everything . The ratings given for aircraft parts, especially cheap ones, are generally unrealistic for EV use.

Even worse is the fact that the average aircraft lithium ion pack doesn't have a hard shell. Lipo batteries are little squishy bags of volatile electrolytes and active alkali metals. I don't know who's great idea it was to make a battery without a shell, but the abuse of a vehicle dictates that batteries must be properly mounted and proofed from shock, impacts, and weather. It makes me cringe a little even recommending using lithium batteries to the public because of those reasons.

You've been warned.

Overall, though, I think my point is clear: R/C model aircraft components are a good economical choice for those looking to begin experimenting with electric vehicle technology . It may not be the best solution for someone looking for a reliable, maintenance-free, long-life commuting vehicle. Many R/C components are definitely not manufactured to vehicle specifications and may fail or become finicky over a period of time. There are definitely commercial EV solutions available which are even plug-and-play - but I'm assuming if you are reading this, you have a little sense of adventure.
<p>This 4 year old instructable is STILL a treasure trove of useful relevant information. Thanks for sharing!</p>
A fun build! Thanks for the awesome instructable!
<p>Actually instructive. Though the term is common I had no idea what a brushless motor was or how it worked, and I am an electrical engineer, an old one. Sixty years ago I was wondering why the brushes of the dead motor that I was rewinding were not semiconductor devices. The transistor was then 10 years old. Life took me in other directions so the idea never matured - and suddenly I know. Thanks! Further I now understand something about the DC/AC drive of the Tesla Auto. My interest is, at the moment, in electric propulsion for a nearly finished Sampan sitting in my back yard. Though off the shelf devices are readily available I am hoping for something better. Your remarks about RC devices and propellers seem to apply. The battery info is also helpful. I am struggling with the tradeoff of a low HP gas outboard, at less than 40lb and a 20lb trolling motor with a 50lb 12 volt lead acid battery. You advice about how to purchase motors, batteries and controllers is most pertinent. - Boatmakertoo</p>
<p>Hi My gfs bike has a 12mm rear axle and she hates the 6kg front hub. Id like to use this motor to drive the back wheel. It looks very similar to my internal motor on a mac 10t geared hub motor ie lots of turns. Could I not just use the infineon sensorless controller? http://www.hobbyking.com/hobbyking/store/__54888__9235_100KV_Turnigy_Multistar_Brushless_Multi_Rotor_Motor.html</p><p>Anyway thanks for the article, Dan</p>
<p>very good article, a great help to all modellers!</p>
<p>Very good, enlightening article !</p>
<p>You Sir, are my hero.</p>
<p>Hi, your<br>article is sooo good!</p><p><a href="http://www.instructables.com/id/The-New-and-Improved-Brushless-Electric-Scooter-Po/all/?lang=es" rel="nofollow">http://www.instructables.com/id/The-New-and-Improv...</a></p><p>I created<br>some links to it at my site <a href="http://www.avdweb.nl" rel="nofollow"> www.avdweb.nl</a></p><p>You've put all<br>topics under each other so they are difficult to localize, it is sooo long now.<br>Can you create a table of contents on the top with links to the separate<br>topics?</p><p>Or create<br>separate items on instructables.</p><p>Kind regards,</p><p>Albert</p>
<p>It looks like the above named A123 ALM_12v7 drop in batteries are available from: <a href="http://www.buya123batteries.com/ALM_12V7_p/400520-201.htm" rel="nofollow">http://www.buya123batteries.com/ALM_12V7_p/400520-...</a></p><p>for $130.00</p>
What is the pinout for the standard, RC esc sensor connector?
Wonderful instructable. Have been giving it some thought for a bit and wondering why you haven't considered building your own ESC. From your descriptions a sensorless controller suitable for our purposes seems very doable, but not available within the R/C airplane realm. We need a custom, self-starting, sensorless ESC. Other's have made them. <br> <br>Once you have the basics together fine-tuning becomes possible. Seems like the perfect solution to a host of problems. Perhaps the springboard to designs otherwise out of reach.
Thanks for your instructable. It's very interesting and complete but I have a, may be, stupid question. I'm planning to put sensors in an outrunner as well and wanted to know how to tie the sensors to the ESC. There seems to be a standard 6 pin connector shared between the different ESC models. How do I wire the sensors to this connector?
This is a pretty sweet little scooter, might make one for my son if he starts behaving again. lol <br> <br>I am legitimately trying to find that gas motor which you showed but did not use. <br> <br>Can you tell me where you found it? I can only find electric models, which are great but not appropriate for my current project. <br> <br>Thanks, <br>-Grey
I found a good place to get thick very flexible 8 and 4 gauge wire is the local car stereo center. Th 8 gauge I used cost $1 per foot. They had 4 gauge but it was much more expensive.
Wow after reading this article now I'm building a scooter. <br>Bad influence I think.. <br>Welding and machining I get but the electrics are not so much my thing :( <br> <br>I bought 2 motors <br> <br>KA63-18L <br>Constant: 259Kv <br>Battery: 10Cell Lipo <br>Operating Current: 25-60A <br>Peak Current: 72A(15sec) <br> <br>Here is the problem.. Do I run one and have a spare or use them both? <br>If both what would be the best way? <br>
If you run both you need a controller for each. Now this may sound easy but you need to be careful to set up each esc the same and use the exact same model of esc and motor or one motor will do more work. Now unless you want to push more than 200 lbs around at 20 mph or more one motor should be sufficient as long as you use the gearing equation from this article as to not burn up your motor. Good luck and feel welcome to ask any questions you want to.
Hobbyking now sells 20C four cell 5 Ah lipo packs from the US warehouse for about $25 per pack: <br>http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18631
Could I maybe use a large pvc pipe to hold the hall effect sensors?
How exactly do you back install hall effect sensors in a motor? I am trying to make an electric motorcycle and want to use a kelly controller. I have a Turnigy 80-100-A 180 KV brushless outrunner (the same class that is on the scooter in this instructable) and have had a really hard time figuring out how to install sensors. I am also having a hard time figuring out how this motor is wound. <br>Any help would be greatly appreciated, thanks in advance.
It is extremely difficult to install *internal* sensors onto a mystery motor (of which you do not know the internal winding pattern). The C80 series is also very difficult to discern because they require so much current. <br><br>Usually, you would run current through two phase wires (&quot;line to line&quot;) and use a test magnet to observe which poles are polarized in which directions - they should always be alternating from tooth to tooth and there should always be 8 of them on in total. Using this and the process of elimination you can separate the 12 teeth of the stator into 3 groups of 4 teeth which you can call &quot;A&quot;, &quot;B&quot;, and &quot;C&quot;, which are associated with one of the three phase wires. Then, the Hall sensors are placed *between* 2 teeth of *different* phases.<br><br>Because the C80s have a very low resistance and few turns, you need either a ton of current or a sensitive magnetometer to determine the direction of the stator field. <br><br>Using external Hall sensors on the C80s is possibly the easiest solution. <br><br>
Thank you for the info, I have tried to run current through the different phases but I could not get enough current to get discernible results. I am thinking of just rewinding the motor so I know where the different phases are. Unfortunately I do not have access to anything to make an external mount for hall effect sensors. Do you know of a website that could make a mount for me? I also do not have any experience using CAD software. Another question I have is do all hall effect sensors have the same wiring scheme? The website I got mine from did not tell me which lead is which.
hi <br>a bit for the sake of accuracy: when you refer to &quot;convection&quot;, you actualy mean free convection(no air speed), as opposed to forced convection. <br>other than that petty note, its a great article and im learning why i shouldnt have bought the esc that i have...
Just wanted to say a quick thanks for this instructable. It's the detail all in the one place that i have been searching for, for years. Thanks for confirmation of R/C parts as well and the technical detail.
Can you use the sensored kelly controllers with a sensorless motor?
Not the KBS - Kelly does have the KSL line which is sensorless, but I have not heard vehicle stories about them nor know what settings they can manipulate (e.g. ramp-up time, initial current, etc.). And they're huge - they're full-size Kelly cases.
Great tips, especially about bore size changing! Thanks for taking time and explaining this!
If I'm going to use LiFePo4 batteries from HK, will I need to include a battery management system when discharging and/or charging? Great instructable, by the way.

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More by teamtestbot: How to Build your Everything Really Really Fast Chibikart: Rapid-Prototyping a Subminiature Electric Go-Kart Using Digital Fabrication and Hobby Components The New and Improved Brushless Electric Scooter Power System Guide
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