THE PUNCH SOUTH AMERICA

Build Your Own ELECTRIC MOTORCYCLE

Now that we made it through the basics of safety and legal, you want to start that search for your"Glider" or "Donor Bike". You may already have something that's been sitting around with a bad engine or transmission. Otherwise start looking for your cycle. You may want to check out Craigslist, the local newspaper classifieds, or stop and see every motorcycle for sale on the side of the road.

Besides just overall style and finding something that fits your budget, here's what to look for in the donor bike.

OVERALL GOOD CONDITION
It might sound obvious, but get something that's in fairly good condition. You want to do a conversion, not a restoration! Make sure the turn signals and headlight work. The horn should work. It shouldn't be all rusted out. Get something that looks nice enough and will be fun to ride. If you happen to be somebody who regularly builds custom motorcycles and restorations, just ignore what I said. Go hog-wild instead. I do have to admit that the cycle I bought to convert to electric was not in very good shape. The price was right though. In the end, fixing all the little things on it took a fair amount of time and work. Looking back on it now, I would have preferred to spend a little more money and and have had fewer things to fix.

SAVE MONEY WITH A BAD ENGINE OR TRANSMISSION
In this conversion, the original engine and transmission are NOT used. If you buy a motorcycle that is in pretty good condition OTHER than a bad engine or transmission, you might be able to get a really good deal on it. Just make sure to keep the engine and transmission with for a while to confirm proper registration.

SAVE MONEY WITH A GOOD ENGINE AND TRANSMISSION
If you choose to buy a cycle in good running condition, make sure to carefully remove the engine and transmission. Keep all the parts together, label everything, and keep it out of the weather. Sell the engine and tranny to make some money back on the purchase of the cycle.

DRIVESHAFT, BELT-DRIVE, OR CHAIN
Most motorcycles are driven by a chain, but some use a belt or even a driveshaft. Get a donor bike with a chain. This will give you the most flexibilty and efficiency. Chains are cheap, don't slip, and are easy to change gear ratios by swapping out an inexpensive sprocket. Electric motorcycles CAN be built with a belt or driveshaft, but it is more of an advanced project and has other considerations.

BATTERY AND MOTOR SPACE
You will want a cycle with enough room in its guts for the motor and batteries. A too-small cycle will limit where you can put the motor and batteries, and how many batteries will fit. An extremely large cycle gives you plenty of room, but the frame may become heavy quickly. Popular choices include sport bikes and medium-size standard cycles.

Sport bikes typically have an aluminum frame (light-weight) and it is shaped with two supports over the engine, and two under it. This gives you a "box" to mount your batteries. Sport bikes also usually have some sort of plastic fairing over the engine. After conversion to electric, you can put the fairing back on, and look almost stock.

A medium-size "standard" will have two frame supports under the engine, which can be re-used as a base or tray for mounting the batteries. You will most likely want to avoid any cycle that has a single piece of frame above or below the engine. It just makes it more difficult to find a way to mount the batteries. You can always fabricate something custom, but it's best to start with a solid foundation.

GET THE BOOK
Most cycles have a mechanics repair manual available for them. You might be familiar with the Haynes or Chilton's brands for car repair. Find the book for your cycle. Although it won't cover the new custom electric system, it will tell you how to fix your brakes, align the chain, painting tips, general repair and maintenance, and have plenty of other useful information.

De-ICE-ing
Once you have your donor bike, you need to De-ICE it. ICE stands for Internal Combustion Engine. You'll be removing the engine, the transmission, and anything else related to that system. That includes the gas tank, the exhaust pipes, and a radiator if it has one. Remove these parts carefully, so you can re-sell them.

You will want to know where to put the electric motor for the conversion. The easiest way to do that is simply to put the electric motor exactly where the output shaft of the transmission was. Locate where the chain goes to on the transmission end and mark that location on the frame. Use a wax pencil or silver marker with a speed square to put a mark on the frame both vertically and horizontally from the output shaft of the transmission. You will later use these marks to position the electric motor.

To power your motorcycle, you're going to need a motor. But what type, what size, and where do you get it from!?

This project used a Briggs & Stratton Etek. It's a DC (Direct Current), brushed, pancake motor, rated at up to 48V and 150 amps continuous. I got it used, through Craigslist, from a college student who built those robots that battled each other. He was using this motor to swing a hammer, but it was too powerful, and he kept breaking hammer handles!

So why this motor?
DC - Direct Current
Direct current motors are very straight forward. They are easy to control the speed of. Also, batteries use direct current. By using a DC motor, there's no intermediate step of converting DC battery power to AC power to run the motor.

Face Mount
The Briggs motor has eight holes on the end (the "face") of the motor to make it easy to mount to a piece of flat steel or aluminum. Some motors have a "foot" on the bottom of them for mounting, which wouldn't have been as easy to use in this situation. 

Permanent Magnet
Permanent Magnet motors tend to be very compact. They create rotational energy (torque) by pushing two magnetic fields against each other. The one magnetic field is produced by current from the batteries (an electro-magnet). The other magnetic field is from mineral permanent magnets. These magnets are much more compact than a second electro-magnet would be, allowing for an overall powerful, yet small motor. The limiting factor in the design is the strength of the permanent magnetic field. Many permanent magnet motors spin equally well in either direction. Just swap the positive and negative battery cables for it to spin the other way. The permanent magnets are ALWAYS magnetic! So don't drop a washer near one of the vent slots, or it will get sucked in and you have to take the whole thing apart to get it out! Since then, I made sure ALL washers are stainless steel (not only are they corrosion-resistant, but they are non-magnetic as well.)

I chose this motor knowing that many other people had used the same one in their electric motorcycle designs. http://www.evalbum.com/mtrbr/BRIG

Permanent magnet motors are generally designed to spin equally well in either direction. If the motor spins the opposite direction of what you intended, all you have to do is swap the two cables. On a large motorcycle, you could take advantage of this with a reversing contactor to have a reverse gear.

It's not all about horsepower....
Electric motors are rated differently than gas engines are in terms of their power. A gas engine is rated in horsepower with the engine running at nearly maximum speed and fuel consumption (full-out!) An electric motor is rated at how much power is can put out continuously - for hours at a time. So, a horsepower rating between an engine and an electric motor is not apples to apples.

More and more engines are also now being rated in Watts. A watt is a unit of power used. Most people understand watts, as in that a 100-watt light bulb uses more power than a 75-watt lightbulb. It puts out more power (as light and heat) but also costs more on your electric bill.

In electric vehicle design, keep in mind that volts x amps = watts. Also, 1 Horsepower is roughly 746 watts. So, it's pretty easy to do some simple math to figure out the power of our motor.

By being connected to four 12V batteries in series, the system nominal voltage is 48V. The motor is rated at 150 amps continuous. 48 x 150 = 7,200 watts. Divide that by 746 (watts to horsepower) and you get about 9.6 horsepower. That doesn't sound like a lot. However, you can pull much higher amperage briefly through the motor - typically three or four times as much. My system amperage is limited by the fact that the motor controller maxes out at 300 amps. That still means we can get DOUBLE the power out of the motor compared to what you might think it can produce, just based on the numbers stamped on it.

Combine that with increased efficiency (by completely losing the transmission) and the fact that you have FULL TORQUE right off the line (a gas engine has to rev up to several thousand RPM to get into it's best power band) and even a compact electric motor has far better acceleration than you think it might.

I later had my cycle tested on a dynometer at a large Harley-Davidson gathering. The cycle "officially" clocked-in as 12hp. But when the guy first went to ride the cycle up to the dyno, he almost threw himself off with how quick it accelerated!

Other Options
What other motors might you use in your electric motorcycle? Besides permanent magnet DC motors there are also Series-Wound and Brushless DC motors as well as some new AC motors. Series-wound motors are similar to permanent magnet DC motors. They are bulkier, but produce fantastic torque! You could use a series-wound drive motor out of a junked electric forklift. Do not use a pump motor. Those typically do not have a male driveshaft. Same goes for electric golf cart motors. They may otherwise sound like a good motor for a cycle, but unless you have a way to easily connect a standard sprocket to the motor, they will be a lot of tinkering to make work for your project. ( A friend of mine is currently working on designing a kit with a specialty part allowing anyone to build their own electric motorcycle using an off-the-shelf golf cart motor. Look for that in the future.)

 
Brushless DC and AC motors are very similar. They require dedicated controllers designed specifically for them. If you go that route, buy your motor and controller as a matched set through a reputable dealer.
   
in general, all these motors are air-cooled, so you don't need a motorcycle with a radiator on it.

For planning purposes, you want to know that your motor will FIT in the motorcycle before you buy it! Made sure to measure the space you have and the physical size of the motor before you buy. If the motor is not in front of you in person, don't worry, most mainstream manufactured motors have diagrams that you can download, that include the physical dimensions. (See Etek_Diagram PDF file attached below.)
Besides the diagram showing physical dimensions, it also lists important information on torque, voltage, RPM, etc. That helps you plan out your cycle design as well.