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Quick Overview

Designing, Converting, and Owning Electric Motorcycles By John Bidwell

Introduction to The Secrets of El Ninja

Smooth, fast, quiet, comfortable, clean, and economically smart—that’s what electric motorcycles are all about. In most locations, oil products are not used to produce the electric energy used for charging batteries, and the cost of running an electric motorcycle is less than one-third the cost of running a gas motorcycle. Plus, the amount of smog-producing emissions created when driving an electric motorcycle is zero.

This book explains how to easily convert a gas motorcycle to electric power in your own garage with standard hand tools (no welding or machining required). It describes all the technology fundamentals, performance tradeoffs, and design decisions involved in converting a gas motorcycle. It then walks you through a straightforward and highly efficient example conversion of a 1987 Kawasaki 750 sport bike, showing you "The Secrets El Ninja." As a bonus, this book also covers maintenance and repair of the electrical components of any electric motorcycle.

El Ninja combines a gas motorcycle (based on a stock motorcycle rolling chassis) with a high-power electric vehicle motor, a high-power Mosfet transistor controller, and a set of affordable, readily available batteries. The result is a long-range (40 miles of stop-and-go driving), high-performance, 60 MPH machine.

The motor used in El Ninja is the high-performance Etek motor that can be operated at 36, 48, 60, or 72 volts. At 48 volts and 450 amps, the Etek delivers 15+ peak horsepower. The El Ninja design accommodates a variety of other motors, controllers, and battery options as well.

The electric components (motor, controller, power switch, throttle, etc.,) are available by mail order and/or from Web electric vehicle (EV) component suppliers. See the Vendor List and Material List in the Appendix for assistance with obtaining these items.

An electric motorcycle conversion is easier than an electric car conversion because you don’t have to worry about the transmission and clutch, power steering, vacuum pumps, heaters, air conditioners, and the weight and size of everything that gets moved around. An El Ninja-type conversion is even easier than most motorcycle conversions because the battery and motor mounting are so straightforward and provide configuration flexibility. After a thorough description of technology, performance and maintenance, this book will describe the design tradeoffs in converting a gas motorcycle to an electric motorcycle. It will then walk you though the El Ninja building process, using step-by-step build descriptions, CAD drawings, CAD mockups, and photographs of the conversion process.

There are other motorcycle rolling chassis available that you can use instead of the ‘87 Kawasaki Ninja to build a comparable motorcycle. By using the design and build concepts in this book, you can convert almost any gas motorcycle to an optimized, useful electric motorcycle.

Motorcycle rolling chassis are available from a variety of sources. See the How to Find the Right Donor Gas Motorcycle section of Chapter 4.

Building El Ninja, as with many motorcycle conversions, is primarily a battery/motor mounting-and-assembly project. No welding or machining is required to complete the El Ninja conversion. Selecting the right motor, controller, batteries, and drive sprockets is fundamental to a successful conversion. This book describes how to select these components after the initial design and offers a strategy for evolving the design with upgrades.

Some of the motor options are: the high-performance Etek motor, the Perm motor, and several Advanced DC series wound motors. El Ninja’s design is especially versatile because it allows you to begin with fewer batteries, providing limited speed and range but a lighter weight. Then, later you can upgrade to more batteries (i.e., a higher voltage) for more performance and longer range. Using smaller batteries for quicker acceleration is another option. One frame accommodates all the configurations. Several of the many possible combinations are shown in the table below. Also, see the Selecting and Mounting Batteries and the Selecting and Mounting the Motor sections of Chapter 4.

Registering and Licensing Electric Motorcycles

When configured with the full-power options, electric motorcycles are registered, insured, and operated as a motorcycle. However, electric motorcycle versions can be configured to meet the 30-MPH moped or scooter licensing rules in most states. (Consult your local authorities for the rules and regulations in your area.)

How Electric Motorcycles and El Ninja Work

Since DC electric motors develop maximum torque at zero RPM, this allows electric motorcycles to have excellent starting performance. The motor-to-wheel gear ratio can be changed easily with different sprockets to provide higher speeds or more low-end torque at the drive wheel. The DC electric motor is a DC permanent magnet type that is specifically designed for electric vehicles. This motor can run continuously and very efficiently at all speeds without overheating. The motor is mounted on the swing arm to collect maximum airflow and maintain a constant chain distance from the motor to the rear wheel for precise chain tensioning (see photo below left).

Electric motorcycles use a solid state, pulse width modulation (PWM) circuit to efficiently handle varying power to the drive wheel. This PWM circuit is in a rugged encapsulated PWM controller package matched to the DC electric motor. An overall circuit diagram is shown below right.

The weight on El Ninja is carried as low as possible in the frame between the wheels. The batteries are positioned to provide roughly a 50/50 weight distribution between the front and rear wheels.

El Ninja carries a large amount of battery energy for its weight. About 50% of a 72-volt version is battery weight. This battery weight, coupled with the low rolling resistance, gives El Ninja a range advantage over most electric two-wheelers. These large batteries also allow for higher amp charge rates, so they can be charged from a completely drained state to full in less than four hours with a standard 110-volt 30-amp charger.

Designing the Right Electric Motorcycle for You

Just like gas motorcycles, electric motorcycles can be designed for many different uses and user preferences. Some are faster, some are more comfortable, some work well around town, some are designed for a dirt country road, and some are designed for racing. Ergonomics help decide between sport bike, standard, and cruiser. Cost, speed, range and weight are key attributes that are always traded against each other. Use the El Ninja models shown below and Chapter 4 to guide your own design.

Top speed (MPH)
Approx. steady 30 MPH range (miles)
stop-and-go range
Approx. best acceleration 0 to 30 MPH (seconds)
Approx. maximum weight (lbs.)
Approx. cost to build (excluding the cost of donor gas MC)
Approx. cost to replace battery pack

After riding and testing with most possible configurations, we determined that four El Ninja models made the most sense:

1. El Ninja Novice Rider – (36 volts, 30 MPH , 22-mile range, big batteries)

This lightweight El Ninja suits a rider who is new to powered two-wheelers, but has good bicycle handling skills. This configuration could be licensed in many states as a moped and would require minimum licensing and insurance costs. Build costs could be minimized by using a smaller controller and fewer options (e.g., no ammeter). This model would be easy to upgrade to have a greater range and higher top speed just by adding batteries.

2. El Ninja Commuter – (60 volts, 51 MPH, 37-mile range, big batteries, on-board charger)

This El Ninja works well for the rider who has a 20-mile one-way commute and the ability to plug-in and recharge at the destination. This would recharge the batteries enough to power the return trip, plus some out-of-the-way shopping. This configuration could be upgraded to 72 volts and geared for whatever top speed required to blend with traffic. However, it is not recommended that the commute include many high-speed freeway miles due to decreased range considerations. Possible options would include a rear cargo case, tank bag, heated handgrips, and an O-ring chain.

3. El Ninja Pro – (72 volts, 60 MPH, 41-mile range, big batteries)

This El Ninja best suits the experienced motorcyclist who wants to enjoy environmentally friendly around-town motorcycling on a vehicle that is also less costly and requires less maintenance than a typical gas motorcycle. The experienced motorcyclist might also like to tweak the gearing by changing out the front sprocket and modifying the throttle ramp profiles of the ALLTRAX to further customize the machine.

4. El Ninja Track – (72 volts, 59 MPH, 8- mile range, small batteries)

This very lightweight El Ninja is a great "play bike" for go-kart tracks or drag racing. It would qualify for the 72-volt NEDRA MTI and MTH classes to run 1/8 mile drag competition. Options might include sticky tires, lightweight components, and exotic brake pads. El Ninja Track is stripped of excess weight, and quick-change battery packs are used to help extend practice times using multiple battery packs. A higher performance upgrade could be to install a second motor on the right swing arm and a second controller for drag racing, thus doubling the horsepower.

El Ninja Every Day

With a tank bag and a good backpack for light cargo, the riders took El Ninja for all kinds of around-town jaunts…to school, meetings, and shopping, then quickly locked up using the built-in fork lock and helmet lock (the ignition/lights key fits all). El Ninja was parked in designated motorcycle lots and perpendicular or parallel car slots— some that were too short for even a compact car. The side kickstand worked best for quick parking, but El Ninja’s center stand can also be handy for tire changing and some parking situations.

We were convinced that El Ninja was ideal for around-town trips and short trips into the country. With 41 miles of around-town range, in many cases we were able to take El Ninja out in the morning without needing to give much thought to how many possible stops and miles we could ride that day. Every night, we zeroed-out the odometer, plugged-in El Ninja, and had a full charge in the morning. After longer rides during the day, we charged El Ninja midday, even though the batteries were not drained (not allowing the batteries to deep cycle too often helps battery life).

Out on the streets and in parking lots, only motorcycle-savvy folks noticed that El Ninja ran silently and had a "strange thing" (the motor) on its swing arm. Others didn’t seem to notice there was anything different about El Ninja, so we removed its right-side battery panel just to see if people would notice that the engine cavity was filled with batteries. Some did notice, and when they realized that this unusual motorcycle passes-up gas stations, they inquired about how to get an El Ninja of their own, how far it would go on a charge, how long it took to recharge, and so forth.

Country of Manufacture United States

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