The Electric Motorcycle: A DIY Primer

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The finished electric motorcycle.
The finished electric motorcycle—road-ready for miles of fun.
1984 Honda VF500F Interceptor donor bike
This 1984 Honda VF500F Interceptor donor bike has its frame stripped and primed, ready for paint.
This 1984 Honda VF500F Interceptor donor bike.
This 1984 Honda VF500F Interceptor donor bike has its frame stripped and primed, ready for paint.
AC brushless motor.
AC brushless motor.
PMDC brushed motor.
PMDC brushed motor.
BLDC hub motor.
BLDC hub motor.
The controller, contactor, and fuse.
The controller, contactor (lower right), and fuse (upper right), with everything neatly laid out, will be hidden under the old fuel tank.
Charger and the controller.
Both the charger and the controller generate some heat, but airflow around the aluminum mount will keep things cool. Note the two chargers: one is a 72 V charger for the main pack. The second, smaller one is a 12 V charger for this bike’s separate 12 V system battery.
Battery mounts.
Battery mounts are another place where hefty design and redundancy are wise.
Motenergy ME0709 motor.
An example of a basic motor mount with a Motenergy ME0709 motor. The mount bolts to the frame at the top and bottom, and a bar counters the rear pull of the chain.
Testing component placement.
Using duct tape to test component placement.
Battery mount.
This mount has three sets of hold-down brackets, able to handle the 90 pounds of batteries.
Two 12 V SLA scooter batteries.
Two 12 V SLA scooter batteries, wired in parallel to give enough capacity for lights and a horn.
The Cycle Analyst display.
The Cycle Analyst display tracks vehicle speed and the propulsion batteries, including voltage, power consumption, and remaining capacity.
Klll switch.
The kill switch operates the main battery contactor to cut power in an emergency.
The throttle.
The throttle, which is electrically connected to the controller, is used to increase and decrease the power that goes to the motor.
The newly converted electric motorcycle.
The author’s son Tyler takes a spin on the newly converted electric motorcycle.
The finished electric motorcycle.
1984 Honda VF500F Interceptor donor bike
This 1984 Honda VF500F Interceptor donor bike.
AC brushless motor.
PMDC brushed motor.
BLDC hub motor.
The controller, contactor, and fuse.
Charger and the controller.
Battery mounts.
Motenergy ME0709 motor.
Testing component placement.
Battery mount.
Two 12 V SLA scooter batteries.
The Cycle Analyst display.
Klll switch.
The throttle.
The newly converted electric motorcycle.

There are a lot of projects that you can take up over a short period of time; start, complete, enjoy, and use. This project may, if you’re not careful, lead you down a path of obsession.

Motorcyclists are generally rabid enthusiasts, and some electric motorcycle builders are quite new to motorcycling, having come from the electric vehicle path. Electric vehicles are riding a wave of technology development. Combining the two can be electrifying.

Why Build an Electric Motorcycle?

Common reasons range from environmental to economic. Some people do it just to save gasoline.

The deeper implications of building an EV, especially one salvaged from the junkyard, can get interesting. Some people just like being backyard mechanics. Many builders like keeping about 500 pounds of scrap out of the junkyard by salvaging, and sometimes restoring, vehicles that others have passed off as not worthy of repair—it’s reduce, reuse, and recycle. And by solar charging, EV/PV enthusiasts can power their rides with completely renewable energy—a 0% carbon footprint.

Many love the attention their unique vehicle gets, using them for RE evangelism wherever they go. They spark questions, conversation, and enthusiasm for the work and ingenuity to convert a gas bike to electric, even among hard-core motorcyclists.

Electric trail bikes have their fans because they open up areas to riding that, because of the noise of gas trail bikes, might not be tolerated. 

There is, however, one thing in particular that stands out about electric motorcycles: the power. Electric motors deliver power in a completely different way than their gas counterparts. Power (torque, in particular) is instantaneous, and the power increases the faster the motor spins. There’s no gear shifting, and going from 0 to 60 feels like holding onto the tail end of a rocket. Many people build an electric motorcycle simply because it’s an affordable way to experience the feeling of an ultra-high performance electric drive train. 

Planning the Build

Going into your project, have a clear and realistic idea of what you want to accomplish. Assess your skill level, and determine the type of donor bike, the desired performance, and how you want to use the completed bike.

Aiming for 100 mph top speeds with a range of more than 100 miles is a recipe for disappointment. Start with a more conservative target: Most bikes can hit a top speed of about 75 mph, with a range of 30 to 40 miles.

Don’t grab the first donor bike you see if it doesn’t suit your plan. Too often people try to make a heavyweight cruiser out of a medium-weight sport bike; a lightweight café from a monster frame; or even a street bike out of a trail bike chassis. Start with the style and weight that you want to end up with.

Check the condition of the chassis you are considering. You need a safe, reliable ride, so consider the brakes, tires, bearings, and suspension, just as if you were buying a gasoline-fueled bike. To register it, it’s got to have a clean title. 

The Motor

The permanent magnet DC (PMDC) motor has a good price, fairly simple control systems, and reasonable weight and efficiency. Brushless DC (BLDC) or AC motors don’t need maintenance, operate at a high rpm, and the controller electronics allow more precise motor control. They are heavier and more expensive, but have more power capacity.

Most motors are mounted where the gas engine used to be, but designing and building a motor mount that’s in the right spot and can handle the stresses of the higher torque requires fabrication skills and careful planning. Another option, the hub motor, is integrated into the rear wheel of the bike, eliminating the motor mount, chain, sprockets, and space in the frame demanded by conventional motors.

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Comments (2)

jerryd's picture

The one thing missed and the biggest factor in EV MC range is aerodynamics. A standard MC has the aero of a brick!! And that at over 25mph just sucks power.

But fairly simple aero mods can double range. Also lowering the seat as much as you can helps lower frontal area.

Even a box behind the rider with curved front corners wider than the rider and gently curving back inward before being chopped off cleanly plus going down to the axle level can seriously cut drag and give lockable space for shopping, etc, by cleaning up the airflow, thus cutting drag.

I'm building a complete aero cabin on my MC to make it a long distance cruiser at 70 mph. Just got the chassis running on it's own power as should be finished by mid Feb with the aero cabin.

Ben Root's picture

Awesome points you make about aerodynamics. Once, back in my bicycle racing days I heard that, at 30 miles per hour, a cyclist is using 90% of their energy just pushing the wind, and only 10% moving themselves and the bike. (or, if there was a 30 mph headwind, they'd be using 90% of their energy just to stay upright). I'm guessing that an MC will have a similar aerodynamic profile...if not worse.

Another thing to remember is that (like the wind turbine guys say), the power in the wind is a cube of its velocity. I assume that it's the same ratio working the other direction...pushing through the wind. So as your speed goes up, the energy that it takes to push through the air is going up at a cube of that. IE going from 20 mph to 30 mph is a 150% increase in speed, but a 337% increase in required power (1.5 x 1.5 x 1.5 = 3.375). So, reducing speed is the best way to reduce required energy. Albeit, who want to slow down on a motorcycle.

We'd love to see you completed aero-bike.
Ben

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