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Electric Dirt Bike

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Several weeks ago I wrote a post asking about Fuel Cell Technology in dirt bikes. A TT'r who invented an electric motocross bike, on a Yamaha 400 frame, sent me his article (published in

Cycle News) and photos. Several of you have asked for the article - here it is.

I can't figure out how to copy the photo's here. If you want copies, send me your email and I will forward. Cool photos!



Scott Freeman’s Electric Dirt Bike


By Chris Jonnum

Photos by Phil Cruz/www.proride.com

There’s a lot of talk these days about alternative fuel sources, what with energy being in such short (or at least expensive) supply of late. When gas is creeping towards $3 per gallon, and utility bills are sinking entire states into the red, it’s only natural that words like “solar,” “windmill,” “electric” and “hybrid” start to come up more often in conversation. Motorcyclists aren’t generally the first to engage in such discussion, enamored as we are with such things as horsepower and race fuel, which could explain why there hasn’t been much in the way of visible development by manufacturers (or even the aftermarket) of serious dirt bikes that operate on alternative fuel sources.

One moto enthusiast who took matters into his own hands is Over the Hill Gang member Scott Freeman, an electrical engineer from El Segundo, California. Freeman has ridden dirt bikes for 30 years, still races Expert class motocross after 26 years, and he has always been mechanically inclined (he does his own motor and suspension modifications). More importantly, he has worked with three companies that build electric vehicles, including Hughes, where he worked on GM’s EV-1 program. That exposure planted a seed of curiosity in Freeman: Could he combine his life experiences and build the world’s first (as far as we know) real electric motocross bike?

“Just seeing the performance of other electric vehicles, I knew that there was some potential here,” Freeman says. “I always wanted to do it, so last year I started doing a bunch of research.”

Freeman visited a couple of EV gurus who had built electric motorcycles, one made a clean cruiser style street bike, the other an electric bike featuring an unorthodox chassis based on old YZ80 components. The aim was not only to see how well they worked and how fast they were, but also to make sure he wasn’t wasting his time and money. Upon determining that it could be done, Freeman located a suitable donor chassis (1998 Yamaha YZ400F) in mid-2000, then took approximately nine months to build the bike you see on these pages, with most of that time spent designing the various parts and modifications on his computer, and the remainder spent on fabrication work (though Freeman has experience in R&D, he enlisted friends’ assistance for machining, welding and sheet-metal work).


Understandably, Freeman is reluctant to divulge too many technical details on his electric dirt bike, and the full body panels he uses not only keep out water, mud, dirt and dust, but also prying eyes. About all he would reveal to us is that the bike consists of a DC motor, a motor controller and a battery pack (he removed the panels in front of us to work on the bike, but we politely averted our eyes – honest!).

Freeman knew the bike would be heavier than stock, and that there was no getting around this fact – at least with the current pool of battery technology. Still, the bike met his projected weight of 285 pounds (about 30 pounds heavier than the YZ was with a gasoline engine). The potential for high-performance electric dirt bikes should improve as lighter, more powerful batteries trickle down from the EV and auto industries, where manufacturers are currently focusing a large amount of R&D effort.

“A lot of [the hype] is more science fiction than science fact,” admits Freeman. “But in the future we may see fuel cells; or we may see some really advanced batteries.”

As it is, Freeman simply chose the best EV specific batteries that are currently available for a reasonable price. Of course that was only half the battle, as he also had to figure out where to place the batteries. He knew he wanted them low, so that the weight they added to the bike would be less noticeable, but it was also important that they not be placed too far forward, or the bike would handle strangely and have a front-low attitude in the air.

Since he was starting off with a conventional chassis design, Freeman was more limited than he would be if he were beginning with a clean sheet of paper, but he got the weight bias pretty much where he wanted it. The battery case protrudes forward from the “engine” area, and is probably the strangest-looking part of the bike, but it’s made sturdily enough from aluminum that it should be able to survive if the rider cases a double. Some observers have expressed concerns about the leading edge digging in upon landing, but it hasn’t hit yet because it is so far forward. In fact, the large flat surface area on the bottom would be less likely to dig into a jump landing than would the YZ400F’s original design. The battery box has elastomer mounts to absorb impacts, and has ground clearance equal to stock.

Freeman had to modify the frame pretty substantially to accept its new powerplant, but the suspension components and basic rider layout are all stock. Oddities include the presence of a key (it goes where the gas cap used to be) and the absence of a shifter, clutch lever or kill button (leaving the left side of the handlebar rather nude-looking).


Freeman first brought his electric bike by the Cycle News offices several months ago, and like most people who first see it, we were incredulous. But when he unloaded it, climbed aboard, twisted the throttle and shot across the parking lot at 45mph – silently! - our incredulity turned to amazement. The bike’s acceleration is astonishing, easily enough to spin the rear tire on asphalt, and the loudest noise is the chain slapping.

Freeman’s testing is fairly limited at this point, but he has enough time on the bike to get an idea for how it works. In his opinion, electric dirt bikes would perform differently than both two-strokes and four-strokes, which means people would have to adapt their riding styles to the characteristics of the bikes. We can vouch for that. On his visit to our office, Freeman let a couple of editors ride it. One, who shall remain nameless (okay, it was the author), had an embarrassing moment when the bike’s incredible torque – combined with the absence of a clutch and rider skill – resulted in an asphalt lowside – the bike’s first crash!

He has ridden it at several Southern California MX tracks, and was easily able to overtake slower riders. Freeman felt that he could turn quick laps on it, but not quite as fast as his usual YZF mount. Although it has met all performance expectations, the only disappointment is the run time. After a few laps, the battery pack begins to reach discharge levels, and power is diminished.

Remember that this is only a first-generation prototype, so the project has not been without its problems. So far, the only mechanical failure has been parts of the driveline, some of which have had trouble standing up to the incredible torque generated by an electric motor. Twice we accompanied Freeman to tracks for action shots, only to have the photo sessions canceled prematurely when the electric bike shattered drive sprockets under acceleration. Planned improvements include a stronger shaft and sprockets. While the driveline is reworked, the overall gearing will be lowered a bit. Freeman expects this to yield both harder acceleration and longer run times, a win/win situation.

Freeman has many ideas for the next-generation design, many of them having to do with component arrangement. “If I was to start from scratch, I’d probably arrange things a little bit differently,” he says. “I might do a different rear-suspension design, and that way I could move some weight to the rear.”

Specifically, Freeman mentions the possibility of the old-style Yamaha Monoshock design, where the swingarm was triangular and the shock was up high, in conjunction with a WP PDS shock like those on link-less KTMs. He also has ideas for different frame designs.


Freeman has achieved his initial goal of proving that it is possible to build an electric dirt bike, but that doesn’t mean doing so is a good idea. Why, you may ask, should you care whether or not the thing works, and why should a manufacturer seriously consider producing such motorcycles on a large scale?

Apart from the obvious benefits of no noise or gasoline, there are several other advantages to consider. Compared to an internal combustion engine-powered motorcycle, an electric bike would require almost no maintenance to speak of. In addition, there are very few limitations as to how the various components are arranged, which frees up the chassis design compared to a gas-powered bike and makes it easier for engineers to adjust weight placement and distribution. Freeman already has many ideas for the next-generation design.

On the track, electric motorcycles would have the advantage of no transmission, eliminating missed shifts and the moments lost when changing gears. Electric bikes are also impossible to stall, and beginning riders would be less intimidated by electric dirt bikes, not only because they’re silent, but also because there’s no clutch or shifting to learn – just twist and go.

Freeman also imagines a Utopian scenario in which people race electric dirt bikes on urban MX tracks, which we have to admit sounds better than having to load up and drive to the boonies every time you want to put in some saddle time. Of course the off-roaders among us hope that such bikes would help in the battle for trail access; loud bikes are probably responsible for creating more enemies of motorcycling than any other aspect of our sport, and although serious tree-huggers would no doubt remain steadfastly opposed to even silent dirt bikes, their arguments would lose some credibility. And when we rode those trails on our electric bikes, we’d be free to talk and laugh as we went, adding the social element of mountain biking without all that pesky work. But perhaps most alluring of all is the prospect of sneaking up behind the race leader as he relaxes late in the moto, secure that he has the win in the bag, then using an electric bike’s acceleration to zap him out of a turn before he even knows you’re there.


Say, Mister…?

When you show up at the local track with an odd-looking bike that has the word experimentalon the side in big letters, and that throws a mean roost without making a sound, you can expect to get asked a few questions. That’s what Scott Freeman, inventor of the electric dirt bike, has learned over the past few months. It has gotten to the point where Freeman - not being an especially verbose sort - has considered photocopying a list of the answers to the most commonly asked questions, to hand out before bystanders get very far into their interrogations. Figuring our readers will have many of the same questions, we’ve decided to reproduce excerpts from Freeman’s list here:

How fast is this thing?

It accelerates well enough to get around an MX track at normal speeds, and will throw some roost out of turns. The top speed is 45-50 mph – plenty for MX. On my second track ride, I had no trouble keeping up with slower riders, and I easily cleared the 50-foot finish-line tabletop at Perris Raceway on the first try. It was easy to get used to riding it, and I will push it harder and jump higher as I put more time on it.

Is the power more like a two-stroke or a four-stroke?

It has some traits of both. It is torquey and tractable like a four-stroke, but coasts into turns more like a two-stroke. The suspension and handling feel familiar and normal, and it is very easy to ride since it has no clutch and no gear shifting.

How long does it take to charge, and how long will it hold a charge?

At Perris Raceway, it took one hour for a full charge. So far, I’ve been able to go three strong laps before noticing any loss of power. It doesn’t stop like a bike that is out of gas, but gradually loses power, and acceleration is reduced.

What motivated you to build it?

I wanted to see if it could be done, and see how well it would turn out. It was a pioneering effort.

What kind of future do you envision for electric dirt bikes?

Several scenarios come to mind. It’s hard to say if electric motorcycles will be a part of our future, but it’s good to know that they have some potential. One of the best applications for this technology is for the rider who has some property or a large enough backyard to build a track, but neighbors who are too close to permit using an internal-combustion engine. Noise is the number one reason for land closures and restrictions, and this bike solves that problem.

Do you have any plans to market it?

Not right now, but if there is sufficient demand, I may build a limited production run some day. Right now I don’t have the financial backing or manufacturing resources to build them in quantity. A motorcycle manufacturer should be able to build electric bikes at a fairly normal price, because of their economy of scale. A custom-builder would have much higher production costs.

Scott Freeman asked for the opportunity to thank his riding buddies for their help with his electric motorcycle, including Skeeter at Sources Unlimited (assistance with sheet-metal cutting, bending and welding), Dick at Gem Machine (CNC and lathe work), Damon, John, Chris, Marty, Mark, and the two Bob’s (EV gurus). Freeman hasn’t yet settled on a name for his bike, and he welcomes suggestions from readers. E-mail him at terracross@earthlink.net, or call him at 310/784-5744.

[ March 24, 2002: Message edited by: mikem ]

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