Motorcycle.com

A veterinary superhero by day and engineering extraordinaire by night, when Dr. Alan Cross isn’t performing orthopedic surgery helping animals, he’s in his garage at home in Atlanta designing and engineering his next creation. Pictured here is what he calls the ExoDyne. This is what you get when you cross a motivated doctor with an engineering degree and a passion for motorsports! And that’s not to mention the metalworking and fabrication skills he’s learned on his own.

The ExoDyne is just one example of Dr. Cross’ long list of accomplishments. He has a passion for restoring vehicles and even built a race-spec Mazda RX-8 that he competes in on weekends. It took nine months of research, design and fabrication to complete the ExoDyne. Cross did all the work himself with the exception of the seat upholstery and powder coating.

Where electricity meets simplicity.

The ExoDyne features an exceptionally minimalist yet functional design with equally impressive style. At the heart of the bike lies a boxed frame that contains 8 lithium-ion polymer (LiPo) battery cells arranged in a 100V 32-Ah configuration and is capable of producing an output of 600 amps. Lithium-ion polymer batteries use a polymer electrolyte instead of a liquid one, which provides a higher specific energy as well as decreased weight compared to other lithium battery types. Complete with the use of carbon fiber, the entire battery box weighs an impressively light 48 pounds. All of this translates to a lighter, faster motorcycle.

Not the typical AAA batteries found in your TV remote.

Paired with the battery, the ExoDyne is driven by an 11 kW (30 kW peak) rear hub motor from EnerTrac and a Sevcon Gen 4 motor controller. This setup stays true to the sleek, minimalist design of the bike by eliminating any sort of a drivetrain, however it does pose a couple challenges. An in-hub motor significantly increases unsprung mass that in turn compromises overall suspension response and handling. Also, due to its natural lack of leverage, it needs incredibly high amperage to operate. However, Dr. Cross says has all these bases covered. He explains that the 600-amp lithium-ion polymer battery produces more than enough power and that output is actually reduced to 200 amps and provides exceedingly good torque.

Now I’m not well versed in the language of electronics; it might as well be magic to me, but my inner throttle-jockey degenerate is curious about what kind of power the full 600 amps produces. I imagine the battery would be drained pretty quick, but not before delivering one hell of a kick!

The in-hub motor may look like a drum brake but in fact does the exact opposite.

When I asked him what his inspiration was to build such a thing he replied, “Inspiration? Nothing significant. I find I always need to have a project of some sort. I’m happiest when I’m creating something.”

His initial plan was to build an electric, adult-sized Green Machine he enjoyed in his youth, but as the planning phase progressed, he realized that for what he was spending it would make more sense to build something street legal.

“I had a general idea in my head of what I was building and it evolved from there,” he explained. “People ask me for the CAD files; there were none.”

The front suspension is from a 2005 Suzuki RM-Z250, and the neck and rear swingarm are from a 1995 Suzuki RM125, eBay and Craigslist finds, respectively. But the rest of the frame is designed and handbuilt by Dr. Cross and has a Ducati-esque inspired skeletal structure to it. An Öhlins rear shock handles the extra unsprung weight of the in-hub motor. The wheels are from Warp 9 and feature a Brembo brake setup in front and a Suzuki setup out back that bring the 248-pound bike to a halt. Dr. Cross explains that weight savings were paramount to the build and that titanium hardware from ProBolt, as well as carbon fiber, was used wherever possible.

Despite having street tires, the RM-Z250 suspension can handle any type of terrain you throw at it.

An Öhlins rear shock – just one example of the many high-quality components found on the ExoDyne.

The fit and finish of the ExoDyne is remarkable considering one man handbuilt everything in his free time. Other cool features that complete the bike include an LED light bar headlight, custom rear-set footpegs and a small Cycle Analyst display that reads speed, amps, total discharge and other essential information. As far as performance goes, the ExoDyne purportedly has a top speed of 60 mph and a total range of about 20 miles in its current configuration – not bad numbers for a do-it-yourself, garage-built bike if you ask me.

A very minimalist, uncluttered cockpit.

Currently, the ExoDyne is for sale in order to fund Dr. Cross’ next project. He tells us that he also just finished building a new race car and is currently restoring a vintage shotgun. Future plans include possibly restoring an old International Scout for a friend. Other than that, though, who knows, but whatever Dr. Cross decides to build next will be pretty awesome, that’s for sure.

Carbon fiber makes everything look better.

An insight into what Dr. Cross has been up to lately:

A Mazda RX-8 race car that Dr. Cross recently completed building.

An MP3 player built from an old voltmeter he’s proud of.