Professional cyclists measure and improve their physical fitness by monitoring their performance with handlebar-mount bike computers called power meters. Power meters were first introduced about 20 years ago and evolved from the first crude bicycle speedometers.

The idea behind a power meter is simple: use a strain gauge (or equivalent) to directly measure the amount of force the cyclist puts on the pedal.  Once the applied force is known, it is easy to figure out the power number, expressed as watts.

While the underlying principle of direct force power measurement is simple, placing strain gauges in a bicycle’s drive train is anything but simple.

Most direct force power meters are heavy and inflexible electromechanical devices that, in addition to their cycling compromises, range in price from $1,000-$5,000.

At the beginning only a few cyclists used direct force power meters for training. However, the pros and their coaches quickly found out power meters gave instantaneous, accurate feedback on cycling performance and that “power training” was the most efficient way to get the best workout possible on your bike. Very quickly, power became the way to train and the way to win races.

Until 2006 the only real difference between power meter products was the physical location of the strain gauge. One company put strain gauges in the crank, another in the rear wheel hub, and another in the bike’s bottom bracket.

Basic physics principles helped engineer Glen Cunningham develop a new way to measure a cyclist’s performance, resulting in a new, less expensive device.

While riding on a long cycling tour from his Boston home to Florida, engineer Glen Cunningham thought about the problems with traditional power meters and went back to basics, recalling some of the things he learned in high school physics. Maybe the whole bicycling industry was going about this the wrong way. All these clunky direct-force power meters were focused on measuring applied forces to the pedals. Why not measure the opposing forces, which according to Newton’s Third Law, had to be equal. Indeed, measuring and totaling the opposing forces caused by wind, acceleration, friction, hill climbs should equal the force applied on the pedal.

Furthermore, measuring opposing forces would require only two inexpensive solid state sensors, an accelerometer and a differential pressure sensor, meaning that the entire power meter could be placed on a very low cost electronic circuit board, without any strain gauges and without any alteration or compromise of the bike’s drive train components. 

Measuring opposing forces meant no special hubs, wheels, cranks, or chain magnets. It also meant no machine shops were needed to manufacture low-volume, waterproofed strain gauge assemblies. Their new power meter would be small, light, portable from bike-to-bike, easy to install and operate, and most importantly, affordable for even casual bicyclists.

Cunningham discussed this idea with John Hamann, now CEO of Velocomp LLP, and fellow biking enthusiast. Could it really be this simple? Could it be that in the highly competitive global cycling industry that no one had yet figured out such an obvious approach?

After researching the idea, Hamann and Cunningham started Velocomp. Product development began in February 2005 with both men working on the design, software, circuitry, and firmware. By May 2005, Velocomp was ready to engage an industrial design firm to design the plastics for their new iBike Pro Power Meter.

By September 2005 Velocomp had a working prototype ready. The iBike was the world’s first power meter based on the measurement of opposing forces: hill slope, wind speed, bike acceleration, even road and tire friction.  Because of the innovative concept of opposing force measurement, the entire “guts” of the unit was in the computer head.  It could achieve accuracy similar to products costing thousands more. Dealers and cyclists loved it.

While Hamann and Cunningham wanted to get the iBike Pro into production for the 2005 holiday season, prototype testing revealed design issues that needed to be fixed prior to production release. Also, going from prototype to production proved to be a bigger-than-planned-for challenge.

Newton’s Third Law of motion provided the idea that eliminated strain gauges in Velocomp’s power meter.

“While wrestling with the problem of getting production plastics, our Boston stereolithography (SLA) vendor suggested we try a company in Minnesota called Protomold.  Eventually we sent them our SolidWorks files and they helped us learn what you could and couldn’t do with plastics. They gave us some pretty well established design rules that helped eliminate our design problems,” states Hamann.

In a matter of weeks Protomold sent Velocomp their first prototype part samples. Though these were supposed to be prototype parts they were, in fact, production quality with a fabulous finish.

Later on Protomold also helped Velocomp through the tough issue of waterproofing.  The prototype iBike was held together by screws, but this was thought to be a risky design for production. Protomold and Velocomp worked together to solve the water-sealing problem—eliminate the screws and seal the parts together using ultrasonic welding.

During design, the engineers needed to find a better way to seal the device than through the use of screws. Protomold and Velocomp discovered the best choice was to seal the parts together using ultrasonic welding.

Protomold’s fast turnaround time allowed Velocomp to extend the length of its design effort, making it possible to make production part changes even a few weeks prior to production. There was no need to “freeze” the design months ahead of the scheduled ship date.  Because Velocomp did not make a large investment in hard tooling, cash flow was improved and there was no need to amortize expensive tooling costs over thousands of parts. Velocomp wasn’t stuck with large inventories of parts to inventory and store…. or worse, to recycle if there was a mistake.  Most importantly, these time and money advantages let Velocomp focus on innovation: with short turnaround times and low tooling costs the company knew it could quickly turn ideas into products.

Between late 2005 and June of 2006 the iBike underwent a series of critical and necessary design changes, some of which were tweaks and some of which were the result of nasty surprises.  Says Hamann, “There’s a huge bridge to cross to go from prototype to production. Some of the problems we discovered were unexpected and nearly finished us off, but we managed to stay focused.  We would talk together about the problems, then Glen would do firmware changes, I would do the testing, and we both would discuss the results.”  Eventually Velocomp overcame the key technical problems and Cunningham finished the engineering while Hamann geared-up manufacturing, marketing, and selling efforts.

By June 2006 the first iBikes were shipped to thrilled bicyclists. Today, after two years, the iBike has found its place in the bike industry and Velocomp is now working on innovative new “Generation III” models.

Protomold
www.protomold.com

MPF

Source: :: Make Parts Fast ::