One of the things that keeps some people from cycling more often is the gears – although they need the gears to manage hills and headwinds, they're never sure which one they should be in. If that sounds like you, then you might like the Autobike. It shifts gears automatically based on the rider's cadence, and manages to do so without a battery.
Instead of a battery, the Autobike has an SRAM Dynamo front hub. This uses the spinning motion of the front wheel to generate electricity, which in turn powers the bike's electronics and gear-changing servo motor. The electronics measure the rider's cadence via a number of sensors, and activate the motor to automatically shift the bike to a higher or lower gear in order to maintain that rhythm.
Also included in the electronics package is an accelerometer, that can detect when the bike starts going up an incline. When that happens, a lower gear is preemptively selected.
Because the Autobike has a continuously-variable Nuvinci N360 rear hub transmission, the rider won't notice any kind of transition between gears – in fact, technically-speaking, they'd be better described simply as drive ratios.
Not everyone wants to pedal at the same rate, however, so users can chose between three pedaling speed ranges. This can be done using either a set of buttons mounted on the down tube, or wirelessly via a smartphone app.
The Autobike is currently available in two commuter-style models, the Voyage and Voyage ST, which sell for US$1,000. A hybrid model, the Evolution, is due to be out soon.
There's more information in the video below.
Source: Autobike
UPDATE (Sept. 22/13): One of the Autobike's creators has informed us that the three pedaling speed buttons are actually used to adjust the cadence in 5 rpm increments (up or down) per push, allowing the rider to maintain a cadence anywhere from 30 to over 100 rpm.
Would also be good if the rider was able to infinitely select whichever pedalling speed (cadence) they prefer for a given situation rather than only having 3 to choose from (the 3 ranges may be user customisable, but the article didn't go that far, if not, why not) because that is effectively limiting the system to discrete gear ratios again.
While Ben demo'd the bike, we made adjustments using the app so we didn't get into the details of the bike-mounted buttons.
Just wanted to point that out since I probably neglected to mention it but it's an important point as the commenters noted. :)
The reason we added the ability to pair the app with a smart phone is because we already do all the computing in the background and all that was needed was the bluetooth system on chip and a little C coding. While not required to use/enjoy the bike, the benefits are possibly avoiding the purchase of a cycle computer, being able to tune/tweak the bike post-purchase, sharing riding experiences with friends, diagnostic/troubleshooting help, and remote firmware/feature updates. We also use it extensively during development as well as in the final testing phase of the bike building process. Plus it's flat-out cool! :)
With all the settings, it just seems like another way to shift gears in terms of the user wondering what cadence is right all the time.