The Alpha Bike, An Electronically Controlled Fixed/Free Concept Bike

Most people probably wouldn’t know what to think if they saw the ALPHA bike rolling down the street. While many probably wouldn’t think anything of it, others may be initially curious of the rather bulbous lugs – until they noticed there is no chain.

The ALPHA bike is a fully functional concept bike that was created by 5 seniors studying Mechanical Engineering at the University of Pennsylvania.  Yes, this project was created by students. You may be thinking “so what?” and from its outward appearance you would be forgiven for thinking that it’s nothing that special.

On the inside however, that’s a different story. Not only are the ALPHA bike’s mechanics almost completely internal, it is also able to convert from fixed gear to freewheel mode with the push of a button.

How does it all work? Find out after the break!

When you see the X-Ray, so to speak, you start to realize the complexity of the project, which is just a little more than your average bicycle. Ok, a lot more. The ALPHA bike originally started as a design challenge to push the boundaries of integrated systems design, a goal that seems to have been met in spades.

Basically, the front hub of the bike houses a standard dynamo hub with a drum brake. As the bike travels, energy created from the front hub illuminates integrated rear LEDs and simultaneously charges two super capacitors used to power the system which is made up of multiple sensors, an M1 microcontroller, and an inertial-measurement device.

The juice also serves to power the  LCD display above, that is molded into the one piece custom handlebar/stem. The on board computer even goes as far as saving information necessary to analyzing the bikes performance to an SD card that is easily removable from he bottom of the handlebar.

Like many of the parts for this project, the one piece handlebar was custom fabricated by the team by wrapping pre-preg carbon fiber around an ABS core that was created with a 3D printer. More than just a form for the carbon, the hollow ABS core was utilized to provide a smooth internal bore in order to route the wiring. As you can see, the ALPHA features one brake lever which controls the front brake since freewheeling mode won’t allow you to slow down like fixed gear mode would. Also notice the barend shifter on the right side. Did I mention that the bike was a 3 speed? Well, it is, and apparently all 3 gears are available in both fixed and free modes, how cool is that?

How do you make a bike with 3 speeds that is capable of both fixed and freewheel operation? To start, you utilize one of the few off the shelf components for the ALPHA, a Sturmey Archer 3 speed internal gear fixed hub which is operated via the standard bar end shifter. Obviously, if you used a hub that had the ability to coast, there would be no way to convert it to fixed gear. But… if you use a fixed hub, and create a way for the crankset to freewheel (yes it’s been done. See old Shimano FFS Schwinn cranks, etc).

More than just allowing the crankset to freewheel, the ALPHA bike took it one step further and added an electronically actuated clutch that allows the bike to switch from fixed to free in seconds, all with a push of the button from the handlebar. The SWIFT drivetrain, or Switchable Integrated Free-Fixed Transmission is completely housed inside the bottom bracket lug.

An exploded view of the SWIFT gives a better idea of what’s going on beneath the surface, but clearly, is still quite complex. To simplify it’s operation, basically the drive pulley (we’ll get to that in a second) is mounted on a traditional freehub body within the bottom bracket. Under normal conditions, this works just as if it were mounted on a hub, allowing pedaling force to be applied in one direction, and still allowing coasting when not pedaling. However, hit the button on the handlebar, and a titanium clutch plate then slips over the end of the freehub body effectively locking it to the drive shaft.

These pictures of the prototype SWIFT provide a better idea of how the clutch plate interfaces with the freehub body(the large cream colored disc on the right is the drive pulley). On the left, the clutch is disengaged from the freehub body allowing it to coast freely. On the right, the clutch has been engaged, being pulled onto the freehub body by the motor driven lead screw, resulting in a fixed drivetrain.

As I mentioned earlier, the SWIFT utilizes a drive pulley instead of a drive cog. Why? Simple, the use of a [what I can only assume is a] Gates Belt Drive, the drivetrain is able to be kept completely internal, and the flexible belt is able to run through a tensioner pulley before running silently, and cleanly through the chainstay to drive the rear hub. Obviously, when building an almost entirely internal drivetrain, ensuring that it will run nearly maintenance free for the long haul is a serious plus, which makes the belt much better suited for the task.

In order to create the ALPHA, the team had to use a wide array of cutting edge tech including high level CNC, and 3d printing. However, none of these are anywhere near as cool as the process used to create the above drive pulley UPenn manufactured for the SWIFT transmission. The drive pulley was created with a cutting edge process called direct metal laser sintering, in which powdered metal is fused together, layer by layer, when exposed to a high powered laser. DMLS allows for extremely intricate parts that would be nearly impossible to machine, to be created directly off a 3D CAD file in just hours, and with no part specific tooling! The finished product is nearly finish quality, with incredible dimensional accuracy.

ALPHA’s frame is constructed with carbon fiber tubes that are bonded to CNC’d aluminum lugs, that are also bolted together. The construction of each joint had to be carefully laid out in order to ensure proper routing of all the wires and cables. Note the use of Nokon housing, not a bad idea if you want to guarantee a maintenance free shifting system. I’d hate to be the mechanic that would have to replace the housing!

Check out more of the ALPHA Bike and it’s build process here. Thanks to Will for the tip!