SHELL Eco-Marathon
To build the most efficient vehicle in the world.
Like the current Guinness world record holder of most efficient vehicle in the world, the PAC-Car II: 5385km/L of gasoline, Ladoux, SEM Europe 2005.
Prototype vehicles are light, low drag, low rolling resistance, compact, efficiency-demanding. Beside custom building all the part for a vehicle, we could always salvage for commercially-available product, such as those from hi-end bicycle, as they provide the right thing that we need, just at some cost of our wallet thickness T_T. Well, it pays for any fast and proven workable things.
Sheldon Brown
Sheldon Brown's page contain a vast amount of data about bicycle part's technical terms, from daily-seen-MTB ( mountain bike ) in Malaysia to very-rarely-seen-tricycle (which is fairly common in European country ). Below are the page for some common hub for bicycle from several manufacturer. Basic yet informative webpage for any cyclist.
Sheldon Brown's Hub Page [Link]
Commonly seen hubs in Malaysia have fixed spokes hole number of 24, 28, 32 or 36 with the holes arranged radially in a plane on a flat or slightly tapered flange.
Hubs for 16" rim have only 20 holes, while some BMX bike's hub have up to 140 holes. Generally, more spokes = higher strength = more weight = less aerodynamic.
Expansive bicycles have little spokes with high strength made from titanium alloy, etc.
A perfect aerodynamic wheel would theoretically have zero spokes, an easier alternative would be adding a wheel cover on the spokes. This will reduce the drag produced by the spokes cutting through wind while rotating.
Figures: covered wheel
( & maybe a disc wheel if money is not a matter )
Figure: 20 holes hub
Figure: 28 holes hub
Figure: 140 holes hub
( Misc. New BMX bike's usually utilize sealed bearing hub or cartridge bearing hub for longer hub life )
Flanges
Flanges of hub hold the spokes that connect to rim. Spoke holes on the flanges often have some degree of countersink to provide easier mounting of the spokes.
Figure: typical hub flanges
Figure: Shimano XTR hub
Figure: Cannondale Lefty Hub
( Lefty's hub in specially designed for cantilever load, see [link] for more details on Cannondales Lefty Bike. ##around 80 pounds per hub!! )
Bearings
Some cheapo aluminium sheet hub have steel ball in between the wheel axle and the hub and acts as bearing which is very unsuitable for heavy normal load and cantilevered load scenarios. In the development of hi-end bicycle, bearings are essential in terms of reducing friction, increase drive train efficiency, increase coasting range and reduce energy wastage. There are several types of hub which incorporated with ball bearings which are getting common in local shop these days, as people are slowly coming back to less-emission lifestyle.
Bearing serves a vital role in increasing energy efficiency, imagine 50% of your paddling force goes to vibration, noise, heat, etc. We would never know our true potential then. The same goes to the vehicles, an environment-concerning engineer would never like to see the low efficiency in any terms. The bearings seem strong and rigid, but it is delicate in terms of the ball's micro structure, we would like to have a 100% working bearing to unleash the vehicles full potential, so proper handling ( do not drop the bearings, do not run bearings without proper lubrication, do not pull or knock the outer and inner ring in opposite direction, do not burn the bearing, etc. ) are very important. A prototype vehicle with good efficiency can easily coast for over 1.5km with engine turn on by only a few second.
Figure: Hubs with angular contact ball bearings.
Figure: Loading in angular contact ball bearings.
( Tapered roller bearings can carry a higher load than deep groove ball bearings but it is noisy and less efficient, while angular contact ball bearings combines the good of both: quiet, high load capacity, axial load capability and smooth )
Figure: Sealed bearing hub.
Figure: Cartridge bearing hub (yes, the bearings are exchangeable).
Figure: Loading in deep groove ball bearings.
( Recommending SKF's energy efficient bearings: at least 30% boost in energy efficiency; hybrid ceramic bearings: lubricant-free, silicon nitrite material which is only 40% density of steel, low inertia, high load capacity, long life, quiet, low thermal expansion, expansive ( 4~5x for hybrid: steel case with ceramic balls, 15x for full ceramic compared to a good quality steel deep groove ball bearing )..phew~
Figure: Standard Bearing Dimension
( some standard bearing size from SKF, ID: Internal Diameter, OD: Outer Diameter, H: Height )
Continue in Part 2..
*composed and produced by: Si Tzen ( sitzen_ng@yahoo.com.tw)
*All links are accessible on 26/7/2011
