a compendium of tech stuff

Dec 4, 2010

On 7:53 AM by Lalith Varun   2 comments

A hubless wheel is a wheel lacking a central hub, first designed by an Italian mechanical engineer, Franco Sbarra especially for motor vehicles. but it is also been seen in the application of many bicycle prototypes over the years. The Orbital wheel, a type of hubless wheel was designed in 1990 by Dominique Mottas. Hubless wheels lack a central hub and an axle which form the major part of conventional wheels. The concept behind this is to reduce the number of rotating parts in the wheel to a bare minimum. Many scientists argue that the efficiency of the wheel is compromised by using hubless and spoke less wheels but others see its advantages as it claims to make the bike lighter and striking in appearance, not many prototypes have actually become commercially viable.
It consists of 3 parts, 1) a bearing with a thin section and a large diameter, 2) rotating part consisting of a tyre, a centre free rim and a brake ring all integrated with each other to form a rotating outer ring of the bearing and 3) fixed part consisting of the non rotating inner ring of the bearing on which the vehicle’s steering system is connected. With this arrangement we get an empty wheel that is free from midwheel structural constraints.
Due to the lack of a central hub this wheel is more advantageous than the conventional wheel. Steering becomes all the more easier due to the elimination of effects of deformation of stub axles and forks of the motorbikes and it is that kinda design that allows for more rational steering systems to be attached in the future. An automobiles stability is dependent on its roll angle, the greater the angle, the more stable the vehicle. But the manoeuvrability will be reduced on turns and tight bends. The hubless wheel comes with a roll angle variator. The greater the speed, the higher the roll angle and hence maximum stability is maintained at all times and when the speed is reduced, the roll angle is reduced thus increasing manoeuvrability. For any vehicle, be it an automobile or a railway car braking is a major source of concern. Conventionally braking occurs at the centre of the wheel which requires a complex braking system. As the hubless wheel has no central hub, braking power is applied close to the ground by using large diameter brake rings or discs and also the braking system has excellent ventilation.
In a traditional wheel, the dynamic forces acting on the wheel at the road-tyre interface passes through the midwheel causing damage to the forks of the wheel. But with the advent of hubless wheels, these forces are transmitted directly to the suspensions. As vibration and jarring are reduced by 50%, the driver is much more comfortable and can drive longer. Goods can be carried in better conditions as they undergo less vibration. There is less strain on the straps used for fastening the goods so road safety is also increased. As each tyre is subjected to the same load, the wear is evenly spread and is greatly reduced and hence its useful life is increased. Thus newer and cheaper tyres with an equal performance level can be used.
Although hubless wheels are striking in appearance and advantageous compared to the conventional wheel, their numerous practical disadvantages have impeded their widespread use as an alternative to conventional wheels. They are difficult and expensive to manufacture and require a great deal of precision while machining. And the design also leaves the bearings and other mechanical parts exposed, the drive system is also very difficult to design and is problematic hence conventional wheels are preferred to hubless ones though they are more efficient.


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