Cardan Shafts
Cardan shafts,Drive Shafts, driveshaft, driving shaft, or propeller shaft (prop shaft), are mechanical components for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement between them.
Cardan shafts are carriers of torque: they are subject to torsion and shear stress, equivalent to the difference between the input torque and the load. They must therefore be strong enough to bear the stress, whilst avoiding too much additional weight as that would in turn increase their inertia.To allow for variations in the alignment and distance between the driving and driven components, drive shafts frequently incorporate one or more universal joints, jaw couplings, or rag joints, and sometimes a splined joint or prismatic joint.
Cardan shafts in bicycles
The cardan shaft has served as an alternative to a chain-drive in bicycles for the past century, never becoming very popular. A shaft-driven bicycle has several advantages and disadvantages:
Advantages
- Drive system is less likely to become jammed, a common problem with chain-driven bicycles
- The rider cannot become dirtied from chain grease or injured by chain bite when clothing or a body part catches between an unguarded chain and a sprocket
- Lower maintenance than a chain system when the drive shaft is enclosed in a tube
- More consistent performance. Dynamic Bicycles claims that a drive shaft bicycle can deliver 94% efficiency, whereas a chain-driven bike can deliver anywhere from 75-97% efficiency based on condition
- Greater ground clearance: lacking a derailleur or other low-hanging machinery, the bicycle has nearly twice the ground clearance
Disadvantages
- A cardon shaft system weighs more than a chain system, usually 1-2 pounds heavier
- Many of the advantages claimed by drive shaft's proponents can be achieved on a chain-driven bicycle, such as covering the chain and gears
- Use of lightweight derailleur gears with a high number of ratios is impossible, although hub gears can be used
- Wheel removal can be complicated in some designs .