27-08-2014, 01:11 PM
FABRICATION OF SHAFT DRIVE BICYCLE
FABRICATION.doc (Size: 57 KB / Downloads: 55)
INTRODUCTION
Shaft-driven bikes have a large bevel gear where a conventional bike would have its chain ring. This meshes with another bevel gear mounted on the drive shaft. The use of bevel gears allows the axis of the drive torque from the pedals to be turned through 90 degrees. The drive shaft then has another bevel gear near the rear wheel hub which meshes with a bevel gear on the hub where the rear sprocket would be on a conventional bike, and canceling out the first drive torque change of axis.
The 90-degree change of the drive plane that is occurs at the bottom bracket and again at the rear hub requires the use of bevel gears. Bevel gears are the most efficient way of turning drives 90 degrees as compared to worm gears or crossed helical gears. The drive shaft is often mated to a hub gear which is an internal gear system housed inside the rear hub.
FABRICATION AND WORKING PRINCIPLE
The engine is fixed to the frame stand. There are two bevel gears are used in this project. One bevel gear is coupled to the engine shaft and another one bevel gear is used to transfer the energy from engine shaft to the differential unit. The differential unit is fixed to the frame stand by the suitable arrangement. The differential unit one end is connected to the wheel by the suitable arrangement.
A disadvantage of shaft drive on a motorcycle is that gearing is needed to turn the power 90° from the shaft to the rear wheel, losing some power in the process. On the other hand, it is easier to protect the shaft linkages and drive gears from dust, sand and mud.
ADVANTAGES
• Compactness: The drive shaft and bevel gears take up less volume than an enclosed chain.
• Ground clearance: The drive shaft system allows greater ground clearance.
• Consistency of performance: Shaft drives operate at a very consistent rate of efficiency and performance, without adjustments or maintenance.
• Gear shifting: Since shaft-drives require gear hubs for shifting at all, they gain the benefit that gears can be shifted while the bicycle is at a complete stop or moving in reverse.
• Enclosed drive system: Enclosing the drive shaft and gears provides several benefits:
• Safety: There is no danger of clothing or fingers being drawn into the enclosed gears.
• Cleanliness: Enclosed gears cannot get grease on hands or clothing.
• Longevity: Enclosed gears keep their performance stable for a long time.
• Reduced maintenance and repair: Enclosed gears are less susceptible to damage and require less adjustment or cleaning.
DISADVANTAGES
• Power loss: A shaft-driven system is less efficient than a chain-driven system. Shaft driven systems are often quoted as being "95% efficient", while chain driven systems are quoted as "98% efficient".
• Complexity: Though the shaft-driven system seems simple on the outside, the manufacture of the necessary bevel gears is complex compared to that of a chain and sprockets.
• Cost: Due to the manufacturing complexity of the frame and shaft drive, the manufacturing cost is typically higher.
• Gear range: Internal hub geared bikes typically have a more restricted gear range than comparable derailleur-equipped bikes, and have fewer ratios within that range (an issue because a rider typically prefers to pedal within a fairly narrow cadence band).
• Weight: A shaft-driven bicycle typically weighs about one pound (454 grams) more than an equivalent chain-driven bicycle.
• Changing a flat: shaft drives are typically more complex to disassemble when repairing punctures.