Axle Drive System

Design

Jettison 1's axle drive utilises a chain and sprocket system. A 60 tooth rear sprocket was manufactured to provide optimum acceleration. This gave a final drive ratio of 4.00:1 using a 15 tooth front sprocket.

Problems in the design of this system were discovered after the engine was fitted to the chassis. A chassis rail behind the engine had the potential to rub against the chain. This can be seen in Figure 6.10.

Figure 6.10: Axle drive system

To address this issue the centre axle was moved forward slightly. This increased the angle of the chain and gave greater clearance between chassis and chain.

The chain and sprocket system also required the use of a chain tensioner. Most chain systems achieve this by moving the rear axle, however this could not be done as the brake rotor also mounted to the axle required that the axle be fixed to maintain the relationship between rotor and caliper. I designed the chain tensioner system.

The tensioner was designed with a large range of adjustment to provide for chain stretch throughout service. The tensioner was mounted on the bottom side of the chain. This side is only under tension while decelerating in gear. In this situation the rear axle drives the engine. The forces involved in this situation are much lower than the forces during acceleration in the top side of the chain.

Some consideration was given to a spring loaded tensioner, however due to time constraints and the lack of data on the forces present in the chain it was decided to use a rigid system. The manufactured tensioner is shown in Figure 6.11

Figure 6.11: Chain tensioner system

The long arm acts as a pivot and locator for the tensioner sprocket. The arm is long to minimise the arc through which the tensioner moves. This was required to give adequate adjustment. The chain is adjusted by tightening the studs which are connected to the chassis. The top of these studs can be seen in Figure 6.10. The studs were angled so that the load on the tensioner is transferred axially through them.

Material Source

The chain was purchased by USQ Motorsport. Armstrong Automotive donated the bearings for the chain tensioner. All other material was supplied by the workshop.

Manufacture

All components were manufactured using the workshop facilities. The rear sprocket was machined using CNC milling equipment.

Cost

Chain $ 185.00

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