GEN 2 will there be a carbon-fiber driveshaft available?

StrikerHawk said:

Structures isn't my specialty, but I beg to differ...

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Actually, mechanical structures IS my speciality, so I wanted to add a couple other comments.

Almost all metals have the same Specific Stiffness (Young's Modulus divided by density) and specific strength (yield stress divided by density). This means that as any given metal gets denser, it gets stiffer and stronger (which makes sense IMHO). There are a couple exceptions (pure moly for example), but all structural metals pretty much follow this rule.

For a driveshaft, this means is that you CAN make a driveshaft out of aluminum, titanium, etc. however it will perform exactly the same if it's designed correctly (and as you said, and aluminum driveshaft would have to be larger in diameter to work correctly since it's weaker and less stiff.)

Carbon fiber, however, has a much higher specific stiffness and specific strength than any homogenous metal, so you CAN make a carbon tube that is MUCH lighter and stiffer than any metallic structure.

However, since a driveshaft is very small in diameter, any change in weight will have a relatively small effect on its rotational inertia. Something like a wheel/tire combo has a much larger diameter, therefore reducing its weight (times 4!) will have a much larger effect on total driveline inertia. If I were considering where to spend money to reduce driveline inertia (to improve acceleration), I'd choose REALLY good wheels first. Also, if you were gung-ho to improve acceleration, a slight change in axle ratio would have a a MUCH larger effect than any of these!






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2011SuperCrew said:

Actually, mechanical structures IS my speciality, so I wanted to add a couple other comments.

Almost all metals have the same Specific Stiffness (Young's Modulus divided by density) and specific strength (yield stress divided by density). This means that as any given metal gets denser, it gets stiffer and stronger (which makes sense IMHO). There are a couple exceptions (pure moly for example), but all structural metals pretty much follow this rule.

For a driveshaft, this means is that you CAN make a driveshaft out of aluminum, titanium, etc. however it will perform exactly the same if it's designed correctly (and as you said, and aluminum driveshaft would have to be larger in diameter to work correctly since it's weaker and less stiff.)

Carbon fiber, however, has a much higher specific stiffness and specific strength than any homogenous metal, so you CAN make a carbon tube that is MUCH lighter and stiffer than any metallic structure.

However, since a driveshaft is very small in diameter, any change in weight will have a relatively small effect on its rotational inertia. Something like a wheel/tire combo has a much larger diameter, therefore reducing its weight (times 4!) will have a much larger effect on total driveline inertia. If I were considering where to spend money to reduce driveline inertia (to improve acceleration), I'd choose REALLY good wheels first. Also, if you were gung-ho to improve acceleration, a slight change in axle ratio would have a a MUCH larger effect than any of these!






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Well said 2011SuperCrew. Spoke like a true Mechanical Engineer or, perhaps, Civil Engineer.