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Unread 02-04-2012, 13:28
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Re: Moment of inertia and turning performance

This is merely an explanation for why a LOW c.g. matters.

Consider a c.g. that's off-center to the right and is 18" off the ground (really high for FRC). When moving forward, that c.g. creates a moving inertia. During a sweeping left-hand turn while moving, that inertia becomes a centrifugal force that attempts to lift the left side of the robot. The higher the c.g., the more leverage the force has to lift the left side. This centrifugal force is easily noticable on robots that do high-speed 0-radius turns in place. It's like an off-balanced top.

This lifting causes a major traction loss, even if it only lifts a few tenths of an inch. Realize that with even a few degrees of lateral lift, a wheel that makes flat contact with the field (such as the KOP wheels) will lose nearly all of its traction. Rounder wheels, like the AM pneumatic wheels, will only lose some of their traction. This traction loss is why high c.g. robots cannot do sweeping turns like the more agile robots. A good picture of this concept is on page 41 of this slide deck: http://www.chiefdelphi.com/media/papers/2597
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