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SP&S #273
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Rebuilding the Lead Truck
Saturday, September 5, 2009 by John NiemannHere is a close-up of #21's blueprint showing the front truck as originally planned. The two 9" long heart shaped arms hanging down are the "rockers". You can see that they are each hung on the top by a pair of pins. As the front truck enters a curve, the axle and frame move laterally causing the rockers to rotate about their lower pins. When this happens, all the weight is instantaneously transfered to a single top pin, shifting the center of gravity 3" off the centerline of the truck. This "off-center imbalance" imparts a desire in the truck to return to center and straighten out.
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