Autodesk 62205-051408-9001 User Guide - Page 320

12 Creating Animations the result is the average speed. In the diagram, the average speed is 1000 / 400 = 2.5 units per frame. Distance Constant Speed 1000 0 0 Time 400 (frames) For an animation, Combustion needs the speed at each frame to calculate how far along the motion path the object should be. At frame 300, the speed equals 750 / 300 = 2.5 units per frame. So the speed equals the slope of this distance-time curve. Distance Slope = speed 1000 750 0 0 300 400 Time (frames) When you change the curve, the object accelerates and decelerates because the speed (slope) is different at different frames. In the next diagram, the speed at frame 300 is changed to 1.3 units per frame, which is slower than it was before. Distance 1000 Slope = speed = 390 / 300 = 1.3 390 0 0 300 400 Time (frames) Notice that the speed (slope) is different at each frame, but the average speed has not changed (it is still 2.5 units per frame). Thus, the slope of the curve is important, and the average speed is not. Distance as a Percentage The actual distance along the path (for example, 390 units) is not as meaningful as the percentage completion (for example, 390 units of a total of 1000 means 39% completion). In Combustion, this percentage is plotted against Time to simply the Timeline graph. This is shown in the next diagram. Speed Graph in the Timeline Distance Percentage 100% 39% 0% 0 300 400 Time (frames) Thus, you set the percent completion along the motion path with the Speed channel (and the tangent handles on the Speed channel keyframes), and the resulting curve defines the speed itself. The values for the Speed channel are always between 0 and 100%. Although the Speed channel defines the 304