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Steering on Motion Paths Issue:
Animating wheels to "steer into" and then "straighten out of" changes of
direction on a motion path.
Solution:
Attach a locator to the same motion path as the object whose rotation you want to control, make sure that Banking is turned on for the Locator. Use set driven key to associate the rotation of the locator, as it banks in and out of curves, with the Y rotation of the object in question. Detailed Explanation: Make sure your object has a hierarchy of at least two nodes. If you have built a car whose wheels need to "steer" into and out of curves, then make sure that each wheel has a hierarchy of at least 2 nodes, and that that hierachy is then parented within the hierarchy of the car itself. The lower node of the wheel will be animated seperately to create the wheel's overall rotation due to translation, while the upper node will be used to drive the "steering" action of the wheel. Attach your object to a motion path using whatever options are appropriate. Create a primitive Locator and attach it to the same motion path using exactly the same parameters as before with one exception, make sure that Banking is turned on. You can leave the Banking options at the default. If you run the animation you will see your object run along the motion path along with the locator. Note that the locator banks as it moves in and out of changes of direction in the motion path. It is this banking that we will use to drive the steering (Y rotation) of the wheel. Rewind the animation. We'll now use Set Driven Key to associate the banking of the locator with the steering of the wheel. Open Keys -> Set Driven -> Options window to open the Set Driven Key window. Select the locator and note the axis it rotates around when it banks. In the Set Driven Key window click the Load Driver button. Once the locator is loaded as the driving object, select theaxis the locator banks on in the right hand column. Deselect the locator. Select the upper node of the wheel and click the Load Driven button in the Set Driven Key window. Select the appropriate axis in the right hand column. Now click on the Key button. This associates the rotation of the two objects. When the locator is rotated to zero degrees on the given axis then the wheel will rotate to zero degrees on it's given axis. Select the locator and rotate it on the given axis to the maiximum rotation it achieves while banking in one direction. Deselect the locator. Select the upper node of the wheel again and rotate it to the maximum amount you want the wheel to steer. Click on the Key button. Now the wheel will steer whenever the locator banks in the first direction. We will now set the wheel to steer in the opposite direction as the locator banks in the other direction. Deselect the wheel. Select the loctor again and rotate it to the maximum bank in the other direction. Deselect the locator and select the upper node of the wheel. Rotate the wheel to the maximum amount in the other direction. Click on the key button. Rewind then play the animation. The wheel should now steer into and out of the changes of direction in your
motin path. | | | | | | | | = | 
