The Link behavior in Motion is a powerful way of animating one one object with another.
This week on MacBreak Studio, I show Steve Martin from Ripple Training one way to use the Link behavior to create a wheel and piston animation similar to a steam locomotive.
In order to demonstrate the flexibility of shapes in Motion, I build the project from scratch, but you could create the same animation by importing photographs or graphics created in an image editing application like Photoshop. Motion makes it very easy to draw lines, circles, rectangles, bezier, b-spline and free-form shapes with intuitive tools very similar to the Pen tool in Photoshop. And by combining shapes with replicators, you can quickly create patterns, like the spokes in a wheel in this example.
The Link behavior lets you connect a parameter of one object, group, filter, or behavior to the parameter of another. For example, the vertical scale of a tree image could be linked to the z-rotation of an arrow on a gauge. Not all parameters can be connected – there needs to be the same number of dimensions for each – but the possibilities are exceedingly far-ranging.
In this simple example, I animate a group containing shapes that form a wheel with a Rate parameter behavior, and then I connect that rotation to the rotation of the “piston” to stop the piston from rotating with the Link behavior. A key feature of the Link behavior is the ability to adjust the Scale value: how strongly one parameter influences another. The trick in this case is to completely remove the influence by using a Scale value of -1. The other trick is to change the anchor point of the piston shape in order to connect it to the wheel.
One thing I really like about using this behavior instead of keyframes is the flexibility you have to adjust the animation. For example, you can decide to connect the piston to the wheel at a different point simply by moving it, and the animation will still work. Check out the video for all the details.
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