Well, I recently had to animate a baby dragon flapping its wings. It involved wiring the rotation of a dummy to the same rotation of two other dummies that are controlling each wing. Then setting one of the wire pararemeters to a negative value. When you rotate the master dummy the other two rotate but one rotates the opposite way giving you flapping wings. Its a bit tricky if you're new to max but if you want a step by step I can write one. let me know. Or I could send you a max file to look at.

Alternatively you could make you're butterfly and then make morph targets of the flapping motion, then you could use it as an animated particle for a whole bunch of butterflys.

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