I'm using particle flow and geometry to create particles at each vertex of the geometry. Particles render as instanced geometry. To start, there is no particle movement and no rotation so that all instanced geometry faces the same direction. I've key-framed a deflector that passes through the particles. Upon collision the particles are affected by wind. This is all working.
Once particles are affected by wind, I want them to transition from their no rotation initial state, to a random rotation to give the appearance that the wind is affecting their rotation. If I use the collision event to trigger a new rotation set to random, particles jump from no rotation to the randomized rotation at the moment of collision.
How can I slowly transition from no rotation to random rotation starting with the collision event, per particle, and ending 10-20 frames after the collision?