"The original Heavy Bounce was fine for shorter loops."
PMVs (Porn Music Videos) are a brutal testing ground for physics. Unlike a narrative film where you can hide bad physics with a cut, a PMV relies on looping, rhythmic, high-contrast motion synced to a beat. The viewer is often watching the exact same bounce happen 128 times over a three-minute song.
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Traditional soft-body physics in programs like Blender, MMD (MikuMikuDance), and early SFM relied on what engineers call "linear restitution." In layman's terms: things bounced back too fast. A hip or chest would collide with a surface, and the "bounce" looked like a rubber ball hitting concrete—snappy, fast, and without mass.
Legacy physics engines fail in PMVs for one reason: predictability . Because the motion is cyclic (synced to a kick drum or bass hit), standard physics engines create a "metronome effect"—the bounce looks robotic.