3 Things To know about quadrupeds
DNEG animation Director aaron Gilman DISSECTS the finer points of animating quadrupeds, Such as the bison for the film alpha
1. know your quads: When animating quadrupeds such as bison, it’s really important to understand all the nuances of how they move. There are numerous gaits such as walks, trots, canters, transverse and rotary gallops. Each of these has a unique footfall pattern that the animator needs to be fluent in, as well as understanding how these patterns transition from one to the other. For example, besides the rotary gallop, all quadruped gaits commit to the ‘rule of diagonals’, which means each fore foot contact must have a corresponding opposite hind foot contacting the ground in order for the animal to maintain balance. This same principle applies to other quadrupeds like cattle, dogs and cats, and reptiles such as lizards.
2. Leg locking: A lot of quadruped animation rigs suffer from ankle and elbow pops or strange interpolations frame to frame, because the animator often has to key the contact leg pose on every frame as the weight passes over it. On Alpha, DNEG made great use of a leg-locking attribute we built into our animation rig. Once the foot made contact with the ground, the animator was able to switch the leg into leg lock mode, which would preserve the angles of all the joints in the chain, effectively stopping the leg from changing shape regardless of how the torso moved around it. As the foot releases from the ground, the toggle gets keyed off, with a seamless blend into the default IK mode.
3. Moving herds: Nothing in nature runs in a perfectly cyclical or linear line or repeats itself exactly from one step to the next. But we needed to go one step further with this sequence, because we also needed to understand how flocking behaviour works in a herd. The bison needed to bump into each other in natural ways, where we constantly feel the negative space between each animal compressing and expanding. Because they are following a leader, the energy of direction change and responsiveness to one another needs to cascade down the length of the herd, so the movement of the mass feels like a kind of controlled chaos. To understand this we studied flocking behaviour in herds such as buffalo, horses, gazelles, zebra and schools of fish.