Actuators

A real control surface doesn't jump to where the stick says. A hydraulic actuator drives it at a rate it can't exceed, so a full-stick roll takes a moment to reach full throw, and the gear takes seconds. The rig does the same.

Two numbers per partCopy Anchor Link

Each part has a target and a value. The target is where it should be; the value is where it is.

• The target is worked out again only when something changes: the flight's version moved, a drive came or went, or something was set by hand. A still flight costs no from calls at all.
• The value moves toward the target every frame, at the part's rate, in its unit a second. Once there it stops, and a part at its target costs nothing.

value += sign(target - value) × min(rate × delta, |target - value|)

The pose is written only for a part that moved. onMove and onMoved are called then, so a gauge reading them updates only when there is something to show.

RatesCopy Anchor Link

The defaults are a fighter's, in degrees a second for what turns: 80 for the ailerons, rudders and spoilers, 60 for the tail surfaces and canards, 40 for the air brakes and the nozzles' gimbals, 30 for the leading-edge flaps and the gear legs, 20 for the petals, 10 for the flaps. The stick, the pedals and the levers are moved by a hand, which is faster than any frame, so they follow at once.

SettlingCopy Anchor Link

On its first read of a flight, the rig jumps every part to its target rather than moving it there. A page that opens on a jet in flight shows it in flight, not lowering its flaps from rest. settle={false} turns that off.

ClipsCopy Anchor Link

A clip is scrubbed the same way: a target from 0 to 1, a position moved toward it, and the clip's time set from the position. By default it moves at the clip's own speed, so a gear retraction animated over four seconds takes four. A clip is posed only once driven, so a model's other clips leave it alone.

By handCopy Anchor Link

set, setGroup and setClip give a part or a clip a target of their own, over any drive. It still moves at its rate, as an actuator would, until it is given null and the drive has it back.