こうかな？

DEF Polator OrientationInterpolator {
key [0, 0.25, 0.5, 0.75, 1]
keyValue [0 1 0 0, 0 1 0 -1.57, 0 1 0 3.14, 0 1 0 1.57, 0 1 0 0]
}
ROUTE TIMER.fraction_changed TO Polator.set_fraction
ROUTE Polator.value_changed TO Y1.set_rotation