Unreal 4 snippet which calculates difference in rotation over time for stunt detection.

TacopocalypsePawn-CalcRotationDiff.cpp

FVector ATacopocalypsePawn::CalcQuatDifference()
{
	//Get the current rotation in quaternion
	FQuat CurrentQuat = GetTransform().GetRotation();

	//Get the quaternion rotational difference
	FQuat TempQuat = PrevQuat.Inverse() * CurrentQuat;
	
	//Update the previous rotation value
	PrevQuat = CurrentQuat;

	//Get the axis values
	float roll = FMath::Atan2(2 * TempQuat.Y * TempQuat.W - 2 * TempQuat.X * TempQuat.Z, 1 - 2 * TempQuat.Y * TempQuat.Y - 2 * TempQuat.Z * TempQuat.Z);
	float pitch = FMath::Atan2(2 * TempQuat.X * TempQuat.W - 2 * TempQuat.Y * TempQuat.Z, 1 - 2 * TempQuat.X * TempQuat.X - 2 * TempQuat.Z * TempQuat.Z);
	float yaw = FMath::Asin(2 * TempQuat.X * TempQuat.Y + 2 * TempQuat.Z * TempQuat.W);
	
	//Convert the values to degrees
	roll = FMath::RadiansToDegrees(roll);
	pitch = FMath::RadiansToDegrees(pitch);
	yaw = FMath::RadiansToDegrees(yaw);

	//Make sure the values are positive
	FVector DifferenceVector = FVector(FMath::Abs(pitch), FMath::Abs(roll), FMath::Abs(yaw));

	return FVector(DifferenceVector);
}