Thank you so much for your advice! 
For my case, I have an animal character which has a turn left in 90 degrees animation with root motion enabled.
In Behavior Tree, I am trying to make the animal turn left in 90 degrees slowly at the starting position and at the same time the turning left animation will be played, so that the animal will look like he is turning left naturally without foot slide. And then a new task of moving to a new location will be fired so the animal will walk forward.
I created a task in which I use an AddLocalRotation and set the Z to 90 to make the character turn left. Without the lerp, the animal will turn left in 90 degree immediately instead of slowly.
Below is my idea of how to do it with the Lerp.
I know this is definitely wrong. The variable Current should be given an initial value as zero when the task begins. And also the task should stay at the InProgress status before the Z reaches 90. Now it is always finished with a failure status and restart itself again and again.
I wonder how to give the variable Current an initial value when the task begins and how to tell the task to stay at the InProgress status so that it can wait till the Z reaches 90.
Or is there another way to do it?
Thank you so much!
