This is another simpler version of Backup of RAC with ASM to File System.
I'm using this script to make backup as copy of the database and the archived logs required to startup and recover the database.
The backup is copied to another server once a week, there I do recreate the controlfile and rename the database.
This script do check the existing sequences for both instances before starting and after finishing the backup. Then it does a backup as copy of all archived logs between the initial and end sequences registered for both threads. That way the database and all archived logs that are required to recover it are placed on the same backup destination, ready to be ftp'ed to the remote server.