I do not believe the controllers accept interactive sessions for ftp or sftp - the file system isn't exposed in that way.
Are you trying to pull configuration backups? You'd need a scripted connection which can log in to the CLI and enable priviledged mode then copy the configuration to an FTP or SFTP server.
I use Airwave for that now, but prior to installing Airwave I used a scripting tool for PuTTY to do it.