Theres a chance your RX does have a built in fail-safe....my tornado s30 does...Heres a link to the video to tell you if you do or don't and how to set it if you do.
To find out if you have a fail-safe built in watch this
http://www.youtube.com/watch?v=juRAZ...layer_embedded
And if you do this is how you set it
http://www.youtube.com/watch?v=-cAN7...layer_embedded
FrostY