I'm looking for a servo that is self locking. So when the power is shut of, the servo will remain in the same position, even if a torque is applied.
Does such a servo exist ???

I havent heard of one. Most servo's can be turned by hand, and offer a bit of resistance when they are off. If there is a certain postion you want it in, you could use a piece of elestic to drag it there. Good luck solving your problem,

Andrew

basbiker,
A 'Failsafe' can do what you want if it has programmable settings. On signal loss (turn off radio transmitter) servos can be 'instructed' to go to a preselected position (until signal is obtained again). Is that what you want?
- 'Doc

Unsure of what your problem is.

If it is signal loss, use a failsafe. If it is actual power loss, a failsafe won't work, so you need to use something else.

Andrew