For halloween/conventions I will be wearing an Altair costume from the game Assassin's Creed. This is my current design for a hidden blade which is both extendable and retractable while maintaining safety.

Imagine a 3 part telescoping blade. The largest part which houses both of the other parts while they are retracted is Part A. Part A is the main housing for the entirety of the mechanism. There is a cap at the open end of Part A. Inside the cap is a spring affixed to the cap and the front of the innermost telescoping blade, call it Part C. when a locking mechanism is released the spring will force the foremost blade portion (Part C) out in turn extending the middle telescoping portion, call it Part B. The spring forcing Part C out also serves as a safety mechanism because if the blade should poke someone it will be pressed down, preventing any kind of penetration.

For the retracting mechanism imagine a wide, thin spool with two wires attached. This spool is located in a separate compartment attached behind the cap on the main housing. The first wire is taut and attached to Part C. The second wire has slack and is attached to Part B. When the motor connected to the spool is activated the spool will turn first pulling Part A inside Part B, the second wire will have that much slack in it and at this point will be taut and the spool will pull both Part A and Part B back into Part C. When parts A and B are fully retracted the mechanical lock will reengage with an audible click and I will stop the motor.


Advice? Suggestions? Flaws?


By the way all of the blade portions will be dulled to a great extent. This is for showing off, not killing people.

Youmay be able to just put a small, sensitive pushbutton switch in the base, so that when blade is fully retracted it would turn off automatically, just an idea.
Just disengage motor and your spring would pop the blade up as planned