Knex Hidden Blade from Assassin's Creed. I only used basic pieces with minor/optional modifications. I also used string for the trigger and rubber bands to move the 'blade.' Taping the bottom of it is optional and makes it more comfortable in my opinion.
Step 1: Parts
2 Red Rods
1 Grey(Black) Rod----*I do not know how it will work with a grey rod. The black rod is stronger.*
1-2 Green Rods---*These can be used on the locks to stop them from spinning completely around.
7 Orange Connectors
15 Grey Single Connectors---*Some are optional, just used to hold the rubber bands*
3 Small Blue Spacers
3 Larger Grey spacers----*Grey spacer = 3 small blue and they can be substituted*
2 Rubber Bands
String---*Length Varies from person to person*
Tape for comfort
Step 2: Putting the Peices on the Red Rods
The stopper for the blade is a grey piece, as shown in the 3rd picture. This is how it should go onto the rest. Once on, push it tight so you can attach the rest of the pieces.
In the second picture, on the orange connectors used as the lock, you can put green pieces onto the ends, this stops them from spinning all the way around.
You have pretty much finished the majority of the mechanism now. All you need to do is add the rubber bands and string. PLus whatever you want to put on yourself.
4th picture shows what you should have so far.
Step 3: Rubber Bands
If you tie it, make sure you tie the end away from the trigger. Also make sure when you tie it that it has enough slack still to still loop around the Grey/Black piece used for the blade. This is where a little fine tuning may be needed.
Repeat this for the other side.
2nd picture is what you should have.
3rd picture is "armed"
Step 4: The String
Step 5: String
Add a loop like the one shown in the picture. You want to try your best to get the correct length. When its on your wrist, it should be able to loop over your middle finger, wrap around your ring finger once, and then around your pinky. In my video at the end, you can see how this works.
In the second picture, I wrapped the excess string around a few times to give it extra strength. I then tied it and trimmed off the excess as shown in picture three.
In the fourth picture, I put some tape on it to hold it together better and make it more comfortable to slide over my finger.
Step 6: Optional Step
Get a piece such as an orange connector. I laid it on the bottom towards the back. I then taped it so there is an angle that moves the rubber bands off your skin.
Step 7: Finished
To keep it on my arm, I used a normal wrap that stretches and wrapped it around my arm to create a layer to put the hidden blade on, then continued wrapping it with the hidden blade on my wrist so it was held in place. When doing this, make sure there isn't too much pressure on the locks because that can stop it from coming out correctly.
You may need to file the "blade" piece down a little so it slides through the holes easier. Be careful not to file it down too much though or it will come out. Before filing, make sure there isn't too much tension on the locks.
For some reason, Youtube made the video darker, so some things are harder too see.
If you see anything that can be improved or added, let me know.
Feedback is nice to get too.
Anything you find that can improve it, if you can let me know so I can try it.
Also, if you have any other ideas for something you would like to see built, let me know and I will try my best to make it and if its good enough, i'll put instructions up for that too.