1. Making the frame
I had some old hinge springs laying in my shop, so I decided to use them due to their insane strength. To secure it to the body I heat it up with my torch and quickly bend one end so we can later attach it to the base with the screw. I drilled two holes and secure the springs with a M6 screw and a nut at the bottom.
2. Mechanism and guide pipe
Then I cut a piece of a 8mm pipe and cut a long groove along the pipe with angle grinder. Do this step slowly and accurately because that will be our guide for the steel rope. After that I cut a small rectangle out of the base with a dremel for the trigger mechanism. There a lots of different trigger mechanisms on the internet so use one that you think is the easiest to make. To trigger the mechanism I used a tiny steel bicycle rope which is attached to the aluminum pipe. If you want to trigger it simply pull the rope or bend your wrist.
3. Finishing up
On the bottom I made 2 small grooves for the belts so I can secure the crossbow to the wrist. For the darts I used some nails but these are useful only for a small distance. Spring are powerful enough to shoot even further but for that I recommend you to make a proper dart with center of gravity at tip of the dart. I hope you like that instructable, please leave some comments if you have any suggestion how would you improve/change it.