I recently built an X8 launcher and thought that I would share the plans. The legs are removable, but at the moment, not adjustable. The trigger isn't anything special and I hope to modify it eventually. It currently is made up of a door hinge with springs welded between it and an extension on the top. The launcher that I built is rather heavy given that it is made out of iron, but the design it is based off of is made out of aluminum. Here is the link to the bungee that I used:
Let me know if there are any questions!