Now lets add the crossbow arms. Cut a skewer or paint brush to 5 1/2 inches in length. Feed it between the two rubber bands like this. And pull the long end toward the back of the unit.

Now push that skewer all the way through toward the front of the unit.

And then swing it to the rear. Don't push it through the rubber band, swing it to the rear. See how that causes the rubber band to twist? Good! Do this a few more times. Slide it forward then swing it to the rear. Repeat this process on the other side of the unit so you end up with two crossbow arms.

TORSION !

The process we are using with the twisted rubber bands is called "Torsion" And it is the same power that gives the energy to a ballisa. I have a foamboard ballista project if you want to check that out. Make a Ballista

Ok! Both crossbow arms have been wound up and I am holding them in place with my fingers. When I release them they spring forward.

Now glue pieces 15 and 16 in place. They go in the front. Piece 1 has dashed lines on it showing you how to place them.

Now glue parts 17,18,19 and 20 to part 1. There is a gap right down the middle where the slot on 1 is. This is the mount for our triggers.

Now let's make the horseshoe assembly. This is what locks and releases the crossbow arms. For this assembly and for the trigger assembly coming up be sure to make the all the holes ahead of time. It will make it much easier to assemble. In this picture I put the holes in 22 and 23 before I glued these pieces together.

Notice that the notch is up on part 21.

Now let's put all this trigger stuff together. All the pieces had the holes pre made before I tried to put this together. Line up our horseshoe and put the trigger (24) in the slot. Feed your barbecue skewer all the way through all of it.

Ok! Looks good. Trim that barbecue skewer on each end. Don't dab any glue on it though. We don't want anything to lock up. It should all move smoothly.

This is how it will work. Go ahead and test it! Bring back those two crossbow arms and hold them in with the horseshoe. And pull back the carriage and push the trigger point down into it. This thing is now locked and ready to fire.

Let's continue with the tutorial

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