Your atlatl in your avatar is halfway there already.
I may have to dig out some scrap wood and video tape one, but I will give it a shot using words.
you have 3 pieces, that you stand up and notch into a shape of a 4.
Starting with the upright. You make a notch halfway through in the middle. You also make a flat point (think chisel) at the top.
The horizontal piece, you make a notch halfway through in the middle. This notch matches up with the upright notch, so the two mate together. You also make a whistle shaped cut near one end - cut straight into the piece, and then take a long shallow notch into your straight cut.
The cross piece. You make a chisel point on one end, and a whistle cut near the other. You want a few inches past the whistle cut.
Now, the assembly.
Take your heavy deadfall object, rock, log, rubbermaid tote, tip that up with your first hand.
Take the upright, hold it up with your second hand.
Take the crosspeice, stick the whistle cut into the chisel point of the upright with your third hand.
With your fourth hand, mate the notch with the horizontal into the notch in the upright. The chisel point in the crosspiece should mate into the whistle cut in the horizontal piece.
When you let the weight rest on the end of the cross piece, it will act like a lever pivoting on the upright, trying to pull the horizontal notch out of the upright notch.
This is a very precarious balancing act, hence, why you need to use all four of your hands to do this. When a critter tries to get the bait off of the free end of the horizontal end, it will wiggle the horizontal arm, causing it to either come apart at the mated notches, or at the opposite end, and the whole trap comes crashing down on your dinner, or my kittens as the situation dictates.
It takes a bit of trial and error to get the proportions right for each piece and also how big the notches are. If the notches and whistle cuts are too shallow, even six or seven hands won't let you set the trap. If you make the notches and cuts too deep, it's too hard for the critter to knock the trap apart and have it come down on them.
Does this sound about how you made yours Haldo?
** Note, no kittens where injured in the making of this post**
