After some field testing I realized the catapult needed some modifications. So I added a foot on the front and on the cross bar to be able to change the trajectory. I tried extending the arm to see if that had any baring on the power. I also added a stripe of surgical tubing that gave more tension to the arm. This was a big help and really gave the catapult more power.
this can also be placed atop any skateboard so you can easily drag it to family picnics or the local park
here's an old video of one of my dad's catapults