For a small catapult you will need props, thrusters, and axis.
Spawn a prop and make it diangle.
spawn 2 props and use axis and click on a prop.
once you have a ghost prop, click it on a prop that is faced diangley.
Do the same thing one the other prop too.
Then use thrusters on the diangle prop.
Hope that helps.
Im not a good explainer :P