Okay, there is a new throwing arm video on the net that you should see. No, it is not a trebuchet. It also isn't made of timber. Take a look here.
and yes, I'm also doing this to test embedded links.
Contrast that video with this one I shot a couple years ago:
as you can see the principle is the same, but the implementations are vastly different. (Neither of these throwing arms were made or contributed by the Dowdberry clan but we did shoot the 2d video.)