hadn't thought of the tennis ball throers as 'atlatl's.
But I guess they sort of are
I've thrown stones with one. Not easy and does take a lot of practice with timing, but works !
Like a staff sling, how and when you accelerate the thrower determines when the missile releases.
Thing is with dream's acceleration - it's just safer to stick with tennis balls.
You never know, one day he might
accidentally run in the right direction !
Would be fairly easy to make one with automatically adjustable jaws - set to open via an elastic band.
But I have way too many projects already, so you'll have to make it yourselves