I've been wondering about something like this, but I'm struggling to visualise how the rack will be secured. It seems like it will need some sort of linear slide/rail.

Im currently designing a feather pneumatic axe which uses a modified top of a ram and toothed round bar for the piston.
This sounds very cool. I read another post from Maddox about customising the ram by replacing it with a round bar rack and pinion, but I'm not sure how you're supposed to get a pneumatic seal with all those grooves cut out! Unless it doesn't fully retract but is a longer shaft that leaves all of the toothed section outside of the cylinder...

Custom pneumatic rams seem like a fairly specialist and expensive option though. I imagine you'd have to get this certified again for pressure too

Quote Originally Posted by Roboteernat View Post
Using the crank style, you will never be able to go full 180 as the ram piston will want to pull horrizontally to itself and will jam the arm as it cant force the rotate. It will work as long as you dont make it go full 180. It will put itself under alot of stress as it nears the '0' and say '270' degree mark, and will also - IIRC, it will loose speed as it approaches the max and min points of its rotation.
Yeah I knew it didn't look the most efficient or practical for a back and forth rotation.