My team (RoboDox Team # 599) had a fully pneumatic arm to manipulate balls, a type of arm that was certainly in the minority last year (though more had some pneumatic components)
A few facts about a multi-jointed fully pneumatic arm:
When everything is pneumatic, you take advantage of the speed of these devices, and their easy controls: Grabbing a large ball (If you're familiar with last year's comp) involved driving up to one and flicking three switches in quick secession, so this was a very speedy and very easy operation.
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I hope that helps.