Catapult as Mechanical Trap? FOR USE BY PCs

Greetings all! I have some questions about using a catapult designed as the link below (it will be exactly the same with the addition of some padding between the launch arm and the cross bar for safety purposes) to be used as a mechanical trap by PCs. At least, from previous discussions I heard that it would be a mechanical trap, and not a weapon. If I am wrong in that feel free to correct me there as well.

PVC Catapult
Size is 1.5ft x 2.5ft x 1.5ft
Will be safety tested when I bring it to the next event.

What projectiles are we required to use as ammunition? Does it need to be packets? Could we use foam balls?
Would it only be allowed to fire one projectile at a time, or would we be allowed to load multiple foam balls or packets?
Would this require being reset each time by a person with the tinkering skill? Would that require expending a new tag for the trap each time?

Thank you!
 
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