Forge Help: Projectile Launchers

Anyone know how I can make a projectile launcher in forge where cannon men continually keep firing crates every 10 seconds or so without having the crate spawn where the cannon man had just had it fired? I have a map I’m working on where I want there to be a risk/reward for getting the rocket launcher where at random intervals crates spawn next to these cannon men and fire towards the location of the rocket launcher, but everytime I place the crates above the cannon men they are fired and stay/spawn where they just landed. I want it to work similar to how that hurricane katrina map worked.