Help with a (peculiar) CR?

[Xhosant]

I want to build an encounter for my 3-man, lvl1 group. It is supposed to be a "training gauntlet" for them to try and cross, but i do not want them to make it through unless they figure they must "take the bullet" for each other (see below) and want to reward them on progress (with each of the "turrets" disabled or left behind considered defeated).

Thing is, the "turrets" are not monsters (since they can't move and take very limited actions) but they are not traps (since they are plainly visible), so I'm at a loss on how to rate them. They are basically a pedestal made of 3 sticks stuck in the ground and some string, holding a up a crystal. Here's a statistics block (kinda).

Turret
Small pedestal, Fine crystal
Hit Dice: -
Initiative:+0 (and immediately aware of the PCs before they're in Line of Sight, they're machines turned on.)
Speed: 0 ft. (static)
Armor Class: 8 All (only size modifier)
Base Attack/Grapple: -
Attack: -
Space/Reach: 5 ft./-
Special:
Any attack made against the crystal (usually ranged or touch) topples it, disabling the device.
One or more of the following:

Burst: Readies an action every round to deal 1d3 nonfatal damage (tied to an element, see below) in a 10ft radius as soon as an enemy is in it (Reflex 12 for half damage).

Shot: Ranged attack for 1d3 nonfatal damage (tied to an element, see below) (range as sling, maximum 2 increments). A Reflex 10 save by an enemy adjacent to target lets him be targeted instead, moving him between this unit and the target (if adjacent to such a square) or swaping squares else.

Link: A beam extends between this unit and another same-element one. Anyone crossing it or starting their turn in it take 1d4 nonfatal damage (tied to an element, see below). A tumble check (as if trying to cross an enemy's square) allows one to cross safely.

Range immunity: Only a touch attack can topple this crystal.

Every such unit is tied to an element (of the 4 classic ones), with all its attacks tied to this element. My 3-man party has each PC tied to an element as well, and a PC of the attack's element is immune to it. The element of a turret is readily apparent.

So, treating the "immunity" only as "1 out of 4 units" to not factor in tactics, what CR are these? And what did you treat them like to calculate it (if anything)? Should i adjust something?

[ngilop]

Sounds like a trap to me like 100% the definition of a trap.

maybe it cuz im from the older D&D edition originally but not all traps were hidden. those swinging platforms over the lake of lava.. yeah traps and very very visible.


in fact doesn;t teh baldurs gate dark alliance game have beholder death ray 'turrets'?

[Debihuman]

It's still a trap. Lots of traps are visible. Does it reset?

Debby