D&D General Is this a fair trap?

[Xetheral]

So this was interesting:



TomB

In the context of choked flow, there are a lot factors that go into determining how fast the liquid can go before becoming choked. Given that waterjet cutters are designed not to choke, I would assume that they can achieve higher flow rates than would be possible in the trap. (Also, critically, we don't know the vapor pressure of the dead cube stuff.)

That being said, it's entirely possible that choked flow simply wouldn't be an issue at the flow rates we're discussing.

Note, however, that even if the flow isn't choked and the initial short pulse of liquid attains a very high velocity, that doesn't mean the flow will have the destructive effect of a waterjet cutter on objects in the room--once the flow encounters the air of the room it will rapidly decelerate. Also, ultra-short pulse lengths have a hard time damaging anything except very brittle materials, like glass.

 

[Ancalagon]

I voted no because that trap is nonsensical. What purpose does it serve? How does the legitimate owner reach the treasure? How is the trap even reset once triggered? Who goes through all this trouble of lifting a stone block weighting tons up just to maybe poison intruders and that only when they cut the rope themselves?

I concur

The "fairness" of the trap isn't an issue. why on earth would someone set this up is the issue.

 

[RobJN]

Since when were traps supposed to be "fair"?

 

[AbdulAlhazred]

In the context of choked flow, there are a lot factors that go into determining how fast the liquid can go before becoming choked. Given that waterjet cutters are designed not to choke, I would assume that they can achieve higher flow rates than would be possible in the trap. (Also, critically, we don't know the vapor pressure of the dead cube stuff.)

That being said, it's entirely possible that choked flow simply wouldn't be an issue at the flow rates we're discussing.

The FLOW RATE is all that matters. The more 'choked' the flow (IE the lower the rate) effectively is just a smaller diameter 'reacting' piston in the hydraulic model, so the velocity will be higher. You could ideally model this like Ohm's Law, V = IR where 'V' is a reflection of velocity and 'I' is a reflection of mass flow, and 'R' represents the pressure drop. Anyway, the upshot is, the more cube stuff that squirts out per unit time, the slower it will come out. If I was designing the trap I would optimize this.

Note, however, that even if the flow isn't choked and the initial short pulse of liquid attains a very high velocity, that doesn't mean the flow will have the destructive effect of a waterjet cutter on objects in the room--once the flow encounters the air of the room it will rapidly decelerate. Also, ultra-short pulse lengths have a hard time damaging anything except very brittle materials, like glass.

I would not think it would be anything like that high velocity. I'd only be concerned about how much cube stuff projected to what distance, and even then I'm just going to wing it and describe it as some save at some bonus or other at 1 or 2 different distances.

 

[AbdulAlhazred]

Since when were traps supposed to be "fair"?

I think the term might better be represented as "does it support Skilled Play as an objective?"

 

[tomBitonti]

Something I found, but not the result I expected. (At 1:10)

Haha, that first drop is really great.

There are two issues: First, there needs to be a stack of more than 10 bowling balls. Bowling ball density is close to that of water. (Bowling balls less than 12 lbs float. The maximum density possible is about 1.3g/cc.) Second, the gel was unconstrained, whereas the GC material is contained except over a very small area.

TomB

 

[AbdulAlhazred]

Haha, that first drop is really great.

There are two issues: First, there needs to be a stack of more than 10 bowling balls. Bowling ball density is close to that of water. (Bowling balls less than 12 lbs float. The maximum density possible is about 1.3g/cc.) Second, the gel was unconstrained, whereas the GC material is contained except over a very small area.

TomB

It seemed like a pretty stiff low-water-content gel too. It certainly didn't break. As Pemerton stated, the trap would generation 100 PSI, that ball was probably less than 10.

 

[Xetheral]

The FLOW RATE is all that matters. The more 'choked' the flow (IE the lower the rate) effectively is just a smaller diameter 'reacting' piston in the hydraulic model, so the velocity will be higher. You could ideally model this like Ohm's Law, V = IR where 'V' is a reflection of velocity and 'I' is a reflection of mass flow, and 'R' represents the pressure drop. Anyway, the upshot is, the more cube stuff that squirts out per unit time, the slower it will come out. If I was designing the trap I would optimize this.

I would not think it would be anything like that high velocity. I'd only be concerned about how much cube stuff projected to what distance, and even then I'm just going to wing it and describe it as some save at some bonus or other at 1 or 2 different distances.

"Choked flow" refers to the maximum speed at which a fluid can be driven through an orifice by a pressure differential. Increasing the pressure beyond that point doesn't increase the flow rate, and the fluid is said to be "choked". In liquids, the effect is caused by cavitation--increasing the pressure beyond the point at which the flow is choked simply increases the rate of cavitation.

 

[barasawa]

The first person to get close enough to see the bottom of the pit would be attacked by the Gelatinous Cube as they aren't smart enough to wait in ambush either.

Would the pieces of a dead gelatinous cube actually paralyze you? Maybe it has to be surface membrane that does that.
Even so, everyone will get hit with the yellow mold spores if the room is only about 20-25 feet across.

This is definitely a Grimtooth trap, even if it hasn't been published as such, though I suspect it has been. It's something that causes a very likely TPK, and is rather extravagant of a trap.

From the viewpoint of killing the entire party, it's rather effective while still leaving a chance for survival, particularly if they refuse to save their friends and run out immediately, assuming another stone slab didn't block the doorway or anything. As to being a trap, it's kind of silly, but it fits for a strange evil overlord or mad architect.
As to being "fair"... In a game with this employed against the players, probably not. It isn't the job of the GM to kill off the party, it's to provide a story and challenges, again, not making more widows & orphans.

Of course that was prior versions of D&D. We are now in 5th edition, and things have changed some.
The cubes are no longer able to paralyze, but it does cause acid damage.
Being hit by the splatter would probably be equivalent to it's attack or trying to pull someone else out of the cube, 3d6 acid.
Since it's trapped in the pit, it can't engulf those around it, but if someone jumps, falls, or tries to climb into the pit, it's reasonable that they'd be automatically engulfed without a save. (If you were nice, you could give a save at disadvantage for someone entering the cubes space voluntarily.)
You no longer have to cast invisibility on it due to how it's transparency now works.
It takes a DC 15 perception to even spot it if it hasn't moved or attacked.
And again, it can still attack those nearby as it's pseudopod it extrudes to attack with has a range of 5', and that thing can come from any part of the cube that's exposed. (I'm sure it could acid attack the floor and walls of it's pit, but that's not going to help it against the players.)
There's a list of conditions it's immune to, and there's a mention that it tries to avoid fire, but it's not vulnerable to it.
If attacking the trapped cube, remember that it's going to automatically fail Dex saves as it is trapped in a pit it just barely fits in, not that a foe with a Dex of 3 is likely to save in the first place.
Speaking of saves, it's Int is 1 (not zero), and it's Wis is 6. Again, don't forget it's immunities to charmed, frightened, etc.
Also, the cube has NO damage resistances or damage immunities, nor does it have any vulnerabilities.
So you can slash it, bash it, burn it, freeze it, hack it, shoot it, and fry it with a lightning bolt if you want, they all work if you hit.

The Gelatinous Cube, the dungeons greatest ever janitor, except when it eats the rugs & carpeting...