Cap'n Kobold
Hero
You mentioned that there is a Strength check to stop the boulder. How does the DC compare to that of the check required to move an immovable rod?
I think it's a great idea and you should just roll with it.In the gaming I'm DMing, the heroes are exploring a trap filled dungeon, and have correctly guessed that there is a giant boulder trap at the end of a certain hallway (based on Rolling Sphere from the DMG, but upgrade because it's a 15-foot sphere instead of a 10-foot). They have an immovable rod, and plan to use it to block the giant boulder.
I don't just want to do a gotcha on my players. My goals are to have fun encounters and encourage clever gaming. With that in mind what would you do?
The DMG version asks for a DC20 Strength check to slow it by 15 feet (starts with a speed of 60). Since my bolder is bigger I'm probably going to increase the DC, but not sure by how much yet. That's vs a DC 30 Strength check to move an immovable rod.You mentioned that there is a Strength check to stop the boulder. How does the DC compare to that of the check required to move an immovable rod?
I like the idea of making them roll. They all dump stated Intelligence though.When in doubt, turn to the dice. Rather than do the math yourself, set a DC for an intelligence/investigation check and let the PCs try to figure out how to do it. If they fail, the bolder crushes the rod. If they make it, the rod holds the boulder (and is sacrificed?)
Thanks for this. If I read this right. Is the velocity in feet per second? I initially did it as 60, because that's the boulder's speed, but then it occured to me that "feet per round" is not a very common unit.2. If it moves (slides down the ramp) while continuing to exert 8000lb force on the bolder, you can figure out how far the boulder rolls before stopping as follows: Multiply the weight of the boulder by the sine of the slope. --> W*sin(slope) = F1, F1 is the force needed to support the boulder. Subtract this force from 8000 --> 8000-F1=F2. F2 is the force that will slow down the boulder. If it is negative the bolder can not be stopped and will in fact accelerate. If it is positive the deccelration of the boulder can be calculated as this force times 32 divided by the weight of the boulder --> F2*32/W=d. With the deceleration figured out you can calulate how far the boulder rolls before coming to a stop by squaring the velocity and dividing by twice the deceleration --> S=V*V/(2*d). The answer is the number of feet the boulder rolls before stopping. Note I did this using scalers, not vectors. If you use vectors the signs can change a bit, but the answer should be the same.
If it's already gathered momentum by running down a steep ramp, the corridor could be perfectly flat and it'll still smash the rod with an order of magnitude more force than its maximum allowance.
Well, it won't "smash" as in "destroy". Per the item description, the rod simply shuts off if you put too much force on it.
Oh, oh, wait! Here's what you do...
Get yourself a big honkin' wedge of really stout oak, possibly bound in iron bands if you can manage it. Set it in the center of the corridor. Place the immovable rod against the downhill side of the wedge, and activate it. Yes, there will be more than enough force to deactivate the rod, but not before that rolling ball - that is traditionally only just big enough to fit in the corridor - will have tried to at least a bit roll up the incline, gotten several inches of wood under it, and wedged itself solidly in the corridor, unable to roll down.
Meat splatters. Stone and bone crack. But wood will first compress first, and there's no room to fit it and the ball in there.
Joking aside, the more you scale up the rock the more clearance there is to avoid it, unless you make the tunnel circular in cross section simply standing aside would avoid such a huge rock. The widest point would be at 7', which is over the heads of most PCs.
There's a Dex save to avoid damage, which I figure it diving into the corners.