AC of a moving object? [Archive] - Wizards Community

AC of a moving object? [Archive] - Wizards Community

Post/Author/DateTime Post
Laszlo Koller
11-03-05, 07:32 PM How would one calculate the AC of a moving object? For example, a barrel rolling down a hill.

Typically, objects have an AC of 10 + Dexterity modifier (-5 for a Dex 0) + -2 for being an inanimate object + the object's standard size modifier. (See PHB3.5 p. 165 for details.)

Thus, a typical inanimate Medium object would have an AC of 3 [ 10+(-5)+(-2)+0 ].

How about if such an object were moving? Would it now be considered to have a higher than zero Dexterity score? What about the standard -2 penalty for being an object (for lack of a better description for this negative two penalty)?

I look forward to your answers. Thank you.
Benny BBQ
11-03-05, 10:54 PM Reading chapter 4 of Complete Warrior, I noticed that, through the explanation for archery contests, they specify that, using the variant moving targets, the AC of the targets is increased by 5. I can only guess that this means it effectively gets an effective Dexterity score of 10. This does not, however, take heed of the -2 inanimate object rule.

Now, since in the archery contest, the targets are swinging on pendlums, this might me due to the fact that their movement is very predictable... but I can't say for sure...

In your case, I guess I'd go with an armor class of 10 (10 +0 size modifier, +0 Dex, +0 for unpredictable movement), but that's just me...

An other way of seeing it would be to supposethat the -2 penalty to AC of the object has indeed been taken into account (which would mean they decided to give the example targets an effective Dexterity score of 4 or 5 (Dex modifier -3). In either case, the result's the same...

This, however, would give your example barrel an AC of 7 (10 +0 size modifier, -3 Dex, +0 it moves [it's not inanimate; remove the usual -2 for lack of movement])

'Hope I could help...

Peace!
Argon_Asimov
11-03-05, 11:03 PM this is fairly oddball and not a direct interpretation of any RaW but here goes...

Isn't there a test out there that calculates a person's approximate dexterity score by how far they can run in 6 seconds?

I believe it is a pretty straight forward equation, something like 5ft / 6 secs = 1 dex ?

Anyways, perhaps you could use this equation to figure out an objects "effective" dexterity score, and then apply a -2 / 0 / +2 modifier to systematic (pendulum or circular motion), predictable (straight line), or unpredictable movement.
Esponer
11-03-05, 11:32 PM Anyways, perhaps you could use this equation to figure out an objects "effective" dexterity score, and then apply a -2 / 0 / +2 modifier to systematic (pendulum or circular motion), predictable (straight line), or unpredictable movement.

I'm all for this idea, while it is by no means by the rules. I'd suggest you play with the numbers a bit until you get something that looks right.

I just realised, though, that using something like this, we'd come very close to showing how ridiculous Deflect Arrows is... as we'd end up being able to work out the touch AC of an arrow, quickly demonstrating that automatic arrow catching is a little crazy.
Super_Demolition_Christ
11-04-05, 12:26 AM I'd say that its 5 + size. Hitting a moving barrel is no different than hitting a moving enemy, exept the fact that the enemy can move on its own and avoid attacks (hence dexterity). At most 7+size to accomidate the 0 dex and a +2 circumstance bonus to AC for moving unpredictably
Nom
11-04-05, 02:08 AM Utterly stationary target: Dex 0 (-5 to AC). Possibly further penalties (helpless characters take -4 vs melee, objects take -2 vs anything).

Predictably moving target: loss of Dex bonus to AC. Penalty still applies.

Target making effort to avoid being hit: normal AC.

I'd treat a rolling barrel as having no Dex mod to AC (+ve or -ve) but still apply the -2 penalty for being an object.
JadeSpider9643
11-04-05, 03:04 AM AC is a defense vs attack system. just because the barrel is rolling doesn't make it any more defensive than it already isn't. And it doesn't make the attacker any less skilled than they are. what you really need here is an appropiate miss chance. Anywhere from 20-50% depending on how fast it's going and how bumpy/random it's trip.
00_Whupass
11-04-05, 03:48 AM Due to the abstracted nature of the combat system, all objects are both constantly in motion and constantly standing still, I would assign an initiative to the barrel and have it move at whatever speed I felt was appropriate on that initiative count.

Say instead of a barrel we have a Orc, now this orc is in a fight with an Rogue a given combat round is six seconds, and in said round each participant acts, those acts are resolved separately in a sequence detirmind by a random number modified to reflect eachs agility, however this is an abstraction since in a real world combat those things would happen simultaneously. So in reality the orc charged and the rogue sidestep him and attacked, these two things have happened simultaneously yet because of the abstraction nessicary for a simple and eloquent combat system they are resolved separately. The orc recieves no bonus for being in motion. Likewise the barrel recieves no bonus.
Bob Loblaw
11-04-05, 11:40 AM I would stick to the basic: AC of 10 + Dexterity modifier (-5 for a Dex 0) + -2 for being an inanimate object + the object's standard size modifier.

The reason for this is that the attacker's Attack Bonus takes into account his skill to strike a moving or stationary target. I would only do this for simplicity.

The big reason I wouldn't adjust for the speed of the target is because then you will have to deal with adjusting characters' AC for speed as well. When dealing with mounted characters, monks, and barbarians, it may become more hassle that it is worth. As it stands right now, a human monk 18/barbarian1 with the run feat and boots of speed (base speed 130) can run at 74 mph and there is no penalty to hit him. If you implemented the rule for the barrel, you player would have a legitimate argument that he should also get that benefit.
Esponer
11-04-05, 12:00 PM The big reason I wouldn't adjust for the speed of the target is because then you will have to deal with adjusting characters' AC for speed as well. When dealing with mounted characters, monks, and barbarians, it may become more hassle that it is worth. As it stands right now, a human monk 18/barbarian1 with the run feat and boots of speed (base speed 130) can run at 74 mph and there is no penalty to hit him. If you implemented the rule for the barrel, you player would have a legitimate argument that he should also get that benefit.

This sort of change wouldn't completely break the game. It would only apply for players when they provoked AOOs when moving through an area, not against most attacks. It is a fairly massive change, though, and I can see the problem. Then again, while they'd have a legitimate argument, the DM's ruling is final so if a DM wants to house rule an AC based on speed for inanimate objects, the players have no say in the matter. If a DM wants to house rule an entire system for AC based on speed for everyone, then more power to him and I'll offer a prayer that he doesn't screw up the balance.
Nom
11-04-05, 05:27 PM I would stick to the basic: AC of 10 + Dexterity modifier (-5 for a Dex 0) + -2 for being an inanimate object + the object's standard size modifier.

The reason for this is that the attacker's Attack Bonus takes into account his skill to strike a moving or stationary target. I would only do this for simplicity.What this line of discussion misses is that Dex 0 implies the target is immobile. A moving target doesn't have Dex 0. Dex 10 (+0) is probably generous for a rolling barrel, but including the -2 "object" modifier gives a net -2 which seems OK to me.

Dex to AC already takes into account deliberate character movement. Characters which are not actively dodging but are still "mobile" lose Dex to AC. You'll notice that a running character also loses Dex to AC, presumably because he is simply moving in a straight line and not actively making himself hard to hit.
ScipioX
11-04-05, 08:23 PM The rules are frequently kinda dumb because of their simplicity. Just think how difficult would it be for an average mook to hit? A small barrel bouncing erratically down a rough slope could be quite difficult to hit. I'd say up to AC 20, as an unskilled archer would have a hard time hitting it, but its possible.

On the other hand, a slow moving object or one that is moving in a predictable pattern would be reasonably easy to hit, even for an average guy. So prob around 7 to 10 AC.

Rules can't cover complex situations, that's your job as a DM.
Bob Loblaw
11-05-05, 03:01 AM Originally posted by Esponer
This sort of change wouldn't completely break the game.
I wasn't saying that this would break the game, I was saying that the extra work involved wouldn't have a sufficient amount of payoff. While it logically would work just fine, I feel that the extra work would slow things down.

Originally posted by Nom
What this line of discussion misses is that Dex 0 implies the target is immobile. A moving target doesn't have Dex 0. Dex 10 (+0) is probably generous for a rolling barrel, but including the -2 "object" modifier gives a net -2 which seems OK to me.

My point was that I would keep things the way they are. I wouldn't worry about making another rule.

Originally posted by ScipioX
The rules are frequently kinda dumb because of their simplicity. Just think how difficult would it be for an average mook to hit? A small barrel bouncing erratically down a rough slope could be quite difficult to hit. I'd say up to AC 20, as an unskilled archer would have a hard time hitting it, but its possible.

On the other hand, a slow moving object or one that is moving in a predictable pattern would be reasonably easy to hit, even for an average guy. So prob around 7 to 10 AC.

Rules can't cover complex situations, that's your job as a DM.

That's exactly what the attack bonus is all about. It takes into account the attacker's ability to deal with changing situations in combat. The mook would have a difficult time hitting because his attack bonus is low. I see no reason to add to the complexity when it isn't really needed.

Strangely enough, most of the time the rules do just fine for complex situations. All one has to do is break the situation down into smaller, more managable pieces to see what is happening. Things tend to work well (and often better) when kept as simple as possible and no simpler.
Wyrd Bearer
11-05-05, 12:32 PM It takes a feat to gain a dodge bonus while moving quickly (I forget the feat's name). A moving barrel is no more difficult to hit than a unmoving barrel in the world of D&D than a moving gnome is compared to an unmoving gnome. This keeps the game simple and doesn't bog action down with needless arguments over such things like the ladened and unladened velocities of sparrows.
Nom
11-05-05, 03:13 PM The problem with this analogy is that you actually have 3 categories of gnome: actively moving (normal AC), incidentally moving (denied Dex bonus to AC), and completely stationary (helpess, Dex 0). Objects normally only fit into the last category, but once they start rolling are incidentally moving and thus need a mechanic to account for this.

Treating them as Dex 10 is probably overly generous, but works. Alternatively, give them a circumstance bonus to AC of anywhere from +2 to +5.
tui
11-07-05, 11:42 AM In the Attack Roll Modifiers table in 3.0, there's a listing for "Defender Running" which gives +0 Melee and -2 Ranged modifiers, in addition to denying dexterity bonuses.

So I'd say you could just use the regular rules for inanimate objects, tack on that -2, as well as any size and range adjustments, and be pretty comfortable.

Post/Author/DateTime	Post
Laszlo Koller 11-03-05, 07:32 PM	How would one calculate the AC of a moving object? For example, a barrel rolling down a hill. Typically, objects have an AC of 10 + Dexterity modifier (-5 for a Dex 0) + -2 for being an inanimate object + the object's standard size modifier. (See PHB3.5 p. 165 for details.) Thus, a typical inanimate Medium object would have an AC of 3 [ 10+(-5)+(-2)+0 ]. How about if such an object were moving? Would it now be considered to have a higher than zero Dexterity score? What about the standard -2 penalty for being an object (for lack of a better description for this negative two penalty)? I look forward to your answers. Thank you.
Benny BBQ 11-03-05, 10:54 PM	Reading chapter 4 of Complete Warrior, I noticed that, through the explanation for archery contests, they specify that, using the variant moving targets, the AC of the targets is increased by 5. I can only guess that this means it effectively gets an effective Dexterity score of 10. This does not, however, take heed of the -2 inanimate object rule. Now, since in the archery contest, the targets are swinging on pendlums, this might me due to the fact that their movement is very predictable... but I can't say for sure... In your case, I guess I'd go with an armor class of 10 (10 +0 size modifier, +0 Dex, +0 for unpredictable movement), but that's just me... An other way of seeing it would be to supposethat the -2 penalty to AC of the object has indeed been taken into account (which would mean they decided to give the example targets an effective Dexterity score of 4 or 5 (Dex modifier -3). In either case, the result's the same... This, however, would give your example barrel an AC of 7 (10 +0 size modifier, -3 Dex, +0 it moves [it's not inanimate; remove the usual -2 for lack of movement]) 'Hope I could help... Peace!
Argon_Asimov 11-03-05, 11:03 PM	this is fairly oddball and not a direct interpretation of any RaW but here goes... Isn't there a test out there that calculates a person's approximate dexterity score by how far they can run in 6 seconds? I believe it is a pretty straight forward equation, something like 5ft / 6 secs = 1 dex ? Anyways, perhaps you could use this equation to figure out an objects "effective" dexterity score, and then apply a -2 / 0 / +2 modifier to systematic (pendulum or circular motion), predictable (straight line), or unpredictable movement.
Esponer 11-03-05, 11:32 PM	Anyways, perhaps you could use this equation to figure out an objects "effective" dexterity score, and then apply a -2 / 0 / +2 modifier to systematic (pendulum or circular motion), predictable (straight line), or unpredictable movement. I'm all for this idea, while it is by no means by the rules. I'd suggest you play with the numbers a bit until you get something that looks right. I just realised, though, that using something like this, we'd come very close to showing how ridiculous Deflect Arrows is... as we'd end up being able to work out the touch AC of an arrow, quickly demonstrating that automatic arrow catching is a little crazy.
Super_Demolition_Christ 11-04-05, 12:26 AM	I'd say that its 5 + size. Hitting a moving barrel is no different than hitting a moving enemy, exept the fact that the enemy can move on its own and avoid attacks (hence dexterity). At most 7+size to accomidate the 0 dex and a +2 circumstance bonus to AC for moving unpredictably
Nom 11-04-05, 02:08 AM	Utterly stationary target: Dex 0 (-5 to AC). Possibly further penalties (helpless characters take -4 vs melee, objects take -2 vs anything). Predictably moving target: loss of Dex bonus to AC. Penalty still applies. Target making effort to avoid being hit: normal AC. I'd treat a rolling barrel as having no Dex mod to AC (+ve or -ve) but still apply the -2 penalty for being an object.
JadeSpider9643 11-04-05, 03:04 AM	AC is a defense vs attack system. just because the barrel is rolling doesn't make it any more defensive than it already isn't. And it doesn't make the attacker any less skilled than they are. what you really need here is an appropiate miss chance. Anywhere from 20-50% depending on how fast it's going and how bumpy/random it's trip.
00_Whupass 11-04-05, 03:48 AM	Due to the abstracted nature of the combat system, all objects are both constantly in motion and constantly standing still, I would assign an initiative to the barrel and have it move at whatever speed I felt was appropriate on that initiative count. Say instead of a barrel we have a Orc, now this orc is in a fight with an Rogue a given combat round is six seconds, and in said round each participant acts, those acts are resolved separately in a sequence detirmind by a random number modified to reflect eachs agility, however this is an abstraction since in a real world combat those things would happen simultaneously. So in reality the orc charged and the rogue sidestep him and attacked, these two things have happened simultaneously yet because of the abstraction nessicary for a simple and eloquent combat system they are resolved separately. The orc recieves no bonus for being in motion. Likewise the barrel recieves no bonus.
Bob Loblaw 11-04-05, 11:40 AM	I would stick to the basic: AC of 10 + Dexterity modifier (-5 for a Dex 0) + -2 for being an inanimate object + the object's standard size modifier. The reason for this is that the attacker's Attack Bonus takes into account his skill to strike a moving or stationary target. I would only do this for simplicity. The big reason I wouldn't adjust for the speed of the target is because then you will have to deal with adjusting characters' AC for speed as well. When dealing with mounted characters, monks, and barbarians, it may become more hassle that it is worth. As it stands right now, a human monk 18/barbarian1 with the run feat and boots of speed (base speed 130) can run at 74 mph and there is no penalty to hit him. If you implemented the rule for the barrel, you player would have a legitimate argument that he should also get that benefit.
Esponer 11-04-05, 12:00 PM	The big reason I wouldn't adjust for the speed of the target is because then you will have to deal with adjusting characters' AC for speed as well. When dealing with mounted characters, monks, and barbarians, it may become more hassle that it is worth. As it stands right now, a human monk 18/barbarian1 with the run feat and boots of speed (base speed 130) can run at 74 mph and there is no penalty to hit him. If you implemented the rule for the barrel, you player would have a legitimate argument that he should also get that benefit. This sort of change wouldn't completely break the game. It would only apply for players when they provoked AOOs when moving through an area, not against most attacks. It is a fairly massive change, though, and I can see the problem. Then again, while they'd have a legitimate argument, the DM's ruling is final so if a DM wants to house rule an AC based on speed for inanimate objects, the players have no say in the matter. If a DM wants to house rule an entire system for AC based on speed for everyone, then more power to him and I'll offer a prayer that he doesn't screw up the balance.
Nom 11-04-05, 05:27 PM	I would stick to the basic: AC of 10 + Dexterity modifier (-5 for a Dex 0) + -2 for being an inanimate object + the object's standard size modifier. The reason for this is that the attacker's Attack Bonus takes into account his skill to strike a moving or stationary target. I would only do this for simplicity.What this line of discussion misses is that Dex 0 implies the target is immobile. A moving target doesn't have Dex 0. Dex 10 (+0) is probably generous for a rolling barrel, but including the -2 "object" modifier gives a net -2 which seems OK to me. Dex to AC already takes into account deliberate character movement. Characters which are not actively dodging but are still "mobile" lose Dex to AC. You'll notice that a running character also loses Dex to AC, presumably because he is simply moving in a straight line and not actively making himself hard to hit.
ScipioX 11-04-05, 08:23 PM	The rules are frequently kinda dumb because of their simplicity. Just think how difficult would it be for an average mook to hit? A small barrel bouncing erratically down a rough slope could be quite difficult to hit. I'd say up to AC 20, as an unskilled archer would have a hard time hitting it, but its possible. On the other hand, a slow moving object or one that is moving in a predictable pattern would be reasonably easy to hit, even for an average guy. So prob around 7 to 10 AC. Rules can't cover complex situations, that's your job as a DM.
Bob Loblaw 11-05-05, 03:01 AM	Originally posted by Esponer This sort of change wouldn't completely break the game. I wasn't saying that this would break the game, I was saying that the extra work involved wouldn't have a sufficient amount of payoff. While it logically would work just fine, I feel that the extra work would slow things down. Originally posted by Nom What this line of discussion misses is that Dex 0 implies the target is immobile. A moving target doesn't have Dex 0. Dex 10 (+0) is probably generous for a rolling barrel, but including the -2 "object" modifier gives a net -2 which seems OK to me. My point was that I would keep things the way they are. I wouldn't worry about making another rule. Originally posted by ScipioX The rules are frequently kinda dumb because of their simplicity. Just think how difficult would it be for an average mook to hit? A small barrel bouncing erratically down a rough slope could be quite difficult to hit. I'd say up to AC 20, as an unskilled archer would have a hard time hitting it, but its possible. On the other hand, a slow moving object or one that is moving in a predictable pattern would be reasonably easy to hit, even for an average guy. So prob around 7 to 10 AC. Rules can't cover complex situations, that's your job as a DM. That's exactly what the attack bonus is all about. It takes into account the attacker's ability to deal with changing situations in combat. The mook would have a difficult time hitting because his attack bonus is low. I see no reason to add to the complexity when it isn't really needed. Strangely enough, most of the time the rules do just fine for complex situations. All one has to do is break the situation down into smaller, more managable pieces to see what is happening. Things tend to work well (and often better) when kept as simple as possible and no simpler.
Wyrd Bearer 11-05-05, 12:32 PM	It takes a feat to gain a dodge bonus while moving quickly (I forget the feat's name). A moving barrel is no more difficult to hit than a unmoving barrel in the world of D&D than a moving gnome is compared to an unmoving gnome. This keeps the game simple and doesn't bog action down with needless arguments over such things like the ladened and unladened velocities of sparrows.
Nom 11-05-05, 03:13 PM	The problem with this analogy is that you actually have 3 categories of gnome: actively moving (normal AC), incidentally moving (denied Dex bonus to AC), and completely stationary (helpess, Dex 0). Objects normally only fit into the last category, but once they start rolling are incidentally moving and thus need a mechanic to account for this. Treating them as Dex 10 is probably overly generous, but works. Alternatively, give them a circumstance bonus to AC of anywhere from +2 to +5.
tui 11-07-05, 11:42 AM	In the Attack Roll Modifiers table in 3.0, there's a listing for "Defender Running" which gives +0 Melee and -2 Ranged modifiers, in addition to denying dexterity bonuses. So I'd say you could just use the regular rules for inanimate objects, tack on that -2, as well as any size and range adjustments, and be pretty comfortable.