Diablo® III

The Tao of Sentries

Note: This post has been updated to reflect the changes made in patch 2.1

After reading a bunch of info scattered around about Sentry behavior (particularly with the 6 piece Marauder's set bonus), I wanted to do a bit more research into the mechanics of Sentry's behavior.

Most importantly, I wanted to try and get a better understanding of the exact Attack Speed breakpoints (as it relates to Sentries and TnT), the cool down timers for most of the skills, and how the skills interact - in order to optimize gear selections.

Rather than rely on how long it takes to kill a mob, I wanted to try and do some more detailed analysis.Be warned, the post is relatively long.

Here's what I've found so far(I'll try to credit those whose information I merely re-verified).

Sentry Break Points:

The goal here was to identify how a sentry's attack speed is affected by the Increased Attack Speed stats on our gear. After doing some forum browsing I found the post below that identified that the sentry's attack rate falls into certain fixed attack rates based on your character's Attack Per Second (see below).

Credit goes to to Dialysis who initially posted the information about these break points.

http://us.battle.net/d3/en/forum/topic/12674158852

I subsequently verified the break points identified in his post and confirmed that the break points listed above are accurate. Unfortunately, the only realistic way to get to a 12 frame attack rate is to use Tasker and Theos.

I've tried to clean up the information Dialysis provided in his table and add a bit more detail. I'm going to use a few abbreviations, to make things fit.


  • Min APS - Minimum Pet Attacks Per Second to achieve this fire rate
  • Max APS - Maximum Pet Attacks Per Second to achieve this fire rate
  • Sentry FPA - Number of frames between each attack a sentry makes
  • Sentry APS - Number of attacks per second the sentry will make


Min APS......Max APS........Sentry FPA.........Sentry APS
------------------------------------------------------------------------------------
0.98182........1.10204...........54......................1.1
1.10205........1.25581...........48......................1.25
1.25582........1.45945...........42......................1.42857
1.45946........1.74193...........36......................1.66666
1.74194........2.16.................30......................2.0
2.16001........2.84210...........24......................2.5
2.84211........4.15385...........18......................3.33333
4.15386........Cap.................12......................5
------------------------------------------------------------------------------------

With the above table, I reference Pet Attacks Per Second. I'm using that term because sentries are treated as pets.

If you're NOT wearing Tasker and Theo, your Pet's APS is the same as your character's APS

If you ARE wearing Tasker and Theo, your Pet's APS is your character's APS multiplied by the bonus provided by Tasker and Theo.

Pet APS = Character APS * (1 + (Tasker and Theo Bonus / 100))

With these fixed attack rates, the break points between tiers can make a significant difference in performance. It may provide the ability to add or subtract IAS on your gear and better optimize your gear for damage.

Internal Cooldowns for Skills and Usage

After locking down break points, the goal was to try and actual internal cooldown times for hatred spenders. Cluster Arrow, Multishot and Impale have a clearly defined cooldown between shots, while Elemental Arrow and Chakram merely replace the sentry's standard shots.

Multishot and Impale
Sentry APS...Sentry FPA...Delay in Seconds.....Delay in Frames
----------------------------------------------------------------------------------------------
1.1................54.................1.8.............................108
1.25..............48.................1.6.............................96
1.42857........42.................1.4.............................84
1.66666........36.................1.2.............................72
2.0................30.................1................................60
2.5................24.................1.2.............................72
3.33333........18.................0.9.............................54
5.0................12.................0.8.............................48
--------------------------------------------------------------------------------------------------------------

Cluster Arrow
Sentry APS...Sentry FPA...Delay in Seconds.......Delay in Frames
--------------------------------------------------------------------------------------------------------------
1.1................54...................2.7................................162
1.25..............48...................2.4................................144
1.42857........42...................2.8................................168
1.66666........36...................2.4................................144
2.0................30...................2.5................................150
2.5................24...................2.4................................144
3.33333........18...................2.4................................144
5.0................12...................2.2................................132
--------------------------------------------------------------------------------------------------------------

The sentries fire at their identified attack rate. At each attack, it makes a determination whether to fire a bolt or a spender. If a spender has reached it's cooldown, the spender (Cluster Arrow, Impale or Multishot) will be fire instead of a bolt.

When multiple spenders are available to be fired, the sentry will always pick the spender with the longer cooldown. As a result, if you have both Multishot and Cluster Arrow on your bar and both spenders are off their cooldowns, Cluster Arrow will be used first (longer cooldown) and then Multishot will be fired on the next available attack.

Sentry Ramp-up

In the past, sentries started at a base firing rate of 1.1 APS and then readjusted their firing rate after firing a normal bolt. This led to significant issues when users had multiple hatred spenders that precluded the sentry from firing a normal bolt - essentially locking the sentries into an incorrect firing rate.

With the release of 2.1, sentry behavior has changed significantly to mitigate this bug. Now, sentries have been updated so they deploy with the appropriate initial firing rate - based on your character's equipment. As a result, the issue with sentry ramp-up has been eliminated and users are able to take advantage of skills like Elemental Arrow and Chakram, without adversely affecting the sentry's firing rate.

Closing thoughts

Hopefully some of the info here was new / useful. Please let me know if you see anything out of line. I've been trying to put together a damage calculation spreadsheet to compare different builds at different attack speeds. I'd hoped getting down to a 12 frame sentry attack would be incredibly powerful, but it looks like you may need to sacrifice too much to get there. It's helped me figure out a few break points, so if I ever get it in a good spot, I may publish it - if there's interest.

Open Notes / Issues:

There are a couple of items that need some additional testing / research to do a full write-up, but are worth mentioning to boost awareness.

Dynamic Attack Speed Changes

While the issue of sentry ramp up has been addressed, the underlying cause of the problem hasn't been fixed. Rather, the issue's been swept under the rug. Fundamentally, sentries still do not re-adjust their firing rate unless a regular bolt is fired.

The end result means that any temporary buffs that boost attack speed won't affect a placed sentry that doesn't fire a standard sentry bolt. This is typically only the case when using Chakram or Elemental Arrow; or when using a lower attack speed and having Impale and Multishot equipped.

In order to prevent abuse, the 2.1 patch seems to have also changed sentries to not only update their attack speed when a sentry fire a standard bolt but also only update the sentry's weapon damage when a sentry fires a standard bolt. This eliminates the option of swapping weapons to abuse the behavior.

This requires a bit more testing, but the lack of ability to have temporary attack speed boosts significantly effect the sentry's firing rate is a disappointing outcome.

Cluster Arrow Firing Rate

There seems to be some oddities with the firing rate of Cluster Arrow. It seems other have seen the issue on PTR, and I haven't done a ton of research but for whatever reason occasionally CA will fire one attack faster than normal.

In my testing this morning, with a hand crossbow - I was able to get CA to fire consistently at a 126 frames between each CA rather than the normal 144 frames between firings, while at the 18 frame break point (3.3333 APS). Oddly enough, I was not able to replicate the issue when using a bow at the same firing rate. I need to do more testing, but I wonder if it has to do with IAS on the weapon.

If anyone has more info / detail about the bug - please let me know.
Edited by Jaybird#1794 on 8/27/2014 10:30 AM PDT
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Thank you for the informative post.
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Noob question: Sentry attack speed is improved by IAS on non-weapon gear? And by paragon IAS?

05/22/2014 12:54 PMPosted by Jaybird
Are Sentry and Spender +Skill buffs additive to one another or multiplicative?


I don't know, but everything points to them being additive. Skill bonus damage is additive with Steady Aim, Marked for Death, and pretty much all item-based damage such as Harrington Waistguard. It's admittedly complicated for more than one skill bonus to be applied, but I'd be very surprised if the devs really thought that through and built in a special part of the formula to multiply the bonuses.
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05/22/2014 03:02 PMPosted by enkelin
Sentry attack speed is improved by IAS on non-weapon gear? And by paragon IAS?


Regular sentry attacks are affected by your IAS on gear, they attack at your weapon speed. They are also considered pets so Tasker & Theo will increase their attack speed even more.

6-piece Marauder sentry when firing spenders are not directly improved by IAS. They are fired based on an internal cool down.
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05/22/2014 03:02 PMPosted by enkelin
Noob question: Sentry attack speed is improved by IAS on non-weapon gear? And by paragon IAS?


Yes, the short answer is that sentry's attack speed is affected by IAS on gear.

The long answer is a bit more complicated. Basically, the sentries have their own attack speed, which falls into 2 categories:

If you're NOT wearing Tasker and Theo's, sentries will will use your character's attack speed (inclusive of any IAS from gear / paragon / skills).

If you ARE wearing Tasker and Theo's, the sentry's attack speed will be your character's attack speed multiplied by the Tasker and Theo bonus for pets.

The rate at which a sentry fires isn't exactly the calculated attack speed. The game has fixed attack rates that a sentry gets placed in based on it's attack speed.Those attack rates are the break points I reference in the initial post.

As a result of that methodology, if I'm using a hand crossbow (1.6 Attacks Per Second) and I have 24% IAS - my character's Attack Speed ends up being 1.984 attacks per second. The game then determines my character's sentry attack speed based on my attacks per second. At 1.984 APS, it falls into the 30 Frame break point (1.74194 <= Sentry Attack Speed <= 2.6 APS) which means my sentry's shooting twice per second.

If I add an additional 5% IAS (total 29%), my character APS is only 2.064. As a result, the 5% IAS has no affect on my sentry's fire rate, because I haven't increased the rate above 2.6 APS which would push me into the tier of fire rate.

However, if I add 12% IAS (total 36%), my character APS becomes 2.176. That then pushes me into a new break point (24 Frames), so my sentry fires 2.5 times per second.

The whole aspect to most of the research I've been doing is to try and figure out those optimization areas - so anyone can maximize their damage. Once the variables are known, the calculations aren't that hard - so you can start weighing trade-offs - rather than relying on sheet DPS or what number's biggest on the screen.
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So these frame values are the length of time it takes the sentry to execute a discrete attack, does this apply to all attacks fired by the sentry, including hatred spenders from the 6pc? Or do normal sentry bolts and fired hatred spenders have different frames-per-attack values?
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05/22/2014 04:19 PMPosted by Myon
So these frame values are the length of time it takes the sentry to execute a discrete attack, does this apply to all attacks fired by the sentry, including hatred spenders from the 6pc? Or do normal sentry bolts and fired hatred spenders have different frames-per-attack values?


The attack speed break points define the number of frames between each attack a sentry makes regardless of whether or it's a regular bolt or a hatred spender. There's only one fire rate for the sentry.

If the character doesn't have the 6 piece marauder's set, it will always be a bolt (note: I did not test Chains of Torment - so I have no idea how it's mechanics work).

If the character has the 6 piece marauder's bonus, at each attack it'll make the determination whether to fire a bolt or a spender - based on the internal cooldowns for each of the spender attacks. If a spender is available, that spender will be shot in place of the bolt. If multiple spenders are available, the one with the longest cooldown will be shot first.
Edited by Jaybird#1794 on 5/22/2014 4:38 PM PDT
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Hey Jay!

I figured out a way to consistently get Chakram/ele arrow to reflect the TnT buff

Here's my link on reddit. There are links in there with video demonstration

http://www.reddit.com/r/diablo3/comments/26ev09/figured_out_a_consistent_method_of_making/
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YT link : http://youtu.be/MMNVeuMWsPs
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So does T&T most significantly only affect the # bolts and # multi shots fired? CA doesn't seem to be affected in your tests.
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Sentry_APS= DH_APS x (1+TaT_Bonus/100)

This makes no sense to me lol.

Do you mean dh aps x 1.5 if I got 50% tat?
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This thread is AMAZING. Thank you.
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Thank you for your good work sir. Please continue your efforts. lf you need any help with testing, I have many gears and can help you.
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Really interesting - thanks!
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05/25/2014 03:28 AMPosted by bobdrix
So does T&T most significantly only affect the # bolts and # multi shots fired? CA doesn't seem to be affected in your tests.


For the most part, the number of Cluster Arrows fired doesn't vary drastically. The sheer length of its internal cooldown makes it harder for the differences to be apparent. If I extend out the test to a full 30 seconds,the 12 frame attack rate (5 APS) fires 1 extra cluster arrow, but the rest shoot the same amount.

05/25/2014 04:05 AMPosted by Powerpuff
Sentry_APS= DH_APS x (1+TaT_Bonus/100)

This makes no sense to me lol.

Do you mean dh aps x 1.5 if I got 50% tat?


You're exactly right. I'm going to clean up the OP to try and make it a bit clearer. I quoted the original post I used as the starting point for my testing, but I want to update it a bit to try and make it a bit cleaner, including attacks per second in addition to frame rate calculations.

05/24/2014 10:08 PMPosted by Synthmonger
Hey Jay!

I figured out a way to consistently get Chakram/ele arrow to reflect the TnT buff


Very cool, it's a good example of what it should be doing. I noticed in your video that it shoots a regular bolt first, which seems to wake up the the true attack rate. Hopefully Blizzard fixes it eventually. Firing massive amounts of Chakrams and Elemental Arrows would be a lot of fun.
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05/25/2014 09:55 AMPosted by Jaybird
05/25/2014 03:28 AMPosted by bobdrix
So does T&T most significantly only affect the # bolts and # multi shots fired? CA doesn't seem to be affected in your tests.


For the most part, the number of Cluster Arrows fired doesn't vary drastically. The sheer length of its internal cooldown makes it harder for the differences to be apparent. If I extend out the test to a full 30 seconds,the 12 frame attack rate (5 APS) fires 1 extra cluster arrow, but the rest shoot the same amount.

05/25/2014 04:05 AMPosted by Powerpuff
Sentry_APS= DH_APS x (1+TaT_Bonus/100)

This makes no sense to me lol.

Do you mean dh aps x 1.5 if I got 50% tat?


You're exactly right. I'm going to clean up the OP to try and make it a bit clearer. I quoted the original post I used as the starting point for my testing, but I want to update it a bit to try and make it a bit cleaner, including attacks per second in addition to frame rate calculations.

05/24/2014 10:08 PMPosted by Synthmonger
Hey Jay!

I figured out a way to consistently get Chakram/ele arrow to reflect the TnT buff


Very cool, it's a good example of what it should be doing. I noticed in your video that it shoots a regular bolt first, which seems to wake up the the true attack rate. Hopefully Blizzard fixes it eventually. Firing massive amounts of Chakrams and Elemental Arrows would be a lot of fun.


Honestly I'm not sure if they'll make the chakram/ele arrow to the proper cooldown based on the hatred forumla to ICDR ratio. It does absolutely insane damage. I should probably find a way to pull a boss into turrets and post a video of 304739043billion hp persecond to garner more views so maybe the dev's will fix it
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So, why did I not see this thread earlier? Maybe OP you should change the title lol. Great job! I'll add this post into my "useful into for 6pc marauder's". Because this information is very important for optimization ^.^
05/22/2014 12:54 PMPosted by Jaybird
Multishot
Sentry APS...Sentry FPA...Delay in Seconds.....Delay in Frames
----------------------------------------------------------------------------------------------
1.1................54.................1.8.............................108
1.25..............48.................1.6.............................96
1.42857........42.................1.4.............................84
1.66666........36.................1.2.............................72
2.0................30.................1................................60
2.5................24.................1.2.............................72
3.33333........18.................0.9.............................54
5.0................12.................0.8.............................48
--------------------------------------------------------------------------------------------------------------
This is a bit strange. Multishot is believed to have a fixed internal cooldown. The upper bound on the cooldown from this looks like its 0.8s. However at 1.1 sentry aps, it seems to have broke that rule. Perhaps sentry is "forced" to fire a bolt after you use all your hatred spenders equiped? Idk~
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05/27/2014 04:09 AMPosted by VocaloidNyan

05/22/2014 12:54 PMPosted by Jaybird
Multishot
Sentry APS...Sentry FPA...Delay in Seconds.....Delay in Frames
----------------------------------------------------------------------------------------------
1.1................54.................1.8.............................108
1.25..............48.................1.6.............................96
1.42857........42.................1.4.............................84
1.66666........36.................1.2.............................72
2.0................30.................1................................60
2.5................24.................1.2.............................72
3.33333........18.................0.9.............................54
5.0................12.................0.8.............................48
--------------------------------------------------------------------------------------------------------------
This is a bit strange. Multishot is believed to have a fixed internal cooldown. The upper bound on the cooldown from this looks like its 0.8s. However at 1.1 sentry aps, it seems to have broke that rule. Perhaps sentry is "forced" to fire a bolt after you use all your hatred spenders equiped? Idk~


It would seem that the Multishot internal cooldown is not one fixed value (maybe it is decreased by attack speed after all) or that there is some kind of secondary logic that affects the rotation.

I made a quick script to simulate the sentry shooting behavior based on the assumption that the hatred spenders are fired in place of regular bolts when they are not on cooldown (CA first then MS etc).

If I set CA internal cooldown to 132 frames and MS internal cooldown to 60 frames, everything matches the values detailed in the original post except when we move down to the 18 and 12 Sentry APS speeds and Multishot. At those speeds 60 frame ICD doesn't match the findings anymore (54 frame MS ICD for 18 sentry APS and 48 frame for 12 sentry APS would match the findings again). Cluster Arrow's internal cooldown seems to be a fixed value (or that it changes so little that it does not affect the rotation).
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Should also double check some stuff here. For example I notice when transitioning from 2 aps to 2.5 aps, the sentry rate of fire increases as described. However the frequency of multishots decreased as a result (from squeezing in another bolt)
Edited by VocaloidNyan#1582 on 5/27/2014 5:14 AM PDT
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