Thursday, June 12, 2014

More on ***Fires, this time in Swarmfires

This is a somewhat incomplete - but good enough for present purposes - analysis of high resistance Swarmfire setups, performed using sound analysis of various high resistance setups firing. I chose Swarmfires to represent electric spring-powered blasters in general as they are one of the two most widely used such blasters with the other, the Stampede, having been supplanted by the Rapidstrike.

One should expect the problems caused by high resistance and compensatory high voltage to be lesser for spring-powered blasters than for flywheel blasters. The motors in electric springers never free-run; they are always compressing a spring, except for brief transitional periods between cycles. This reduces the variation in desired current draw and thus reduces the severity of the Morton's fork described previously. For Swarmfires at high rates of fire, the inertia of the gearbox is significant relative to the energy required to compress the spring (enough to fire a few times after the trigger is released), further reducing variation in motor speed during firing. This makes trigger response time the primary performance-related problem caused by low current capability.

There is an interesting parallel here with high-resistance high-voltage flywheel systems. Both can have good performance with regard to a characteristic which is readily measured and prominent when showing off (max range and ROF), but falter in a characteristic which is (arguably more) important in actual gameplay (rapidfire range and trigger response).

Given the severity of the problems inherent to compensatory extra voltage in flywheel blasters, it is plausible on theoretical grounds that such problems would be (reduced but still) very severe for springers, or that they may be tolerably mild. That is the question which I address here, by analyzing videos of modified Swarmfires on Youtube. Unfortunately, as Swarmfires lack cycle control, they may stop and restart at various points in the firing cycle, causing the trigger response time to vary randomly. So, videos of multiple high resistance setups had to be analyzed. This includes setups with both alaklike and ***Fire cells. Alkalines have worse resistance than ***Fires because, while each cell has roughly the same IR when fresh and incurs similar cell contact resistance, a greater number of cells are required to achieve similar nominal voltages.  

Sound analysis was performed using RavenLite. (Incidentally, I recommend this software for anyone who wants to use sound to analyze ROF - it's good for what it does and, best of all, it's free. Those significant figures aren't just fluff - you really can get that much precision if you zoom in far enough.) The greatest source of uncertainty was that the time at which each Swarmfire's firing began was difficult to place due to ambient noise. As such, two trigger response numbers have been taken in some cases, one which uses conservative assumptions and one which uses generous assumptions.

All rates of fire are measured in seconds per shot rather than the more conventional shots per second, as this made comparison with the trigger response time a little easier.

This video shows a Swarmfire running on 12 AA alkaline cells firing four bursts of at least 20 shots each. The video description states that the ARs were removed and did not mention any other modifications.

The following picture shows the sound profile of the first few shots in each of the four bursts, and illustrates the uncertainty in the true beginning of the latter two bursts.

Power:    12 cell alkaline AA
ROF:    0.171
Response as proportion of ROF:

    1.66 or 1.51
    1.53 or 1.29

This video shows a Swarmfire running on various battery setups. The description states that the ARs were removed and that be blaster is otherwise internally unmodified.

Power:    6 cell alkaline AA
ROF:    0.288
Response as proportion of ROF:

    0.283 or 0.428

Power:    12 cell alkaline AA
ROF:    0.151
Response as proportion of ROF:

    0.689 or 1.07

Power:    4 UltraFires
ROF:    0.155
Response as proportion of ROF:


Power:    6 UltraFires
ROF:    0.241
Response as proportion of ROF:

    0.705 or 1.03

The painted Swarmfire from the previous video was also shown firing twice. The description states that this Swarmfire has a stronger spring (presumably an upgrade was performed since the last video).

Power:    24 V (unspecified cells)
ROF:    0.122
Response as proportion of ROF:


Another video: the cell type and count was unspecified but, judging by the size of the batteries, probably alkaline.

Power:     24 V (probably alkaline)
ROF:    0.205
Response as proportion of ROF:

    1.36 or 1.88

A fourth video: four UltraFires and a 10kg upgrade spring were used.

Power:    4 UltraFires
ROF:    0.172
Response as proportion of ROF:


Looking at the distribution of these results, we can roughly estimate that the maximum trigger response time using alkaline AAs is over 1.5 times the sustained ROF with generous assumptions or about 1.7 times the sustained ROF with ungenerous assumptions. This isn't good - we'd need to do a more thorough comparison with pack-powered SFs to determine how suboptimal it is - but it isn't as bad as I expected.

Only three ***Fire setups were examined, including one with a stronger spring. We should expect that ***Fires would have a better proportional trigger response than alkalines and nothing which would refute this has been observed. Otherwise, the data on ***Fire setups is too scarce to be conclusive.

How you use your SF determines whether this worsened trigger response time is tolerable (as it would be for cautious skirmishing) or a serious problem (as it would be for self-defence).

***Fires in cells are by far cheaper than high-discharge battery packs, if you only consider powering one Swarmfire. Trustfires cost about $16 for 4 cells. A pair of cheap 7.4 V LiPo packs costs about twice that much. Battery trays for 4 cells cost only a few bucks. A ***Fire charger typically costs about $10 or less, whereas a LiPo pack charger typically costs at least twice this much. Overall, a the total cost (trays, cells, charger) for powering a Swarmfire on Trustfires at 14.8 V is about $28 - probably less. Using packs would cost about $50 - probably more.

Swarmfires with high resistance achieve lower rates of fire on the same nominal voltage, so a pack build needs less nominal voltage to achieve the same ROF - but this is not enough to compensate for the discrepancy in cost per volt. Here is a Swarmfire running on 3S (so 11.1 V) - as you can tell from the channel name, it's one of Toruk's swarmies - with 0.199 sec/shot when using a low-end spring pack and 0.207 sec/shot with an OMW 8kg spring. For comparison, the Swarmfire in the fourth video had a 20% higher ROF with four UltraFires and a slightly higher-rated spring.

On the other hand, if you also use flywheel blasters, having packs is a good idea, and a second 7.4 V pack to put in series is cheaper than a complete set of ***Fire cells and charger.

It is worth noting that ***Fire cells do not offer drop-in convenience for Swarmfires as they do for flywheel blasters unless you have battery resizers and are not making a Swarmpistol.

Furthermore, safety is always a concern when using cells of dubious quality. Packing many such cells together, in high-resistance trays which will generate heat, in many cases inside an enclosed tray which does not allow for good heat dissipation . . . well, people do this and get away with it, but that does not make it a good idea.

In conclusion, if you already have a pile of ***Fires and want to use them in something, then you'd do much better to put them in a Swarmfire than in a flywheel blaster - but you'd do better still to use packs in both.


  1. Good analysis, and that is my observation as well, it is generally more combat-worthy to put a weak battery on an AEG than a flywheel gun, even if the current shortcomings are actually more severe.

    However, I will note about my test Swarmfire:

    That was a Sanyo SAX (power tool cell) pack at about half charge. Hybrid cells lose a lot of voltage when discharged compared to RC lipos. I didn't bother charging it, because I only wanted to compare the springs.

    The OMW 8 kg and the SGnerf 10 kg are (or may be) not rated the same way.

    Stampedes offer a much clearer picture of ROF and trigger response effects of battery parameters. The gear ratio is slightly different, the components are heavier and springs usually stronger, and if you compare Stampede LiPo versus Stampede ****fires you will see huge combat-significant differences.

    1. I see that, since the HvZ forums are down at the moment and that cuts off our means of communication, you've gone ahead and posted this without a message. There was one more thing that I was wondering whether I should add: a proper comparison with pack-build SFs. Though, I'm not in a position to make such measurements right now, so I would have had to ask for some recordings (long story made short: knowing that I won't see action until I start organizing games myself has made me rather lazy about replacing power supplies).

      Come to think of it, do you think that it would be a good idea to have a ROF/trigger response data archive, much like the chrono archive? If you send me audio, I'll analyze it.

      Stampedes are a can of worms that I deliberately avoided opening because the limiting factor on compensatory extra nominal voltage is runaway firing - and the point where that sets in is very hard to analyze from a theoretical standpoint. Besides, I question whether Stampede mods are relevant where Rapidstrikes are available, and the question that I wanted to address isn't how bad this problem can be, but rather how bad it is in a common/relevant case.

      I've a post in the works on an idea which could combine HvZ-typical handling and ROF with NIC-typical range, and it should be done soon-ish. Would you like to continue to check for formatting before publication, or shall I publish it myself when it is done?

    2. I was a bit concerned that I posted this too soon, but I took the removal of DRAFT from the title to identify it as complete. Perhaps that method can be kept.

      I have various Swarmfires and lots of battery packs of varying specification, so I will get some video/audio of firing them to fill out the hole in the data and post it on the youtube.

      As to the ROF/response database idea, while I am all for objectivity, I do think both of these are secondary next to velocity (which in absence of chronographs is known as a trouble source in the NIC).

      My thoughts with Stampedes are that Swarmfires and their typically light springs, and non-cycle-controlled nature that can stop anywhere (hence the varying response values) may not represent all possible cases of nerf AEGs fairly. Stampede is obsolete, but still in widespread use.

      I am interested to hear that concept; does it involve HPA or other compressed gas as an energy source? I have those ideas as well (ranging from QEV/DCV/hopper semi-auto parts bin homemades to full custom magfeds), and if I can ever start up or find a super-NIC event to play such a gun in (think HvZ/stock class attitude with 300fps and stefans) I will certainly build something along those lines.

  2. This comment has been removed by the author.

    1. This was supposed to be a reply, and was accidentally posted as a non-reply comment. There seems to be no way to remove it completely now. Please ignore it.