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:

    0.988
    0.725
    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:

    1.33

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:

    1.34
    1.48

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:

    1.06

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.