A Call for Revolution: Supercapacitors in Airsoft

[Pseudotectonic]

Introduction: The lost art of capacitors in airsoft

The mythical powers of "capacitor banks" is not a new idea in airsoft, but the original sources and theories are lost in time, with only faint forum posts remain (all the links are dead in https://www.airsoftsniperforum.com/threads/capacitor-banks-revisited.8688/).

 

In my pursuit of the ultimate trigger response in AEG, power supply remains a big unresolved issue because batteries (LiPo or NiMH) do not really give enough oomph for lack of a better word. We need something better, I thought, we need supercapacitors. And so I set out to rediscover the elementals of such dark magic from scratch (but based on the same principles). And I believe I have revived this magic which I will share my formula below.

 

And dare I say, the surface of this dark art has not really been scratched, because the predecessors either did not use enough capacity (some examples were in the order of millifarads which is not nearly enough), and did not really use the correct type of supercaps (stacked coin cells hybrid types are not capable of high amps). And perhaps the right modules were not available until very recently, so this study will also represent a fresh look into this subject.

 

If you want the bottom line:

Spoiler

14% improved trigger response! All with a plug-and-play module you simply plug in!

 

 

 

Why supercaps at all, isn't LiPo good enough?

 

In short (excuse the pun), LiPo cannot provide sufficient peak current for the amp spikes during start of motor which is often in the region of 45-60 A. These micro-events of shorts (from the perspective of the battery) is also a main pathology of LiPo degrading and swelling over time.

 

These spikes happen every shot in semi, and in the first shots in full-auto. This status quo practice of relying on abusing LiPo as sacrifice for performance does not sit well with me, because firstly it is electrically primitive, and secondly it is a safety risk in this toy gun industry that I think is unnecessary and should be done away with, at least as much as possible.

 

The whole premise of using supercaps is to provide a voltage reservoir for surge power during these initial amp spikes. This is needed because these amp spike often exceed the capabilities of the battery (even LiPo) and the batteries drops voltage in response (for milliseconds) and unable to feed all the current needed for this initial spin-up of the motor.

 

In theory, it can achieve the following:

• Surge power for much more responsive motor, resulting in snappier trigger response.
• Stabilised voltage supply for full-auto, resulting in better ROF.
• Protecting batteries from surge currents, prolonging their lifespan and minimise risks of LiPo fire.

My evidence and theorisations are as follows.

 

 

What is the actual energy requirement?

 

To begin to figure out the solution, we need to ask, what is the minimum capacity to be effective?

 

We can analyse these two graphs from airsoftlab.eu for theorycrafting. http://www.airsoftlab.eu/docs/experiments/motor_current/

 

To figure out the ballpark of energy levels we are talking about, I have picked two cases representative of a high stress build (with a 16 TPA motor) and a more optimal build (with a 28 TPA).

 

The first graph is with 16 TPA motor, SP130, 13:1, to illustrate a typical suboptimal setup with a low torque motor paired with a high stress spring and gear ratio.

 

The second graph is with a more comfortable 28 TPA motor with SP130 and 13:1 to show a more efficient setup.

Just by eyeballing the graphs (and the blog), we can character these spikes (and the energy required to tame them) to be about 45A to 60A, for a duration of about 60ms.

 

16 TPA:

 

28 TPA:

What do the numbers mean? There is a simple answer, and a more complex one.

 

A simplistic way to translate this to farad (the capacity we need), using the 16 TPA setup as example, 60A for 60ms is 3.6 coulomb, which at 11.1V is about 0.324 F. For the 28 TPA example, this would be 2.7 coulomb, at 11.1 V this is 0.243 F.

 

Therefore we can say our ballpark figure is about 0.25 F to 0.33 F as a minimum target. If we are aiming to create a unit that can work with worst case scenario, let's go with 0.33 F.

 

However because supercaps discharge their voltage linearly (meaning their 11.1 V drops down to zero as it discharges over the 60 ms), we can think of it as sharing the workload with the battery in a 1:1 ratio (this is very simplified), meaning it is only doing half of the work while the batteries still need to supply the other half of the current (which is a big improvement already).

 

Here is a prediction:

 

 

In this predicted scenario, the amp spike seen by the battery should be reduced to less than half, because the supercaps will react faster to supply the spike, but as the supercap runs out of voltage, the battery will notice the difference in voltage and catch up, eventually supplying the full load in full-auto, but at a much improved stability. And as the trigger is released, the current stops, the supercaps are charged up again to battery voltage as the battery recovers from voltage sag.

 

We can offload even more work from the batteries if we multiply the supercap capacity (say 3 times, to 1 F) so the they will perform in a 3:1 relationship i.e. 75% of the work are done by supercaps, which will stabilise the current even more. If we go bigger, say 1.66 F, the ratio will be 5:1, or 83% of work being done by supercaps.

 

(The actual result will probably be better, the ratios e.g. 1:1 at 0.33 F are just conservative notional numbers I made up for ease of explanation. Supercaps are more responsive than batteries, and the overall lowered battery stress should further reduce overall voltage sag, so the battery should see less than 50% of the peak current, but I don't have the equipments to proof this hypothesis.)

 

So let's say our notional baseline is 0.33 F, now we just need to implement this theory.

 

 

 

Designing a supercaps unit

 

Here is our goal:

1. Supercaps with total capacity of 0.33 F or more, bigger the better.
2. Voltage should be ok for airsoft usage. (Say a fully charged 11.1 V LiPo is around 12.6 V)
3. Overall size to be small enough to fit in a typical buffer tube, with room for cable management for most cases. Smaller the better.
4. (Bonus feature) built-in safety to drain residue voltage when unplugged.
5. (Bonus feature) LED to indicate presence of voltage.

 

The obvious (and probably the only viable) strategy is to use 3 no. of 5-6 V supercaps in series to give us a 15-18 V headroom for the maximum 12.6 V we are expecting from a fully charged 11.1.

 

The first problem is selection of supercaps. The second problem is designing the whole package that can physically fit inside the buffer tube.

 

Long story short, here is my blueprint: (Just connect the supercaps in series, and then parallel with the batteries, I don't have a drawing)

 

The Eaton supercaps I am using are the highest capacity that can still fit inside a typical buffer tube and wiring, and with one of the better ESR in its class, and can theoretically suffer 115 A of thermals over 60 ms, and tested to MIL-STD 202G for shock and vibration.

 

They are wired (I'm using some fancy SPEC 44 16 awg wires) to a connector that goes between the AEG wire and battery wire, so it is completely plug and play, and removable for safety and for storage. It can in fact be stacked up (if you have multiple units) to give extra performance.

 

For extra safety I have included a bleeder resistor to discharge the residue voltage in maximum 3 hours after it is unplugged. Also for safety (and aesthetics) I added an LED for visual indication of voltage presence.

 

I am tempted to call it the PASTA 1000 (Pseudotectonic Advanced SupercapaciTor Array 1000 mF) but any suggestions welcome.

 

 

Here is what it looks like in real life:

 

 

 

Testing

AEG: Specna E-19, completely stock (which has an X-ASR mosfet preinstalled.)

Battery: 9.6 V NiMH, fully charged, measuring about 11.32 V when testing.

 

This is just a simple A/B test to see if the supercaps work at all. I will simply alternate between plugging and unplugging the supercaps several times, then take measurements with groups of 6 to 7 shots, until the data are fairly consistent and/or a pattern can be identified. The groups are measured in Audacity and averaged and rounded to nearest millisecond.

 

Also note I am not testing with any magazine inserted because A. that is not going to make massive difference either way and B. it is one less variable to worry about and C. if a BB goes off it is going to affect my measurements with sound.

The results:

Stock setup (without supercaps), group #1:
Trigger response: from trigger action = 83 ms, from motor spin-up = [data missing]
ROF: ~17.17 RPS

With supercaps, group #1:
Trigger response: from trigger action = 81 ms, from motor spin-up = 57 ms
ROF: ~17.48 RPS (+1.8%)

Stock #2: (I stopped measuring full-auto because it is getting too loud for the neighbours)
Trigger response: from trigger action = 96 ms, from motor spin-up = 64 ms

With supercaps #2:
Trigger response: from trigger action = 74 ms (-23%), from motor spin-up = 62 ms (-3%)

Stock #3:
Trigger response: from trigger action = 90 ms (+22%), from motor spin-up = 69 ms (+11%)

With supercaps #3:
Trigger reponse from trigger action = 71 ms (-21%), from motor spin-up = 62 ms (-10%)

Stock #4:
Trigger response: from trigger action = 84 ms (+18%), from motor spin-up = 68 ms (+10%)

With supercaps #4:
Trigger response: from trigger action =  76 ms (-10%), from motor spin-up = 62 ms (-9%)

Stock #5:
Trigger response: from trigger action =  80 ms (+5%), from motor spin-up =  69 ms (+11%)

With supercaps #5:
Trigger response: from trigger action =  75 ms (-6%), from motor spin-up =  61 ms (-12%)

 

Analysis of results: Definitely a noticeable audio difference in trigger response. The only way to describe it is it sounds more "instant" and there is less of the spin-up whine. I am not sure why the groups vary quite a bit (maybe battery and/or gearbox settling) but I think it is fair to say the supercaps are making a difference. If we average the data after group #3, with supercaps, the overall trigger response is about 14% improved, with the cycling time from motor spin-up is remarkably consistent at about 11% improved. The shorter lag time from trigger action to motor spin-up can be explained by the voltage stability provided by the supercaps. Overall I didn't know what to expect but I would say 14% improved trigger response is pretty good. It is definitely not a negligible difference, and definitely noticeable when compared side by side.

 

But going by feel alone, it definitely feels a bit more snappy.

 

ROF is probably improved a little bit, but more testing needed.

 

The installation: This may be the only draw back. To actually fit the unit inside the buffer tube along with the X-ASR is a massive hassle, which I have to actually remove the original long heat shrink around the three wires to get them to flex, and re-crimp two out of three of the spade connectors to the X-ASR because they were damaged by too much bending. And even when the supercaps are in, it is still very stuck and you need to wrestle the wires to get the battery on and close the butt plate. Although I have done it with the stock fully collapsed and if I install it with the stock a few positions out, it will be easy. Once it's on, it works. But it is definitely not ideal if you have any in-line mosfet like mine. However if you use a proper mosfet inside the gearbox and just have wires in the buffer tube, it should fit very easily, potentially upping the supercaps to 5 F ones for even better trigger response.

There is no noticeable sparks or heat or anything when install and in use. It simply lights up when you plug it in and it just works with zero drama.

 

Here is how it looks like installed, with a fully collapsed stock, and without the stock: (it barely fits)

 

 

 

 

To uninstall: If the battery is disconnected with just the supercaps plugged into the gun, the gun will barely able to do one shot and the second shot will be stopped by the mosfet because the voltage will have dropped too low. This is just as expected and fairly consistent with the maths.

 

The LED: When you unplug everything, the LED stays on but slowly dims down over the course of about an hour (just as designed). This shows the draining resistor and the LED are all working as intended. I could also feel zero heat from the resistor, which is great and again matching expectation. The LED still visibly faintly glows even at as low as 2 V so it works perfectly for its purpose as a voltage indicator. The red LED is pretty to look at, although I might change the colour to something like blue or green, because the red can be mistaken as error from the mosfet. I might also move it to the "top" side of the "plug".

 

Conclusion of experiment: The prove of concept is a success. Most importantly there is certainly a performance benefit (14% in my test). All the maths check out. The unit is fully functional and fully match the expectations. It literally is plug-and-play. The installation can be a hassle for wire management but that is purely down to physical space and should not be a problem if you are not using in-line mosfet.

 

 

 

Conclusions and speculations

 

• More testing is needed with other setups, if you would like one for testing I can make you a copy for a fee.
• The tech tree can potentially branch into AKs or other platforms or even external compartments, but I don't have any of these for development.

 

Here is a summary of what this device can do.

• The biggest feature for me is safety, because when the LiPo (or any battery) is shielded from stress they are much less likely to puff up over time and starting a fire.
• Another key thing is of course the performance. It works very well in my very first little experiment.
• Electrically the overall voltage floor and current ceiling is improved. Adding supercaps is a bit like transitioning from NiMH to LiPo, but on steroids. There is also where the drawbacks are, because a mosfet is probably a good idea for such power, and if you want to collapse the butt stock you will need a more advanced mosfet that sits inside the gearbox rather than the buffer tube, for cable management reasons. (If you copy what I did you will risk breaking some wires)
• In terms of use cases, it will benefit NiMH the most because the performance is suddenly brought closer to that of LiPo because the performance gap is effectively closed, making NiMH a viable option again. In fact it makes NiMH better than LiPo because NiMH is much safer.
• This is also a must if you are chasing the state-of-the-art trigger response or battery efficiency in any build.
• It will also help with cold weather performance.
• And the best thing is, this is essentially a "free upgrade" because it is an entirely new component added to the system, it does not replace or compete with any existing parts, and it doesn't need any complicated installation, it is literally plug-and-play.
• The only downside for now is with wire management inside the buffer tube to make room for it. I am not sure if there is enough space for guns other than an M4 but maybe you can find creative ways to fit it e.g. longer wires.
• This can potentially benefit rental fleets because it is the easiest upgrade possible with zero overhead on tech, plus it makes your NiMH or LiPo inventory much safer and longer lasting. The savings in overhead for battery management could be worth the investment. And when a gun dies you can very easily transplant it to the replacement gun.
• In theory, you can actually stack multiple units for extra performance (the only problem is finding the space to put them).

 

Conclusion is, and I am probably biased, supercaps could be the next best thing in airsoft. If the space problem can be resolved.

 

Please do comment if you spot any issues in the theory or in the blueprint.

 

Thank you for reading.

 

[Egon_247]

Awesome. 👍

I knew those years studying electronics wouldn't be a waste. I'm a bit rusty but the theory stacks up ok in my head. I'll read it again when I'm awake a bit more tomorrow. 

 

[Enid_Puceflange]

Read the title

Thought it was one of the recent spammy witch doctor cnuts at it again 😂

[Adolf Hamster]

Interesting idea.

 

It does raise a few questions;

-how does it fare with precocking? Intuitively the motor having to fire up with additional load might inferr even more benefits from a higher current supply at startup.

-is this more space effecient than the same space used for a chunkier battery that's capable of a higher burst current?

-wonder how the current crop of brushless motors handle it, possibly they have current limiting built in which might negate any benefit, although i suppose the key selling point for this is being a more cost effective alternative to acheive the same result.

 

Many moons ago i did have a crack at the ol' using a big solenoid to pull the spring idea (idea being the trigger would be entirely mechanical), but mans isn't an electrical engineer so that went about as badly as you'd expect. That was using conventional capacitors though which were chunky, kinda makes me want to dust off the ol' emp generator.

[Sewdhull]

I love this kind of research/investigation.

 

You are using the caps to compensate for the batteries and nothing wrong with that, the data says it improves them.

 

Would you see further improvement if you used a lipo?

 

Since you are drawing comparisons with them it would seem a good idea to find out if a super capped NiMh comes close to a lipo, or life perhaps and go some way to validate your summary, which it needs since there's some claims in it.

 

It should be noted that the ESR for the cap pack is 300mOhms, a NiMh (9.6v) pack 60 to 100mOhms and a lipo (7.4v) 6 to 20mOhms.

 

 

 

 

[Pseudotectonic]

@Adolf Hamster

Precocking: should benefit even more, yes.

 

More space efficient than simply another battery for surge power: yes.

 

Brushless motors: possibly can still benefit from the more stable system voltage, but someone needs to test this.

 

Linear solenoid: very interesting idea, but I think it also has to do with the architecture of an M4 (or any rifle shaped object) and how to make use of the space, and I suspect using solenoids may not be the most effective strategy in terms of making use of the space available to translate electricity into moving a piston of a particular shape, I don't know. Btw, the Systema PTW Infinity gearbox is somewhat innovative in this regard and I suspect their design may be a step in the right direction. Although I'm not entirely sure considering complexity and cost etc.

 

@Sewdhull

Many thanks, for LiPo, yes it should still benefit from it (but not as much as NiMH I would imagine), the graphs were measured with an 11.1 LiPo so certainly the theory would still apply.

 

Not sure about LiFe batteries but I would think the premise still stands, my understanding is LiFe does not have dramatically improved peak current over LiPo, the only advantage seems to be in safety if I'm not mistaken.

 

Good point about ESR. The guy at Airsoft Lab actually says something similar about ESR being more informative than the C rating. (see below)

 

And by the way, someone from Reddit questioned the voltage sag which prompted my to re-examine the whole voltage sag issue. I have noticed I have actually read the graph wrong and in those examples the voltage is not sagging as much as I thought (the vertical scale is off for the blue voltage curves), however, upon investigating this subject the same website is proven useful again with http://airsoftlab.eu/docs/opinions/c_rating/ which actually shows the Vdrop of several LiPo batteries at different current amps. And I think the data is potentially very interesting (I will just repeat what I typed in Reddit below) and potentially making supercaps even more useful:

• The Vdrop at nominal currents are wildly different from one LiPo to another
• Their top of the line LiPo of 2.2 Ah (which is too big for an M4 stock anyway) can do 110A with just 5.5% Vdrop
• However the other brands which are probably more representative of your average LiPo (used by "teenagers") goes from doing ~30A with 15% to 25% Vdrop, to 72A with 50% Vdrop (!)
• If we extrapolate the data we can assume the average LiPo inside an M4 at 60A is going to Vdrop in the region of 40+% albeit ± a big margin with different brands
• So the assumptions are really not too far off at all, and depending on your LiPo brand (which is really a mystery because no one has tested all of them) the benefits can skyrocket if you happen to have a below average LiPo unknowingly, which is 50% of the chance!!!

40% voltage sag is a big assumption, I know, but the key take away is LiPo quality vary so much that I think 40-50% voltage sag at 60A (as I understood originally) is still entirely within the realm of possibility, even with very good probability, so much so it only reinforces the whole premise of using supercaps to plug the gap in surge power performance, in my opinion.

[Sewdhull]

I can see why benefit is derived from the addition of supercaps with NiMh batteries, because NiMh is inferior in current delivery, by a long way in comparison to lithium batteries.

 

I can tell you that just as lithiums have wild variance in quality, so too do Nimh or Nicads for that matter, but you'll notice it less because they are generally lower performing.

 

 

I suppose what I was suggesting before was that as useful as adding caps to NiMh batteries might be there's no reason to suppose it is as well performing as a lithium, nor that there would be anything to be gained from adding caps to lithiums. You could easily run the tests to show what happens, id be interested.

 

 

 -Airsoftlabs is calculating the currents, from IR values derived from experimental data with a 70% variance from a simple load model and choosing the one that suits. It is important to understand that IR varies by load, time, state of charge and method used, probably some other things too. A battery isn't a resistor, proper devices measure IR taking account of battery resistance, capacitance and inductance. Certainly you could compare the same battery over time to see its health and snapshot the IR for a specific circumstance. I use my meter to monitor battery health and see if what I have bought is as good as what I have. I couldn't use the data to compare my batteries to the data sheets with any accuracy.

 

-You wont see volt drops like Airsoftlabs says because its not possible to drop voltage and maintain the current. They are calculations from data, hypothetical.

 

-You cant extrapolate because of the above line.

 

-You can't make any assumptions if you are being sciency, you can measure data and draw conclusions.

 

 

 

Airsoft labs did some cool experimentation, i wish there was more, but more sciency.

[Adolf Hamster]

6 hours ago, Pseudotectonic said:

Linear solenoid: very interesting idea, but I think it also has to do with the architecture of an M4 (or any rifle shaped object) and how to make use of the space, and I suspect using solenoids may not be the most effective strategy in terms of making use of the space available to translate electricity into moving a piston of a particular shape, I don't know. Btw, the Systema PTW Infinity gearbox is somewhat innovative in this regard and I suspect their design may be a step in the right direction. Although I'm not entirely sure considering complexity and cost etc.

 

Yeah the packaging isn't the easiest, the coil i made was vaguely m4 buffer tube dimensions but it would have left zero room for the electronic side of things.

 

I have heard of a few folk having almost success over the years, and there's the semi-mythical bo dynamics system. Tbh mine was exactly the half-baked uni project that was never going to go anywhere.

[Pseudotectonic]

@Sewdhull Yeah definitely a lot more testing and more data is going to give more insights, but again I don't have the equipments for this, but I am hoping anyone can just make their own units and test the working principles which should be the same even if the components are similar

 

I think I have dropped enough hints as to what supercaps I am using and how to actually wire them, but the working bits are really not complicated, the one I built is using some 3F supercaps, they are just wired in series to make total 1F with 18V headroom, and then parallel with the batteries, I mean I think the photo alone should have enough information, but for avoidance of doubt the drain resistor is a 2.2k ohm 1W, and the LED has a built-in resistor so I don't need another one for current limiting, plus the wires, plus the heatshrinks, plus the deans, that is literally all the parts

 

@Adolf Hamster Is it the Lonex BAW system? Never seen this before, very interesting, it seems they are using the buffer tube as some sort of recoil system but the gearbox seems to be a traditional v2 gearbox

 

I guess if there is ever a linear solenoid system, probably the best way is use some off the shelf units if there is one that fits (I have no idea), for cost and repairability reasons

[Steveocee]

Had a read through as "back in the day" I used to work in car audio and there was occasionally the ask for a "power cap" from some of the boy racers, they liked the LED flashing lights and display on them.

Back then it was always the answer of - ok-ish if you want something very quick and wasn't too hard on the draw, otherwise if your bass note dropped low and stayed there, it was additional strain on your battery trying to supply the amp and the cap simultaneously.

 

In the given examples, I would imagine that semi response I guess "should" be likened to a paced tight beat but I would imagine a long pull on auto would be like dropping low for a few seconds (so not advised?)

 

Good read. Thank you.

Edited December 18, 2023 by Steveocee

[Adolf Hamster]

8 hours ago, Pseudotectonic said:

Is it the Lonex BAW system? Never seen this before, very interesting, it seems they are using the buffer tube as some sort of recoil system but the gearbox seems to be a traditional v2 gearbox

 

Dont think so, iirc the company was bo dynamics, they made a promo video about it revolutionising airsoft then the whole thing went dark with the rumour mill churning out things like they'd been contracted for special forces training systems and werent allowed to sell them to the public.

 

The whole thing was semi-mythical could well have been folk reading too much into intentionally vague marketing material.

[Sewdhull]

7 hours ago, Steveocee said:

Had a read through as "back in the day" I used to work in car audio and there was occasionally the ask for a "power cap" from some of the boy racers, they liked the LED flashing lights and display on them.

Back then it was always the answer of - ok-ish if you want something very quick and wasn't too hard on the draw, otherwise if your bass note dropped low and stayed there, it was additional strain on your battery trying to supply the amp and the cap simultaneously.

 

In the given examples, I would imagine that semi response I guess "should" be likened to a paced tight beat but I would imagine a long pull on auto would be like dropping low for a few seconds (so not advised?)

 

Good read. Thank you.

Lipo packs are used now to even the battery load for hi power in car entertainment. Its not my thing, but interesting none the less.

[Sewdhull]

9 hours ago, Pseudotectonic said:

@Sewdhull Yeah definitely a lot more testing and more data is going to give more insights, but again I don't have the equipments for this, but I am hoping anyone can just make their own units and test the working principles which should be the same even if the components are similar

 

I think I have dropped enough hints as to what supercaps I am using and how to actually wire them, but the working bits are really not complicated, the one I built is using some 3F supercaps, they are just wired in series to make total 1F with 18V headroom, and then parallel with the batteries, I mean I think the photo alone should have enough information, but for avoidance of doubt the drain resistor is a 2.2k ohm 1W, and the LED has a built-in resistor so I don't need another one for current limiting, plus the wires, plus the heatshrinks, plus the deans, that is literally all the parts

 

@Adolf Hamster Is it the Lonex BAW system? Never seen this before, very interesting, it seems they are using the buffer tube as some sort of recoil system but the gearbox seems to be a traditional v2 gearbox

 

I guess if there is ever a linear solenoid system, probably the best way is use some off the shelf units if there is one that fits (I have no idea), for cost and repairability reasons

 

You should definitely try the same experiment with a lipo instead of a nimh. Also a lipo alone to see how much the caps compensate for the NiMH  batteries. Conducting the experiment on the same set up allows you to compare where others would have to do the entire suite of tests from scratch.

I posit there would still be some benefit to be had, esp if the capacitor esr could be reduced. Certainly you don't need that much capacitance, but the esr gets higher with smaller caps because the electrode area decreases so its tricky to find parts with small size enough capacitance and high enough rated voltage.

 

I used anti surge xt90s on drones because of the surge of current into the electronics when batteries were connected, it was quite a pop connecting 20Ah of 26v to the things, im doubtful there's enough draw with caps, unless you get their esr down.

[Sewdhull]

The stroke is very short for a solenoid, as magnetism works best close up, like our motors ( put the magnets closer to the armature and the motor performance rises)

 

You want something like a linear motor dragging the the piston back, but i wonder how well they miniaturise.

 

Brushless motors are like a linear motor curved back on itself, the airsoft ones have 6 poles, but the drone type can have many more.

[kadamski]

18 hours ago, Sewdhull said:

Airsoftlabs is calculating the currents, from IR values derived from experimental data with a 70% variance from a simple load model and choosing the one that suits. It is important to understand that IR varies by load, time, state of charge and method used, probably some other things too. A battery isn't a resistor, proper devices measure IR taking account of battery resistance, capacitance and inductance.

[...]

Airsoft labs did some cool experimentation, i wish there was more, but more sciency.

 

I don't understand what you mean here, could you elaborate?

 

I did not calculate currents from IR (because IR is unknown) but the other way around - I calculated IR at currents cloe to the nominal current (as "specified" by C-rating) by measuring the voltage drop. I don't know what you mean by 70% variance.

 

I agree you can't expect the battery will have the same IR over different loads, it won't remain the same over time too. That wasn't my point when I did those measurements, though. I think the numbers showed that C-rating can't be used to reason about the performance of the battery for our purposes, as some batteries will have a very significant Vdrop despite having better C-rating.

 

So, what would you suggest to improve in my measurements (apart from bigger sample size) so they are more scinecy?

Edited December 18, 2023 by kadamski

[Sewdhull]

1 hour ago, kadamski said:

 

I don't understand what you mean here, could you elaborate?

 

I did not calculate currents from IR (because IR is unknown) but the other way around - I calculated IR at currents cloe to the nominal current (as "specified" by C-rating) by measuring the voltage drop. I don't know what you mean by 70% variance.

Hi, Love that you're doing this type of thing...

 

I concur that C rating is not greatly useful, but IR can be, certainly for comparison.

 

Standard IR measurements are either using DC in 2 stages or an AC meter. I use mine just to monitor battery health.

 

Firstly the variance I mention is from IR calculations, in the IR meter report, using the same current but over different time periods leading to different IR values and another IR value in the C rating report. IR values probably vary more than that depending on who knows what else. We have from about 12 to about 21mOhms. That variance is expected, but it limits the usefulness of IR since it is specific to a set of circumstances.

 

 

Your table, for the C ratings says they are measurements, the last 3 columns, say nominal values. Nominal current, volts drop and %. You don't discuss your method so it seems like you have measured the IR ,measurements in the table, put it in the table and calculated the nominal values, I realise you have to calculate a %. Nominal is a word used to describe something in name only or a specification, not a measurement or used or actual value. You don't mention the voltage of the batteries but the volts drop of the GPX would indicate 7.4v was used which is not a fully charged battery, unless it was but you used the nominal 7.4v for 2S Lipos.                                                                                                                  

Then when discussing the GPX battery you say it 'would' drop its voltage by half at because of it's IR when 'does' indicate a thing that has happened. You use 'would' again for another battery. 

 

Having said the above if you did indeed draw 72A from that pack and halve its voltage and calculated the IR from that, I apologise for the comments. This bit ' not possible to drop voltage and maintain the current'  is wrong, I meant something else which is irrelevant if the IR is calculated.

 

 

 

1 hour ago, kadamski said:

 

I agree you can't expect the battery will have the same IR over different loads, it won't remain the same over time too. That wasn't my point when I did those measurements, though. I think the numbers showed that C-rating can't be used to reason about the performance of the battery for our purposes, as some batteries will have a very significant Vdrop despite having better C-rating.

 

So, what would you suggest to improve in my measurements (apart from bigger sample size) so they are more scinecy?

I think the C rating can't be used either, it has been my experience that only occasionally has it reflected the current supply ability of the cells.

 

The key when conducting some sort of experiment is for the reader to be able to replicate your experiment so all the necessary information must be present for that to happen. A precise duplication of your results probably wont be possible but the same basis of your experiment must be possible.

Standard terminology, a repeatable framework ( aim, hypothesis, method , results, discussion, conclusion). Where you have diagrams or pictures etc, they have to be clear. 

 

When looking at the motor current experiment you did, which I really liked over all, there's no baseline motor speed measurement shown but you refer to it and it's relevant as this will tell you where the motors sit in the speed or torque camp. You may not have had the means to measure it, but without it it's harder to make meaningful comparisons.

One thing that puzzled me was why the inrush current changed with a stiffer spring, it's not as if the motor windings reduce in resistance to draw more current. Did you do multiple runs or just one of each set up, because you have anomalous results. But great work anyway and valuable.

 

You've probably looked at the Airsoft Trajectory project, a large experiment, a good example. A lot of work tho.

 

Here's an example of a small experiment, https://www.powerstream.com/lithium-phosphate-charge-voltage.htm

 

 

My background is many years in a lab, a lifetime of engineering, some law enforcement, education and about to take my first pension

 

 

 

 

[Pseudotectonic]

I can perhaps chip in about the motor question, if we go by this graph (another semi-educated guesstimation of mine) 16 TPA is on the high speed side, and 28 TPA would be in the high torque camp.

And about spring vs current, the higher the load, the higher the current draw from any motor, that is completely normal and not anomalous at all

[Rogerborg]

On 16/12/2023 at 21:46, Pseudotectonic said:

Very interesting stuff

 

Typical airsoft player:

 

 

 

Semi-conductor-seriously though: supercapacitors + NiMH?  Seems a bit like...

 

 

 

[Pseudotectonic]

That thing looks incredibly fun to drive so I take that as compliment

[Sewdhull]

No, it was the inrush current that was getting higher that puzzled me.

 

You can equate the inrush current to the current to the current the motor takes when stalled. If there's a big spring stalling the motor the current should be the same if its a small spring.

 

It's possible that different rotor positions on start up mean it takes longer to get going so the current gets closer to the stall current in the time the measurement can be taken, but I don't know. hence the puzzlement.

 

I have a couple of watt meters which will display the current but its not continuous sampling, its periodic. One has a neat graph thing but displays the peak amps also.

 

Setting aside the build quality of motors, high TPA motors with lower currents will always be the most electrically efficient, but if you want speed at the sector gear you'll need appropriate gears, which may not exist for some applications, like a high speed build with a high torque motor. 

11 hours ago, Rogerborg said:

 

Typical airsoft player:

 

 

 

Semi-conductor-seriously though: supercapacitors + NiMH?  Seems a bit like...

 

 

 

Whilst The NiMH and caps might be outdone by lithium, it is possible that caps and lithium will yield some benefit. Altho part of the rationale was not use lithium for a number of reasons and close the gap between the two types.

[Pseudotectonic]

I think the rabbit hole of brushed DC motors and inrush currents goes deep and I'm not ready to jump into it, sometime to do with back EMF or something

[Sewdhull]

Inrush in this context if the current the motor would take when it's not rotating.

When you first apply power the current the motor will take is just the voltage applied divided by the resistance of it's windings.

As the motor rotates the magnets create an opposing voltage in the windings which effectively reduces the voltage applied to the windings.

As the motor rotates faster there's more opposing voltage until the point where the motor cannot go faster.

This is why more voltage spins the same motor faster.

 

The inrush current starts at it's max then reduces as speed increases, because the effective voltage in the windings reduces (the resistance remains the same) until the point is reached where the amount of current becomes stable.

Current then rises with load because the voltage reduces as the motor slows because of the load and speed becomes stable at the new load.

The power dissipated in the windings increases with the square of the current and this power heats the motor (with some help from the commutator and bearings from friction and contact resistance.

 

Torque, the turning force in the motor, is created the magnetic field generated by the current, interacting with the permanent magnets magnetic field.

More current, more torque...Stronger magnets , more torque...more turns, more torque.

 

Higher speed motors go faster than slower ones because they have fewer windings for the permanent magnets to generate an opposing voltage in and so for the same motor speed fewer windings generate less opposing voltage and a faster max speed.

 

You can fit fatter wire on the armature with fewer windings so that the motor can take more current to try to get more torque on a fast motor.

 

More windings is more efficient because the heat (waste) generated is linear with resistance, but exponential with current.

 

I have deliberately avoided things like commutator timing.

 

[Pseudotectonic]

I thought it is common knowledge that higher load means higher current, and that of course includes the initial spike, and the measurements confirm that. I am not sure what you are trying to get at, but I think if you are trying to theorise higher load will not induce higher current, not sure if that is a feasible exercise because I think it goes against conventional wisdom and also empirical data.

 

If you are talking about the micro events at speeds of electromagnetic waves (which approaches speed of light) maybe you are onto something but I don't think this affects the "macro" effects of higher load inducing a higher inrush current.

 

https://youtu.be/O-WCZ8PkrK0?feature=shared&t=666

 

[kadamski]

On 18/12/2023 at 19:28, Sewdhull said:

Standard IR measurements are either using DC in 2 stages or an AC meter. I use mine just to monitor battery health.

Can you elaborate on this standard IR measurements. What you mean by using DC in 2 stages?

In any case, the better chargers does show/measure the IR value. My standard method of measuring the IR value was to use 1Ohm load and check the voltage drop. The values displayed by my charger where roughly the same than the ones I got this way.

 

On 18/12/2023 at 19:28, Sewdhull said:

Firstly the variance I mention is from IR calculations, in the IR meter report, using the same current but over different time periods leading to different IR values and another IR value in the C rating report. IR values probably vary more than that depending on who knows what else. We have from about 12 to about 21mOhms. That variance is expected, but it limits the usefulness of IR since it is specific to a set of circumstances.

I did explain that difference in the IR on the "cheap IR meter" page. What I did not specifically mention, though, is that when I use "IR" term, I mean "IR at some specific conditions". Like, when the battery is fully charged, when the load is 1 Ohm, when it is kept under load for 1s, when it is new, etc. Changing any of this, changes the IR (although not always in significant way). I might have explained that more clearly.

 

On 18/12/2023 at 19:28, Sewdhull said:

Your table, for the C ratings says they are measurements, the last 3 columns, say nominal values. Nominal current, volts drop and %. You don't discuss your method so it seems like you have measured the IR ,measurements in the table, put it in the table and calculated the nominal values, I realise you have to calculate a %. Nominal is a word used to describe something in name only or a specification, not a measurement or used or actual value. You don't mention the voltage of the batteries but the volts drop of the GPX would indicate 7.4v was used which is not a fully charged battery, unless it was but you used the nominal 7.4v for 2S Lipos.                                                                                                                  

Then when discussing the GPX battery you say it 'would' drop its voltage by half at because of it's IR when 'does' indicate a thing that has happened. You use 'would' again for another battery. 

My "C rating" post was in the "opinions" section. Probably that is why I was so short and not well described. Even I couldn't figure out what exact method I used to produce this table, which is bad. But my other page "Batteries review" describes this a little bit better.

Anyways, the table has "Nominal Current", which means the current the C rating is allowing (I do understand this term might not be the best, but this is how I called it). So the Rhino battery is 2.2Ah and has 50C so the "nominal current" was assumed to be 110A. Of course measuring anything at that high current isn't easy so I did the IR measurements at lower currents but I expect the IR to only grow at higher currents, not drop, so this is still the "best case scenario". I also did not see a big variance in the IR (as the ratio of Vdrop and current) when the current was doubled for a given battery. So the calculations, for the sake of simplicity, are assuming the IR is similar for any current up to the "nominal current as specified by C rating". So, I calculated the IR by measuring Vdrop at say, 10A or 20A and then used that value to extrapolate the Vdrop that would happen if the battery was loaded with the "nominal" (again, as allowed by C rating) current.
This was a quick test just to show that C-rating is just arbitrary and one can't, contrary to common myth, use this value to reason about the battery behaviour under load. The voltage the battery has under load is an important factor for me. So saying a battery is OK to be used with currents of 40C while at this current it drops its voltage by at least 50% is inappropriate in my opinion and that was all I wanted to show in this short article.

 

On 18/12/2023 at 19:28, Sewdhull said:

Having said the above if you did indeed draw 72A from that pack and halve its voltage and calculated the IR from that, I apologise for the comments. This bit ' not possible to drop voltage and maintain the current'  is wrong, I meant something else which is irrelevant if the IR is calculated.

Something went wrong with this paragraph as I can't understand the meaning of that. In any case, I can modulate how much current my load takes and obviously the bigger the current, the bigger the Vdrop. But some batteries will drop more voltage at the same current, some will drop more, depending on their IR.

 

On 18/12/2023 at 19:28, Sewdhull said:

I think the C rating can't be used either, it has been my experience that only occasionally has it reflected the current supply ability of the cells.

Yes, that was the exact conclusion of my article there - C rating does not reflect the current supply ability of the cells. IR is much better at that. But it is also not a constant value in the function of the load or time. The manufacturers could come up with some value that reflects the situation a little bit better, like "how much current can I roughly take from this battery for a period of 1s so that the voltage does not drop more than 10% at full capacity" or something like that. But nothing beats proper graphs showing the situation at different conditions.

 

On 18/12/2023 at 19:28, Sewdhull said:

The key when conducting some sort of experiment is for the reader to be able to replicate your experiment so all the necessary information must be present for that to happen. A precise duplication of your results probably wont be possible but the same basis of your experiment must be possible.

Standard terminology, a repeatable framework ( aim, hypothesis, method , results, discussion, conclusion). Where you have diagrams or pictures etc, they have to be clear.

That is completely true. But writing such an article requires not only much more work but also usually involvement of some other people, like reviewers. Like, it's often hard to asses what is obvious and what is not, if you are the one who writes the article. Reviewer may easily spot that, though. That being said, this "C-rating" article was in the "opinions" section, the articles in "experiments" section are a little bit better at that.

 

On 18/12/2023 at 19:28, Sewdhull said:

When looking at the motor current experiment you did, which I really liked over all, there's no baseline motor speed measurement shown but you refer to it and it's relevant as this will tell you where the motors sit in the speed or torque camp. You may not have had the means to measure it, but without it it's harder to make meaningful comparisons.

One thing that puzzled me was why the inrush current changed with a stiffer spring, it's not as if the motor windings reduce in resistance to draw more current. Did you do multiple runs or just one of each set up, because you have anomalous results. But great work anyway and valuable.

You know, I was not aiming at writing a scientific paper grade article and my time and resources where limited. I did do multiple runs and choose the most common/typical one for each configuration. To me, this change of current with different springs was expected - the more stiff spring creates higher resistance so the current must be bigger to start the motor. If you disconnect the motor from the gearbox and let it run freely, the "inrush" current is also much smaller.
Now, I guess, the problem is again in the usage of "inrush current" term. My measuring equipment has a limited resolution/bandwidth so the actual, theoretical current peak may be the same for each setup (and it lasts some fractions of millisecond), but I can't measure that. Instead I can in practice see just the "average" current over some short periods and this is what I see on the scope. This is what I am in fact more interested in - how much current the motor takes in the first few tens of milliseconds after starting but before settling on a max speed. That takes many revolutions of the motor and this obviously is influenced by the resistance the gearbox and the spring gives.

 

On 18/12/2023 at 19:28, Sewdhull said:

You've probably looked at the Airsoft Trajectory project, a large experiment, a good example. A lot of work tho.

I also read many scientific papers. Of different quality. Creating a very good quality one is just *tons* of work. I did not aim at that. My aim was to do some measurements and describe them so that they are not lost. This was, in my eyes, much more than most people in airsoft do and that is why there are so many myths here. But I didn't care too much about someone being able to reproduce my experiment but I did want to describe my experiments properly and I did not succeed fully. Even if scientific method should aim for that, this is often not met in the officially published scientific papers so I feel excused for my results published on some random website

 

All in all, the most important conclusion from the perspective of the original discussion here is that the trigger response and RoF in classic airsoft gun (without precocking, etc) depends highly on the capabilities of the battery. The biggest struggle for the battery is at the spinup of the motor as the current is very high and this may make the battery drop a lot of voltage. The smaller the voltage, the slower the motor reaches full speed and thus the worse trigger response. The max speed will also vary between batteries because the speed depends on the voltage and this depends on the voltage drop caused by the current.
I can see how the supercapacitor could help the battery at the motor spinup time, when the current draw is the highest, providing the ESR of the capacitor is low enough for the current to be taken from the capacitor and not the battery itself in large portion. As was said here several times, this would have the biggest impact with NiMH batteries, and I expect it to be much smaller with beefy LiPO. I someone prefers using NiMH battery, such an approach with capacitors may give you some noticeable benefits. Would that help with LiPO? That would have to be checked. It is possible, though, especially with cheaper ones. Problem is - space. The batteries tend to be able to provide more current if they are physically bigger. So by the time you add the size of those caps to the size of the battery, you might get similar or better results by just switching to some bigger battery. Depending on the cost of the caps, it might also be cheaper. The caps, on the other hand, could be reused after switching the battery in very long games and may have a bigger lifetime. All in all, it would be good to measure if there is a noticable difference when using caps with LiPO batteries.

[Sewdhull]

3 hours ago, Pseudotectonic said:

I thought it is common knowledge that higher load means higher current, and that of course includes the initial spike, and the measurements confirm that. I am not sure what you are trying to get at, but I think if you are trying to theorise higher load will not induce higher current, not sure if that is a feasible exercise because I think it goes against conventional wisdom and also empirical data.

 

If you are talking about the micro events at speeds of electromagnetic waves (which approaches speed of light) maybe you are onto something but I don't think this affects the "macro" effects of higher load inducing a higher inrush current.

 

https://youtu.be/O-WCZ8PkrK0?feature=shared&t=666

 

Inrush current or peak current, not to be confused with current under load. 

So the maximum current a motor can take is when it's not turning. Inrush begins here and is not dependant on load, unless ofcourse that load stops the motor turning. Once turning the current drops until some sort of equalibrium is reached.

 

I can't describe that more clearly than in the previous post.