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Stryfe Battery Mod: Upgrading to Lipo while Retaining Stock AA capabil


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#1 TheBrickDad

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Posted 03 October 2014 - 06:19 PM

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After much Nerf-related reading, it’s unclear clear to much of the community that Trustfire/Ultrafire Li-ion batteries are not ideal for Nerf Stryfe battery mods due to their severe current sag under load compared to a Lipo battery pack or LiFePO4 batteries (A LOT more on this here). This current sag or lack thereof is critical to consecutive shots retaining a high velocity, so instead of ZING!!...whoosh..whoosh..whoosh we want ZING!! ZING!!ZING!! ZING!! (not sure about you guys, but that’s the sound my darts make, so deal with it).

Thus, all this reading stirred the following question in my mind, “How can I add a Lipo battery pack without losing stock AA battery tray functionality for ease of use while in the field or just gaming with the kids?” The last part there is important to me because otherwise I will take no mercy I don't need crying kids and angry parents.

Enter the Turnigy Nano-tech 2S 7.4V 300mah 35c-70c Lipo Battery Pack. This Turnigy Lipo battery is absolutely TINY, but packs a punch! It weighs 80% less than 4xAA’s coming in at 17g (roughly the same as 3 nickels) and measures 1.7” x.47 x.66, which means it occupies a whopping .52 in³. And as you’ll see, when mounted via ¾” velcro under the jam door, it’s a neat solution to the aforementioned question.

The Mod:
Installation of a Turnigy Lipo beneath the jam door hatch, which will provide power (8.4v) in place of the stock AA's, thus leaving the AA battery tray empty and unmodified, preserving it's use for times when lower power is preferred.

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Materials:
1x JST Female plug (pre-wired @$4)
¾” Velcro sticky back @$6
2x Turnigy 2S 300mah @$5/ea from Hobbyking (for swapping out when one runs low)
1x Blade 130x Celectra 2S Balancing Charger (done right these can be found for ≤$15)
Total: $35.00

Installation:
You disassemble the gun and solder the female JST plug leads to the corresponding +/- tabs under the battery tray. Next, just reassemble with the JST connector laid out to reside under the jam door. You are then left with a MINISCULE yet high performance battery hidden underneath a trap door.

Battery Life:
~1270 darts (SD +/-240) to take the 2S Turnigy Lipo from 4.2v/cell to 3.3v/cell.
Darts were shot at 1shot/sec during testing. At the rate of voltage drop seen between row 8 and 9 the trend gets me to 1030 shots per charge even after subtracting the standard deviation.
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The Results:
Flywheel spin-up time is greatly decreased while flywheel RPM is clearly increased over stock using this 8.4v (7.4v nominal) Lipo. The result being more sustained distance on consecutive shots when firing rapidly. However, the performance I'm seeing could surely be matched by some LiFePO4's, but they inspiration for this mod wasn't purely performance.

I feel the performance of this Stryfe rig at 8.4v will undoubtedly outperform a Trustfire 2S 8.4v setup due to this Lipo battery pack's high discharge rating and low internal resistance. Less weight, less volume, less voltage, and more performance than a Trustfire or IMR rig? Quite possibly, yes.


Comments? Questions? Suggestions for a more elegant implementation of this mod? Fire away folks!

2q0sow4.jpg2pzxtax.jpg2vvw6z9.jpg11aia06.jpg
I know what you're thinking, but no, the wiring does not get in the way of breech when firing or reloading. It's hard to tell in the last photo, but the black rectangle in the center is the Turnigy Lipo nestled inside it's new home.


Edited by TheBrickDad, 21 July 2019 - 02:19 PM.

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#2 Lunas

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Posted 04 October 2014 - 12:42 AM

is that the dart sensor still in there?
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#3 TheBrickDad

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Posted 04 October 2014 - 03:34 AM

is that the dart sensor still in there?

Yes, you are correct.
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#4 Guest_TheSilverhead_*

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Posted 04 October 2014 - 02:51 PM

Could you make a wiring diagram? Did you upgrade the motors?
If I understand, you have it in parallel with the stock batteries, correct? Different voltage and amperage in parallel.... I would put in a battery selector, so that only one power source is in line at a time.
Still, awesome idea. I usually just tell the kids to run faster.
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#5 TheBrickDad

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Posted 04 October 2014 - 04:10 PM

Could you make a wiring diagram? Did you upgrade the motors?
If I understand, you have it in parallel with the stock batteries, correct? Different voltage and amperage in parallel.... I would put in a battery selector, so that only one power source is in line at a time.
Still, awesome idea. I usually just tell the kids to run faster.


Stock motors and wiring (stock wiring is crap, but I'm not sure it matters a lot if I'm already hitting near 100FPS). The power sources are currently mutually exclusive. So that when using the Lipo we're shedding the weight of the stock AA's by leaving the battery tray empty.

On motors, it's my understanding thus far, that stock motors are more reliable in the long run (as long as they're not excessively overvolted). I'm shooting for this to be a reliable mod that will last for many years.
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#6 Lunas

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Posted 04 October 2014 - 10:58 PM

Yes, you are correct.

If that is the one thing you remove from the internals i highly suggest it. It is just a mechanical lock that gets in the way more than it helps honestly i would pull all the mechanical locks and trim the top of the rev trigger so the dart trigger does not hit it rather than trimming the dart trigger like most guides suggest.


Also what are the run times like for that battery pack?

My next mod is going to be the addition of a volt meter inside my stryfe when i do ill get pictures of my rewire with solid core 18 gauge it was interesting to work with. I may or may not swap the stock rev switch to a 10A switch. and i may or may not use the jam door switch to turn off and on the volt meter i also thought about placing the volt meter where you have your battery so when i check the voltage i flip it up get the reading close it turns off the meter. I tested it and when placed against the plastic you can read the numbers through the plastic so it can be super stealth.

Edited by Lunas, 04 October 2014 - 10:59 PM.

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#7 TheBrickDad

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Posted 05 October 2014 - 12:13 AM

If that is the one thing you remove from the internals i highly suggest it. It is just a mechanical lock that gets in the way more than it helps honestly i would pull all the mechanical locks and trim the top of the rev trigger so the dart trigger does not hit it rather than trimming the dart trigger like most guides suggest.


Also what are the run times like for that battery pack?

My next mod is going to be the addition of a volt meter inside my stryfe when i do ill get pictures of my rewire with solid core 18 gauge it was interesting to work with. I may or may not swap the stock rev switch to a 10A switch. and i may or may not use the jam door switch to turn off and on the volt meter i also thought about placing the volt meter where you have your battery so when i check the voltage i flip it up get the reading close it turns off the meter. I tested it and when placed against the plastic you can read the numbers through the plastic so it can be super stealth.


Good tips, thank you. I like these ideas.

I have not formally monitored the battery life. However, I have fired about 200 darts through my Stryfe with the Turnigy Lipo and it's dropped from 4.16v/cell to 3.96v/cell, which linearly extrapolates to 860 darts before the Turnigy Lipo needs to be swapped out (low voltage alarm is set to go off at 3.3v/cell.

Start/End Voltage: 4.16/3.96 = 0.2v used
Darts Fired: 200
4.16v-3.3v = .86v/.001 = 860 dart battery life (SD +/-80)


Dang, I like the idea of a digital voltage meter. I could probably trim out a window on starboard side and rig my digital voltage meter/alarm for viewing. I like your top side idea better though, more functional.

Edited by TheBrickDad, 05 October 2014 - 12:14 AM.

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#8 Lunas

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Posted 05 October 2014 - 12:34 AM

Good tips, thank you. I like these ideas.

I have not formally monitored the battery life. However, I have fired about 200 darts through my Stryfe with the Turnigy Lipo and it's dropped from 4.16v/cell to 3.96v/cell, which linearly extrapolates to 860 darts before the Turnigy Lipo needs to be swapped out (low voltage alarm is set to go off at 3.3v/cell.

Start/End Voltage: 4.16/3.96 = 0.2v used
Darts Fired: 200
4.16v-3.3v = .86v/.001 = 860 dart battery life (SD +/-80)


Dang, I like the idea of a digital voltage meter. I could probably trim out a window on starboard side and rig my digital voltage meter/alarm for viewing. I like your top side idea better though, more functional.

http://www.amazon.com/gp/product/B00BZPKV4Y/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
Those are the ones i got. Like i said no cutting needed the plastic of the nerf gun lets enough light through that you can just glue it to the inside and it shows through. In the stryfe on either side of the magazine area the meter is thin enough that it doesn't interfere. I'm also thinking near the back on the left half of the shell it should not interfere with the trigger but ill have to decide when i get around to putting it in where exactly it will end up.
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#9 Draconis

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Posted 06 October 2014 - 01:07 AM

I call bullshit on those shots-per-charge calculations. 300mAh is a tiny battery. Stock motors have winding impedances of something like 12-15 ohms, right? Even if we give them a relatively conservative number like 20 ohms, they'll still be pulling about 300-350mA at 7.4V. That gives them less than an hour of operation under ideal conditions. So I don't buy it.
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#10 Lunas

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Posted 06 October 2014 - 02:16 AM

I call bullshit on those shots-per-charge calculations. 300mAh is a tiny battery. Stock motors have winding impedances of something like 12-15 ohms, right? Even if we give them a relatively conservative number like 20 ohms, they'll still be pulling about 300-350mA at 7.4V. That gives them less than an hour of operation under ideal conditions. So I don't buy it.

The shots per charge was not calculated in a very accurate way it doesn't take into account that as the battery drops it drops quicker the lower it gets. Also the 35C constant 75C burst is 300mA * 35 and 300*75 for 10.5 amp constant and 22.5 amp burst this kinda puts it down to imr range.

For those that did not know C rating is a measure of how much current can be discharged it represents the capacity of the battery array * rating C = amps possible. So if you have a battery that is 300mA with 25c constant it can deliver 10.5 amps constantly.

I think unless your running non stock motors that pull 20 or more amps you dont really need to run these lipo packs you can do IMR. Are they ideal? No, but the good chargers for them can do other chemistry too. I use a nitecore d4 to charge mine it does NiMH, Li-ion, Li-Mn, Li-Fepo4 and Nicd and it has a 12v input so i could use my car accessory plug to charge them.

my stryfe is running on a pair of these they are ~14c
efest v2 IMR 14500 3.7v High Discharge
Maximum Continuous Discharge Rate: 9.75A
Maximum Continuous Charging Rate: 1.3A
Chemistry: Li-MN
Rated Capacity: 700mAh
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#11 TheBrickDad

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Posted 06 October 2014 - 02:20 AM

I call bullshit on those shots-per-charge calculations. 300mAh is a tiny battery. Stock motors have winding impedances of something like 12-15 ohms, right? Even if we give them a relatively conservative number like 20 ohms, they'll still be pulling about 300-350mA at 7.4V. That gives them less than an hour of operation under ideal conditions. So I don't buy it.


I thoroughly agree your hypothesis may be correct since I oversimplified the estimated battery life by assuming it's drop would be linear, so there is significant room for error. As such, I have added "estimated" to the current battery life numbers I have listed. When I get around to wasting God knows how much of my time finding out the real world answer I will post it as my "observed" battery life under controlled non-game conditions.

That said, you have stirred my interest to find out the actual dart capacity it takes to reduce each cell to 3.3v on these 300mah Turnigy Lipos.
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#12 TheBrickDad

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Posted 06 October 2014 - 05:21 AM

I call bullshit on those shots-per-charge calculations. 300mAh is a tiny battery. Stock motors have winding impedances of something like 12-15 ohms, right? Even if we give them a relatively conservative number like 20 ohms, they'll still be pulling about 300-350mA at 7.4V. That gives them less than an hour of operation under ideal conditions. So I don't buy it.


It looks like I get to call bullshit on you calling bullshit. Check out the OP, I have updated it with test results for shots per battery charge. We were both very wrong, this rig can put out at least 850 darts and possibly 1200 darts on one charge!

Anyone know how many shots per charge people are getting out of their 2S IMR rigs?

Edited by TheBrickDad, 06 October 2014 - 05:25 AM.

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#13 Draconis

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Posted 06 October 2014 - 07:53 PM

It looks like I get to call bullshit on you calling bullshit. Check out the OP, I have updated it with test results for shots per battery charge. We were both very wrong, this rig can put out at least 850 darts and possibly 1200 darts on one charge!

Anyone know how many shots per charge people are getting out of their 2S IMR rigs?



That is a ridiculously high capacity, and I can't help but remain a little skeptical. If all of this is as you state, then that is a pretty impressive battery.
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[15:51] <@Draconis> Titties.
[15:52] <+Noodle> why is this so hard?


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