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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.
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.
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!
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.
