This 4" 4S lightweight rocket was intended to be my next bigger/faster build and an upgrade from my GP3 (3S 3" TP3-like toothpick) and my Blind Pig (2S 3" line-of-sight trainer build).

I was looking at various other RTF 4" toothpicks, in particular the Betafpv X-Knight 4, but also the Betafpv Twig Mutant 4, the GEPRC Dolphin 4, and the Diatone GTB 4. None of them felt quite right though, so I decided to build something myself that hopefully improves on these existing options. In particular, I wanted something that has:

• less dry weight than all of those (111g vs. 130g, 148g, 136g, 118g),
• a better camera (new Caddx Baby Ratel 2 vs. Caddx Ratel, Caddx Turbo EOS2, Caddx Baby Ratel),
• BlHeli32 ESCs to learn how to configure it and to play with the new variable PWM frequency feature (all the other ones are BlHeli_S),
• blackbox logging for tuning (the Dolphin doesn't have any),
• lower pitch props (Gemfan 4023/24 as recommended by KababFPV vs. HQ4x2.5x2, Gemfan 4032, HQ4x4.3×3),
• LEDs for line-of-sight (Flywoo Goku FC and VTX each come with four LEDs, although I broke off two of them by accident pretty quickly),
• FrSky R-XSR to get support for telemetry for line-of-sight (not sure about the GEPRC and the Diatone, but the Betafpv ones only come with FrSky XM as far as I know),
• a buzzer (none of the other ones come with one).

Since my BabyPickle build, I have been a fan of Alexandre Arvinte's open source frames, which is why I chose his PickleBig 4 frame for this build. I had it cut in 3mm and it weighs about 13g (about 17g at 4mm if you want more durability). The canopy and the stack spacer are leftovers that came with the HaloRC Guitarpick frame that I used in my GP3 build.

For the motors, I considered 1404 (to significantly reduce the weight even more) and XNOVA T1804 (inspired by Dave_C) or even BrotherHobby 2004 (inspired by quadmovr). I didn't know how to decide though, so I just went with what the X-Knight 4 uses for now, which seemed like a safe bet in terms of power and efficiency. I might try others in the future though. The 1505 motors pull about 15A at 100% throttle with 4S voltage, so I needed a battery that can sustain about 60A burst. Betafpv recommends a 4S 850mAh 75C for the X-Knight 4, but I chose a 4S 750mAh 95C instead since it's 20% lighter but only 12% less capacity and should easily sustain 60A (even if the C ratings are totally off). The 1505 motors with the 750mAh battery give this build a power-to-weight ratio of about 13 (or about 14.5 with a 4S 550mAh 95C). The 750mAh gives me flight times of about 4-5 minutes while the 550mAh gives about 3-4 minutes. So far, I think I prefer the 750mAh, even though it is 23g heavier and makes the build a little less nimble, but it causes noticeably less voltage sag.