With 4" quads becoming more popular over the past few months, I'd been keeping an eye out for a frame compact enough to run a 20x20mm stack, but with enough breathing room to keep the build relatively clean, and a top plate long enough to fit a top-mounted battery. So when I saw that GRVDIGR had begun selling the gorgeous Tombstone 4sX, I knew this was the perfect frame for me. Right after I ordered mine, I realized I'd forgotten to add spare parts and quickly placed a second order. Huge thanks to Corey at GRVDIGR for combining my orders and refunding the difference in shipping, a thoughtful gesture that I appreciated immensely. He's a standup guy. :)

This build is based on the XJB F428 stack from HGLRC, with the optional TX20 video transmitter mounted atop the flight controller. It's very similar to the VTX03, except it runs on lipo voltage instead of 5V, which made the wiring a hell of a lot simpler. The included antenna was a bit too short for this frame, but this one from Pyro-Drone fits perfectly. I put a small dab of solder on the U.FL connector to prevent it from working loose, and so far it seems pretty secure.

The frame has M3 mounting holes for the stack, but the XJB boards will only fit on M2 standoffs. Fortunately, GnarlyFPV makes a fantastic TPU adapter that fits snugly into the M3 holes on the frame and effectively reduces them to M2. The stack was a breeze to install, and the stretched-x layout left plenty of space to fit a 330µF capacitor on the ESC board with no risk of a prop strike.

I chose the new F20II 1408 3750Kv motors from T-Motor, for no reason other than being a sucker for marketing hype and a sexy color scheme. I matched them with HQ 4x4.3x3 V1S props and Rotorgeeks soft mounts. For a little extra bling -- and to match the color scheme of the videogame gun that gave this build its name -- I secured the standoffs with some gold screws I'd bought as spares for my in-progress 6" Alien.

The only challenging part of this build was securing the XT30 pigtail away from the props, as there's very little clearance from the rear standoffs. I wrapped the pigtail in heatshrink to protect it from the edge of the top plate, and used a pair of zipties that seem to be holding up well enough. As always, only more flights will tell me whether this works or not.

Pocket Infinity weighs in at 154g dry, and 208g with a Tattu 650mAh 3S pack. I did a few quick hover tests on Betaflight 3.2 RC4 today, and this thing jumps off the ground with far less throttle than anything else I've built. I have no idea if it could handle 4S without blowing itself apart, but it already feels like a monster on 3S.

Now all I have to do is become a halfway decent pilot...