Update - 23 July 2017: I ran a few more bench tests with a clamp meter on the battery lead. On the upside, the Wave 4x18A can handle the Spintechs at full throttle (around 19A per motor) without breaking a sweat. However, the motor bells got a bit too warm for my liking on the Gemfan 3025s, so I tried again with the rebranded DYS 2435 props that PiroFlip RC sells for the Torrent 110. The motors were much happier with these props, so I'll probably use them for everyday flying and save the Gemfans for special occasions. :P

After my first brushless build went so smoothly, I decided to challenge myself by trying my hand at a 2S micro racer. I'm not generally a fan of frame designs that mount the flight controller on structural standoffs, so that eliminated a lot of popular options right off the bat. I settled on the Tomoquads XBL2 for its Micro Swift mount and 4mm brick house of a baseplate.

Spintech's new 1106 8000kv motors are absolute beasts, but notoriously amp-hungry even on 2.5" props. I hadn't considered using them for a 3" build, but changed my mind after I saw a few people reporting decent efficiency and sub-20A current draws with Gemfan 3025s.

I knew it would still take a substantial 4in1 ESC to feed this motor/prop combo, and I wasn't encouraged by reports of shaky quality control on most of the 20x20 boards rated above 12A. I ended up taking a chance on some just-released boards from Airbot: the Omnibus F4 Nano V3 and the badass-looking Wave 4x18A.

Because they're new and still sparsely documented, I've included shots of the boards along with the FC schematic. The FC runs Betaflight 3.1.7 on the OMNIBUSF4SD target, and the ESC runs a 16.4-based firmware that BLHeliSuite didn't recognize, so I didn't risk updating it. The boards connect with a single 8-pin cable that carries motor signals and lipo output, but no current sensing.

The Wave 4x18A is only rated for 2-3S, and Airbot was adamant about the need for an external capacitor. Thankfully, the board has lipo pads on both sides, so the XT30 pigtail went on the bottom, and a Rubycon ZLH 25V/330µF cap went on top. The solder joint on the pigtail was quite close to the frame, so I placed some electrical tape over the carbon for peace of mind.

Because all four edges of the board are used for motor output, the solder pads are generous and a breeze to solder. I would love if this became the new standard for 4in1 micro ESCs.

Soldering everything else to the flight controller was mostly straightforward. I attached the XM+ receiver using the pins that came with it, but I ended up having to add a small jumper to connect the output to a different RX pad (F4 boards can only receive an SBUS signal through a port that has a built-in inverter, which on this board is UART6).

The hardest part of this build was organizing the ass end of the frame. The capacitor, buzzer, and VTX all had to be routed out the back and secured as far from the props as possible, which took a lot of patience and a cat's cradle of zipties. The rearmost standoff is squeezing the hell out of the XT30 pigtail, but at least it should provide a bit of strain relief in a crash.

Without a current sensor, it's difficult to tell whether this ESC can actually handle these motors in practice, but bench and hover tests went perfectly smoothly. Once my new goggles with DVR arrive, I'll take it out and maiden it.

I do like how this one turned out, but I don't know if I want to build any more micros for a while. The tolerances are so tight that it's frustrating to even think about opening this thing up to make repairs, and I'm not crazy about having to secure so many components to the outside of the frame.

I bet it's gonna heckin' rip though!