So I decided that I was going to build myself a little 3" quad as an always available freestyle rig for travelling. It just so happened that the Runcam Split was announced whilst I was pondering, so I ended up speccing a build around it. Also started to get into racing around the same time, so the build switched focus a little towards going fast too.

Parts

Obviously the Runcam Split was an integral part of the build, finalised straight away. I also decided soon on that I wanted use a TBS Unify HV Race for ease of use and its acceptance in race events. Knowing I'd board mount the Unify, and that the Split's board would be to deal with, I had to pick an FC with a built in PDB. Recent positive experience meant that Betaflight OSD was also a must, so I went for a Kakute F4. Being as it wasn't going to be a featherweight build, I went for Tornado 1407s. 20A ESCs from Unmanned Tech and an RSFSB OrangeRx receiver rounded out the electronics.

The frame was a different matter. Initially I bought an Atto DC130, which is a lovely frame but the short rear arms meant it would be near impossible to fit the ESCs on the arms. With a full size FC, the props overlap with the boards too, making for a tricky build with 3 boards in the stack. As a result, I picked up a GEPRC GEP130X instead - it has loads more room. I also swapped the short standoffs for standard 35mm ones to get enough vertical clearance.

Build

The build went remarkably smoothly considering the small size of the frame and despite the fact it was my first non-5" build. I started with a dry fit of the components in the stack to check clearance, and found that there was very little wiggle room on the Split's camera module - the angle would only be tweakable from around 35 to 50 degrees. I also discovered that the front standoffs show in the HD footage (being slightly wider field of view than the FPV feed), so I swapped the chunky green standoffs for skinnier black ones at the front to try and minimise the amount of the picture lost.

After this I started soldering it all together. The Kakute was mostly nice to work on - one slightly awkward part was the frontmost solder pads for the camera power and video in, which are under the ribbon cable to the IMU. I found the best way to get it out of the way was to push it backwards and tack it down with electrical tape until the soldering was done.

I soldered the Unify cable straight to VCC on the Kakute, having had no noise issues in the past running it straight off the battery. I also soldered a 5V pigtail to the board to power a race transponder if required. An XT60 on a pigtail was added for battery connection - whilst a lot of smaller 4s batteries use XT30 connectors, I was planning for 1000mAh packs and the affordable ones I found used XT60s.

In order to fit the ESCs on the arms I had to leave the motor wires a little long and coil it on top of the ESC. To help with the soldering the motors to the ESCs I taped the ESCs to my work mat in place of using a third hand. Once in place and soldered to the Kakute I covered the ESCs with electrical tape which also hides the extra wire. The receiver was cable tied to the inside of the top plate, and a cable routed through the stack to it from the flight controller.

Antennas were routed out on heatshrunk cable ties, and the Unify pigtail was cable tied to the rear standoffs, allowing for easy access to the flight stack after unplugging the receiver. There is enough free space behind the stack for an i-Laps race transponder.

Final build weight without battery comes in at 196g, and 320g with a 1000mAh pack - quite weighty for a 3"! Considering the HD recording and grunty motors though, it's more bearable. Initial flying impressions are good - it flies like a 5" quad, but every little gap looks so much more makeable. All in all, I'm really happy with how the build went and am looking forward to putting it through its paces on the track!

Flight video