Intro

So after smashing my old 4" into a tree I rebuild it with a new frame.

Karl just got the design of his new 4" frame ready, the 40r, so I ordered, with a 850 4s, a pre-production frame for testing (final version is the same however).

I am super satisfied with it - flies great on stock pids and 3.5-4 min of ripping on 850mah 4s.

Very agile, fast and sturdy. It's 166g dry (without battery) so with a 850 4s it has a power to weight ratio of about 15:1 :D

With a 650mah 4s it clocks in at 246g making it sub 250g.

Video

Changes compared to my old br3 build

Please refer to my BR3 - 4" Splitmini Beast if you are interest in more details.

I used most of my old parts, as only the frame broke, however I did change this:

Used a HGLRC Elf camera (rebranded microswift with some slight changes that came with my f428 stack) instead of the split - I'll probably swap it for a predator 3 soon.

Wired up the cam to the LED pad and remapped it in order to be able to change cam settings via OSD (awesome btw, i'll add that to all my builds now).

Wired up the tx20 for smartaudio control

Used soft mount m2 standoffs instead of the steel screw with tpu printed slide on spacers.

Build & Challenges

I initially had the camera control ground wired to the fc - this caused lots of noise and some ground loop I believe. Wiring it to the same ground as the camera got rid of that.

Camera control only required a 220 Ohm Resistor resistor wired inline to the LED pad to make it work.

Apart from that I only had to resolder the rear motors from the underside to make clearing the rear standoffs easier.

They can work from the top too but you have to solder them at an proper 90° angle then.

Canopy

Printing the canopy will be stronger if done vertically but then you get an ugly front. Printing horizontally will need lots of support.

I'll probably reprint it at some point to look nicer but its ok for now.

The tubes are only held by friction but did not came loose yet, I may glue them in just in case.

I have no idea where I got the tubes from - they were in my stash of antennas :)

Tuning

Stock Betaflight 4.0 PIDs and filters worked really well. All I had todo was increase motor idle a few points to get rid of deathrolls when rolling.