I learned to fly quads with the Hubsan H107L and when I heard about the H107D I thought it was the best thing in the world. A tiny micro with a camera that transmitted video. Amazing, at that time I hadn't seen anything like it and I had to have it. Many crashes later I am building my own quads and have a fleet of brushless craft but I wanted to go back to where is started.
H107D-hack was born. The body of an H107D plus the best brushed motors I could fit and it had to have a proper betaflight setup and of course a camera and VTX with OSD!

Now, there isn't much space inside an H107D so some small sacrifices were made but relatively few. I sourced a tiny brushed F3 board with onboard frsky RX and after shaving some weight off the bottom of the internal battery tray I was able to slide the FC under the battery tray and leave it with the micro-USB plug accessible from the rear without needing to open the frame. The entire FC+RX fits into the space that was used for the hubsan VTX!
Likewise, to fit the camera required a little shaving of the internals but with some patient work it fitted.

Then the maiden. Sadness. Frame seems so flexible that uncontrolled oscillations make FPV impossible. I try to tune, to filter, to do anything but nothing works. I started on Betaflight 3.2, then try 3.5 then in desparation try the cut-down 4.0.6 release even though the F3 has lost many features. Nothing works. Just oscillations all the time.

I shelved the project with a sigh and went back to making brushless models for a while. After learning how to use RPM filter and JESC I noticed the Betaflight "F3 Performance Edition" which is used to enable RPM filter for older F3 FCs. Interesting I thought, didn't really think much of it. Then I thought "what about the H107D-hack?". Sure enough after loading the performance edition of 4.1.1 for F3 I was able to tame the oscillations. Whatever dynamic notch magic was included is exactly what this little quad needs!