Y4 frames are noted for their quick yaw spins. The original Whyfor spun so fast that Betaflight threw the Runaway flag and crashed the copter to the ground. (Reminder: always turn off Runaway) The crash bent a front arm and cracked the lower rear arm - giving me an opportunity to design and build some 3D printed parts.

The original frame seemed to be severely underpowered, as the flight video was full of roll checks. I decided to upgrade the motors and props to improve the thrust to weight ratio.

Armattan Titan Mini 1407 motors with Lumenier 4x4x3 V2 props power the front. I was very impressed with the low amp usage and thrust of the Lumenier 3x4x3 V2 3" version of this prop, so I am hoping that the 4" version will have similar success. To get the CG in the right place and to make the front motors take more of the total weight, the arms were rotated backwards. Since I favor deadcat frames, this shouldn't be a big deal for me to fly.

A note about Armattan; they are the only supplier that I know of that sends their packages registered mail. For me, this means I have to wait for Saturday to drive across town aiming for a 1 hour window to pick up my packages. Buyer beware.

Since the length of the rear arms are not changing, the rear motors stay with a 11- series, but I switched from the previous battery-killing Emax 1106 7500kv to DYS BE1104 6500kv. The DYS motors have proven themselves to be strong performers with very efficient battery usage, especially when paired with the Racerstar 2435pro props. They also come with a decent length of cable so I don't have to make those ridiculous jumpers like with the previous motors.

The original build weighed 101 grams plus a 80 gram battery. The props put out an estimated 220 grams. The rear underside motor, since it is running in turbulent accelerated air, should only develop 80% thrust - for a total force of 886 grams. Dividing results in a T/W of 4.6. No wonder it was wobbling.

The new model weighs 117 grams plus an 80 gram battery. The front two props are expected to put out 460 grams each and the new rear motors and props should develop 240 grams each (again, the rear lower motor is 80%) - for a total force of 1352 grams. Our new T/W is 6.86 which isn't super exciting, but will get us out of the dangerous wobbly zone.

Overall, I would classify this as a "harder" build. The upper arm structure requires you to solder various bits together somewhat out of phase from what you would like to build. Removing the bottom front slide-on holes eased the build considerably since I could move the carbon half as one piece rather than the half-assembled-until-the-last-moment assembly that it was before. Also, the bottom rear prop forces you to turn the esc backwards. Not completely crazy, but you do have to switch motors 2 and 3 in your Resource list. Overall, you will need to have a bit more patience and plan things out a lot better than when assembling a normal quad build.

edit: The lower rear motor was coming down pistol hot on 3S. Perhaps 6500kv is too high for this build. I'll also look to remove Dynamic Filtering to see how that improves the cooling.

For the printers:
Taulman 910 nylon
.2 layer height
2 perimeters
3 top layers
3 bottom layers
15% gyroid infill