This is a rebuild of the existing XCLASS size quad. Here is a link to the original build: https://rotorbuilds.com/build/16529
Most of the electronics is being swapped out for an 8s setup and I will be also added a DJI FPV system too. I am happy with my original setup, but it really worries me to use a 55a 4 in 1 ESC with such a large motor (Brotherhobby Tornado T7 4215 Motor). Plus, the 520kv motor is under powered at 6S and I am curious to see what happens when I step it up to 8S.

The Build

To start off the build I will be using a Matek XCLASS PDB FCHUB 12S because of the 4 individual ESC. I could have kept the Radix FC because the Matek PDB also has a 5v BEC, but I really like the simple ribbon cable that connects the FC to the PDB. That is why I switched to a Matek F722-STD FC instad.
It seems like I need to do less soldering when I use the DJI FPV System. All I need to do is hook up one UART to the Crossfire RX and another UART to the DJI Air Unit. Then 5v from the FC for the RX and 12v from the PDB for the Air Unit.

As for mounting the ESC I chose to mount it on the arm because it was easy to work with. I was lucky enough that someone already created an iFlight SucceX X80A ESC holder, but it was meant to be mounted to a flat surface. I remixed the mount and added a round contour to fit a 21.5mm tube. Now the ESC will be zip tied to the inner edges of the arm. I am still wondering it I mounted the ESC on the wrong side of the arms. Would it be better on the inside or outside of the arms? I been looking at out people’s setup and they tend to have the ESC on the outside of the arms. Even with the 13” props the props would not hit the ESC because it is further down the arms. I hope the ESC placement is okay. I originally ran the motors wires on the inside of the arms to keep it protected and it worked well when I had the 4 in 1 ESC. But now, with the individual ESC it would be awkward to run it that way. If I ran the motors wires on the outside it would be a direct path to the ESC, but it will be more exposed to a prop strike or the elements. I hope the nylon breaded wire cover will help keep it protected.

I am still trying to figure out how I am going to mount the lipo batteries. There will be two 4s lipos for a combined total of 4s. I am planning to run four 4s 1500mah, to get a total of 3000mah 8s setup. I have the battery harness setup in serial to each side of the frame. They have a parallel adapter to run more than one lipo. I wanted to do it this way so I can use the same 1500mah 4s Lipos that I would use on my 5” quads. I did not want to buy a few sets of lipo dedicated for the quad.

Next up is how I plan to mount the DJI FPV AIR UNIT. Unlike the smaller quads, I have plenty of real estate to place it on the frame. I was not able to find something I want on thingiverse so I ended up creating my own by merging 2 different mounts together. I took the base of one DJI Air Unit and added a antenna mount from another.

First Test Flight - May 8th 2020

Unfortunately, the first test flight with 8s did not end well today. ESC #1 died midflight. Check out the black box video below, I was not doing anything crazy either. I even followed the ESC setup instructions that iFlight included.

Brake On Stop - Off;
Motor Timing - Auto

I might have considered that one bad ESC could be a fluke. But that was the third one that died. I thought the first 2 died because of ID10T error, but after doubled checking my wiring and soldering I did not find anything wrong. The first 2 ESC that died was Motor #4 and it was still on the bench. One was after a few power tests and betaflight firmware update. When I went into BLHeli32 suite to setup the esc, Motors 4 will not show up. I switched the ESC out for a new one and did one test hove. The next time I powered it up, ESC #4 was not responding.

Before the first flight I did a few slow flights around the park to make sure the ESC and motors where not running hot. The next day I only started to push it a little more because of the new PIDs I just used where feeling good.

I am using Betaflight version 3.5.7 with an old tune that I got from Sergi Ros on a X Class Drone Facebook group:

P I D
90 65 35
85 60 30
85 75 0

Feedforward:
Roll - 100
Pitch - 100
Yaw - 110

TPA: 1700

Gyro Lowpass 1: 40
Gyro Lowpass 1 Filter Type: BIGQUAD
D Term Lowpass 1: 40
D Term Lowpass 1 Filter Type: BIGQUAD
Yaw Lowpass: 40

It’s Now 12s Capable - May 23th 2020
The iFlight SucceX X80A 2-8S X-Class ESC were a major failure! Long story short, I lost 2 ESC on the bench and a third one during the first test flight. I broke down and bought the APD 80a F-Series 80F3 8s 34v ESC but the very next day I found someone selling a set of APD 120a F-Series 120F3 12s 50v ESC with APD 500a PDB500 12s 52v PDB. I end up returning the 80a esc and got the used APD 120a instead.

3D Printed Battery Tray - June 1st 2020
I designed and 3d printed a battery tray for the four CNHL 4s 1400mah lipos. I did not want to get a set of lipos just for the XCLASS, so now I can share the same lipos I would normally use with a 5" quad.

Here is a video of my first full pack with the APD 120a ESC. I am still kind of scared of it dying like with the iFlight ESC, so I am still babying my throttle.