Is autotune really working with really large multi's?

Log Analysis -- deprecated Copter Logs -- deprecated
1

Did an autotune on a 1300mm X8 with 28" props, U8 motors and an all up weight of 18kg. Flight characteristics could be described as choppy and uncoordinated. Funny thing when looking at the desired pitch and roll vs recorded, some places it follows and other areas it’s opposite. BTW, this is using a Pixhawk. Noticed something else odd, when flying forward it drops altitude. In mission planner it shows now change in altitude, but it’s obviously dropping. Anyhow, more concerned about the opposite graphing of the pitch and roll axis. Oh, I had to zip the log (.bin) for to upload as it was 2.4mb. Or is it better to leave a link on dropbox?

Thanks for looking!

2

Your X8 is underpowered, it hovers at > 70% throttle. So when you’re pitching fwd it is struggling to accelerate and at the same keep the altitude.

For desired vs measured roll and pitch, try to redo another auto-tune until you’re satisfied. or play with PIDs yourself using one of the pots in ch6

3

Wondering if there’s something up with the motors. According to Tmotor, the U8pro on 6s and a 28X9 prop should be arount 58% throttle at hover with a maximum thrust of 36.72kg (using 8 motors). So either they’re fudging their performance numbers or this X8 configuration is losing a lot of efficiency.

4

Using eCalc I got 62% @hover with AUW of 18Kg and max 24.4 Kg with high risk of overheat.

So yeah, although t-motor is my best motor brand, specs might be overstated
I prefer verify the Amps and KV myself.

5

I think I’ll have to rethink the power system. This payload is actually 2kg under what I really need to carry. May have to switch to KDE7215XF-135 motors and 4 6s22ah pack, two series and then wired parallel for a 12s supply. 12s is a pain in the butt lol! At least I can keep the same propellers lol!