Hey all, hope everyone’s doing well!
I’m setting up a large-ish (25kg) hexacopter and need the community’s input and assistance to get this tuned and flying autonomous missions. This is the first time I’m setting up a multirotor this big, I’ve previously setup a 7.5kg 850mm build with 22" props, and multiple smaller ones so I’m familiar with the basic process.
I’m facing some issues with attitude control particularly a wobbly position hold (PosHold, not Loiter) and would appreciate a review of the setup so far and inputs on how to proceed towards an Autotune.
Size: 1600mm motor to motor
Airframe mass (no payload, no batteries): 9kg
Batteries, 4x Tattu 6S 22Ah: 4x2.5 = 10kg
Empty mass (airframe + batteries): 19 kg
Takeoff masses tested:
2.28kg payload: 21.28kg
5kg payload: 24kg
Motor: T-Motor U8XL 110kv OEM
ESC: T-Motor Flame 60A HV
Propeller: T-Motor 30X10.5
Battery setup: 12S2P 44Ah (4x Tattu 6S 22Ah)
Flight controller: Cube Orange, soft-mounted with the blue rubber dampers
Rangefinder: Lightware LW20C on I2C
I setup the initial parameters for the battery, motor and PID controller following the Initial parameters.xlsx
Setup min and max PWM outputs to 1100us & 1940us for the T-Motor Flame ESCs
Setup MOT_THST_EXPO = 0.2 for the Flames
Parameter file before calibration, with values from Initial parameters.xlsx:
M1500 Initial Params Pre Cal Pre Tune.param (18.4 KB)
Performed sensor and radio calibrations.
After verifying motor & propeller directions, proceeded to fly.
Initially the flight controller was hard-mounted. After looking at the vibes, soft-mounted the flight controller and noticed a reduction in vibes, and that’s how it’s mounted currently.
Flight Notes - 08 Sep 2021
All logs available here.
Flight specific logs are linked below.
01 - Zero payload flights
- Windy, ~3m/s gusting to 6m/s
- Stabilize & AltHold working as expected, felt okay, however could feel the aircraft getting unsettled with gusts.
- Altitude hold is good.
- Attitude overshoot visible in logs
- PosHold was very wobbly, with oscillations on gusts, possibly because of the low hover throttle?
- I noticed MOT_THST_HOVER was not updating, maybe because CTUN.ThO did not go higher?
02 - Added payload of 2.28kg
- Did not notice a significant improvement.
- Hover throttle increased slightly
- Decided to proceed with setting up the Harmonic Notch filter
03 - FFT Flight - Pre filter setup
Harmonic notch filter settings from FFT
- Frequency: 36 Hz (72 Hz had a higher amplitude but selected 36 Hz)
- Bandwidth: 18
- INS_HNTCH_REF: 0.264 (I used the average value of CTUN.ThO since MOT_THST_HOVER was not updating)
04 - FFT Flight - Post filter setup
Left - before, Right - After
Issues & probable causes
Overshoot in roll & pitch
Wobbly/oscillating PosHold, especially with gusts
MOT_THST_HOVER won’t update
I’d guess most of the issues are due to the low hover throttle.
Does the overshoot indicate overpowered copter?
Thank you for making it through that wall of information, appreciate your help and looking forward to suggestions.