Large Y-6 Copter Simulation Flies Poorly

Problem:
I am having trouble with larger Y-6 Copter not flying the same in RealFlight as it does in reality. I am using Arducopter sim as the controller, so my real model and RealFlight model should in theory fly the same. The RealFlight model is far more reactive and oscillates out of control very quickly, where the real craft is pretty stable.

** This is a cross post from the RealFlight forums since I believe it may also be an issue with my Arducopter simulation setup.

Request:
I am out of ideas of what to try, below is what I have done so far but am really struggling to understand what I might be missing. Any suggestions would be greatly appreciated.

What I have tried so far:

1. Validated the RPM/thrust curve of the RealFlight motor/prop combo against the motor manufacturer’s test data (see attached plot)

• This is what led me to choose the Invertix 400 propeller for the RealFlight model

2. Verified mass and CG in RealFlight are exactly the same as the real world model

• I measured the weight of the model and the CG and then modified the RealFlight model to be the same

3. Removed the additional aerodynamic effects in RealFlight

• I turned off prop wash and helical wash to see if they were causing any issues, but didn’t notice a difference

4. Reduced the output of the lower propellers on the model

• Y6 copters typically have a lower efficiency on their lower 3 motors due to the prop wash from the motors on top. I reduced their output to 80% which seemed to be the generally agreed upon value.

5. Tested the copter using RealFlight’s built in mixer

• I took Arducopter out of the loop and flew the model directly in RealFlight using the built-in hexa-copter mixer and the same tuning parameters from Arducopter. This worked surprisingly well, although it still doesn’t match reality- there is just less violent oscillation

6. Decreased the Servo Speed (increased the number of seconds) of the motors in RealFlight

• Since the motors and props are pretty large, I assumed maybe they are just being modeled as too reactive- but this didn’t have any significant effect.

Copter Specifications:

• 28x10 in propellers
• 100 KV Motors
• 12s2p Battery
• Total mass: 33.67 lbs (At some point an additional payload will be added, which is why this currently might seem overpowered for the weight)
  

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