Tuning a large copter

Hi all,

I have a large octocopter (~10-15kg) built on the Tarot T18 frame. The first test flights were almost fine but there were some twitches in the roll angle, i.e. the copter suddenly flew a few meters to the side. An autotuning did not clear the problem. After changing parameters according to the tuning process instructions and another autotune, the copter finally crashed into a bank, maybe after another of those twitches. I could not prevent the crash as the copter did not react fast enough in the end. Now I am wondering how to safely tune the parameters of a large copter and which are good start values. I never had tuning issues with smaller copters.

The log files do not show any evidence of vibration. However, the desired and actual roll angles do not match at all. I uploaded the autotune logfile and the logfile where the copter crashed here.

I am grateful for any hint and advice.
Thank you.

When you performed the auto tune did you go right for a .1 aggressive setting? On all my large copters (hex and octo) I always tune one axis at a time to start. I also will start at .05. Then once pitch and roll are done, I repeat at .07. After those are done I will do pitch and roll together at .09 or .1

I feel that gives a much better result without all the violent twitching in the large copters during auto tune

Do you have a log file from your flight?

Thanks for your reply. I’ve gone directly for 0.1. But this should not have any effect on the copter’s response to remote control and general behaviour, should it?

I uploaded the logfiles, which you can find here.

@smartdave which are your default settings when you start tuning? I started with the ones mentioned in the Documentation. I don’t want to crash that copter again :wink:

I can post my config file this evening. You can grab all the pid settings to use as a start.

This would be great :slight_smile: