Throttle oscillation in mission modes

Anton_Rothwell 2017-04-24 10:50:39 UTC #1

I am trying to tune an aircraft for flying accurately to airspeed in mission mode. It's ok for altitude control to be compromised to some extent. Increasing the SRATE parameter allows for accurate speed control, however, it introduces oscilations in throttle (often amplitude can be from 0% to cruise throttle%). Reducing cruise throttle % alleviates this to an extent, but it's still not great.

What is the best way to dampen and eliminate (or at least drastically reduce) these throttle oscilations but maintain accurate speed control?

dagar 2017-05-15 13:14:48 UTC #2

Which version of PX4? We only recently found a bug in TECS where the height rate feed forward was being ignored.

We could definitely use documentation for TECS tuning.

Anton_Rothwell 2017-05-17 07:53:04 UTC #3

Hi Daniel,

I noticed the fix for the Height FF and merged this into my codebase a while ago, but it's yet to be tested (it's an older codebase based around 1.3.1). The Height FF is 0 anyway so have not noticed any problems related to that. What sort of values would you recommend for the FF - do you think it would reduce the throttle oscillation? Our test flights tend to be fixed height missions, I think it's fair to the oscillation is noticed more on windier days but can't be absolutely certain of that.

dagar 2017-05-17 13:11:32 UTC #4

Hard to say without going over logs, but I would start the feed forward at the default value (0.8), then you should be able to decrease SRATE.

Anton_Rothwell 2017-05-25 11:26:39 UTC #5

Thanks. We've tested this now and values between 0.5 and 0.8 work well. Height tracking is good and throttle oscilations seem reduced.

garlinplus 2017-05-25 13:10:48 UTC #6

dagar,today I find some problems in tecs.cpp.
I have submit issues in github,you can refer it.
Maybe I'm careless.