Pitch Wobble - Autotune Didn't Fix

ArduPlane Plane 4.0
1

I’m new to fixed wings. I’ve built a Dart 250g and I have run AutoTune a few times, but I still seem to get sluggish response and wobbles when I pitch up. Can someone help me troubleshoot this?

here is a log of one of my AutoTune sessions: https://drive.google.com/file/d/1rv3EId2Ljbupn2N8Syq3iY7QgYxaVI7I/view?usp=sharing

Details that might be relevant:

  • I have set the cg so that the wings are level when I hold the cg points on my fingers.
  • I’m running DJI and I’m using a 3S 18650 pack, so it’s pretty heavy.
2

You may need to manually tune the plane if the C of G is correct.

What mode are you flying in? FBWA, even after autotune, is pretty conservative unless you get into the tuning. Have you flown it in manual mode?

The google drive link is password protected. You’ll need to unlock it so it can be downloaded.

3

I’m flying in FBWA mode. I haven’t had the courage to fly it in manual mode yet. The wobbles are what concern me, I’m afraid that if it wobbled like that in manual mode it might become difficult to control. I fly quadcopters in Acro mode all the time, but fixed wing is a bit more intimidating!

Thanks for letting me know about the link. I just changed the setting, so it should work for anyone with a link now.

https://drive.google.com/file/d/1rv3EId2Ljbupn2N8Syq3iY7QgYxaVI7I/view?usp=sharing

4

I totally understand the feeling about switching to manual mode, but it will help to tell you what’s going on. If you switch to manual and the wobble goes away you know you’re dealing with a tuning issue. If the wobble continues or get’s worse then it’s an aerodynamic or C of G issue and you should land and and fix that right away. You don’t need to stay in manual for long, you’ll know the answer pretty quick. The old rule for RC flyers was “start 3 mistakes high”. Give yourself lots of room, and don’t be afraid to switch it back to FBWA.

I do think your plane is on the heavy side. I noticed the throttle is over 65% for much of the tuning. It may help to reduce the weight if you can.

Verify the C of G. I don’t know the Dart-250, but Andrew Newton or Painless360 have a bunch of videos about them. What do they set the C of G at? Many manufactures will set the C of G a little too far forward to be safe.

I’m starting to form the opinion that ArduPlane sets the D term too high for wings. I noticed there is D term pitch oscillation in your logs. If you get the auto tune to a more satisfying place it might not hurt to reduce the D term by ⅓ to ½ depending on how much it’s oscillating. Also make sure you tune it while it’s glassy calm wind. Especially on a smaller plane like the dart if there’s any wind acting on it while it’s tuning that could mess things up.

5

I took it for another flight today. I flew a bit in FBWA to get comfortable. Then when I was about to switch to manual mode, I crashed into a parking lot. I’m not 100% sure what happened, but I think I stalled while turning and I could not recover. Of course I got the chip full warning a few moments before the crash, so I’ll never know, haha. I’m currently gluing it back together and will hopefully get another chance to fly this weekend.

6

Aw man, that sucks. FBWA will usually protect you from stalls, but physics will always beat the flight controller if you hit the limits. Too bad there’s no log.

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