QuadPlane Pitches Up using v3.8.0 beta 5

That’s so far 2 for 2 that we have seen the Ranger working flawlessly but happens to be on PX4. Therefore, I would venture to say, the issue may not be completely structurally related but somewhere in the settings. Have you tried going back and testing without an airspeed sensor? I recall one of your initial FW tests without the sensor worked well and didn’t create the “pitch-up” issue. Just curious.

Alex,

Yes, you are correct. In the first flight of my latest video above, the plane worked well without the AS sensor (because it was covered) but it also had the fishing line band-aid. Without it, there were loss of control issues as seen in my previous videos.

My next test will likely be as a normal wing APM plane. This worked well and I want to repeat it as I have two wing sets for my Ranger EX. I’m still contemplating this issue as I work on my mini Talon conversion. I feel that maybe my current PID settings for hover may be causing a startup issue that causes the see-saw effect. There may also be an issue with my Q_M_SPIN_ARMED setting of 0 (no spin) as compared to a slight spin setting. Looking at the current graphs above, when FBWA initializes, the current drops to near 0. Could this be stop/starting my ESCs?

Actually you mentioning the “see-saw effect” just reminded me of a test I made using your PID’s at one point. I also did get a “rocking” effect as well during hover. However, in your latest videos I didn’t see any issues during your hover.

By the way, the initial flight I was referring to was this one below. It felt you were able to manage a “successful” fw flight for some time before the crash.

Alex,

The issue is caused by the hover motors re-starting up in FBWA mode, not the initial transition from QSTABILIZE to FWBA. QSTABILIZE mode is fine because once the motors start, they stay on…even when tumbling.

The various effects you see are with and without an AS sensor which kicks in (and out) the hover motors more accurately in sync with the true airspeed and GPS ground speed differential. Without an AS sensor, the Q_ASSIST_SPEED trigger can only go on GPS ground speed.

In summary, my PIDs were adjusted for a good hover response. When starting from the ground, the plane is stabilized by the wheels. In flight, however, the hover motor re-start is an issue.

@GregCovey, sorry for weighing into this discussion so late. Just thought I’d mention that the first 3.6.0 log you posted (59.BIN) also showed a large pitch up in FBWA twice. It went to 35 degrees up the first time, and 61 degrees up the 2nd. It didn’t go as far up as the other logs, but the problem is definitely there.
One possible clue to the difference in extent of the pitch-up is that you had THR_MAX at 75 in the 3.6.0 flights (which was the default in versions prior to 3.8) but THR_MAX at 100 in 3.8. The faster transition due to higher fwd throttle may be a contributing factor.

@GregCovey have you tried setting up this quadplane as an H frame? You’re clearly getting a lot of wing twist, and the frame is laid out as an H, not an X, but it is configured as an X. The difference between X and H is the direction of the twist the motors impart to the frame.
I think you should try Q_FRAME_TYPE=3 and reversing the vertical motors (thus making it a H frame).

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Hi Tridge,

Thanks for visiting! I like your suggestion and will give it a try. Also, nice catch on the THR_MAX default setting. If I had one last question to ask, it would be what you thought the best setting is for Q_MOT_SPIN_ARMED on a QuadPlane?

Cheers!

I just use the minimum setting that keeps the motors spinning without and hiccups.

that depends on the individual hardware. You want it to be a level that causes the motors to reliably spin, but not so fast that it would hurt someone if their hand got in the way. I usually adjust it up and down until I’m happy with it based on that criteria.

Ok, thanks guys, I’ll change my setting from 0 to a slow spin when armed.

When I built this QuadPlane, I used the HK 3.5mm bullet connectors so it was an easy change from X-frame to H-frame buy swapping one of the connectors 180 degrees to swap the two outer wires. The props were then changed front-to-back and back-to-front. I then changed the Q_FRAME_TYPE from 1 to 3.

I didn’t have much time to test yesterday but in QSTABILIZE I could bring the tail up and move the plane properly forward, backward, left, and right with the transmitter stick. As soon as I lifted the gear mains off the ground, the plane would spin clockwise (when viewed from above) about 90 degrees per second. I’m not sure if I need to change PIDs or reverse the rudder control on APM.

That usually means Q_FRAME_TYPE is wrong. It is exactly the effect you get when you try to fly X as H or H as X
Double check your settings, and try using motortest to check the direction of each motor

Tridge,

Thanks for the suggestions. I’ll give it another look soon…

I found the issue was that my front right boom had broken again after landing in the tall bushes. It was originally broken on my first crash a few videos ago. The Q_FRAME_TYPE is 3 (still v3.6.0) and motor test worked perfectly using 7% throttle. The Ranger EX hovers perfectly as an H-frame in my backyard.

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That’s awesome Greg. Any videos yet on forward flight attempts?

I may get to test it on Sunday as the weather seems reasonable. I won’t go back to the tall bush area as the rain this summer has created monster weeds!

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Awesome! Good luck this round. I’m confident you’ll have a successful flight this round.

Congratulations :grinning:

Sometimes the dumbest thing in front of our eyes drives us crazy.

This is where experience and good work are noted.

Now version 3.8.0 is just coming out of the oven :stuck_out_tongue_winking_eye:

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Today the larger fields were busy so I could only test QSTABILZE mode at a smaller school field. The hover testing worked fine with my new H-frame setup but there was an issue with MANUAL mode. The video shows two of the quad rotors turning in MANUAL mode that also increased with throttle.

Since I won’t be able to test again until Labor Day Weekend (2 weeks), my plan is to upgrade from v3.6.0 to the newly released v3.8.0 by first loading Rover firmware so I get a clean parameter list. I will then manually enter my critical parameters from v3.6.0 by hand using Mission Planner and post the file here for review. I will also re-test MANUAL mode to see if the quad rotor issue was resolved. Comments welcome…

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Hi Greg

Just a note about resetting the parameters. I previously always reset the parameters as you commented but… One day configuring the mutirotor, I loaded the arduplane version to later put the arducopter version again and… disaster… First, never set up with the propellers on… It took off with such bad luck that it was towards me, hitting me. A little pain and a broken carbon fiber propeller. I was lucky :slightly_smiling_face:

I comment on the forum and the teachers that we have here told me the correct way to reset the parameters without doing anything weird. :upside_down_face:

Now looking exactly as it is done I found that they have already posted it on the wiki, Thank you so much guys
:kissing_heart:

Ardupilot Parameter Reset

It is much safer and out of trouble :rofl: