Dual-motor tailsitters

Development Team
551
  1. This is not the right place for “Tail” Plane questions.
    And for 2 Motor Tailsitter (VTOL) the Servos are on CH 1 and 2, the motors on Ch 5 and 6.
    For 2 Motors vectored Tailsitters the Motor Tilt Servos on Ch 3 and 4
    Here:
    SERVO1_FUNCTION=77, Left Elevon Output 1
    SERVO2_FUNCTION=78 , Right Elevon Output 2
    SERVO3_FUNCTION=75, Left Tilt Servo, Output 3
    SERVO3_MAX = 2070 , 90° up
    SERBO3_MIN = 900 , 90 °down
    SERVO4_FUNCTION=76 , Right Tilt Servo,Output 4
    SERVO4_MAX = 2100 , 90° up
    SERVO4_MIN = 900 , 90 °down
    SERVO5_FUNCTION=73 , Left Motor Output 5
    SERVO6_FUNCTION=74 ,Right Motor Output 6

  1. Yes, on the Servo Rail is no Power (5 Volt)

  2. With safety Switch enabled, the Servos are moving only if the Safety switch is On.

552

hi everyone, plane 3.8.0 is out, with dual-motor tailsitter support. I’ve like to offer a huge thank you to everyone in this forum for helping with the testing of this release!
This is more coming on the tailsitter front, with pending patches from @kd0aij and @priseborough that will take it to the next level, but I’m delighted that we’ve got a release out with support for these aircraft!

553

Versa Tailsitter on Plane 3.8.0

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Airframe is based on FliteTest Versa, this is maiden flight, flight mode was Q_HOVER. After some basic attitude respon test, the plane suddenly pitch up and go backward. I used the new Plane 3.8.0, log file will be uploaded soon.
Tomorrow I will test it again, and hopefully I can test the transition and FBWA mode (if the pitch up problem is solved)

I think this is a very good result for a maiden flight (using only the default tailsitter param setting, no tuning yet)
Thank you for all the developers and contributors!

554

not bad at all for a first flight!

hopefully the log will help us solve the pitch issue. Pitch is usually the most difficult axis for tailsitters like this.

555

Yes, that was the reason why I changed to the vectored Tailsitter.
After changing the Props from 9 to 10 inch it needs more tuning
of Roll and/or Yaw?
Log
https://drive.google.com/file/d/0Bxldq38bfbqHVnJScVNERFNTYmc/view?usp=sharing
Video

1 Like
556

Versa Tailsitter on Plane 3.8.0, pitch up on hover mode

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here is the video:

(total 4 video)

and dataflash log:


and for the maiden hover flight (photo and video on my previous reply), here is the log file:

I mount the servos on opposite direction, so for elevator action, both servo pwm output is inverted to one another, and for aileron action, the pwm output is on the same direction

Overall, it fly really good, but sometimes on hover mode, it pitch up uncontrollably (the pitch is uncontrollable, but roll and yaw is ok), luckily the pilot (my friend, not me) is skilled enough to roll the plane and switch to FBWA. At first glance, I think it is caused by wind, but after multiple occurrence on a variety of bearing angle, I’m fairly sure wind is not the cause.

I think it is caused by the thrust line. Because my motor is located under the center of mass of the plane, so it create a pitch up moment. On FBWA, I think this pitch up moment is countered by the elevons and other aerodynamic forces, but on Q_HOVER, I think the forces from the elevons is not strong enough (on the video and log, we can see the elevon is really trying to pitch down).

Based on that reasoning, I think the solution is either move the motor up or tilt it down so the thrust line is coincided with the center of mass.

Is there another solution? or is there another analysis? (can I solve it by increasing the pid value on pitch axis?)
Thanks for the help!

557

@Wisnufireball: interesting video and interesting contribution

@Tridge:

We tried for the first time a transition and were surprised,
that the vectored tailsitter tilts backwards.

Logfile: https://www.magentacloud.de/share/hetje-ou0p

Another question:
Are the Q_A_RAT_PIT / RLL / YAW axes seen from aircraft view, regardless of whether Q_TAILSIT_INPUT = 0 or 1?

Regards Rolf

558

the reason it went backwards is that it was already pitched back by 20 degrees when the transition started. The controller was already trying as hard as it could to hold the nose straight up, but it was failing to do so. So it couldn’t pitch forward, as it didn’t have enough pitch authority in that direction.
It needs more pitch authority, either with larger Q_A_RAT_PIT_* values, or with larger Q_TAILSIT_VHGAIN.
I notice that Q_TAILSIT_VHGAIN is only 0.1, which means it is mostly using the elevons for pitch control. Did you try larger values?

559

@wisnufireball

Nice Frame and it behaves verry stable.
Can you poste more details about the frame( Weight, Motors, Prop)?

By the way, .bin Files are needet to help, see below.

Rat an Wisnu.jpg1240×687 36.2 KB

Regards Otto

560

Yes, we come down from 0.8 for Q_TAILSIT_VHGAIN. With such a high value, the plane had fidged and rocked terribly despite far down-regulated Q_A_RAT _ *** _ * Gains. 0.1 is certainly too low. We will try with 0.3 and then optimize the individual PID values for each axis.

The names of the Q_A_RAT_ axes refer to the earthframe or copterframe ?

Rolf

561

@lorbass
Thank you

Here is the propulsion system specification:

Weight : 915gram (with battery)
Motor : KDA 2022L https://www.tokopedia.com/robotronix/motor-brushless-kda-20-20l-1050kv-outrunner
Prop : Gemfan 10x45
ESC : Maytech 20A https://www.alibaba.com/product-detail/Maytech-RC-model-aircraft-ESC-20A_60096253490.html
Battery : Lipo 3S1P 2200mah 25C
Servo : Towerpro MG92B

Full static thrust is 800gram per rotor.

I’m sorry for the log file, I thought .log is the same with .bin, here is the bin file:

Maiden flight
https://drive.google.com/file/d/0B3BWCAEF49bWempEVWkwcWZDbzQ/view?usp=sharing

Wingborne flight
https://drive.google.com/file/d/0B3BWCAEF49bWNWFyeFNYTWt2YVE/view?usp=sharing Center of Mass 1cm behind normal
https://drive.google.com/file/d/0B3BWCAEF49bWajhXdklpZ0lRZ2c/view?usp=sharing CoM 3cm behind normal

I moved the center of mass backward (hopefully to increase the pitch stability on hover mode), but the pitch up event is still happening.

Thanks for the help!

562

right, changing Q_TAILSIT_INPUT doesn’t change the meaning of the PIDs, only of pilot input

563

Thanks for the data.
Nearly the same setup as my Caipirinha.
I had the same effect as Tailsitter (non vectored)


After 3 crashes I changed therefore to the vectored Tailsitter because
I suspected that the effect of the small elevons can not enoughe compensate the pitch.
Especially when descend.
Now the result is good and the frustration gone.


And the log: https://drive.google.com/file/d/0Bxldq38bfbqHMDdtSGhkcWpmd3c/view?usp=sharing
564

looks good!
have you tried a transition to FBWA ?

565

the values of those parameters always refer to the “bi-copter” orientation. So roll is differential thrust on the motors, and yaw is opposite tilting of the motors, to yaw in earth frame.

566

Not yet, but “I’m afraid” this will be soon.:grinning:

This time, I’ve tested succesful Mode QLOITER.
And the tuning of the Elevon (Midposition) made that it do no longer turn during
“Standup” from Belly to Sit.

But as you can see between Min.4 and 5 still oscillating but stops itself.
I would appriciate if you could analise the Log. I’m not shure, if to tune Yaw or Roll.
The video shows oscillating Yaw, but the Log Roll
Thanks for helping
Otto
https://drive.google.com/file/d/0Bxldq38bfbqHU3Bmb3NLZVNrWDQ/view?usp=sharing

2 Likes
567

Hi, Tridge, a tuning question,in stabilize mode when I move the control stick very slightly in pitch or yaw the serfaces are moving very quickly and more than they should then they settle to a more proportional position,can I tune that behavior out, if so how? also tryed to download latest and got a printout of the code not the usual download, and in mission planner when you go to download the links go away? Thanks Rick

568

I’m trying to build my first VTOL plane with a delta wing with non vectored motors.
I have a weird problem with 3.8 firmware.
One of the motors move a little when the system is powered but not armed.
The two esc with BlHeli have the same config and calibration 1000-2000 ms.
Motors are on servo Output 1 and 2.

In FBWA mode the two motors start always together while in Qhover or Qstabilize one of the motors, the right , start to turn when the left one has already started .
Sometimes a lot, 200ms later, sometimes it start almost at the same time .
Then it seems that the right motor push quite a lot less.
Other times the “lazy” right motor do not start at all, but if I change to FBWA mode it start immediately, run smoothly and push the same .

My maiden flight in Qstabilize ended with a crash in a tree, the plane was very difficult to control .

569

The motors should be connected to output 5 and 6. Output 1 and 2 are for the elevons.
How to do is described in earlier posts.

In QSTABILIZE or QHOVER my motors do not start always a the verry same time. Just a little bit
different. May be it depends how the wing ist lying on the ground.

The center of gravity must be exacly in the center view from the side when sitting on the back.
The elevons should be larger than with a standard Nuri.

For a small wing the default Params for Q_A_RAT_P … I…D are to high and therefor the wing
makes strange wobbels.

Here my newest Video about the tuning of the Pitch.

or other tryels and errors.



Need more wihtstand than other “toys”:grin:
My first 6 flights ended as crash.
I didn’t dare to use FBWA mode. I wanted to be sure, that in case of trouble I can sucesfull switch back to QSTABILIZE
Good luck
Otto

570

Thanks Otto for suggestions,
My wing is 130 cm wide.

I tried also with motors in 5 & 6 output and elevons in 1 & 2 with exactly same result, so I do not know is it an hardware error of my Pixhawk but I think it might be more a software/config error since in FBWA the motors are perfect.

In Qhover the motors start to really push the plane up when throttle is much above 50% , perhaps 75% and then it accellerate very fast.
Do not think it can be possible to fly for me in Qhover .

In Qstabilized the elevons position is not neutral for both , one is quite a bit off while in Qhover they are much more similar.

Is a GPS mandatory as I read in Quadplane docs ?
I do not have one mounted and disable it since when vertical position the Gps would not get a good signal but only reflections .

Tomorrow I will change the Esc and the flight controller and I’ll try again.

BTW Otto, finally how did you solve vibration loop when in vertical position ?
I already have digital servo but especially in Qhover that vibration loop due to servo movement are terrible, in FBWA they disappear.