Copter Tailsitters

Tanks to all for analizing.

Do you mean I should turn down?

No, already difficult enoughe to get it back. I think there was no time to let it to tune.

@kd0aij, Was always at 2700, will try higher. But in the Wiki the Range goes up to 72 000. ?
@Mallikarjun_SE, what is your Q_A_ACCEL_Y_MAX now?

A correction of the direction needs the full deflection of the stick and then it turns slowly.

In your comment I see, it should be solved by tuning and I will work on it.
But there is another effect which makes me doubtful.
In the log the Des.Yaw changes without command. Sometimes when the Pitch stick is released. I think then the controller will have to follow. Sometimes it changes during forward flight.

I will check the maximum for P,D,I (as used in the early days) in the rack by setting Roll and Pitch Params to Zero to avoid influences. Because of the good results in SITL I’ve been too lazy so far.
Will report the results.

Was helpful and “nescessary”, thank you.

@lorbass Try changing Q_TAILSIT_INPUT from 0 to 2 for MC style bodyframe roll. That mode treats yaw errors differently and should eliminate any drift in the desYaw setpoint.

Yes. Yaw is differential torque. You can listen to motors screaming during yaw.
Re Smooth transition, I just had to figure out right speed to transition back. I have had change in altitude during transition from high forward speeds.
I was wondering whether we can add some parameter to slow down aircraft to required airspeed before doing transition back. Or make q_assist to gradually decrease airspeed before completing transition back to hover(exactly like how it assists during transition, but to transition back).
@iampete @kd0aij what do you guys think?

Currently I’m at 45000. Yaw is good but not great.
FILTE and having D term helped me from having horrible yaw authority. I have 0.005 as D term I guess. I’ll share a log once I’m back at work.

I have a quite old branch that does this, it triggers the normal quadplane airspeed wait transition phase before going to the tailsitter angle transition. There is no way to do it using parameters alone. What modes was that back transition? I guess the thing to do is try some slow transmissions from min airspeed in FBWB to Qloiter, maybe try to Qhover as well. It looks like it transisions fine but then is trying very hard to stop the drift in the hover, it has to lean almost back the way it came to stop. I guess entering more slowly will help but maybe we could also relax the loiter controller abit so it is less aggressive.

Hey @iampete
I switched from FBWB to QHOVER. It’s pretty good at 14 to 15m/s speed. It’s not great at more or less speeds than this. Is there a way to merge the branch you mentioned about?

Just a interim report.

Exactly, that was it!!
I increased Q_A_RAT_YAW_P from 0.18 to 1.6, I from 0.018 to 1.0 and FF from 0 to 0.2.
No oscillations so far to see.
And it behaves on the line as usally in the rack with stick inputs. Escpecially P was much to low.
Now I will continue with other Params.

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During the Rack Tests I’ve seen, the Wing tend to roll with stick input Neutral. The Accel is calibrated in FBWA position. (Belly) But when in Tailsitter position, the Wing shows 4° roll. When adjusted with the param AHRS_TRIM_X then it shows a roll in FBWA Position. The same in Pitch which could be compensated by TRIM_PITCH_CD. But roll not leveled in “both” Mode has negativ effect. Either in Hover it drifts away or in Level flight it makes continuous turns.
Are there other Params than AHRS_TRIM_ … to adjust this diefference?

TANDEM WING Tailsitter Question- Hi all, I’m new to this thread and so excited to see @losawing flying his Black Fly(ish) Tandem. I see a lot of collaboration amougnst the forum participants to make it happen (very cool) Seeing the Full scale Black Fly at Oshkosh over the past 2 years inspired me to explore RC tandem wings. Here is a link to my version of a tandem wing tailsitter flying:

I’m a little embarrassed after seeing how well losawing’s Tandem flies, but here is some specs:
6 motors (4hover motors and 2 pushers used for forward flight… fwd flight wing motors shut down)
8 control surfaces - 4 on the front Canard wing, 2 on top wing, and 2 drag tip rudders.
Hover all 6 motors are running but only the 4 wings mounted motors provide stability control (2 pushers are just slaved to the throttle)
Hover yaw is from only from the outboard elevons on each wing. (in the video the winds were 16km with very good yaw control)
Forward Flight - Outboard elevons on each wing provide roll… Pitch utilizes and 4 control surfaces on the canard wing, and the top wing provide about 40% proportional pitch through the elevons.
Forward Flight Yaw is only through the drag tip rudders (very coordinated turns).

Construction: shaped foam board, hot glue, painter sticks and a few square carbon fiber tubes for the struts and landing legs. 48 Inch wing span (Canard wing has a 7inch cord and top wing has a 9inch cord… both wings would be close to a ClarkY airfoil.

I have a DX6 Tx and needed 14 outputs(8servos+6motors), so I slaved two KK2 boards together running openaero VTOL. The KK2 board is very easy to work with but is very limited when wanting to work with Mission Planner etc.

QUESTION(s): I have a Pixhawk 4 flight controller with the separate power distribution board witch integrates 8 Motor (io) outputs and 8 FMU/PWM outputs. I have some experience with Mission Planner and QGround, but I’m having a hard time understanding the mapping for the servos and motors. Does anyone in this thread have experience with Pixhawk 4 with the extended power distribution board and outputs?

The original documentation say I should load ArduPlane and activate setting for quad tailsitter. From what I can see in this thread… should I load ArduCopter and go tailsitter from there?

I originally has PX4 firmware loaded on the Pixhawk, switched to ArduPilot. Which firmware should I use/flash?

Sorry for the big info dump and multiple questions!
Any help would be appreciated.
Cheers

Tim
Cambridge Ontario Canada

There is a q_trim_pitch parameter that I never used. But nothing for roll.
I think AHRS_trim is populated by accelerometer level calibration and should be manually modified only if you are not happy of the plane attitude when flying level.
I never had a drift issue with any axis when hovering.
Are you sure your Tx send a PWM value within the dead zone?
Maybe make again TX calibration.
Do you have q_a_rat_rll_I high enough ?

hello tim,
Nice to hear a new tailsitter fan.
I do not have experience with pixhawk 4.
In the ardupilot world a Tailsitter is a specific quadplane and quadplane belongs to arduplane. So your documentation is right.
https://ardupilot.org/plane/docs/quadplane-support.html

Great… so the path I should follow is copter X tailsitter through the arduplane stream? I thought at the beginning of the thread one of ArduPilot developers was making the adjustments to your Tandem Wing through ArduCopter. Looking forward to see if I can mirror the results I had with the KK2’s and incorporate some automation.

I’ve never noticed the roll axis neutral changing between FW and VTOL modes. But the FW mode roll axis is bodyframe X and the multicopter mode roll axis is bodyframe Z. And I wouldn’t expect AHRS_TRIM_X to affect multicopter mode roll…
Do you still have Q_TAILSIT_INPUT=0 ? It would be interesting to see whether changing it to 2 has any effect on this.

Welcome Tim. Congratulations on making another multiwing tailsitter fly!
I’m not familiar with OpenAero; did you have to modify the code to support your configuration?
Was the motivation for the pusher motors to optimize efficiency in forward flight? What are the pitch speeds for the hover and pusher props?

I haven’t used the Holybro Pixhawk4 or PDB either. As Pierre says, you want to use ArduPlane and set the Q_ENABLE parameter to 1 to get quadplane features. We might need to add a new frame type to support your motor configuration though.

Hi Mark,
OpenAero worked without any mods… basically you have 5 inputs and 8 outputs. Any output would be mapped to servos or motors.
The intent for the pushers is battery efficiency, flight duration and speed. The ultimate goal was to use stabilization in hover, but have the ability to fly the plane in forward flight as a traditional airplane with the ability to glide under full control even if I loose the pusher motors… that’s why I didn’t want to rely on differential thrust in forward flight.
Pitch speed were very low… the hover motors will pitch the vehicle over immediately into forward flight and spool down over a 3sec transition. Because the wings are blown, it had very good slow flight characteristics. (3sec transition out and 2sec transition back).

I will work through the ArduPlane and Q_Enable setup. I’m just have to wrap my mind around the 8motor IO outputs on the power distribution board and the 8FMU/PWM outputs on the same board. Not sure if these are the same or if I can use all 8 motor outputs + 8 PWM outputs for the servos.

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Tanks for the info, this will help for Pitch.

Will checkt it next time.

Param I is at 0.8.
But Roll issue loacated. The FC was not fixed verry precise in longitudinal Axis (Z) which can’t be calibrated. And when in Tailsitter Position this means 4° Roll as level. And with this roll, it drifts away.
Now I will reassemble it precisely as possible (vibration damping) and if nescessary use adjusting screws :wink: I know, an old fashioned method beside the 1000 Params.

I noticed, that Roll and Pitch Integrator runs up, when Throttle is increased slowly and the wing not exacly leveled on the ground. Und then, when Throttle is high enoughe, it lifts of with a overreaction to level. I did not see this with my copters. The Integrator should start when Throttle is above Q_M_THST_HOVER only or another Param who define it is in the air. I try to show it in the graph. (Especially Pitch)

Hi Mark @kd0aij and Pierre @losawing
Hours and hours of research reveals that there are many Pixhawk 4 uses having many problems with Mission Planner and Qground.
Which flight controller would you guys recommend that would allow for 6 motors + at least 6 servos for control surface?. Which FC is in Pierre’s Black Fly?
Would love to hear your thoughts.
Tim

The standard Pixhawk hardware design provides 8 PWM outputs on the IO coprocessor plus 6 on the FMU. Those I’ve used include the original Pixhawk and the mRoX2.1 (both available from mRobotics)
https://ardupilot.org/plane/docs/common-autopilots.html
There’s also the “Cube” line of controllers, but I don’t have any of those.

If you are willing to use SBUS servos, or SBUS to PWM converters, you can also have that many outputs on a PixRacer…

From my side the biwing fly with a pixhawk lite


It has 8 main pwm output and 6 aux pwm output. I have 4 control surfaces assigned to servo 1-4 and 4 motors assigned to servo 5-8. I have never used aux output but I think they can be used for more control surfaces.