Copter Tailsitters

I tested also Q_frame_type=0 and it works again perfect. Q_tailsit_motmx was set to 15 and I cant see any difference in FW flight nor with transitions. I pushed manually the wing to yaw it while hovering and I can hear the Differential torque working. Great…
I begun the construction of my tandem wing, already 2 foam core cut.


Great! Thanks for testing both the PID updates and differential torque.
Does differential torque provide much additional yaw authority in hover?

You may want to retune your feedforward gains with the PID updates and try playing with the new filter parameters. There are now 3 filters per axis, target, error and derivative:

I haven’t seen any documentation or discussion on setting the new parameters, but here is what I had in my last Stryker_quad SITL run:

Q_A_RAT_PIT_FF   0.100000
Q_A_RAT_PIT_FLTD 10.000000
Q_A_RAT_PIT_FLTE 0.000000
Q_A_RAT_PIT_FLTT 20.000000

Q_A_RAT_RLL_FF   0.000000
Q_A_RAT_RLL_FLTD 10.000000
Q_A_RAT_RLL_FLTE 0.000000
Q_A_RAT_RLL_FLTT 20.000000

Q_A_RAT_YAW_FF   0.200000
Q_A_RAT_YAW_FLTD 10.000000
Q_A_RAT_YAW_FLTE 1.000000
Q_A_RAT_YAW_FLTT 20.000000

One flight this morning with above parameters. Yaw is stable even at the max descend rate which is 250cm/s and that’s already impressive. But there were almost no wind this morning and the comparison with previous flight is not easy. I will play with FLT parameters next coming days to make my mind.
When I manually push the hovering wing CW or CCW, yaw authority is less when the perturbation is CW (view from above), this is because there are no control surfaces behind top and bottom motors. I expect the quad X configuration to have better yaw authority.

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Hi everyone,
I have read +1800 post in Dual-motor tailsitter topic and then I came this topic. Your works are so great that’s why I’ m very excited about it. I just made a quad + tailsitter. I’ m curious about When will the codes for copter-tailsitter release for Beta version?
This is my ugly baby :joy:

wingspan= 170 cm
cord = 40 cm
wingarea= 55 dm2
weight: 2750 gr ( no battery )
Ready to Fly :yum:


@mono Thanks for posting, that looks like an interesting airframe.
Copter tailsitter support is already in master, only the PR to add the gain scaling options has yet to be merged. The gain scaling isn’t necessary for slow flight in VTOL modes though, so you should be fine using master until you want to try going fast.

I’ll post here when that PR is merged, in the meantime you can use the custom binaries here:
if you’d like to help with flight testing.

2 photos of my copter X tailsitter in progress. I changed a little my mind in order to get something more compact. Vertical distance between wing = wing cord. Longitudinal distance = 1/2 wing cord.


Are those figures somewhat arbitrary or based on aerodynamics/fluid dynamics theory/empirical? For the relative placement of the two wings and the sizing of the wings themselves.

Also, is the extension of the fuselage past the back of the bottom wing simply for static tail-sitting while on the ground or is that going to be a fifth control surface ?

the fuselage is a 17% thick symmetric airfoil. Its leading edge is 4 cm behind wings leading edges. This position together with the outline give a position of the 25% fuselage mean cord well behind the aircraft CG (around 7cm). I hope it will be enough to ensure aerodynamic yaw stability. the aircraft will also sit on the trailing edge of the fuselage. I do not plan to add a control surface for yaw (plane frame), this can be done very well with differential thrust either in copter or plane mode.

Nothing very clever behind. I believe It would be much better for stability and performance to position wings as far as possible to each other but I wanted to make something compact as my workshop is already full of plane. I think also the wind resistance will be better like that.

Makes sense!
From visual comparison, the Opener BlackFly does have a much greater distance between the wings, which makes sense given your stability argument and the intended human application.
That may be a question for @kd0aij but do you know if the firmware would support two motors rather than one (per half wing) ? For redundancy and prevent vehicle failure if any one motor fails.

I looked at some picture of the blackfly and It seems to me that motors on a same wing spin the same direction. Converted to ardupilot it could be two quad motor layout, a small inside an a larger outside rather than an octo. Nevertheless there would be a big flaw with all plane modes as plane control rely only on control surfaces. I mean there is no feed back from attitude error to differential thrust so a motor failure would be catastrophic.

Looking at one of their videos, it seems that the front port inboard (vehicle left) motor rotates CW and the starboard inboard motor rotates CCW (looking from the front). It looks like the rear inboard motors rotate opposite to the corresponding front motors. That looks like a good configuration to me, assuming the outboard motors rotate the same direction as the inboard motors on each wing.

I’ll try configuring a RealFlight model that way and add a copter tailsitter frame to simulate it.

(with a little glimpse of Missionplanner 15sec into the video


Oh interesting – I know about that vehicle but I didn’t know that they relied on AP in any way.
Does anyone know if the autopilot is actually AP??

The use of Missionplanner is a strong indicator, but not definitive. I doubt anyone will confirm one way or the other, as those types of programmes are generally wrapped in tight NDA’s.
Still: a cool vehicle, and cool to see Missionplanner pop up in the video.

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Ah I see. Could the autopilot infer a motor failure from the flight response – or lack thereof – and compensate accordingly? Does ArduCopter/Plane overall not have any contingency for motor failures/redundancy? It would be quite tricky on a quad of course but w/ more rotors it might be possible.

That’s probably a question worthy of it’s own thread, rather than hijack this one.

thanks for sharing. Amazing aircraft !!
It seems they solved the yaw control problem also by tilting motors. A linkage can be seen at 7s and 1.01s and motor position at 8s suggest they can tilt.
I can not see any control surfaces on wings but horizontal tail surfaces seems to be actuated. As far I can see, airfoil seems not to be reflex. So it look like more to a biplane aircraft than a flying wing.

I think it can in copter mode but not in plane mode. From my dual motor tailsitter experience, when a motor is stronger than the other, it cant be seen in copter mode (just the weaker motor run with higher pwm) but during transitions and FW flight I can see non symmetric flight (the same pwm value is sent to all motors)
@kd0aij probably have a better understanding

The copter code does look for unbalanced thrust (demand) to detect motor failures:

I suppose Plane could look at yaw rate and rudder demand to detect an imbalance in port/starboard motor thrust.

This is a photo of my copter X tailsitter almost finished. Calibrations and parameters are OK, I already made a small hover flight, stability seems to be very strong. However I have a glitch problem that affect RCin and RCout (and rc8 which is my mode channel)… I suspected the BEC to be responsible and changed it but glitches again. Today I have inspected my TX frsky DJT module and made an other test on the ground, no glitch.