Servers by jDrones

Dual-motor tailsitters

(tridge) #503

there may be an airflow effect with the barometer. It thought that it stayed within 40cm of the desired height, but the video shows it didn’t.

yes, good idea. We don’t have have support for differential thrust for yaw in forward flight, so it will be reliant on yaw stability of the airframe

(tridge) #504


I look forward to it. Good luck with the flight testing!

( research air) #505

we are going to need that, .01 to 5 %would probably do in my case and maybe mix with aleron/elevon

( research air) #506

pull that off the shelve, sounds like Tridge fixed it !!

(Jeff Street) #507


This conversation mentions SERVO(1-6)_FUNCTION, but I only see RC(5-9)_FUNCTION in Mission Planner 1.3.48 (Advanced Layout) with Plane 3.7.1 on a Pixhawk1.

Feels like I’m missing something pretty basic. Would you please steer me in the right direction?

I tried a couple of things:

  • Plane documentation shows SERVO#_FUNCTION, but not RC#_FUNCTION.
  • This Copter post suggests the two are synonymous.
  • Added SERVO#_FUNCTION parameters with a text editor, but Mission Planner rejected them upon trying to load the file.

Thanks in advance!

(Rolf) #508

You have to load 3.8obeta5 firmware.

(Rolf) #509

Unfortunately we had an ESC burnup. Blessing in disguise that it happens at startup. Until the next test it will take about 2 weeks :sob:


(tridge) #510

ahh, sorry, I must be getting forgetful in my old age. We do have differential thrust in fwd flight with vectored tailsitters. Just set RUDD_DT_GAIN to the percentage of differential thrust with rudder. It will mix from ailerons with KFF_RDDRMIX.

( research air) #511

that"s great, Thank you !..forgetful? what were we talking about?

(Jeff Street) #512

Ah! Thanks a million @Rolf.

(lorbass) #513

Maiden “flight” of my Caipirinha now vectored.
Heavy oscillation of the Tilt Units produce a nice Yaw-dance. But far away from hoovering.

Remarkable: Even with back touch during start, no damage.

And the Log file:

Due to weak thrust, difficult to get Roll. With Roll cmd loose altitude (one mot reduce thrust, the other can’t because already on max.
I think it needs tuning, but which param in which direction?

(Jeff Street) #514

Foamboard Fixed-Motor Tailsitter

Here’s the maiden flight of a new foamboard fixed-motor based on the FliteTest Spear. It’s pretty manageable with the default tuning in QStabilize, QHover, and QLoiter.

Working on a write-up with plans, video, and log files.

(Walter) #515

Congratulations on the "nice Yaw-Dance"
But you’re already a bit further than us.
Walter + Rolf

(Jeff Street) #516

Foamboard Tail Sitter

I was thrilled to find this thread! The firmware seems to be moving forward very quickly and it’s exciting to see that there are people flying various configurations.

In hopes of making things more approachable to others, here’s quick rundown of how I put together a dual fixed-motor out of foam-board that seems to be fairly manageable in hovering and forward flight modes on the default parameter values. I’ll be very grateful for your corrections and feedback, especially regarding the log file analysis for tuning.

All the files mentioned below (airframe plans, parameters, log files, photos, and videos) are in this Dropbox directory:


Inspired by @ag-sys in this post (Dual-motor tailsitters), I started with a FliteTest Spear and added dual motor pods. The Spear has plenty of space in side the fuselage for electronics and battery, bringing the vertical location of the CG into good alignment with the motors.

Motors from FliteTest Power Pack D

Motor rotation:
Right: CW
Left : CCW

Battery: 3s 2200mAh

Takeoff weight is 835 grams.

Wiring for Pixhawk1, HolyBro version
All external module connections as normal. No airspeed sensor.
Output 1: ESC Right
Output 2: ESC Left
Output 5: Elevon Right
Output 6: Elevon Left

Place aircraft in fixed wing flight orientation.

Install firmware ArduPlane V3.8.0beta5
Setup Accel, Compass, Radio as normal

Q_ENABLE=1 (was default value)
Q_FRAME_CLASS=10 (Tailsitter)
Q_TAILSIT_INPUT = 0 (was default value)

Write and refresh parameters

ELEVON_OUTPUT=3 (frame specific)
Reverse pitch axis with checkbox in Mission Planner > Radio Cal. (Not sure what parameter this flips.)

SERVO1_FUNCTION=74 (right motor)

SERVO2_FUNCTION=73 (left motor)

SERVO5_FUNCTION=4 (right elevon)

SERVO6_FUNCTION=19 (left elevon)

FLTMODE_CH = 5 (your preference, using 3-position switch)

Save parameter file (TS1-V7.param)

ARMING_CHECK = 0 (Disabled for testing)
ARMING_RUDDER = 2 (your preference)

Check for reasonable output

Upon boot, right aileron sometimes goes full down for 2-5 seconds, then returns to neutral.

Mode: FBWA, lay plane on it’s belly
Control surfs: yes
Motors: Disarmed, nothing. Armed with zero throttle, nothing. Armed with throttle, normal throttle response. No differential throttle.

Mode: QSTABILIZE, stand plane on tail
Control surfs: upon pressing safety button, deflect a bit, then stabilize. Sometimes wind up over time and sit against stops. Respond to sticks. Respond to picking up and moving aircraft around each axis.
Motors: Disarmed, nothing. Armed with zero throttle, nothing. Armed with throttle, normal throttle response. Motors spinning, pick up and move aircraft, differential response as expected.

Investigate QSTABILIZE arming motor behavior. Default values
Increased these to 0.2 and 0.25. Motors still don’t spin upon arming. Returned to default values.



  • Should motors spin upon arming?
  • Question: Does the output number matter, if the correct SERVO#_FUNCTION value is assigned?
  • Why does right aileron go full down on boot? Maybe choose another output channel?

This is pretty long, so I’ll post the testing notes separately.

(Jeff Street) #517

Foamboard Tail Sitter - Flight Test - Hover

Log files 45-48. (I think log 47 includes all three modes, but one log includes two flights, i.e. didn’t disarm between) and I’m not very familiar with the log analysis tools.) Link:


Hovers at ~50% throttle.

QSTABILIZE - Fairly stable, even in light wind. Good authority in pitch and roll (earth frame). Yaw has weak authority and a some roll/yaw coupled oscillation when fighting gusts (i.e. pitch lean). Moving CG up seems to reduce this oscillation.

QHOVER - Fairly stable, despite wind gusts. Performed takeoffs by using full throttle to get off the ground before reducing to 50% once in the air.

QLOITER - Less stable. More roll/yaw coupled oscillation (earth frame) when fighting gusts (i.e. pitch lean).

4 flights short flights with one battery. Consumed 1703 mAh of 2200 mAh.




  • It seems like a bit of yaw tuning is needed. I’d appreciate any advice on the appropriate adjustments.

Foamboard Tail Sitter - Flight Test - Transition

Hover was fairly manageable, so I decided to try transition.

Log files 49-52. Link:



  • Pitch oscillation following transition. Dies when throttle is reduced to ~50% and does not recur when throttle is raised.


  • Roll authority and control good.
  • Pitch oscillation upon big pitch up inputs.
  • Level flight requires ~100% throttle and a little up elevator.


  • Climbs ~8 meters. Good stability.

Feels unstable at even modest descent rates. The video doesn’t look too bad, but it felt looser than the hover tests. I tried to hold altitude during wind gusts and descending in calm air.

Climbs ~8 meters. Slowed the motors way down. Knowing the motors stop at zero throttle, and knowing pitch is unstable in descent, I switched to QSTABILIZE.

Landing QHOVER
Feels unstable at even modest descent rates, though it was easier to hold a slow descent.


  • Try more cruise thrust. Maybe higher prop pitch or more motor rpm. (Currently 1045 prop on 935kv motor with 3S battery.)
  • Try more cruise angle of attack.
  • Reduce pitch oscillation. Try reducing pitch gain. Q_A_RAT_PIT_P currently 0.25. @agsys “halved the roll and pitch P and I gains for fixed wing flight.” Dual-motor tailsitters


( research air) #518

congrats! all the swept wing foamies that I mess with seem squrilly to me as well, lots of yaw and decend issues, might be the light weight? my stright wings go 3.5 to 6 lb. also looks like very fast transitions,we might want to find a way to slow those down, or better,be able to fly into and out of transition with more pitch movement ,might be a structural issue( that’s a hint Tridge )

( research air) #519

also try to do your landing transitions upwind so you don’t fight the breeze as much on descend

( research air) #520

Hey ,Tridge been working on illusion, testing yaw and transition in hand, dif yaw = good… when switch to fbwa throttle goes to high and serfaces abrupt switch to horzontal seems good for fixed motor mount but I am concerned with vector setup. with baseflight bicopter software, my normal transion is t/o in horizon mode (3pos switch) pos 2 is switch off horizon fly to nose down to horizontal and switch to airplane pos3 that one also changes to a 2nd controller setup for inav and is reverse for landing, my observation with baseflight is that I can hold 1/2 down elevator and the tilt might still point the motors up to hold whatever position the stick is in, is it possible to get that control with a pix ? my controller also uses 2 IMU’s 1 vert and 1 horizontal ,also with the new radio’s can we get more mode channels ? hope this is helpful and doable

(lorbass) #521

First succes with Caipirinha dual motors vectored Tailsitter.

Remarkable issue:
Q_M_THST_Hover does not work. Even set to 0.8 the thrust increases proportional (linear)
to CH3in. With stick in the middle CH5out or CH6out ppm = 1500
This makes the mode change from QSTABILIZ to QHOVER difficult as shown in the video.
Regards Otto

( research air) #522

lookin good, better and better,love that it can go upside down and still go, big thunbs up!