Servers by jDrones

Dual-motor tailsitters


(letpi) #1463

Make again accelerometer calibrations carefully. Normally, the pixhawk should be able to sense a drift and compensate provided this drift is linked to a bad equilibrium and not due to the wind. Where is the CG according to the thrust line ? Maybe you need to rise Q_a_rat_pit_I to increase the ability to compensate for bad equilibrium (I suppose the drift is along the pitch axis).
Yes, you have to increase q_a_rat_pit_p to the maximum in order to improve the pitch response. The maximum is when you get oscillations. After that you can tune pit_d and see if you are able to increase again pit_p. What is the distance between the CG and flaps ( I mean the projection along the longitudinal axis) ? If this distance is too short, you can expect more a translation than the desired rotation. Also increase the flaps deflexion up to ± 45°.
Are your servos fast enough and linkages rigid and without slope.


(Mark Whitehorn) #1464

@losawing I rebased my latest quad tailsitter code onto master (there have been a lot of changes since I last worked on the stryker_quad branch) and ran the result in SITL using a RealFlight 8 model of a quad tailsitter. Backtransitions consistently take about 3 seconds to complete, and I haven’t seen any evidence of software bugs yet:


The new branch is https://github.com/kd0aij/ardupilot/tree/pr-quadTS
and the parameters I used in SITL are here: https://drive.google.com/open?id=19SDMbb4irSJrOeBXA1an_yw6xAZaWnQn

When I have my new airframe ready to fly, pr-quadTS is the branch I’ll be using.

–Mark


(lorbass) #1465

My vectored Tailsitter shows a similar Transition with FW V 3.9.2 but without Roll.
But why had it to Roll 20 ° in your Version?

  • Otto

(letpi) #1466

@Mick_McNamara
I forgot to mention, for tuning pitch PID:
1-begin with q_a_rat_pit-d almost 0 (0.0001 typical) because you can get oscillations from D and can get confused where oscillations come from. Increase P as much as possible. At the end a small amount of oscillations only from time to time is acceptable.
2-set q_tailsit_thscmx=1 , if higher you get oscillation at low throttle and you will not be able to increase P.
3- set q_m_thst_hover correctly.


(letpi) #1467

@kd0aij
Thank you for this work.
I think there is a bug somewhere probably not in your code but maybe a bad interaction.
I am wondering if this can be related with a bug I reported in a previous post 1034 (third video). Because the problem seems to be related to oscillations during the transition. The video shows oscillations when I switch to Q_hover. A lot of oscillations can also be seen in my jetwing log during transition, this is strange because I had no oscillations in any fw mode neither in hover mode.
I still have my test wing to test your quadTS branch. I will see if I am able to compile it.
I am very impatient to see your next aircraft.


(Mark Whitehorn) #1468

That roll was commanded by a stick input, as the red trace shows.
Other transitions show max roll deviations of about 5 degrees during the transition.


(lorbass) #1469

I asked because with V 3.8.5 I had 90 ° Yaw without stick input during the transition.
After the transition the wing showed in an other direction.
With V 3.9.2 this ugly behavior has disapeared.
Otto


(Peter Hall) #1470

Independent roll and pitch angle limits have just made into master.

Pitch angle is still set but ANGLE_MAX. If none zero TAILSIT_RLL_MX limits maximum roll angle. This allows large pitch angles in Q modes while limiting roll.


(lorbass) #1471

Another usefull option. (Like Q_TAILSIT_THSCMX) :slight_smile:
Thank you.
Otto


(mick McNamara) #1472

Thanks for all your help.
Have been finding it hard to do some testing due to windy conditions but was able to get a short flight in the other night.
I set q_tailsit_thscmx=1 as suggested and it flew very poorly with motors oscillating badly.
I have noticed that it is very unstable in any wind as it weather cocks badly.
I hope to test a transition next week weather permitting so will Keep you posted.

https://youtu.be/4L1my6DKMiA

Dose anybody know how to get the Dashware Data Profiles /calculators to show up in the data values of the gauges drop down selection box?
Having no luck


(lorbass) #1473

Did you add the appropriate “value Inputs” in the Gauge Designer (double click on a gauge) ?
Dashware is not so easy, it’s a challenge for non flyable days :slight_smile:


(letpi) #1474

what do you mean by motor oscillating? I do not see motor oscillations in your video. Just some instability with yaw (earth frame) axis. Maybe you need to increase q_a_rat_yaw_p and I. Also I would try to increase Q_a_rat_rll_d as you wing roll from one side to the other. Your wing already fly correct but it needs a little more tuning before testing a transition. One axis by one axis try to increase P until oscillations. Begin with pitch, then yaw and rll at the end.
The most critical is the CG position. I found it is very good to have the CG exactly at the 1/4 of the wing cord measured behind the motor. The goal is to have the CG at the neutral point of the wing section submitted to propellers wash. The important question : is this CG position compatible with the fixed wing flight ? For that the CG must be in front of the 1/4 of the wing mean cord with at least a margin of 3%.
Q_tailsit_thscmx is a parameter which was added lately because all q_a_rat gains are a function of 1/x where x is the throttle level. It means a low throttle all gains become too high and cause flaps oscillations. Q_tailsit_thscmx limits gain increase by a factor of its value: if 2, gains cannot be higher than 2 time. The central throttle value around which gains are modified according to the 1/x function is q_m_thst_hover.