Servers by jDrones

Dual-motor tailsitters


(Peter Hall) #1311

Hi all, I have put in another pull request. This shorts out the ‘pumping’ seen at high airspeeds in Qmodes. Essentially if your at a low airspeed it uses the VTOL gains and if your going fast it uses the plane gains.


(David Kaden) #1312

I don’t know for sure. In your latest log file there are values for PIDR_I in FBWA and no values in Copter modes.


(David Kaden) #1313

Here guys, may be useful:

PID Test Sheet.pdf (81.3 KB)


(lorbass) #1314

Good Idea is really usefull

Otto


(lorbass) #1315

Yes, in the new version of MissionPlanner they are now shown in the graph.


(letpi) #1316

Among new features there is one concerning VTOL: improved VTOL flight code, with improved transition support and loiter
It should be applicable to tailsitter, however I don’t really understand what improvement has to be expected.


(David Kaden) #1317

(Peter Hall) #1318

I have added Q_assist support to my latest pull request, here is a quick demo with then without it enabled.


( .) #1319

Mark, your ‘Dart’ quad-tailsitter has inspired me very much. So far I built single copter and carried out few succesful flights. I can see that tailsitter software is giving more possibilities than single copter one. I am looking for proper assignment of SERVO#_FUNCTION. I can see that for dual motors tailsitters elevon feature is quite good. But I would like to use single motor and four fins below in the prop wash. My idea is to use elevons for two fins and rudder for third one. Still do not know what to do with the fourth one? Just duplicate rudder or there is another assignment for this type of frame. It would be appreciate to get some guidance. Kind Regards.


(David Kaden) #1320

First flight after some time.

AUW is now 1400g from the before ~800g.
6s 5200, 10x6, 580kv.

Again calculated PIDs for Q_roll with Ziegler/Nichols method but they were not usable because of oscilations. Had to manually reduce them. For hover pitch and yaw I used the same PIDs as I used in my earlier videos and It seems to work. Did not try to retune them.

In Horizontal flight you see the yaw drift while doing the transition.
Then you can see enormous oscilations in both roll and pitch. They increase with speed. Log said that it had a maximum of ±11g (!!!) where I put full throttle and went to about 28 m/s.
I dont think that I will be able to make this more stable in horizontal flight and still use the symmetrical airfoil (NACA 0015).


(David Kaden) #1321

FYI BLHeli passthrough currently does not work with tailsitter https://github.com/ArduPilot/ardupilot/issues/9340


(letpi) #1322

You have got probably the best stability in hover for a non vectored ardupilot tailsitter.
Did you try to move forward the CG ? It will stabilize your wing in fixed wing mode. The more you move forward the CG the more the elevons neutral position will be upward giving some positive moment. It could be at the expense of the lift coefficient though.
How do you look at the acceleration ?


(David Kaden) #1323

When I move the CG forward it won’t hover that great…

I think I first need to have another airfoil and then try to find a CG which works acceptable in hover and forward flight.

For Hover the CG optimum is where the wing has its pressure point, bus this means tha the wing is completly instable in FF.
For FF the CG must be a bit more in front of the pressure point, depending on required stability, but this means that the wing won’t hover at every angle of attack with zero flap deflection because it will always have to counter the aerodynamic moment of the wing.


(David Kaden) #1324

Was flying again this week. Tried to tune the pitch axis. No luck yet. I also destroyed the craft after the last flight and will go on building a completely new one with adjustable CG location and other fuselage + other airfoils. Should then solve all problems. :slight_smile:


(lorbass) #1325

Great, thats staying power.
Good luck

But for me perfect tuning in the first flight until autotuning.
Perhaps to much trust in “Autotuning”
Or not enoughe autotuning cycles.
PlaneWiki:
So you need at least 20 full stick movements to learn a reasonable tuning value.

Otto


(.) #1326

Hi palm369
nice project! I have three questions

  1. Where is your COG? Wouln’t it be better if you had a wing with more wing sweep that you could put your propellers nearer to the COG? I read that tractor configuration on wings had a destabilising effect.
  2. Can you post a pic of your motor mount? It looks strong and easy.
  3. Do you have any down thrust because of your tractor configuration?

(David Kaden) #1327

Autotune does not work when the plane is aerodynamically instable. Actually the only thing that can make it fly is a super fast and perfectly tuned control loop. Or building it aerodyn. stable, so with the CG infront of the wings pressure point and not right ontop of it.

Thx.

  1. CG is at 1/3. What difference you think it makes if props are in CG location?
  2. Actually I destroyed plane after last flight. sorry
  3. Don’t unterstand the question

(.) #1328
  1. I thought it could make it more stable if the pulling propellers are more near the CG or pusher configuration. Is your airplane aerodynamically instable? I think not, CoG at 1/3 seems to be normal, maybe tail-heavy for a wing.
  2. Bad news! Hopefully easy to fix.
  3. In german it is called “Motorsturz”. Normally tractor configurations have a little negative and pushers a little positive. Do you have that?

(David Kaden) #1329
  1. According to FLZ Vortex its instable. I did it intentionally so I have good hover performance on any AOA without saturation of flap angles. Take the Tailsitter of ETH Zürich as reference. I also explained a lot of my design rules in this thread already, including this.
  2. I threw away the plane because I want to built a new one with “S-Schlag Profil” like MH45 or so.
  3. No I don’t. “motorsturz” is done so that the thrust vector passes through the aerodynamic center. eg with high-wingers and no pitch up moment is induced by gas. Everything is intentionally symmetrical with mine.

(.) #1330
  1. When it is instable, can you fly in manual mode (horizontal)? I though flying an instable airplane is impossible without fly-by-wire.
  2. Can you tell me how you attached the motors to the x-shaped wood? I would like to do it like you.
  3. Okay so I won’t use it.