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Nimbus Tricopter VTOL


(Greg Covey) #363

Hi ovolkmann,

You may try posting your questions directly in the AUTOTUNE Blog here. I haven’t read any indication that AUTOTUNE has been successful on a tricopter or Numbus VTOL, nor can I find it in the Wiki. The quote below may be old but I haven’t seen anything that contradicts it. Perhaps you are the first to try it?


(ovolkmann) #364

Hi Greg,

Yes, I do believe we are the first to do this q_autotune on a tilt-rotor platform. Today I’ll be running the YAW tuning after having repaired the nimbus. We’re doing this testing for two reasons, 1) To improve our VTOL flight characteristics and 2) to get the dev’s some data to analyze to further improve on the q_autotune protocol for tilt rotors. Hopefully they’ll get a chance to review the logs :). Will keep you updated if you are interested.


(Greg Covey) #365

Yes, it is interesting for several reasons so please post your findings here as well. It is interesting because you are using a Nimbus. Also, it will be interesting to see if the Q_AUTOTUNE feature results in better performance than what others are currently seeing. I have suspicions that there may be expectations that a tricopter design with vectored yaw can perform as well as a true quadplane using 5 motors.

Cheers!


(ovolkmann) #366

@GregCovey, I think that a true quadframe with 4 lifting and 1 forward vector motor is less sensitive to the hardware choices for tuning than a vectored yaw setup but I think that with the right components and settings one can get similar “copter” performance in both designs. That being said, the yaw axis is most likely the most difficult one to tune due to the difference between the width of the aircraft and the distance between the vector motors. Just got back to the office after completing the pitch and yaw tuning. Will put all the logs up soon. Did a test flight with the autotuned results and I’m not quite happy with the yaw still but pitch and roll seem great. Will share the post here shortly. Cheers!


(ovolkmann) #367

Alright guys, here are logs and vids of all three axis Q_Autotune.

https://discuss.ardupilot.org/t/q-autotune-tricopter-tilt-rotor-results/40998

Remember to give your ESCs some time to cool off after each session, especially if you have thermal cut-off.


(ovolkmann) #368

@GregCovey, can you confirm that the plane should be CG’d at 100mm from leading edge? Does the distance between the propeller to the CG make a difference to the fixed-wing portion of the flight?


(Greg Covey) #369

Yes, 100mm from LE sounds right. We have seen various distances that the prop sticks out from the LE and have not heard of any negative comments. I would think it has minimal effect on forward flight.


(ovolkmann) #370

@GregCovey, we’ve had it at 85-87mm and even 120mm before. The plane seems to be very tolerant of poor CG for sure :-p. Thank you for confirming the 100mm from LE.


(ovolkmann) #371

Hey guys,

Pulled off a nice 51 minute automatic flight today including VTOL Take-off and VTOL Landing. The flight was done at 16m/s and during the flight, it seemed that the plane was “hanging” on the nose with a 10-15 degree pitch up during the flight (which was done perpendicular to the wind). Now, I did CG the plane at 100m from leading edge which gave me a vast improvement on flight time however I am now thinking that perhaps the tail control surfaces are not properly setup due to this “hanging” phenomenon I noticed. Should the aircraft not maintain a level flight for the majority of a flight? I mean, it was very consistent. The flight prior to this one lasted 40 minutes and was at 18m/s and that behaviour was still there, just perhaps not as pronounced. Your input would be greatly appreciated!

https://youtu.be/EPwG_CiNCXI


(Wasim Akram) #373

I really don’t know much about the Nimbus but I can give you my advice from my background in aerospace engineering.

Should the aircraft not maintain a level flight for the majority of a flight?

Ideally, YES, but that will be case only if the wing is mounted at the right angle of incidence relative to the fuselage for the design AUW (with careful consideration for the tail mount angles too).
Let’s say an aircraft of weight W is designed with 0 degree wing angle of incidence, but the angle of attack (AoA) that is required to provide the lift required at level cruise condition (where lift = W) is 5 degrees. In such a design, the plane will cruise with the fuselage at an angle of say approx. 5 degrees to the horizontal (assuming that the tail and the fuselage doesn’t do any lifting, which may or may not be true). However, if the weight of the plane is increased, the angle that the fuselage makes with the horizontal will likely increase even more. Typically, you need the fuselage to be horizontal as you really dont want the fuselage of a conventional aircraft to generate excessive drag or any lift (because lift-induced drag increases). A fuselage pitch-up angle of 15 degrees at level cruise flight sounds a bit too high, as it’s quite close to typical wing stall angle. What was your AUW for this flight?

The flight prior to this one lasted 40 minutes and was at 18m/s and that behaviour was still there, just perhaps not as pronounced

The equation for the lift generated by the wing is: Lift = 0.5 x (lift coefficient) x (ambient air density) x (wing planform area) x (aircraft airspeed)^2

Since ambient air density at a given altitude is fixed by nature, and the wing planform area is fixed by the airframe you use, the aerodynamic lift generated by the wing at cruise condition can only be increased by either increasing your lift coefficient (by raising the AoA) or by increasing your cruise speed. So when you increased your cruise speed from 16m/s to 18m/s, the AoA doesn’t have to be as high, so the wing drops slightly. I hope that makes sense.


(Greg Covey) #374

Are you using SERVO_AUTO_TRIM? It should take care of leveling your plane in forward flight.

P.S. Love your flying area!


(ovolkmann) #375

Thanks Greg! I’ll give SERVO_AUTO_TRIM a try. Any words of caution about using that feature?


(Greg Covey) #376

Don’t let your jaw drop too far when you see your plane fly straight. :slight_smile:

I have been using it for years and never need to trim a plane…


(Matthew ) #377

you guys have such a nice flying area thats awesome!!! Mine is full of mountains. Is that the vmapper i see attached to the top of the nimbus? How are you liking it and pros or cons? @ovolkmann might want to try and throw up some logs to help folks diagnose the issue.


(ovolkmann) #378

@Matt_C, Yeah, not too bad of a flying area but I miss mountains! lol Florida is just too flat for me. Yes, you see the V-map antenna attached to the top of the aircraft. The receiver itself is sitting in the nose. We love it, but since we make it, we are a little bias :-p. That being said, the results speak for themselves. I’ll try and get a log up for the flight here soon so that you can see what I am talking about but I will try the SERVO_AUTO_TRIM feature as recommended by @GregCovey


(Musa Wilmar) #379

@GregCovey @Graham_Dyer
here is my first time successful auto flight,


but i think the descending speed is to slow on VTOL Land…
currently my Q_LAND_SPEED = 50 do u think it’s ok to increase it?

(ovolkmann) #380

transition to VTOL at a lower altitude. I have mine set to the same decent speed. If you come down too fast, you’ll break landing gear and unfortunately also run the risk of breaking the the wood that holds the landing gear to the plane.


(Michael De Leon) #381

Hello Guys, its been a while i work on our Nimbus from foxtech.
replace servos on wing and tail control surfaces. I was reading all through out the conversation.

Its fun sharing ideas and parameters.

For us i like to share ours.

AHRS_EKF_TYPE,2 - 2
ARSPD_FBW_MAX,18 - 25 (good max speed for this type/size of plane)
ARSPD_FBW_MIN,11 - 14 (Just above the stall speed of 10m/s)

LAND_DISARMDELAY,10 - 20sec

LIM_PITCH_MAX,2000 - 2000 (no need to pitch up more than 20°)
LIM_PITCH_MIN,-1500 - -2500 (no need to pitch down more than 15°)
LIM_ROLL_CD,4500 - 4500 (Limits bank angle for heavy plane)
MIXING_GAIN,0.5 - 0.5

MNT_RC_IN_TILT,0 - 0 (for our camera gimbal)

PTCH2SRV_D,0.04 - 0.03 (increased for tighter tune)
PTCH2SRV_FF,0.4 - 0.4
PTCH2SRV_I,0.15 - 0.15 (increased for tighter tune)
PTCH2SRV_IMAX,3000 - 3000
PTCH2SRV_P,0.7 - 0.6 (increased for tighter tune)
PTCH2SRV_RLL,1.15 - 1 (keeps nose more level in turns, less loss of height)

Q_ANGLE_MAX,3000 - 3000

Q_ASSIST_ANGLE,30 - 30
Q_ASSIST_SPEED,0 - 0

Q_TILT_MAX,60 - 45
Q_TILT_RATE_DN,50 - 50
Q_TILT_RATE_UP,200 - 200
Q_TILT_TYPE,2 - 2
Q_TILT_YAW_ANGLE,13 - 13

Q_TRAN_PIT_MAX,10 - 3 (default of 3 resulted in a worrying dip/loss of altitude during transition
Q_TRANS_DECEL,2 - 2
Q_TRANSITION_MS,3000 - 4000 (changed from 5 secs, plane transitions quickly so 5 secs seemed too long)

Q_VFWD_GAIN,0.05 - 0 <----??? (Wind resistance in hover)

Q_WP_RADIUS,500 (now 200, use 400?) - 500 (looser waypoint radius)

Q_WVANE_GAIN,0.2 - 0 <----??? (wind vane enable)
Q_WVANE_MINROLL,2 - 1 (activate on 2 deg of roll)

RLL2SRV_D,0.1 - 0.03 (increased for tighter tune)
RLL2SRV_FF,0.4 - 0.4
RLL2SRV_I,0.2 - 0.15 (increased for tighter tune)
RLL2SRV_IMAX,3000 - 3000
RLL2SRV_P,1 - 0.7 (increased for tighter tune)
RLL2SRV_RMAX,0 - 0

WP_LOITER_RAD,80 - 60 (good distance for QRTL transition, allows plane to slow down enough)

WP_MAX_RADIUS,0 - 0
WP_RADIUS,10 - 30 (more accurate waypoints, especially with flying grids)

YAW2SRV_DAMP,0.08 - 0.02 (tuning to stop tail wag)
YAW2SRV_IMAX,3000 - 3000
YAW2SRV_INT,0.3 - 0.1 (tuning to stop tail wag)
YAW2SRV_RLL,0.8 - 0.8 (tuning to stop tail wag)
YAW2SRV_SLIP,0 - 0

i was able to get @GregCovey and @Graham_Dyer comparing there para. Our nimbus is V1 with 13" on front, 14" on the rear motor.

also ive notice that or AUX1 which suppose to be Right Servo is on the Left side. Is this how Foxtech set up is?

Thanks guys. hope to share mo details when i test today


(Michael De Leon) #382

I was able to HOVER again the NIMBUS. Still tuning the tail wag. Currently my issue is compass i cant seem to calibrate all 3 compass right. There will always be a failed compass everytime we do live calibration.

I was wandering about the Pixhawk 2.1 compasses. Is this correct?
Compass 1 is external and primary (GPS onboard compass)
Compass 2 is internal
Compass 3 is internal

In the picture it seems there are two external compass. Is this wrong?


(Michael De Leon) #383

Updates on yesterday remaiden flight
-Tricopter flew . Compass error variance always pops out on HUD.
-Compass calibration done many times.
Compass 1 - external
Compass 2 - internal
Compass 3 - internal
-We mounted the GPS puck a little higher than before. This lessen the EKF 3 triggering compass to change from 0-1
-Improve a little on Compass error.
-Change Flight Modes form foxtech recommendation QLOITER/AUTO/CRUISE TO QLOITER/CRUISE/FBWA. (I have already fly this bird last year with Foxtech set up)
-Remaiden to transition to FIXEDWING mode and all parameters are Foxtech tuned.
-Transition to fixedwing successfull.
-circle 3 times. cruise mode seems faster than 15-17ms.
-big difference in airspeed and groundspeed.
-had to abort the flight on the 3 circle. ive lowered down throttle for the unit to slow down and approach for transition to vertical and land. Ive felt that the unit was not responding with my roll inputs going back to LZ. Switch back to qloiter and return the unit safe.

Sharing my tlogs and bin.

Thanks.

https://drive.google.com/open?id=1EO-2JvWrgjx-m5puxMjYF0nfOz6AHQlN
https://drive.google.com/open?id=1BEzd7yjOBSKd-xVlYXcYl1qChuOh9ibn