Hello APM forums, I’ve finally come over here from DIYDrones.
I just put together a flying wing with APM 2.0. I set my LIM_ROLL_CD to 5000, or 50 on the basic tuning screen. In FBW the further the airplane will bank is about 25-30 degrees. In other auto modes, like RTL, it seems to bank up to the max just fine. In manual the control authority is excellent and can loop and roll. Is there some other setting I’ve missed?
This forum is not allowing me to post my param file. It says its not allowed…
I had this problem too with elevons. I never really got clear on the solution. It improved when I switched back to the old style elevon mixing.
Try increasing the mixing gain.
Hi, the problem is likely your gains. Elevon output mixing is bulletproof - same as having a hardware mixer on the output. I don’t suggest increasing the mixing gain.
I suspect that setting up the elevon output mixer may require doubling the RLL2SRV_P/I/D and PTCH2SRV_P/I/D gains. The default tune is extremely soft. Try cranking up P.
oke doke, Ill give it a shot tomorrow and report back. But something doesn’t sound right as in RTL it more than happily banks 50 degrees…
So I upped the RLL2SRV_P with no luck. So I decided to start fresh and instead of having my JR8103 transmitter handle the elevon mixing, to let the APM 2.0 do the work. So I changed nothing in my param file except the elevon mixing (and some P gain for pitch) and the plane will happily bank to the 50 deg mark.
I am using a JR8103 with a FrSky 2.4 module and a receiver with PPM sum. I checked the raw PPM values while in manual and FBW with full aileron input. Both are somewhere in the 1900 range.
I think it has something to do with the way APM handles elevons.
Attached are my parameter files with JR8103 mixing and with APM mixing. Maybe I missed something obvious? I’d rather not have the APM handle the mixing.
This website will not allow me to attach files as param or txt. It says “txt extension not allowed”. It does allow me to attach a .zip file, go figure.
Given your description of the problem one likely cause is that the RC1_MIN and RC1_MAX values don’t correspond with the values your transmitter sends when you give maximum aileron input.
If you post a tlog of a flight where you try for maximum bank in FBWA we can confirm it, as the NAV_CONTROLLER_OUTPUT.nav_roll won’t be 50 when you are turning.
One thing that often catches people out is if they setup their transmitter with dual-rates. If you calibrate your transmitter on high rates and fly with low rates then you get exactly the problem you describe.
One thing I noticed with the elevon setup and Arduplane, when calibrating your radio in the MP be sure to move the sticks to all four corners or complete full circles not just up/down & left/right individually.
You’ll get a lot more throw this way.
I once did it just up/down/left/right on an X8 wing and couldn’t understand why FBW_A was so soft and the bank angle poor.
I am having this exact same issue
Raptor 140 wing
Elevon mixing done in the transmitter (Taranis)
Note: this is my second flight on the APM in a plane
The plane does fine in manual mode but FBWB (the only FBW mode I have tried) limits the roll so much there is no way to turn it around while flying LOS. I almost wondered if it was trying to turn the plane with rudder IIRC mine is set to the default which should be 45 degrees.
RTL allows much more significant banking but seemed to want to lose too much altitude.
I have the exact same problem and am flying with rudder (hooked to the aileron output) elevator airplane. It has a Pixhawk and the latest firmware. I checked the transmitter and it is getting 100% servo travel. Auto missions it gets 45 degrees but in FBY_A and FBY_B it only gets about 20 - 25 degrees max (about half). Is there a devide by 2 error somewhere in the firmware?
This airplane has been flying for a couple of years with APM and it never had that problem until I get the later versions of firmware.
No airspeed sensor.
[quote="woodc"The plane does fine in manual mode but FBWB (the only FBW mode I have tried) limits the roll so much there is no way to turn it around while flying LOS. [/quote]
You need to tune your roll loop. Your roll angle is not tracking your demanded roll angle properly.
Fly plane in manual, trim it and set the throws you will be using.
Repeat the RC calibration in mission planner
Tune your RLL2SRV gains (try auto-tune)
There is no divide by 2 error. You likely haven’t done the RC calibration step properly.
[quote=“iskess”]I had this problem too with elevons. I never really got clear on the solution. It improved when I switched back to the old style elevon mixing.
Try increasing the mixing gain.[/quote]
I use the output elevon mixing feature on a Skywalker X8 and X5 without problems with a mixing gain of 1 . It’s no different to having a hardware mixer on the output. If the servo throws and mixing gain let you fly well in manual, then it will fly well in auto modes given the right PID gains and RC calibration. Common problems are:
a) Users not performing the RC calibration after setting up the final throws and trims for manual flight so the demanded roll and pitch angles are incorrect in FBW
b) Users flying with different rate settings on their handset that were used to perform the RC calibration
b) Roll and/or pitch gains that are too low
Thanks for the input!
I have done #1 and #2…just waiting on a chance to get back out to the field to see if it is same/better/worse
After setting the trims and redoing the radio calibration it is better…can get a touch over 30 degrees of roll now. Unfortunately that is not close to LIM_ROLL_CD 5499
dropbox.com/s/6walvymx1oqo0 … 140606.png
Hmmmm…after reviewing the video closer it seems Stabilize is abiding by the 55 degree limit…
Once the video is on youtube I will post a link here.
I don’t believe Stabilize has a bank angle limit like FBW.
“You will find that while it is possible to do maneuvers like rolls and loops in stabilize mode, the tendency of the plane to right itself will make these maneuvers difficult.”
[quote=“woodc”]Hmmmm…after reviewing the video closer it seems Stabilize is abiding by the 55 degree limit…
Once the video is on youtube I will post a link here.[/quote]
Stab is not limited by LIM_ROLL_CD. You could do a roll in Stab, but it would be ugly. (EDIT: Iam beat me to it. )
Can you do a flight in Stab and FBWA and post the dataflash-log?
Before flying, set TRIM_AUTO to “0”, unless you had it enabled intentionally. It can lead to dangerous trims if used wrongly.
(In the .tlog, it looks like you switched between Manual and FBWA with aileron stick inputs.)
Set maximum servo-throws to -96 and +96 for channels 1-4 in the Taranis Servo menu.
(The wiki states typical limits as lower 1000 and upper 2000)
Set trims to center and re-calibrate radio.
(Your RC1_TRIM is set to 1500, but in the .tlog is looks like center stick is ~1380, also RC_1 never goes above 1650 in flight, while RC1_MAX is 2018)
Based on you .tlog, the navcontroller is doing what it’s supposed to, but it never commands more than -46 and +46 degrees bank.
Once you have the FBWA issue sorted, I can highly recommend using Autotune.
Very interesting. Thanks for the input. It will be next week before I have a chance to fly again but I will certainly report back