I have a DFC FBL Trex-450 setup flying with 3.0.1 and I'm hoping for some tuning/setup suggestions. Just finished several packs tuning the stab mode and It's flying well. There seems to be some problems however with my APM and saving settings, and I would like to fix these before moving forward to do advanced tuning.
My PID's are:
Stab Roll-Pitch 4.50, Stab Yaw P 3.8
Rate Roll-Pitch P-0.0350 I-0.050 D-0.0 Rate Yaw P-0.130 I-0.0200 D-0.0
Rate Pitch-Roll-FF 0.0200
Issue #1 - servo's bind on startup, pre-arming stage.
- Plugging in the battery the swash plate/servo's jump to exactly center position, or 0 degrees swash.
- After 6 seconds the servos jump to low collective, -35 degrees, basically the full extent of servo travel.
- After arming the collective jumps to -5 degrees, where my pitch curve is set on my radio at low throttle.
When connected by Mission Planner in the Heli Setup under the servo swash setup I am able to change the MIN and MAX values on the servo's. Two are reversed so I have RC1_MIN 1200, and RC2~3_MAX at 1800. This stops the binding issue on the bench. As soon as I power cycle the board and reconnect the MIN MAX values are back to default settings of 1000 and 2000 for all 3 servos. However if I set the TRIM values they are persistent.
Is this a know bug in the APM, or do the values need to be saved a different way to persist in the configuration?
edit: sorry I think it's HS1, HS2, and HS3 values, not RC1~3 values when It's in the full parameter list.
Replies
Not sure if you'll get this message but I gave up on this helicopter. I don't have the final settings, sorry. The swash plate would jam up every start up before settling into proper position, no settings seemed to fix the min-max. Also this kit was a bit of a mish-mash. It was a converted to DFC 450 pro, with Hengli or something servo's. It did somewhat fly in stabilized mode OK.
I've decided to start from scratch. I purchased a new T-Rex 450 DFC 2014 kit no FC and 2 x Pixhawk's. Will start from scratch setting it up after I've set the heli up with a BeastX to verify it can fly 3D/regular modes and its tuned well. I've also picked up a Mikado 500SE, and that will hopefully be the eventual home of Pixhawk #2 for verified settings/code and the 450 for development/testing.
Ok I would say that worked very well. ALT-Hold is perfect! It responds like my multicopter in ALT-Hold. Very smooth up-down transition, with decent authority now. Set THR_ACC P waaay down, and I down 1/3 to 0.5.
Does THR_ACC P/I/D and THR_RATE P/I have any effect in STAB mode? because that feels very/over reactive.
Wow guys, thanks for the great replies!
I did try the Throttle Rate/Accel, but not settings that dropped the values by a factor of 10! I just intuitively (and incorrectly) thought that was wrong, and I was looking for the sweet spot much closer to the initial values. I also missed that amazing post on Sean's 550 setup, just finished reading it. It makes sense that Alt Hold should be 1.0, I'll go test/change the other values and see what happens.
Hey Rob,
Hoping to get a bit of insight on where I'm going wrong with setting up ALT Hold here.
What happens is with Alt Hold P at 1.0 it starts a wild oscillation as soon as I hit the switch. I'm actually surprised my servo's and heli can jump up and down that fast and not rip apart. It moved about 1ft in what seemed to be several times per second!
I tuned down ALT Hold P to 0.2, and now as long as I'm in a stable hover and switch to ALT hold it will stay there, sometime it starts to oscillate and the only solution is to switch to stab then back to alt hold. However now its just a slight oscillation, still very fast though. I'm sure I could have it never oscillate at P1.0 or 1.5.
My problem now is that with ALT Hold this low I have almost no control over ascending and descending with the throttle stick.
Watching your video(s) it seems you have plenty of control over height, I don't think your ALT-H-P is that low? any thoughts on what I can check/correct?
A quick follow up, should the collective swash travel be configured for +12 -12, or should it be +20 - 20 to account for cyclic movement. On some controllers if you wanted 8' cyclic and 13' pitch you would set -21' and +21' for the full range. Do you know if this is how the APM works?
How are you setting the collective travel range? There are two steps to this.
First, is to set the full range using H_Col_Min and H_Col_Max. This is easiest done in the Heli Setup page. You should program in a typical "acrobatic" range here, because it gives the Alt Hold controller lots of collective to play with. So, for example +/-12. Then you use Stab_Col_Min and Stab_Col_Max to set the collective range you will have in Stab mode. I typically use +10/-4.
If you've done this correctly, then I don't think you should have any binding on startup. But the mere fact that you were able to fly it makes me think that you must have done this already.
Also, if you can get that much collective travel (35°!), then maybe you should move the ball links in on the servo arms. This will give your servo outputs better resolution.