Odd swash behavior

Hi guys

Please forgive my english. I will do my best to make myself clear

I build a trex 450 pro for test and tryout purpose before my dominador 550L


Trex 450 pro DFC
Pixracer flight stack. 3.6.9 Heli (tryed legacy too)
Hobbywing Platinum 40A v3 ESC
KST 215 Metal coreless digital servo V3.0
Mavpixel MwOSD SiK etc
Pixflow 1.3 Disable
GPS uBlox 8

Well, the odd behavior start when the flight controler is armed and throtle is above 1776 PWM
The swash tilts backwards “elevator” and left “aileron” slowly then it jams in that position and don’t respond to Stick moviments. Then I bring throtle down below 1776 pwm swash levels and unlock working normaly

I tryed to limit RC3 input to 1776 pwm but no luck at all

The only way to solve the issue is to limit on the radio throttle to 1776 PWM. But it brings me some head speed and colective issues.

This behavior only happens on armed situations
On Stabilized althold acro modes. Do not try others

Looks like some kind of leak in the loop because it slow to the position and stay there

Any help on that?

@MephistoPFBR please post a param file so I can look at your setup. Thanks!

PATRIK.param (14.4 KB)

Thanks for the param file. Have you completed a radio calibration? I noticed some of your RC min and max parameters to be 1000 and 2000. It’s not often I see that. I also noticed that your aircraft has not been tuned. Please read our tuning wiki to make sure you safely tune your aircraft. The default params that load with the software are not considered defaults.

So now about your problem you are seeing. I don’t believe that what you are doing is a good test of the control system. Bench tests are misleading especially with how this control system is designed. Be sure you go through the setup videos and read the tuning wiki. They are both in the traditional helicopter section of the copter wiki. Trad heli wiki


I calibrated the radio it goes from 998 to 2014 then i manualy ser 1000 - 2000 pwm. And trim 1500 neutral.

I dont tune it because is on bench then i came across this issue on the thr

I made a vídeo for best view of the issue

Be sure this is actually the trim value for your sticks.

@MephistoPFBR do you have motor interlock enabled when doing this? Obviously your motor would start but I thought you might have disconnected it for this test?

I just wanted to add that if you are conducting this test with the motor disconnected and the motor interlock enabled then you will definitely get unusual behavior. It is important to realize that this control system tracks your inputs to predict where it thinks the aircraft attitude should be. Then it makes inputs to drive the acutual aircraft to that attitude. Since it cannot then you see the swash behave oddly.

Well. Maybe we get a point here

On the test the motor was disconected.
I really dont understand de real concept of the motor interlock.

Actualy it is a copy of the thr Channel on my rádio mix. Maybe this can be the problem

Probably I made some kind os mess there.

Can you explain the radio setup for it?

Your transmitter radio should use a plane model not a heli model. There should be no mixing done in the radio. All of your trims should be centered and remain centered. The throttle stick of the transmitter controls the collective pitch. Throttle is handled by either your ESC if it has a governor or the throttle curve in the arducopter software if it does not. It looks like you use channel 6 for your motor interlock switch and it is a pass through (RSC mode 1). You really should use mode 2 for ESC governor or mode 3 for throttle curve.

Still not get it.

My transmiter is on plane Mode
CH1 ail
CH2 ele
CH3 Thr
CH4 Rud
CH5 6 pos Knob for flight modes
CH6 Pot for future tunning
CH7 switch for Camera
CH8 if I left it open no arm and motor interlock msg
What the set for it.? Switch Knob stick?

Maybe this is all the point i dont know configure motor interlock. The way I found to make it arm was to mix channel 3 on it

I think we are set now…
I send you a video to see the behavior

Its still tilts de swash over 1776 pwm vem motor is engaged.


When I hit the switch for interlock and add pwm the servos stay still until disarm

Sorry I stand corrected. Do not use a mix to the throttle stick to start the motor. Use channel 8 to enable/disable motor interlock. Do you have an esc with a governor?

No I set it to Curve
but a set a very low curve just for safety

The set channel 8 on transmitter to a switch. Typically I set it to the same switch on the transmitter that I use for throttle hold. With the switch low the motor interlock is disabled (motor off) and with switch high the motor interlock is enabled (motor on).

Yes now is set correctly I set it to thr hold switch

but on the video you can see the behavior stays

but when I hit the interlock switch while armed the behavior dont appears only whith motor engaged

I understand your concern. I can’t fully explain this behavior. I’m not sure that I have ever put the aircraft in that situation (i.e. full collective with some cyclic input) but we have not received any issues with aircraft in flight. Like I’ve said earlier, bench tests can be somewhat deceiving with this type of control law design.