Re: [Paparazzi-devel] 127 ways to reverse a servo

[Gautier Hattenberger]

Hello,

You can't change the sign of the control loop. It's a negative feedback 
control, and the way it is written, the coefficients have to be negative.

Your problem is that your radio xml file and the autopilot doesn't match 
when they send orders, so your commands will be different between manual 
and AUTO1/2 (and there is no way to make it work!). To work properly, be 
sure that your RC gives the min value when turning right (roll) and 
going down (pitch) (http://paparazzi.enac.fr/wiki/Radio_Control). Be 
careful that all your RC channels are not set to reverse. When it's 
done, change the min/max value in the airframe xml file (servo section) 
so that all surfaces move in the right direction in manual. Now, if they 
are reversed in AUTO1/2, change the command laws (command_law section) 
but it shouldn't be necessary.

If I have not missed any step, this leaves only one (good) way to do it ;)

Gautier


Martin P a écrit :
> Hi, 
>
> I am still ground testing only. 
> I was happy to see that my ailerons moved in the correct direction in manual mode. 
> When the ailerons moved in the wrong direction in AUTO1, I changed the sign of ROLL_ATTITUDE_GAIN from negative to positive and saw that the ailerons moved correctly when I rolled the aircraft left and right. All right, but then I started the simulator and the plane went in a small circle. ROLL_ATTITUDE_GAIN back to negative, and it moved nicely in the simulator but wrong again in the real plane. 
>
> Well, before venturing into the air, I would like to have everything correct. Even when I plan to do only AUTO1 flights, there is a chance that I lose the 35MHz connection (interference, broken PPM wire,...) and fall into AUTO2. Then I would like the plane to fly and not to crash. 
>
> What possibilities are there to reverse an axis? 
>
> 1) in the transmitter  
> 2) in the radio xml-file 
> 3) in the servos section 
> 4) in the RC commands 
> 5) in the command laws 
> 6) in the outer loop 
> 7) in the inner loop 
>
> 1) and 2) should be the same, but when I tried it with the throttle, it wasn't. 
>
> 2 to the power of 7 is 128, minus the setting you have, gives 127 ways to reverse a servo, probably 126 of them are wrong ... pretty confusing. 
>
> Does the simulator tell it right or is there something to reverse as well? 
> Are there laws to reduce the number of cases, let's say that ROLL_ATTITUDE_GAIN and COURSE_PGAIN should have the same sign? 
>
> Greetings, Martin 
>
>
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