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Re: [Paparazzi-devel] Time to fine tune...


From: Christophe De Wagter
Subject: Re: [Paparazzi-devel] Time to fine tune...
Date: Wed, 5 Oct 2011 10:35:49 +0200

Dear Vladimir,

The dash button changes the NOMINAL_CRUISE_THROTTLE to the MAX_CRUISE_THROTTLE while the loiter button changes it to MIN_CRUISE_THROTTLE. 

This makes it easy to suddenly make the UAV fly a bit slower or a bit faster. However, when chaging the throttle, you also need to change the elevator trim in order not to climb/descend too much. This it what AUTO_THROTTLE_LOITER_TRIM and AUTO_THROTTLE_DASH_TRIM are for. (I think the unit is MAX_PPRZ = 9600 = full deflection?) 

The auto-throttle loop is actually the most difficult loop to tune as it has both the speed and altitude that are correlated. Controlling both speed and altitude with high performance is very hard.

---------------------

Step1: outerloop: if altitude is not good -> compute a climb/descend rate. (including MAX_CLIMB)

e.g. 10 m too low x 0.1 alt gain = climb_command at 1 m/s
e.g. 50 m too low x 0.1 alt gain = climb at 5 m/s > MAX_CLIMB -> climb_command = 2m/s

---------------------

Step2: innerloop: [many many options here, but since you ask for simple I'll only give one robust and simple:]

too low -> pitch up and extra throttle (if you only apply throttle, airspeed will increase, if you only apply pitch airspeed will decrease, with proper tuning you can get a pretty constant speed even while climbing and descending) 

pitch_command = climb_command x pitch_of_vz
throttle_command = nominal_cruise_trim_throttle + climb_command x throttle_climb_increment

e.g. climb_command at 1 m/s x pitch_of_vz 0.15 = 0.15 radians pitch = 9 degrees pitch up
       climb_command at 1 m/s x throttle_climb_increment 0.25 with nominal_cruise_trim_throttle 0.5 = 75% throttle

-------------------

If you use AGRESSIVE_CLIMB then if the altitude error is larger than the chosen threshold a precomputed pitch and throttle will be applied. 

AUTO_PITCH is for constant throttle and control height with elevator only

auto_throttle_p/i/d_gains are to regulate the climb rate more precisely








When you fly too low, ideally you should add throttle AND pitch up a little. Without  pitching up the speed will first increase, a


-Christophe 



On Wed, Oct 5, 2011 at 8:33 AM, Volodymyr Khudyakov <address@hidden> wrote:
Dear friends.
Many thanks for answers...
I'm pretty understand how to add sliders & papgets to Paparazzi GCS panels.
I do this many times. My question completely unrelated with MAVLink or QGC
(thanks, Meier).
I only ask for 3 variables:

AUTO_THROTTLE_LOITER_TRIM
AUTO_THROTTLE_DASH_TRIM
AUTO_THROTTLE_PITCH_OF_VZ_PGAIN

Simulation is bad example (thanks, Gareth) because I flew on real plane in
real condition, too far from ideal.
I need to understand how them work and how I use it for fine tune.
If many of yours familiar with theory of operation - why nobody explain this
in really simple terms? For example:
If you set up
<define name="AUTO_THROTTLE_PITCH_OF_VZ_PGAIN" value="0.35"/>
value 0.45  - you plane response faster for elevator...

Sincerely
Vladimir


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