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Re: [Paparazzi-devel] Energy and catapult launch question

From: Christophe De Wagter
Subject: Re: [Paparazzi-devel] Energy and catapult launch question
Date: Wed, 19 Dec 2012 15:09:28 +0100

1) Mentor_energy seems not to have energy gains on the paparazzi git. (see post of yesterday) 
3) The post-catapult pitch dip has nothing to do with the control loops. It is attitude estimation only. Your define looks good. 

However: the "integrate-pitch-up-fast-if-already-accelerating-forward-faster-than-needed-while-still-low" approach of energy control might help with the attitude estimation pitch error. The control loop will pull the nose up "any needed angle" to make the plane accelerate as required towards the wanted airspeed and climb as much as possible with the spare energy. 


catapult launch 10m/s
wanted airspeed 20m/s

normal energy control:

phase 1: accelerate @ 1/4*g forward, full throttle, -> climb angle 10 degrees
phase 2: 20m/s reached, still full throttle -> climb angle 35 degrees (no more energy wasted to accelerate)

pitch error with energy control

Suppose after 3 seconds your pitch estimation is off by 20 degrees. Normally your controller that holds your pitch at say 15 degrees would now steer an actual pitch of -5 degrees: causing it to dive violently. This pitch error appears to the energy control loop as a deceleration: (the estimated pitch is higher than the real, so if the estimated pitch is zero then the real pitch is -20, that means the real gravity (positive up) will appear to the autopilot as pointing backwards (decelerating with sin(20)*g). In the mean time the diving plane will accelerate forward at least more than the sin(20)*g. So if you set the desired acceleration in the outerloop not too high, then the energy loop will still integrate pitch up however big the pitch error grows. 


On Wed, Dec 19, 2012 at 1:32 PM, Chris <address@hidden> wrote:
I am trying to test the energy control together with the catapult launch module but i have 3 questions.
First i don't see where in the "Mentor_energy" airframe file the gains for the energy loop are defined,
are they set to 0 by default?
Secondly is there an example how to use the catapult module in a flight plan?
Thirdly which control loop is better (if any) for catapult launch in order to avoid the pitch down problem
during high acceleration after the airplane leaves the ramp?
I use the float_dcm AHRS and i have defined <define name="USE_AHRS_GPS_ACCELERATIONS"/>

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