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Re: [Paparazzi-devel] Failsafe values

From: Reto Büttner
Subject: Re: [Paparazzi-devel] Failsafe values
Date: Fri, 13 Sep 2013 15:39:23 +0200

Hi Alonso
Failsafe is a complex issue and many experts are debating which way it can be achieved best.
RC.xml refers to the radio control xml, see:
Forget about trying to fly by heading and altitude, except you are a real expert. In this scenario the GPS signal is missing, but the telemetry and RC connection are still alive and the plane is flown home by compass and barometer. Very tricky, I don't know if anyone has ever done it.
Concerning the commands versus FAILSAFE section, I guess you don't understand the difference between "totally out of control" and "still involves the inner loop". The first is when neither GPS nor attitude sensing (IMU or IR) and RC don't work, the second is when GPS (and ev. RC) are missing, but attitude sensing still works.
Concerning strategy there is no general answer. That depends on failure mode, your equipment, your mission and your personal preferences. As said above, failsafe is a complex issue and many experts are debating which way it can be achieved best. You must find your own personal preferences.
The Paparazzi default setup works well for most users.

2013/9/12 alonso acuña <address@hidden>
Hi. Yes I did but it did not help.  That page appears to be talking about failsafe settings on a RC receiver which I do not have and mentions a file RC.xml which I also cannot find.

I understand that the failsafe values on the servos in the airframe file are the positions that will be used if it goes to failsafe mode but I do not understand when exactly this mode is activated and how it can be disabled

It says "In this mode, the autopilot uses the failsafe roll, pitch and throttle settings defined in the airframe file. It is recommended to disable throttle and make a shallow turn at low flight speed. When barometric information is available and compass heading information, it is recommended to disable this safety mode and train the GCS operator to bring the plane home on heading and altitude only.

Do not mix up the <commands> failsafe_value and the <section name="FAILSAFE" prefix="FAILSAFE_"> default values. The first result in fixed servo positions with the plane totally out of control, while the latter still involve the innerloop to stabilize the plane."

So given that I have a Lisa/M should I go for disabling this and trying to use heading and altitude?  If the operator can be trained to fly by heading and altitude why not have the aircraft do it?

And I still do not understand why there are failsafe values in the commands section and in the FAILSAFE section and which if any should I use. 

And I do not understand if the strategy is to keep the plane in the air or bring it down softly or something else?

Seems like a complex subject at least for a beginner.

On Thu, Sep 12, 2013 at 5:25 AM, Reto Büttner <address@hidden> wrote:
Did you read the wiki:
Regards, Reto

2013/9/12 alonso acuña <address@hidden>
Hello. What is the procedure to set good values on these settings:

    <axis name="THROTTLE" failsafe_value="0"/> <!-- range is 0 to 9600 -->
    <axis name="ROLL" failsafe_value="0"/> <!-- range is -9600 to 9600 -->
    <axis name="PITCH" failsafe_value="0"/> <!-- range is -9600 to 9600 -->
    <axis name="YAW" failsafe_value="0"/> <!-- range is -9600 to 9600 -->
    <axis name="KILL_SWITCH" failsafe_value="-9600"/>  

  <section name="FAILSAFE" prefix="FAILSAFE_">
    <define name="DEFAULT_THROTTLE" value="0.4" unit="%"/>
    <define name="DEFAULT_ROLL" value="15." unit="deg"/>
    <define name="DEFAULT_PITCH" value="5" unit="deg"/>

    <define name="HOME_RADIUS" value="DEFAULT_CIRCLE_RADIUS" unit="m"/>
    <define name="KILL_MODE_DISTANCE" value="(MAX_DIST_FROM_HOME*1.5)"/>
    <define name="DELAY_WITHOUT_GPS" value="3" unit="s"/>

thanks for the help.

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