Adjust Airspeed In Flight

For our UAV project we are using the Pixhawk and Mission Planner 1.3.34. During flight we'd like to adjust the airspeed of the UAV. We are in AUTO mode flying the waypoints and are using the "Change Airspeed" under the ACTIONS tab. However, the speed of the airplane doesn't change. We can change the altitude using "Change Altitude". Is there another parameter we need to set in order to make this happen? Thanks.


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  • Developer

    I've tested it in the simulator and it works - I reduced the flight speed from 22 to 18.  I assume your screen shot isn't with your plane connected - 100 m/s is a lot.

    Note the initial value comes from TRIM_ARSPD_CM and that's what your changing when you adjust that value.

    Also, make sure both ARSPD_ENABLE and ARSPD_USE are both set to 1.

    I'll be interested to hear how you go.

    Thanks, Grant.

    • Right, the airplane is not connected. I was showing where I was adjusting the speed and yet nothing was happening. Which brings up an interesting question. I have the unites set to FPS (feet pound seconds), but is the speed change button still in SI? But I'll check the parameters that you say check. We'll fly here soon and I'll report back.

    • Developer

      Just for completeness I should point out that if you aren't using an airspeed sensor (or have it disabled) then the value in this box will be TRIM_THROTTLE.  Perhaps that's why you have it set to 100 - is your TRIM_THROTTLE at 100?

      Thanks, Grant.

  • Are you using a pitot tube?  If not, then you may need to change throttle % demand instead of airspeed.  My understanding is that APM has two separate throttle control systems, one based only on throttle %, and one based on airspeed if an airspeed sensor is installed and enabled.

    • Calvin, I think this may be what you're looking for?

      If that's the command that you are already driving to the plane, you may want to try sending a throttle percentage instead of airspeed. Maybe despite having a pitot, it isn't active in the flight controls?

      I haven't attempted this though, so I'm only really supplying you what I dug up.
    • Thanks! We'll try this on our next flight.

      By the way, I've included a picture and circled the command that we were using to attempt to change the airspeed in flight.3702733453?profile=original

    • Yes. But when we command an airspeed change, it doesn't happen. I know there is a setting where you can set a typical cruise speed, but that might not always be convenient for what we are doing. Therefore, it would be nice to change it on the fly.

  • @Calvin R. Walker

    I am independent developer with DJI and other drone manufacturers.

    Generally you plan a mission with a mission planner or Ground Control Station

    set waypoints and run self-test procedure if the mission is possible.

    Changing airspeed within a mission should be done off-line at the level of mission planning.

    You plan 2 or missions for the same waypoints but set dirrent airspeeds and run test if 2 missions are possible.

    If yes, you upload the missions to flight controller and start one of the missions

    and switch between missions  1 > 2 or 2 > 1.

    But in practice, such switching may appear not possible since flying at higher speed, another route is generated, so for the given geolocation of your drone it may no be possible

    to complete another mission and vice versa.

    Intelligent controller, in theory , could re-calculate if follow-up of the mission at changes airspeed is possible and change the airspeed, but this is still theory but in practice, every mission flown should be posssible, so pretested at the ground station against Google Maps

    or other mapping system, to avoid collision points, obstacles.

    Birds, generally change speed during a flight and change mission, since they are equipped with 3D obstacle avoidance controller ( eyes + brain).

    Group of researchers from MIT presented an intelligent, fix-wing drone with obstacle avoidance system (radar), so a preset route can be modified on-the-fly and real obstacles in underground parking lot can be avoided.

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