Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Airflow on/around quadcopter drone

  1. Sep 26, 2015 #1
    Hello,

    I'm a journalist interested in using an air-quality sensor on a drone, and I'm wondering how the airflow will affect the readings. This would be assuming that I will use a DJ Phantom 2 quadcopter with a GoPro underneath, the drone specs can be found at this link. For the project, we will compare results using a drone along with a weather balloon — just to be sure that it is actually feasible, but I thought I would come here first, as this community has knowledge that I do not.

    So I have a few questions:

    What would be the ideal place to position an air-quality sensor?
    Could I use a formula to correct for the difference in results?
    What factors do I have to consider?
    Is there a realistic way to come up with reliable results?

    Thank you,
    Daren
     
  2. jcsd
  3. Sep 26, 2015 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    What does the "air-quality" sensor measure (and how)?
     
  4. Sep 26, 2015 #3
    It's measuring particulate matter — pm10 and pm2.5. I'm not sure how it does it, though. Here is the information from the website.
     
  5. Sep 26, 2015 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    I guess testing is the best way.
     
  6. Sep 27, 2015 #5

    JBA

    User Avatar

    1. If you place the collection point below the rotors' then it will be subjected to turbulence that effect the particulate count. Alternatively, by placing the air collection point above the the rotors' height you may be able to collect a sample from a more linear minimally disturbed air stream. Unfortunately, in either case the air stream due to the air flow required to support the copter you are still going to have a relatively high velocity that can effect the particulates' distribution. Additionally, unlike a floating balloon, unless it is tethered, that can move laterally in concert with the wind, your hovering, or moving copter will have a lateral air flow across it that, again, could effect the particulate distribution of the collected air.

    2. I seriously doubt an equation could correct for any error due the amount of unidentifable variations that can be introduced by turbulent air.

    3. See no. 1

    4. The balloon method already does that.

    Regardless of all of the above, your method's accuracy can be determined by your planned ballon comparison test; so, if the resources are available, address all of the issues presented on this thread as best as you can and give it a try.
     
  7. Sep 27, 2015 #6

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Two ideas to minimize the effect of air flow:
    - put the sensor in the middle, preferably on top.
    - attach a cable to the drone to have the sensor several meters below the drone

    The drone can also follow the wind if necessary.
    The comparison to the balloon or the sensor far away from the drone could reveal some pattern.
     
  8. Sep 30, 2015 #7
    What type of sensor are you using?
     
  9. Sep 30, 2015 #8
    I'm using this one:
    http://www.tzoa.com/#homepage

    However, if you think there is a better one, I'm all for looking at other options as well.
     
  10. Sep 30, 2015 #9

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    It seems to me the drone will just mix the air around it; as long as its an electric drone and the sensor is exposed to the free air around the drone I'd be surprised if it affected your readings at all. The main limiting factors will be that the drone will be severely limited in operating altitude and flight time compared to a weather balloon.
     
  11. Sep 30, 2015 #10

    berkeman

    User Avatar

    Staff: Mentor

    I'd be inclined to put the sensor on a vertical boom about a meter above the drone to get in more quiet air, and also put a wind direction and velocity sensor on the boom as well. That way you can follow the wind when you want to take that variable out of the equation...
     
  12. Sep 30, 2015 #11
    How much would that cost? And how much weight would it add to the mix?
     
  13. Sep 30, 2015 #12

    berkeman

    User Avatar

    Staff: Mentor

    A quick search looks like you can get something for around $50, and it should be pretty light weight. Heck, as long as you have a visual on the drone, you can just put a red ribbon at the top of the boom with the sensor. Fly the drone to keep the ribbon vertical... :smile:

    Here is a Google Images search on wind sensors:

    https://www.google.com/search?q=win...ChMI8fTI2vGfyAIVCUmICh30ogvp&biw=1164&bih=804

    .
     
  14. Sep 30, 2015 #13

    rcgldr

    User Avatar
    Homework Helper

    I'm wondering about the effect on stability of the drone, since the boom would increase angular inertia about the pitch and roll axis, and could also create an adverse torque when moving laterally (due to the relative crosswind).
     
    Last edited: Oct 4, 2015
  15. Sep 30, 2015 #14

    berkeman

    User Avatar

    Staff: Mentor

    Excellent point, as usual. :smile:

    So a good addition would be a symmetric boom on the underside of the drone. Better yet (and more practical for takeoff and landing the drone) would be a 3-element pyramidal structure below the drone that counterweights the top single boom, and forms a triangular landing leg structure. This could be a pretty cool looking drone...
     
  16. Sep 30, 2015 #15

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    Is any of that really necessary? The sensor is detecting air particulates nearby, the drone is in the air you're trying to sample. Case closed? The only possibility of a problem is if for whatever reason the prop wash from the drone is somehow incompatible with the sensor?
     
  17. Sep 30, 2015 #16

    rcgldr

    User Avatar
    Homework Helper

    That would further increase the angular inertia about the roll and pitch axis. As long as the center of mass is below the plane of the rotors, that should be good enough for stability, and if the boom is light, then any added mass would not have to be that large or located that far below the the plane of the rotors.

    The main issue would be potential adverse torque due to aerodynamic drag during lateral movement (relative crosswind). Having a boom extend below would compensate, but the increased angular inertia could be an issue. All but the lightest of cameras are usually gimbal mounted, effectively acting as a bearing (when holding the camera's orientation fixed), reducing the effective angular inertia somewhat.

    An alternative would be to attach a horizontal boom (carbon fiber tube) to the under body of the drone, with both ends extending outwards just enough to be past the induced downwash, with a sensor on one end and a dummy load on the other end. The boom would have to be mounted so that it doesn't interfere with the camcorder. This should involve less of an increase in angular inertia, and also keep the center of mass below the plane of the rotors.

    The other issue is if the drone can be set to remain level and just drift with the wind to avoid cross wind issues. Trying to use ribbons and have the pilot compensate could be difficult.
     
    Last edited: Oct 4, 2015
  18. Oct 1, 2015 #17

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    Again, it seems to me there shouldn't be any problem in directly sampling the particulates in the turbulent prop wash air?
     
  19. Oct 1, 2015 #18

    JBA

    User Avatar

    Because of the CG shjift issue, as an alternative to placing the collection point above the copter, I was among those who suggested it, what about extending (two diametrically opposed for balance) horzontal tubes from the copter with cup ends joining under the copter at a common collection chamber with the sensor enclosed and a bottom opening so the downwash from the copter blades will draw the undisturbed air sampling thru the tubes and past the sensor.
     
  20. Oct 1, 2015 #19

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    Why bother? Why not just sample directly in the prop's down wash??
     
  21. Oct 1, 2015 #20

    JBA

    User Avatar

    Because the downwash area is turbulent. In the extended arms arrangement the turbulence will be downstream of the sensor and away from the collectors sampling regions
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Airflow on/around quadcopter drone
  1. Airflow around a wheel (Replies: 2)

  2. Spanwise airflow (Replies: 5)

  3. Building a Quadcopter (Replies: 12)

  4. Airflow for cooling (Replies: 4)

Loading...