directional ultrasonic beacon

Discussion in 'General Electronics Chat' started by kubeek, Aug 4, 2014.

  1. kubeek

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    This is not strictly electronics, but anyway.
    I want to make a device that would allow an autonomous drone to land inside some specific area, hopefully in bad weather as well as nice weather, and should be used for the final approach only.

    Since time of flight systems will be quite susceptible to wind, I want to try make something new. Aircrafts, especially on aircraft carriers use a device that shows different light patterns based on the angle of approach http://en.wikipedia.org/wiki/Optical_landing_system

    I would like to try and do this using directional ultrasound transducers, such that each one will have different modulation, and the drone will determine its angle based on those.

    Do you think that such system would be possible to do and could guide the drone to land on say 2x2m landing pad with 0.5m span quadcopter? The idea is that gps will guide it to the approximate location, and then the landing system will guide it the precise landing spot.

    Please tell me what you think about this, or if you have some other idea that would be not too hard to implemetnt and would work in bad weather - imagine rain, fog and wind, so no optical quidance and problems with ultrasonic TOF measurements. Actually I am no too sure this would be a better solution than TOF beacons..
     
  2. Alec_t

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    Ultrasound will be attenuated significantly in air, so would provide only a short-range homing system. How close could you get to base using GPS?
     
  3. kubeek

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    Not entirely sure, but I´d guess about 15 to 20 m.
     
  4. Alec_t

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    A quick google suggests ultrasound attenuation would be ~4dB per metre at 40kHz. So you'd have to pump out a fair bit of power for reliable detection at 20m, especially in the presence of ultrasound generated locally by the rotors/motors of the drone.
    Could you perhaps use optical beacons, an on-board camera and some clever image processing instead?
     
  5. sirch2

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    I've done over 11m at 40kHz with a tuned circuit on the transmitter giving around 40V into a standard piezo transmitter and a 2 stage op amp on the receive end to get a 5V peak to peak signal. Better transmitters and amp stages may get you a bit further.
     
  6. ErnieM

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    How does the drone "hear" the directional beacons that are pointed in another direction?
     
  7. kubeek

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    My idea was that all the transmitters would have the same carrier frequency, and different AM modulation frequencies. There would be a single receiver on the drone, and from the levels of the different modulation frequencies it could exctract the position relative to the axis of the landing pad. Kind of like the simple solar tracker schemes work.
    This all assumes that the ultrasound coming from each transducer is going to stay in mainly a fairly narrow beam, which I am not too sure about. Maybe parabolic reflectors would help with this?
     
  8. kubeek

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    From what I can find it should be around 1.2dB at 40kHz and 4dB at about 80kHz. This gives me much favorable numbers than the previous 80dB at 20m. But still at 20 m I should be facing around 24 dB from the attenuation, and another 26 for the spreading loss.
     
  9. THE_RB

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    Rain and wind will totally kill your ultrasonic performance. You are better with optical beacons in both cases.

    Even in fog a low freq optical (ie IR) will work pretty well, possibly better than ultrasonic.
     
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  10. sirch2

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  11. kubeek

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    It seems that IR would be much better in bad weather, so I will start experimenting with that.

    How would you go about modulating and demodulating the light such that I would be able to extract relative intesities for each transmitter? Is it possible to use a single frequency for each transmitter and then a single receiver? Or maybe I could transmit each one in turn in some pattern that would let me know which is which. That might actually be easier to implement, as it would have less analog circuitry involved.
     
  12. sirch2

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    Before you get to far into it I would check how well IR works in rain, especially with raindrops on the IR LED and phototransistor. As far as modulation goes, TV remotes work by IR modulation and there are chips for it, or just use an MCU.

    What sort of drone are you flying anyway? Most consumer level drones are not going far in bad weather anyway.
     
  13. kubeek

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    I am not flying anything right now, but want to start making a drone that would be able to say guard a property, in all weather. Most likely a hexa or octocopter, but I am quite far from having the actual first drone in hand: I still need to plan a lot of things in advance to get it working the way I want. Without this landing functionality it would be pretty much useless, as I dont want to have some operator manually bringing it down for recharging. In normal weather I could use a camera and optical recognition, but in bad weather this is not going to be enough.
     
  14. Alec_t

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    Is that going to be possible? Flight time for most hobby drones is only a few minutes before the batteries need re-charging.
     
  15. kubeek

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    I expect around 20 minute flight time, which should be plenty for the sizes I have in mind.
     
  16. Shagas

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    Would it be possible to implement a navigation system like this using radio or ultrasonic triangulation?
    I mean setting up 3 Tx in a 100m perimeter and using time -> digital converters to determine a reasonably precise position within the perimeter.

    Also , have you considered all the technical difficulties of bad weather on the quad (exposed motors etc) ?

    EDIT: Another idea(using only 1 beacon): If the clocks on your quad and the ultrasonic beacon were synced down to microseconds then
    you could simply use pulse delay times to calculate the positional radius of the quad from the beacon and through a bit of "Hot , cold " trial and error , calculate the movement towards the direction of greatest decrease of pulse delay.
     
    Last edited: Aug 5, 2014
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