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  • Dr Prior,

    I've never heard of COFDM before, and I've only related thing I've been exposed to is CDMA and it's use of orthogonal numbers, but it's very cool.  Those are great flight time numbers; thanks again for all the information and keep us posted on new developments.

  • Mohamed, thank you for your comment. There are always compromises to be made. We try to realize the largest props (for efficiency) with the most compact size in terms of diameter and height, and also minimum mass for max endurance. So far we are very happy with the performance and stability.
  • Hi Josh, we have used linear polarized base station antennae successfully. However, they can be large and heavy for high gain. We definitely have multi path when operating in urban environments and also when operating over long range and at high power. COFDM systems are great for multipath, but tend to be very expensive $5-$10k each. 5.8 GHz has less penetration, but the fresnel zone is smaller and the frequency is less congested. 2.4 GHz is good for the UK, but has limited range. We can hover for 32 min, during the DARPA UAVForge challenge we were flying for 20-25 min.
  • Dr.Prior,

    Halo is very good machine ,  I have doubt on the force / torque acting up on each arm of  the copter , if the distance between the coaxial motor are increased the resultant torque will be predominant at the center longitudinal axis of the arm, i think that would interfere in the overall stability of the uav.  could you please correct me if i have mistaken your statement 

  • Dr. Prior,

    I was more curious about your use of linear polarization  and if you had any multipathing issues on your video feed.  My understanding of 5.8 GHz is that it's objection penetration is poor, and overall has less range, but it does OK in clear line of sight applications.  1280 MHz CP antennas are quite large; can you use a 2.3/2.4 GHz in the UK?  I feel that they give a decent range/size trade-off.

    Also, what's your average flight time with your full payload?

  • Jean-Baptiste, here is a good paper from MIT:
  • No, though I understand that this could be advantageous. The CF props that we use only come in certain configurations. Variable-Pitch multirotors have been used by various researchers in the recent past. They have clear advantages in terms of control, but also add a layer of complexity.

  • Thanks Stephen.  Do you use a higher pitch on the bottom props?  Also, do you have any thoughts on variable-pitch multirotors?

  • I should state that we have tested circularly polarised antennae at 5.8 GHz, however they have limited gain and at 1280 MHz (legal US VTX Frequency) are rather large. Remember, that we were trying to transmit over a distance of 2 miles (3.2 km).
  • Circular pol. Video Antennas are really improving the videoquality !! I did my own set for 5,8ghz. I the mean time they are "ready made" available (

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