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.
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
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.
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).
We use an 7 dBi big stick omnidirectional antenna for the VTX on the UAV and a Yagi for the GCS. The choice was mainly based on mass and gain. Thanks for the tip, if you know of any that are less than 50 g let me know.
Hi there, our prime concern was compactness, portability and low mass (high endurance). The Y6 has approx. 15% less thrust than a Hexrotor of the same size. We are prepared to accept this, given the other advantages. We set the rotor separation at an optimal distance of approximately 1R. Although, this is not very sensitive to variation. We use large CF rotors of about 16 inch diameter which are efficient and run at low speed (2000-3000 RPM) with low current draw.
Comments
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
http://acl.mit.edu/papers/GNC11_Cutler_uber.pdf
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?
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 (http://www.hobbyking.com/hobbyking/store/__27750__5_8GHz_Circular_P...)
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