Good wind resistant drone

Ewen Rankin June 20, 2014 at 12:20am

Hi Nick

Living in the UK, my thoughts for what they are worth is that the props seem to give the biggest headache in wind.

I have a slowfly long duration quad and hex and the larger the disk, even at slower rotations, the more the wind hits it.

Smaller frame sizes with lower profiles (something more like a wing profile) Higher RPM motors with 3 blades and smaller blade diameters do the best in wind.

From my own experience using alternative materials for frame, the smaller you go the more critical the flexion of the material becomes. Flight controllers can accomodate flewing and pitch changes in motors easily from 300mm upwards but getting smaller with flexible frame materials sends them into massive overcorrections and instability

Happy to chat more if you want

Ewen

James Overington > Ewen Rankin June 20, 2014 at 3:43am

Hi Ewen, Can you give us the battery voltage, motor kv, prop diameter and pitch of your copters? Is it possible that your props just have too low a pitch speed to handle wind? If they are designed for long duration then I presume that you have opted for the largest diameter/lowest pitch speed props possible for the motors you have to improve energy efficiency. As the wind speed approaches your pitch speed your performance will suffer. You say that the 'larger the disc, the more the wind hits it' but for any prop under normal operating parameters, the air flowing through the 'disc' actually 'hits' the under side of the prop and produces a lift force. For the wind to 'hit' the top of the disc and produce a drag force that forces the copter 'down', the prop has to have a negative angle of attack (with respect to how they would normally be used) and would essentially be blowing air in the wrong direction!
- Ewen Rankin > James Overington June 20, 2014 at 5:37am
  
  BTW. Dead interested to hear any theories you have to extend flight times. My end goal is 1.5hrs with a 'Normal' Rig
- Ewen Rankin > James Overington June 20, 2014 at 4:44am
  
  Hi James. I find that its the gusts that influence the stability with the larger the prop diameters. I've used a large number of props including 2 blade and 3 blade. In a hover, smaller props with higher RPM have move a lot less in gusty conditions in my experience.
  
  The longer flight units I have are using 15x7 CF Props. I use 3cell batteries from 2200mah to 8300mah at 35c, The motors I've got on the longer duration rigs are 390kv and 340kv. At the moment I've managed just over 45 mins with a Tarot Frame (600mm) Quad with Brushless Camera Gimbal and GoPro 3+ attached. I'm currently building an aluminium frame which I'm hoping to take over the hour mark. If the wind is up tho or gusting a lot, I find that it shortens my flight time by around 1/3
  - Aaron Curtis > Ewen Rankin June 20, 2014 at 10:39am
    
    Why 3S? Isn't it more efficient to go for higher voltage, lower kv motors?
    - Ewen Rankin > Aaron Curtis June 20, 2014 at 11:25am
      
      The 8300mah are just in 3s and I have 4500mah in 3s. All my 4s & 6s top out at 2200mah which isnt giving me the flight time but yes, I need to invest in bigger batteries
      
      I will get there tho
      
      Cheers

nick rymer June 17, 2014 at 10:31am

Thank you for the input guys, I have another question. For the motors do you think it is preferable to go with say 4 larger motors or 8 regular sized motors in a x formation over under. Do either of these configurations seem to fair better against the wind?

Hugh Hemington June 16, 2014 at 8:45am

Stability is the product of many factors. Torque and power. Rapid positional awareness. Minimized wind resistance.

Longer arms can help with stability because a longer moment arm makes finer adjustment easier.

A hexacopter has the potential to be more stable, if the controller is able to exploit the extra props to make finer adjustments.

The one factor that is most likely to kill stability is cutting corners anywhere in the power, drive or "brain" trains. One weak link will handicap all the strong ones.

F. C. Bearsch June 14, 2014 at 6:53pm

Agree with all of your comments... And the same as what I have experienced... I do kite surf and never thought about using the UAV also... Not sure why as now it seems obvious... I guess I have been happy with the view from the kite, and then I just fly it

James Overington June 14, 2014 at 3:25pm

I built a quad for filming kite surfing. I fly typically in 15-20 knots but have been out in up to 30 without any trouble. Larger craft typically have more mass relative to their frontal area which means that the unwanted accelerations due to wind are proportionally less. I chose a quad for simplicity and also because fewer arms is less wind resistance. My quad spans over 1m between motors and has an all up weight of 5.5kg. I think that pitch speed is often overlooked when designing for wind handling ability. Multi rotors typically have low pitched props as this allows for increased diameter for the same input power and gives better efficiency. This is fine in hover but as your horizontal speed approaches your pitch speed, you lose thrust. I would say you should design for a pitch speed twice that of the intended operational wind speed. I currently use 16x8 props which with 620kv motors on 4s gives me a max pitch speed of around 50 knots. A number of folk advocate the use of smaller props with the belief that smaller, lower mass props give better response. I am not sure that this is always the case, however it appears that I an in a minority... You can see a discussion on this topic here: http://diydrones.com/forum/topics/design-for-wind-size-matters

Discussions

Good wind resistant drone

Replies

Activity