Drones Design

Drones ( like hexacopters) are not the best option when low noise and authonomy are main requirements.

Please consider an hand launched rc airplane with 1-2 electric engines, 1-2 kg mtow and 1-2 m wingspan.

Thanks, but unfortunately, I wouldn't be able to hover just 2 or 3 meters away. And I'd like to avoid fast movements. ;-)

It is an interesting idea, but there is a limit to the diameter possible.

As the diameter increases, so does weight. The motor must also drive much harder to push such a large blade, which reduce battery life, so a bigger, heavier battery is used... etc.

I'm not a drone expert, but I'd be willing to bet the existing prop sizes were selected for a reason, and not to simply make drones loud and annoying. There would be a huge market for silent drones.

A very large prop may also cause as much of a disturbance visually, as the smaller props do with their noise.

How would you feel about a dirigible, or balloon based drone? It would require some props for stability and navigation, but it would reduce the amount of noise significantly.

If the noise is from motor casing use moulded foam to cover the casing.To dec the noise by the prop it need to be less diameter so that it can have a enclosed frame around it covered with rubber or foam material.

Prop can be of carbon-fiber or plastic

if you increase the diameter of the rotor doesn't the noise start to increase again because of the rotational speed of the air at the tip of the rotor?

I've seen rotors with kinda ring around at the tip of the rotor-blades. This should reduce noise and increase lift at given Rpm -> less rpm needed.

Instead of designing and build a new drone ( not an easy task) may be a better solution is:

buy a standard drone ( with low rpm propellers, 3S lipo bats ) and add a long cable with the recording system attached ...

Robert,

I record audio as well and have had the same thoughts several times - I don't think that the physics work in our favor - at least not for a good full range and high fidelity recording -

What I would like to try are the little camera blimps - they stay aloft via the helium in the balloon/structure and only use the motors to maneuver - potentially staying completely silent when not moving... There have been free flying and teathered ones over the years.

I haven't have the budget to chase this idea but it seems like adopting that older (actually pre drone) concept holds more promise for a nearly silent platform.

The size of the blimp determines the amount of gas and the total lift capacity, but especially if teathered, the ability to bring mic lines down to a ground based recorder could yield nearly unlimited time aloft - and possibly also carry power and video signals if the cables are kept light enough.

I've done some projects with very long booms (up to 12M) with counterweights but its not the same as actually having an airborne platform unless you know exactly where the animals are going to be.

Mark

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Did you ever discover a solution to your problem?

The only reason I can think that large propellers are avoided is because they are harder to control, speed up or slow down. The drone would be fighting the inertia of the blades to maintain balance. But if all you want to do is hover maybe a different design that isn't a quad or hex but rather a coaxial setup. Steering can be done by changing the rotation on one of the two rotors. while moving forward or back can be done by shifting the weight beneath the blades, much like a hang glider.

If your needs are to stay up for a long period of time and be as silent as possible, then a small blimp with slow moving motors for navigation is the best way to go. This will have the least noise and also the least complexity.

The key is to reduce weight down to the minimal and then design the blimp around your maximum weight requirements. That will dictate the overall size.

Have considered to explore other areas such: increase directional audio with a professional microphones and upgrade camera to be distance but with a great zoom.

Another option is to cover the propels allowing air to flow but reducing noise.

Hold up, don't get me wrong, look: https://redshift.autodesk.com/life-saving-drone/