I would like your help.  Safety is my number one issue with drones. Last year I was learning to fly my  Parrot AR. Drone that I had fitted with carbon fiber blades.  I was doing a simple take off and landing in the living room to impress a friend.  I was hovering and accidentally hit the "Home" button. Instead of a soft landing the AR Drone took off from a distance of about 10' from me and came right at my face.  As I was trying to deflect it, the carbon fiber blade put a gash on my left eye, just missing my eyeball.  I don't know about you, but that really soured my experience and nearly put out my eye. 

I had every intention of taking the money I had saved to start a Real Estate Photography company.  Instead I became afraid of the drone. A friend purchased a Phantom from DJI and had a very similar experience on his very first flight.

Oddly enough I became so fascinated with the industry that started to look for solutions to the danger of any multi-rotor with plastic or carbon fiber blades.  I came up with what I affectionately call DroneKone.  It is complete and substantial propeller protection to help make drones safer.

I started a small company with my limited funds and developed a model of my concept.  I was able to get a provisional patent on my safety device.  Then I had a devastating life event and was out of action for a year.  I have recovered.  I don't have any funding at this point except out of my pocket and started seeking funding. I was told by a potential investor that I needed to survey 100 people to find out if my product is market worthy.

Okay enough story.  Simple Survey for Safety:

  1. Yes or No  Are you concerned about drones flying around Children? 
  2. Yes or No  Do you have a concern about your personal safety when flying a drone?
  3. Yes or No  If a safety device was available would you consider purchasing it?
  4.                  What would a safety device look like to you if you could design one?
  5.                  How much would you pay for a safety cage if one was available when you purchase your drone.

I greatly appreciate you reading this far and ask for help.  If this is just plain stupid, then I would like to know that now, before I spend any money on moving further.

Thank you so much for listening.  I am grateful to be a small part of this awesome community.


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I can totally agree with the comments about the patent. We've recently had a UK and US patent granted and the costs to get this far have been about 10x what we originally expected. It's an expensive and very painful process.

On the physics side of things, the above post is not correct. I designed a VTOL UAV for my master's degree and have designed shrouded rotor ducted fans since so have battled with this problem a few times. There is certainly no "vacuum" at the inlet, and the rotor disk does in fact raise the pressure. If it didn't there would be no resultant force and (if Newton got his second law correct) anything with a ducted fan (such as a hovercraft) couldn't accelerate.

This applies both to a open propeller and a ducted fan or shrouded rotor. Here are the calcs for an open propellor and I'll upload the details for a ducted fan when I get time.

A correctly designed ducted fan does have an increased static (have a look a this paper from Rutkowski and Krusz) over an open rotor but you've got to think about tip clearances, inlet diameter, duct weight and other potential problems.


Worthington Sharpe

This is not the place to have this discussion ... but your reference article and your assumptions assume there is a constant source of fresh air. Suppose I put the propeller several feet into a duct, would you agree then that just above the propeller is a vacuum as long as the prop rpm speed is greater than the ability of the air to flow into the 14.7 psi (STP) vacuum?

Have you wondered why the efficiency of a hover falls off with RPM? It is because the fresh air, only driven by atmospheric pressure, hasn't had time to refill the vacuum left by the prop's rpm.  

If so, there is some point down in the duct, depending on prop's RPMs that the hovering prop removes all the air in one sweep and has to wait for 14.7 psi to push 0.07lbs/ft^3 of mass into the propeller area. (also Newton's second).  

I'm afraid "no "vacuum" at the inlet" would be tough to convince a vacuum cleaner or leaf blower designer. I do admit this level of detail is above a master's degree. Please PM me and we can take this off line and I will explain who I am and my experience. Thank You (my apologies to Bob Cooper) 


You are obviously a noted scholar on the subject.  It may be that the open rotor is a reason for popularity, but as we move forward in the industry no one in their right mind would allow any commercial vehicle such a lapse in safety.  I'm certainly not a engineer or aerospace type, but I'm certain the "math" of the situation is really just thrust vs. weight.  I know that is way to simple, but if the motor can create a variable of rpm's from 0 to 40,000 rpm and hovers with just 30% of power, than I'm certain as the industry grows, thrust will not be a problem.

I get that it is not a trivial problem, but if it was easy everyone would have done it. 

I do thank you for your excellent thoughts and understanding of the issues.  Thank you for the math reference.



1) 50 percent of the market is the DJI Phantom line.  I believe they have placed over 400K units on the market. I'll take 20% of that industry and do just fine.

2)Okay a screen for a house fan.  Fans were first make without a safety screen or enclosure.  That was the dark ages of technology.  Today no one would even think of having a house fan without adequate protection.  It is just the norm.  Just because drones are in the dark age of their technology, doesn't mean we can assume safety from propellers is not an issue.  There are plenty of examples of injuries, accidents and multiple lacerations from drone propellers.  Oh by the way, provisional $3,100.  Non-provisional priceless.

3) Physics - Sam Worthington has the math that makes this statement incorrect.

Sorry?  When an average Joe is actually cut enough times by some young user, I won't have to do anything.  The FAA or US Congress will make it mandatory.  Besides, why should we not consider safety as an issue for "young emerging technology under fire from so many"?  I know it goes against the grain, but the discussion is valid and needs to be discussed here and in other forums.

I've had 3 crashes in 3-4 years. One was I simply screwed up and ran out of battery power. The other two were a plastic prop snapped off and the quad crashed to the ground. CF props might be nasty to get hit with but they don't easily break in mid flight so I'd say you have to consider that as well. 

wow... really. See my earlier post. Might want to back off on the insults their buddy. 

1- Yes

2- Yes


4- I picture a single square [ for a 4 motor MR ] shaped wire as small as possible around the entire outside. I think that would be less weight and material than 4 individual circles. If it could somehow incorporate it's mounting as landing gear it would justify it's added weight even more so. 

5- $40-$80 depending on quality / durability


Thank you for taking the survey. 

I have seen a device that you describe. For the life of me I can't find an actual web address. AEXO is the name of the product.  I could only find that it raised some money at this web address: https://www.kickstarter.com/projects/aexo/aexo-the-protector-drone.  It isn't cheap. 399 Euro for Inspire. That is almost 500 US bucks (don't know the current exchange rate so I'm guessing.)

I appreciate your honesty and thoughts.


For further information I just put up:  www.safethedrones.com


Seen them all before.  What is your point?


That sure seems like an awful amount of mass / air restrictions. That would be safety at it's maximum. Virtually bullet proof. Speaking for myself however I'd be interested in something in between nothing and that. 

I'm sure you have thought about just about all aspects but one thing that occurs to me is I bet the biggest threat is a MR coming at you horizontally not vertically.  I'd like to see something that just protects against that. That is of course far less protection than your design.

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