It's raining robots-
That will be the headline all of us will cringe at, when the Media goes manic over the first commercial drone crashes of any significance. The same way they do anytime something new takes a stumble (or two).
The thought of my craft hitting somebody really haunts my mind. I'm sorry to be a downer, this topic is definitely a buzz-kill from the heady intoxication of being in the midst of the next great economic boom, but I can't let it go.
So the topic is failure. Despite what your high school sports coach told you, failure is not just an option, it's a guarantee. Yes- our thrust makers, power systems, flight controls, and firmware will get better quickly. However, even if we could magically achieve 100% reliability with all of our flight critical components, failure will still be there. The most random shit is always going to happen.
The project-
I'm focusing on multicopters in particular with this project, but I feel that a similar strategy would be effective with fixed wing craft as well, in fact it's used all the time.
The specific type of failure scenario I want to tackle here is a total loss of thrust and/or control. Deployable parachutes are being developed, and seem to be working well. I would like to pursue a more passive system, an aerodynamic design built into the airframe itself. Inspired by watching Marcy fly around and wingsuit pilots, I hope to achieve a passive "auto-rotation" or glide of the entire airframe. If the the craft looses thrust, the actual act of falling makes the conversion into an alternate flight mode. A slow spiraling glide to the ground, with a gear down orientation maintained. Energy absorbing landing gear, maybe even a supplemental air bag would compliment the design. The key in my opinion is making the recovery mode completely non-dependent on any system other than gravity and wind resistance. Time is so critical in a recovery scheme for these types of failures at the altitude multis usually work. No sensors, servos, or firmware required, just a thoughtful arm and frame design. The challenge will be to prevent undesired flight characteristics while in normal powered flight, in fast controlled descents we don't want to be induced into a flat spin! Can the free fall decent rate be slowed enough to usefully lower the risk of damage on the ground and airframe itself?
Step one- Get to the sewing machine and build a Bat suit for one of my quads
To be continued.
Comments
I agree with R_Lefebvre, Forget Autorotation- it will never happen as you have no energy stored in the rotors, everything esle is too complex.
the KISS aproach is always better and more relaible (Keep It Simple or you'r Stupid). every additional part that you put into a system doubles the probability of failure. A multi-copter is a collection of parts that you fly until something fails, then its an expensive brick. Thats why I fly planes. nothing wrong with Multi-copters but for me the combined risk is too great. If you accept the risk than use a parachute BUT how do you determine the minimum deployment height that it needs to operate and slow the brick down to a speed that it will not injure someone. On top of that the legs and frames on some multicopters look dangerous in themselves. sharp edges and points everywhere. Safety is not just about reacting to a failure in the air. sometimes the failure is the human variety but for the unsuspecting vctim the result is the same.
JAB, I agree. Combine that with the fact that with so many newbies, and their first model is highly complex, they are very likely to build a machine which is quite likely to fail. We see that over and over.
My opinion, it is will be hard to improve upon the parachute approach. Seems everything else being suggested is a massive compromise of weight, complexity, and aerodynamics. You can't have anything on the multi-rotor that will catch the wind until you WANT it to catch the wind (ie: when falling). Otherwise any gust of wind will flip your copter over.
I think an Octocopter which can survive a motor failure, along with a parachute is about as safe as you're going to get.
Does anybody know of somebody who has developed a parachute like system for multicopters, that can be deployed in case of failure?
So you could potentially set it up as two separate systems, with complete redundancy. You would have to be sure that both setups was powerful enough to fly by it self.
Of course there would be things that would be hard to implement and I'm far from sure that the two systems would not just work against each other.
There could be different ways of setting it up.
Dual TX where you'd add trust from one TX and the other one would be in control.
The single TX but with two RX on the same frequency.
Just a thought
I think much of this is about what mindset you have, and where you are coming from.
People with experience from R/C flying airplanes and helicopters won't even blink if there is a crash. To put it bluntly, crashing is just another part of the hobby.
But on the other hand, for people new to the hobby jumping straight into the drone aspect. Crashing the new expensive drone that is supposed to fly all by itself, can be a traumatic experience. But the fact is that regardless of how much money or autopilot electronics you put into your drone, it is going to crash. It is just a matter of time. At the hobby level, we are all flying motors and electronics made as cheap as possible in some Chinese factory, with little or no maintenance done between flights.
And for the average R/C pilot this is just fine. Flying in a regulated R/C field, a crash has no consequence. Other then burning a hole in you wallet and entertaining your friends that is. But at the same time a R/C pilot would not even dream of flying over a populated area, like you see in many, many drone videos.
Matthew, I just wonder if that would make it difficult to descend under normal conditions. In my mind the rotation is key because it can happen very quickly and it gives us effective relative airspeed even if ground speed is zero.
Edit: Sorry, I see where you address adjusting the required closing pressure to avoid closure in normal speed descents. I can picture what you're saying, like punched louvers on a hot rod(but flexible), could be a nice way to direct air flowing through the frame in specific directions also.
This Idea is way out there and slightly crazy but here it goes.
Build a frame that has lots of small flaps that when air is applied to the top (or with very low pressure on the bottom) they stay open. But when air pressure is applied to the bottom they close, thus causing resistance. Like an air diode. If it worked it would not affect flight to much, and would help slow it down in free fall. You would just have to keep as much of the weight as possible below it.
Sounds good at least.
Gary,
I used auto-rotation with quotes because I don't mean typical prop disc auto like a mono-copter, but rotation of the entire craft working toward large gliding spirals as vertical speed builds. I like your idea of the flexible poles for deploying a traditional parachute!
Multicopters in particular suffer from the WileCoyote Syndrome.
Basically if anything goes wrong they simply fall straight out of the sky.
They have no real flight speed and for the most part autorotation isn't even an option.
The only real option for current multicopters is some sort of deployable parachute like device.
You could build a multicopter with substantial built in airfoils that could permit some sort of rapid autonomous but perhaps non lethal descent but that would add weight and the aerodynamic surfaces would no doubt interfere with normal flight and respond unfavorably to winds and gusts in normal operation.
Aside form deploying them at the right time and only at the right time, existing parachute systems suffer from a reasonably high likelihood of getting entangled in the multicopters superstructure and thus becoming part of the problem rather than the solution.
Even spring, air or rocket ejected parachutes don't work to well if the copter happens to be upside down when it is deployed.
I came up with a design that uses four thin flexible fiberglass poles (fly rod stock is good) extending upward and outward from the copter body.
The poles would be bent back and down to the center of the copter and a square Chute could be folded and kept in a servo released "pack" when released the poles would snap upward and the chute (the edges of which would be directly attached to the end of the poles) would unfurl. It couldn't get caught in the props or other copter mechanism and should even cause the copter to rapidly right itself if necessary.
Probably you would size the chute adequately to slow descent to at least a non-lethal rate, maybe not enough to save the copter completely from damage. This would also work much closer to the ground than most "deployable" chutes.
Just a thought, multicopters are dangerous and eventually we are going to be forced to address this.
I should mention that I'm a firm believer in motors mounted under the arms, so with a truss style arm made of flat vertically oriented members it will be easy to attach a fabric gore along the top of each arm, normally tucked in, but a strong relative upward airflow would balloon them out, possibly this action could then deploy other more tightly packed surfaces elsewhere. Ultimately I guess it's still a parachute when it comes down to it. Plus some lifting body shape to the airframe center maybe. There's just so many possibilities here I think. Thanks for the feedback guys, like I said "To be continued", lot's to figure out still. I now have a use for my old APM1s and pile of cheap motors! One quadcopter bat suit free fall video is worth a thousand words, as they say ; )
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