For commercial delivery service, it seems quite clear that we'll need either
1) "enterprise-grade" drones (like difference between consumer and enterprise SSD's),
2) reliable sensors to detect imminent failure before a flight,
and/or 3) easy replacement of failing parts.
I mean, for many hobbyists 100-200 hrs seems like a reasonable cost/benefit tradeoff... but not even close for commercial delivery services.
It doesn't really matter what fails, what matters is that there is no way to do a controlled descent once anything goes wrong on a loaded drone because there is no margin for error. A drone this heavy relies on the whole chain of components functioning perfectly.
I'm surprised it is as good as it is given the number of parts. If it were a winged drone you'd at least have a chance to glide it to a safe spot, but a drone that is kept up by spinning props can only crash uncontrolled. There was a video of downing one in a more controlled way but the only fault it could cover was single rotor failure and even then the amount of control was very limited.
These things have absolutely no business over areas occupied by people.
Not entirely true. The drone had a parachute system to allow a controlled descent in situations like this and an alarm to alert nearby people to its descent. The problem here was that the parachute's single tether was severed shortly after deployment.
The parachute would allow the drone to avoid a rapid descent. Most parachute systems are not steerable/flyable so they won't make it a controlled descent.
If it were a winged drone you'd at
least have a chance to glide it to
a safe spot, but a drone
Seemed to me the quadcopter response to communication failures was a much safer one. Is this still the case? It was quite some time ago.
Once you have a quadcopter you've got enough digital hardware and software that adding "return to base" is basically free since it's just an additional software routeine.
RC planes don't already have the required hardware/software to implement a return to base feature because they don't need it and of course nobody is going to greatly increase the cost and complexity of the product just to add that one feature.
That isn't really accurate at all.
> https://hobbyking.com/en_us/turnigy-t1000fc-auto-pilot-syste...
>https://www.amazon.com/Parrot-Disco-FPV-minutes-goggles/dp/B...
Very few micro and mini quads have this functionality.
Return To Home functionality is common any medium and larger RC aircraft intended for FPV flying.
Often fixed wing RC with RTH functionality won't attempt to land, it return to home and enter a circular holding pattern until contact is re-established or the battery fails.
In comparison, a helicopter will have a clutch that can disengage the rotor from the engine and let it turn freely. The pilot still has the ability to control the rotor, so she has some control during the autorotation. At the end, just before landing/impact, she will perform a flare, using the rotational energy in the rotor to slow the helicopter's descent.
All of which are not present in a typical multirotor.
There are RC aircraft with collective pitch controls, like most RC helicopters and even some multirotors. These RC aircraft generally can autorotate, as well as do things that are probably not practical for full-scale aircraft to do, like fly upside down. :)
A collective pitch quadcopter flying upside down: https://youtu.be/MVL_Hf4ilLg?t=162
An RC helicopter doing, well, all sorts of acrobatics that hardly make sense: https://youtu.be/KmPchrGW1TQ?t=48
An RC helicopter autorotating: https://youtu.be/bxQ5kwqiPN4?t=136 (this one has an internal combustion engine, although that shouldn't make much of a difference for autorotation)
Just a guess: stronger strength to weight, and power to weight ratios, compared to the real thing. The tail rotor in particular appears to be quite a bit more powerful for the weight of the model than would be expected in a full size aircraft. And then also, these kinds of movements with a person inside? Haha! No!
Is it less mass and therefore momentum in the rotor/drivechain?
A real helicopter (or an auto-gyro) is best modeled as a rotating wing, as long as the blades rotate you can control the craft to greater or lesser extent. It still won't be pretty in a proper helicopter but at least you have a chance.
Very nice definition.
There isn't AFAIK such a neat distincion in English, in Italian the iron (the device you use for ironing, maybe flatiron?) has a specific name "ferro da stiro" so it is common to use it as a term of comparison for such a behaviour.
In my defence, a quick search shows this story:
https://www.digitaltrends.com/cool-tech/amazon-delivery-dron...
So apparently it's not a stupid suggestion and Amazon are thinking along the same lines.
I only ask because it seems making drones land safely is hard. I mean, a paracute with a whistle is a great idea until it drifts in front of a car moving at high speed, or lands on a deaf person or shorts out a high-voltage cable. They all have problems. If there was a way to convert the failed drone into widely dispersed very small objects, the harm may be much lower.
It's because many drones, even "commercial" ones, are built using hobby parts with poor QC. If you use high end components then the reliability will be up by a two orders of magnitude, as will the price.
(Also as mentioned by others, multirotors and especially quadrotors have many single points of failure and so even with reliable parts the whole contraption isn't very reliable.)
In the case of failure of a prop in this configuration (the most common failure in my own experience with quads and octos), it is possible to program the n-copter to automatically change to flying in 7 prop mode or 6 prop mode or 5 prop mode, and so on and so forth as a redundancy feature. This could help with a not insignificant amount of crashes but obviously comes with increased costs.
My bet is on the power electronic semiconductors, mostly MOSFETs, in the motor controllers. Life time of these components decreases exponentially with the temperature difference they see in the semiconductor junction, i.e. the difference between hot (current is flowing, heating the junction with a power of I^2 * R_ds_on) and cold.
To make this deltaT_junction small, you need to choose big components, but at the same time you want to save weight, which is fundamentally at odds with overdimensioning everything.
I'd think the motor and rotor itself would be much more likely to be the problem.
Most hobbyist multirotors use smaller controllers (which are essentially a PWM'd set of mosfets) zip-tied or otherwise affixed to the arms of the machine, with short connections to the motors and to the controller/and power-supply distribution board on the body.
Consumer multi-rotor craft will generally have the ESCs integrated on a motherboard or daughterboard in the main body of the craft (cheaper to manufacture), well away from the prop wash and enclosed (not good for cooling).
I'm not sure what commercial (or large-scale) multi-rotor craft use, but it is probably similar to the others.
Again - I'm not saying it hasn't been done, or couldn't be done; in fact, it seems like a good idea. I can even envision how it could be integrated on the motor itself (board on the back with mosfets, with an extended shaft with fan for cooling the mosfets (inrunner motor), or with the fins of the mosfets in the wash of the prop, or something like that for an outrunner motor).
It wouldn't surprise me if such motors don't come on the market (or maybe they already exist - I haven't looked)...
Ok - well, apparently the idea isn't a new one:
https://www.rcgroups.com/forums/showthread.php?1149319-brush...
...and it has been tried and sold to some success. So I imagine such motors are still available somewhere. TIL.
https://www.youtube.com/watch?v=ek0FrCaogcs
Obviously there are still other single points of failure such as the battery or controller, but at this point there's no excuse for crash landing a commercial drone just because a single motor (or rotor) has failed.
There is a reason why pro grade filming setups carrying $40,000 to $150,000 cameras are all coaxial octocopters or flat octocopters. Even a hexacopter cannot 100% reliably recover from a single motor failure.
Personal opinion, any craft that is over 3 to 4kg and spends time over people needs to be an octo.
Zipline is, imho, the real out of the box thinker. Catapault launch plus the snag line is Short takeoff, effectively-vertical landing, main downside is you need ground gear to land without damage. Main upside is weight savings for peak power (takeoff) is reduced, landing gear gone, and your engineering space is shrunk to solely the problem of steady state flight.
I foresee the paradigm of winged mothership for last-hundred-mile, plus n-rotor drones for air-to-land leg of delivery.
As you point out it provides a lot of advantages in not needing to carry the extra weight for a VTOL, no landing gear, extra energy boost on launch. It's very close to the optimal energy usage in watts for motor, per size of craft, that can be achieved right now.
The other advantage of using a single motor fixed wing craft is ability to use lithium ion batteries which are relatively higher Wh/kg density. These are not as capable of instantaneous high amps as lithium polymer are. The best commodity, commercially available lithium ion batteries are in the range of 210 to 248Wh/kg right now. The best lithium polymer batteries are about 178Wh/kg.
FPV hobbyist fliers who build fixed wing and flying-wing craft use lithium ion for longer range.
https://www.google.com/search?q=insitu+scaneagle&client=ubun...
If you look at the pilot projets for drone delivery in Canberra, it's all VTOLs.
https://www.google.com/search?q=canberra+drone+delivery&clie...
The instantaneous watts required for forward flight with wings at a reasonable speed are much lower than the watts required for the same weight of craft, same general dimensions, same speed, forward flight with four, six or eight rotors.
Furthermore, safety critical systems are all about layers. Yeah redundant motors are good, parachute is nice, but what about passive measures?
Maybe drones should have stub wings which, in addition to lift boost, have deadman switches which cause one to spring 180° on power loss, forcing the hull to autorotate in the event the chute fails.
Ok, the gps dies, the motors fail, chute fails to deploy, and the wing ripped off, you are dropping at full speed. Well now the rapid descent causes a pressure differential (artificial eustacian tube, if you will) which trips some azide charge, inflating an airbag.
It's like they are putting in bare minimum of effort with the quad+parachute.
Rapid descent sensors don't necessarily need to be pressure based at all. While in controlled flight there is a limitation (as governed by flight controller and ESCs) for how rapidly a quad, hex or octo can descend. Accelerometer data can be used to trigger a parachute and/or airbag system. A multiply-redundant array of small accelerometers that can detect freefall is very tiny and light weight.
Most higher end flight controllers have double or triple accelerometers onboard.
Four large motors and four 28" CF props produce less thrust than four arms, each arm with two motors stacked, and eight props.
Octos are not a conservative, redundant, fail tolerant design decision just for the sake of protecting expensive gear. Many of them still have 1+0 non redundant power systems.
Problem is that most of the components (batteries, motor controllers, flight controllers) are built by and for hobbyists. Motor burns a winding? ESC spontaneously lets the smoke out? Whatever, they're $15 bucks each. The field of "commercial grade cargo multirotor" is still in its infancy. The balance of safety and cost for the components hasn't been struck in the market. You either deal with random chinese components and control algorithms written by intrepid RC airplane nuts, buy very expensive industrial/aerospace grade components, or roll your own solution.
There are some quad copter controllers that try to deal with single motor failures, but they're mostly experimental (at least on the hobby end to the space) since they need to be able to reverse a motor, which most motor controllers used in these applications are not build to do.
Found a vid: https://m.youtube.com/watch?v=bsHryqnvyYA
Losing them, crashing them, having people steal them or throw them in a lake - those are things to include in your VC funded "operating costs" and to mitigate/offload the risks in your TOS...
(Small print: "The delivery customer shall be wholly and solely responsible for any damages and costs incurred by their delivery and any company equipment used in the completion of the customer's delivery, including but not limited to the drone crashing into a playground full of children." Just like Tesla's abrogation of responsibility when their "autopilot" software is driving the car they sold you...)
So while they gently introduce such rules (mostly centered around see and avoid for now, also identification), the main way they use to ensure safety is restrict where and who can fly them.
You know they can't be trusted, so you don't fly them above sensitive areas. As processes mature, reliability increase and trust is gained, you will see drones expand the airspace in which they are allowed. It's already happening for BVLOS (beyond visual line of sight) flights which requires a waiver from the FAA in the US (with paperwork such as risk assessment, collision tests on mannequins and so on), as well as specific equipment/processes.
Pretty much no one besides DJI has the scale for custom made, except on a few select components. Drones are still in their infancy, those companies are still trying to see if they have a business model and improving/creating technologies. You can't expect mature processes from this environment.
Fixed wing drones have the big problem that they need to go fast to stay in the air. Which requires a lot more motion planning.
My point is that multicopters are a lot simpler mechanically. No articulation, no transmission, just propellers on an electrical motor, controlled by pure electronics with no mechanical components in the loop except the drive coils.
Arguably multicopters are easier to control automatically (with modern electronics), though that wouldn't be THAT big a factor today, I guess.
Also electrical engines can deal a lot better with variable load and RPM. Multicopters with combustion engines (driving the rotors directly, not through a generator) seem to be quite uncommon.
Still, if multicopters are supposed to be routinely used in the presence of people, they need similar standards of maintenance and failure control as would bigger aircraft, be they manned or unmanned...
The limiting factor of a quad's ability to fly is the motor and unexpected failure of the battery. Higher end brushless motors have a life expectancy in the tens of thousands of hours. Battery failure is already mitigated in consumer drones by having independent packs each of which provides enough current to continue operation.
Quads do occasionally just fall out of the sky because a defective bearing ceases or a defective cell sags, but it's very rare. Most of the time they crash due to operator error.
On a quad there a 4 motor controllers on board, and only one needs to fail, greatly increasing the odds of overall failure.
None of this is even really relevant. GP quoted a figure from a paper that pulls the figure out of thin air and doesn't justify it in any way. The figure can be disregarded. I'm just pointing out that the figure seems much lower than mtbf of any of the critical components of a quad.
the 10-kg drone suffered an uncontrolled crash “in a wooded area of Zurich’s university quarter only 50 yards away from a group of playing kindergarten children.”
One of the things that few people are aware about is quadrotor MTBF is very low relative to other common vehicles. For many drones, the expectation for failure dramatically increases just after 100-200 hours of operation[1]. Figuring out points of failures, building systematic fault trees and increasing MTBF by order of magnitude or two would be big part of the drone delivery projects.
[1] https://catsr.vse.gmu.edu/SYST490/490_2014_SPDAV/DST-NSPDAV_...