Drones flying on less than 4 motors.

[42FrankZ]

At 200 feet up I doubt that would have been easily saved with a software routine or a skilled pilot.

 

[syotr]

When you lose one rotor, you have effectively lost two. You cannot get any lift or yaw power from the motor opposite of the one that was lost, because it would flip the quad. You now have half the power and a quad spinning at full yaw speed. The best you can hope to achieve is a partially controlled upright descent right where you are.
If you lose one rotor on a hexcopter, it becomes a quad. You have 2/3 of the original thrust and no uncontrolled spinning. For an octocopter, losing a rotor means you now have a hex with 3/4 of the original thrust and you still have yaw control.

 

[Gearbox]

I'm not sure how well this will link/play (it's from a FB group) but it shows how quickly things go south with we lose a prop on a QUAD set up:
Inspire Loses a Prop

Yep , I watched it happen in person & thats what it did & real quick . One can bring up about computing power , but thats assuming its all going to be used to alter power & control to the motors to save the Drone & still ,I don't think it would help .

 

[Fishie]

It can be easily done by stopping two motors opposite of each other. Watch this TED talk starting 6 minutes in!

 

[Kirby Johnson]

A couple of bits on the BBC Click programme (22.10.16) regarding drones was interesting.

In particular around 13min in is a piece about making drones that can still fly on less than 4 motors, allowing the drone to land (relatively) safely, or at least not plummeting from the sky!.

They were not using any special equipment to do so, but basically putting the drone into a spin to regain some control if a motor failed.

They were saying that any drone manufacturer could do this, so just wondering what people's thoughts were as to DJI doing something like this?

Click, 22/10/2016: www.bbc.co.uk/iplayer/episode/b08163fg via @bbciplayer


Sent from my iPhone using PhantomPilots

Just to throw something out: As our drones have much more lift than is needed to simply hold the aircraft aloft, IE:
They can fly straight up very fast, one could assume that they could hover or at least descend slowly on just two motors. Thus if a motor is lost, kill the opposing motor so that thrust is balanced, and land as gracefully as possible on one.

I spent many years in the fighter aircraft industry, and believe me fighters in real combat for sure will fly on one engine. Admittedly there is a vast difference, but what I surmised above makes sense. That was always the selling point of twins from McDonnell Douglas (F18) versus General Dynamics little single (F16).

 

[Mosa 98]

I was going to post Raffaello's TED talk, but it's already there, here's his website's page on it - fascinating stuff, and while not possible on all quads, (due to symmetrical weight distribution being required) I think it could be done with a phantom pretty easily!
Raffaello.name | Flying Machine Arena

 

[42FrankZ]

I think it could be done with a phantom pretty easily!
Raffaello.name | Flying Machine Arena

I think if it could be done easily that DJI would have done it already. It would be good marketing for reliability if nothing else.

 

[pe9999]

I believe jjrc has a toy quad that can fly on damaged props.

 

[pe9999]

I rest my case.

Does anyone think the folks are DJI are any less skeptical than the majority of the readers here? "IT CAN'T BE DONE!" It is indeed a simple software routine. The hardest part is the decision tree to decide WHEN to jump to it. Patented software routine? HA! There are 17 ways to do the same thing. The responses are as amusing as they were a year ago!

Have you considered this business scenario.
When an user crashed a drone, he went out to buy a new one.

A crashed drone equals a new sale. A saved drone equals to one lost sale.

If you want to sell more, what option should you pick.

 

[Mosa 98]

As some have asked, why hasn't DJI implemented this failsafe before?

I think the answer is partially because they don't want to release an aircraft with all the features they can possibly offer, all at once. DJI has learned from Apple, step by step upgrades are they way to make money.

Second, as I mentioned earlier, the craft has to be completed symmetrically balanced - otherwise two motors just aren't enough.

Thirdly, motor power and strain - you need to have at least 120-140% required thrust, from two motors. Phantoms are about a 2.2:1 power to weight, which isn't quite enough. Once you have all the above sorted, you also need a frame that can handle the centripetal forces, and a battery and camera that won't just go flying.
I think we'll see it on DJI craft eventually, probably on the P6 or I2/3.

 

[iflyhelis]

So, how come the "Ocatgon" drones have the capibility to compensate for a lost prop or motor?

I think we may be underestimating the complexity of this problem. You lose a prop, the first (and often only) thing that comes to mind is the lift imbalance, which you can sort of deal with by feathering the prop diagonally opposite the failed one, with the loss of most directional control. That only exacerbates a potentially more significant problem: angular momentum/torque imbalance. The bird is going to want to spin, and there's very little you can do to counteract that.

I don't see "limp home" as a viable possibility. At best, you might be able to land before the spin gets out of hand.

The above assumes the Phantom configuration of diagonally opposite props spinning in the same direction. I assume DJI had a good reason for going that way (it allows in-place yaw, which the other configuration doesn't). The alternative configuration, props on the same side spinning the same, does offer more potential for recovery from a "lost prop" situation, including a possible "limp home" capability. The reasons for that are left as an exercise for the student