What!? The P4 has regenerative brakes!?

[WetDog]

Yes - that works fine for linear or angular kinetic energy in vehicles or tools, where the existing angular momentum of the system drives the electric motor, which then behaves as a generator and induces current that can be used to do other work, or charge batteries. However, the equivalent simple energy balance that you describe for the aircraft is incorrect, because you are forgetting the changes in kinetic energy of the surrounding air - see below.

In the case of propellers operating in a working fluid (air in this case), that could also be achieved, but only in very limited situations for an aircraft with no other source of lift. For example, if one stopped actively driving the propellers and allowed the aircraft to drop, then the airflow through the propellers would cause them to turn, rather than just stopping (equivalent to a wind turbine), and the work done by the airflow turning the props could be used to generate electrical energy in the motors. In this case one is converting aircraft potential energy (rather than kinetic energy) into electrical energy, but at least the principle is similar.

In the "active braking" case described, however, this isn't going to work, because rather than the motor drive being reduced and allowing the aircraft to coast to a halt (which would not work well anyway because most of the thrust is still needed to maintain altitude) energy from the battery is being used to produce extra opposite thrust to slow down the aircraft. More work is being done on the working fluid (the air), not less, so it isn't even reducing the power consumption of the motors, let alone allowing energy to be recovered.

The main reason that this is confusing, compared to cars or machine equipment, is that the energy partition is not as simple for an aircraft. In the former cases one can simply consider the linear kinetic energy of the vehicle, or angular kinetic energy of the machine, and if one reduces that by motor braking then one can recover significant energy by using the resulting induced currents in the motor windings. But in the case of a quadcopter, it's not simple motor braking - the props change the momemtum and kinetic energy of the aircraft by pushing air around - i.e. changing the kinetic energy of the working fluid in which it moves. As a result, most of the kinetic energy of the aircraft cannot be recovered by the props/motors and is instead converted (and lost) to increased kinetic energy of the surrounding air.

Ah, so we're adding to global warming by slowing our Phantoms down. I just knew it was a problem....

I don't have any analysis data right at the moment nor do I remember just what happens but you should be able to see what the motors are doing by looking at the log files in your viewer of choice. Does the voltage to the motors decrease? Increase?

 

[Sim597]

Ah, so we're adding to global warming by slowing our Phantoms down. I just knew it was a problem....

I don't have any analysis data right at the moment nor do I remember just what happens but you should be able to see what the motors are doing by looking at the log files in your viewer of choice. Does the voltage to the motors decrease? Increase?

He didn't say lost to heat, although I tiny amount is always lost but....you know what I meant lol

I'd bet it increases, I still say "active braking" just means when you release the stick, it "brakes" or slows itself rather then coasting to a stop. How did the Phantom 1 and 2 fly? Didn't they always provide reverse thrust from whatever direction?
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[sar104]

He didn't say lost to heat, although I tiny amount is always lost but....you know what I meant lol

I'd bet it increases, I still say "active braking" just means when you release the stick, it "brakes" or slows itself rather then coasting to a stop. How did the Phantom 1 and 2 fly? Didn't they always provide reverse thrust from whatever direction?
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I didn't say "lost to heat" but in fact any transfer of energy to a gas, whether by direct heating or by mechanical work, always degrades to heat in the form of molecular kinetic energy.

The Phantoms have always braked using reverse pitch (thrust) in GPS mode. In ATTI they just coast if you release the sticks, and take much longer to stop.

 

[With The Birds]

DJI can take credit for Lightbridge, which is a technology that's way ahead of others for the time being, however this regenerative sales pitch is total BS. It's certainly not a leap of technology like Lightbridge, far from it. SAR104 is right, there is no way the props can retrieve enough force from air to generate anything of significance at the speeds these birds fly. This is total crazy talk. I think something was lost in translation from Chinese to English. That's likely what's going on here. Just like when DJI marketing states 28min flight time, we all know that's total BS. I tend to think this regenerative pitch came from the same marketing genius, or translator. As great as this DJI technology is, and it is great, DJI needs to oust the guys that continue to embarrass the company with false or misleading information.

John you will probably find that lightbridge is simply a highly polished implementation of the "wifibroadcast" protocol. Its in the standards. There are a lot now in the diy arena that have wifibroadcast running on rasberry pi's getting the same or greater distance than us on the phantoms with lower latency in some instances. My intent is not to take anytjing away from DJI, they bring to market awesome technology at good prices but you dont have to look too far to see the tech elsewhere. I have been amused on several occasions by the suggestion that DJI might develop everything without relying on western technology. That probably isnt entirely true.

 

[John Locke]

John you will probably find that lightbridge is simply a highly polished implementation of the "wifibroadcast" protocol. Its in the standards. There are a lot now in the diy arena that have wifibroadcast running on rasberry pi's getting the same or greater distance than us on the phantoms with lower latency in some instances. My intent is not to take anytjing away from DJI, they bring to market awesome technology at good prices but you dont have to look too far to see the tech elsewhere. I have been amused on several occasions by the suggestion that DJI might develop everything without relying on western technology. That probably isnt entirely true.

I agree, I don't think lightbridge should be that difficult, but then I wonder why it's been almost two years since DJI released it in Inspire and nobody else is doing anything like it yet. If it was simple others would have it..... right? 2 to 3X the distance! One way comm with no check sums doesn't seem difficult, but everyone else uses plane old wifi, which can communicate directly with smart devices, complete with TCP/IP, which wasn't designed for video transmission from the air. Someday another competitor will do something like Lightbridge, and I think that's going to be Broadcom, who is hot an heavy at designing drone boards with flight controllers, the works. Broadcom has the communications savvy to pull it off. It's going to be interesting to see what happens next year. However, I think Lightbridge 2 will be in the upcoming Inspire2, and then the Phantom 5, sporting lower latency and 1080 downlink video. Oh yeah....I'm in.

 

[Sim597]

I didn't say "lost to heat" but in fact any transfer of energy to a gas, whether by direct heating or by mechanical work, always degrades to heat in the form of molecular kinetic energy.

The Phantoms have always braked using reverse pitch (thrust) in GPS mode. In ATTI they just coast if you release the sticks, and take much longer to stop.

So, then it's not a newer advertising pitch or something then. I thought someone said at least since the P3 they used the term "active braking", which he is prolly right.


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[Sim597]

John you will probably find that lightbridge is simply a highly polished implementation of the "wifibroadcast" protocol. Its in the standards. There are a lot now in the diy arena that have wifibroadcast running on rasberry pi's getting the same or greater distance than us on the phantoms with lower latency in some instances. My intent is not to take anytjing away from DJI, they bring to market awesome technology at good prices but you dont have to look too far to see the tech elsewhere. I have been amused on several occasions by the suggestion that DJI might develop everything without relying on western technology. That probably isnt entirely true.

There's only one problem with what you said, they already have stolen about everything they can get their hands one, literally every piece of tech they've ever gotten, or had, has started with them stealing it! Even if they didn't steal it, they stole the idea from some western company, their track record is ****, and I will doubt for many years, likely until I die, that they've ever done anything without stealing the idea, the tech or the ways to implement whatever it is they've stolen This week.

Um, the Chinese as a whole have stolen everything, not just DJI, but they're definitely part of the process meant to steal everything they can, it's a state sponsored thing, any company that want to do business in the fastest growing segment in the world, they have to give up 51% to the Chinese state, this is all the tech and everything. It gets worse, these companies know they're going to be ripped off, but it's that, or not be on the biggest boon to whatever market they want to be in, or have to be in. So they steal it legally. Those things that you lean on, with two wheels? Segway's , they were bought out by a Chinese Knockoff!! Yeah, the real company couldn't compete with the fake company, and they made enough to just by the real company, and then had millions left over, the Chinese don't play by any rules, I hate Trump, but we do need to wake up and do something about the unfair advantages they reap from real companies.
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[With The Birds]

There's only one problem with what you said, they already have stolen about everything they can get their hands one, literally every piece of tech they've ever gotten, or had, has started with them stealing it! Even if they didn't steal it, they stole the idea from some western company, their track record is ****, and I will doubt for many years, likely until I die, that they've ever done anything without stealing the idea, the tech or the ways to implement whatever it is they've stolen This week.

Um, the Chinese as a whole have stolen everything, not just DJI, but they're definitely part of the process meant to steal everything they can, it's a state sponsored thing, any company that want to do business in the fastest growing segment in the world, they have to give up 51% to the Chinese state, this is all the tech and everything. It gets worse, these companies know they're going to be ripped off, but it's that, or not be on the biggest boon to whatever market they want to be in, or have to be in. So they steal it legally. Those things that you lean on, with two wheels? Segway's , they were bought out by a Chinese Knockoff!! Yeah, the real company couldn't compete with the fake company, and they made enough to just by the real company, and then had millions left over, the Chinese don't play by any rules, I hate Trump, but we do need to wake up and do something about the unfair advantages they reap from real companies.
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And the problem with what i said is?

 

[John Locke]

There's only one problem with what you said, they already have stolen about everything they can get their hands one, literally every piece of tech they've ever gotten, or had, has started with them stealing it! Even if they didn't steal it, they stole the idea from some western company, their track record is ****, and I will doubt for many years, likely until I die, that they've ever done anything without stealing the idea, the tech or the ways to implement whatever it is they'v stolen.

What irks me just as much is the US educates 10,000 non citizens from Asia every year with college degrees. Then they go home and compete with the US economy. We literally invite foreigners to come to the US and learn all the technology we know, instead of educating our own as the priority. Sorry for the hijack, let's stay on subject.

 

[Sim597]

And the problem with what i said is?

Lol, yeah, not sure why I stated it that way, I guess maybe I felt you gave DJI too much credit for bringing lightbridge to the masses, but your right, whether it was hijacked or, Shanghai'd ' I guess they still brought it to us first.
I wish they weren't pulling our **** here, and they really were working on, well it doesn't make sense for a drone I guess, as was pointed out, even in fast descent, your still using enough voltage to keep us from storing any energy, basically until we can descend using no power at all, could we even consider sparing or even making some, this braking thing is laughable guys.


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