Flywheel as quadcopter power source

I stumbled upon this interesting concept:Flywheel energy storage - Wikipedia and I was wondering if it could be used for devising a small quadcopter power source. It would allow much faster charging than conventional batteries. I found this video that demonstrates flywheel concept on a very crude example:- YouTube device design seen on video can be largely improved. Does any have any experience concerning this matter? What's the maximum power density that can be achieved by using this approach?

Cool demonstration!

For high energy density people use flywheels in a vacuum, and ones made of many fibres (to avoid catastrophic failure).
Then you may get interesting energy density, but the one in the video is not useful.

If you assume the fan goes to 4000rpm, the flywheel is 1kg and about 6cm in radius, then it will store 0.3kJ
A single AA rechargable battery (1.2V, 2Ah) holds 8.6kJ and weighs a tiny fraction of the flywheel... For lithium
polymer the battery energy density is still higher, upto 720kJ/kg - around a thousand times as much.

Or put another way you'd have to spin the flywheel 30 times faster to be comparable, 120,000rpm

The other factor thats missing from the demo is how much power was put in to spinning up the flywheel
compared to what was stored.

Also I note the OP mentioned power density, but probably meant energy density as well. An electrolytic capacitor has
very high power density for instance!

Ok, so magnetic frictionless bearings and vacuumed container. There are obviously many other things that can be modified. But the main question is whether is possible or not ? My budget is about five hundred dollars. I have next two-three month to spare on this project. Could it be done ?

If you have to ask, then it probably means you didn't understand any of the reply and you have none of the skillset necesary to make any of the components. An honset answer - NO.

Probably 3 orders of magnitude out?

Dr_Freeman:
My budget is about five hundred dollars. I have next two-three month to spare on this project.

No

When you're spinning these flywheels you're going to get a tremendous gyroscopic effect that would make the quadcopter impossible to maneuver. I would assume it would start yawing out of control as well.

In my experience (sigh) it takes about 3 months just to get the basic quadcopter flying properly :wink:

“When you’re spinning these flywheels you’re going to get a tremendous gyroscopic effect that would make the quadcopter impossible to maneuver.”

Of course, but this is also true for each of the rotors on your quadcopter :slight_smile:
One possible solution is to use two flywheels with the same speed and shape but with different directions. (i.e. exactly the same solution you use for your quadcopter)

It would be impossible to maneuver QUICKLY. Maybe it would be more stable in theory?

FooTheBar:
“When you’re spinning these flywheels you’re going to get a tremendous gyroscopic effect that would make the quadcopter impossible to maneuver.”

Of course, but this is also true for each of the rotors on your quadcopter :slight_smile:
One possible solution is to use two flywheels with the same speed and shape but with different directions. (i.e. exactly the same solution you use for your quadcopter)

I am curious how you will get the fly wheel to spin? If you use a power source, not only will you add unnecessary weight to the quad, but you are also adding inefficiency to your project. Why would you use power to spin a flywheel to make power?? Even if the system was 99% efficient (which it wouldn’t even be close to), you are still using more power than you are making. Cars that utilize a fly wheel, such as a KERS system, capture small amounts of power from braking that would otherwise be lost as heat. What quad system is analogous with the braking system of a car?? I can’t think of one, but that doesn’t mean one doesn’t exist. What are your thoughts on this issue?

I never said it would be a good idea to use a flywheel, I just said that you can compensate the gyroscopic effect with two flywheels of different direction.

“Why would you use power to spin a flywheel to make power??”

I think the most important argument was the short time needed to speed up the wheel. If you could fly some minutes and recharge within some seconds, you would be flying much longer than with a battery with which you could fly for 20minutes but need 3hours to recharge.

FooTheBar:
I never said it would be a good idea to use a flywheel, I just said that you can compensate the gyroscopic effect with two flywheels of different direction.

"Why would you use power to spin a flywheel to make power??"

I think the most important argument was the short time needed to speed up the wheel. If you could fly some minutes and recharge within some seconds, you would be flying much longer than with a battery with which you could fly for 20minutes but need 3hours to recharge.

Sorry, I initially quoted the wrong text. I aimed my comment at the author.

I think that the overall efficiency of the fly wheel would depend on what the author is trying to use it for. By that I mean how big of a quadracopter is he looking to design? I agree, the recharge time would be greatly reduced with the fly wheel, however, fly wheel's also discharge their energy load quicker than batteries do. Also, to achieve maximum efficiency, the flywheel system would need to be vacuum sealed on magnetic bearings. This would add both expense and weight to the system. Can he use a fly wheel? Yes. But is it the most efficient power source? No. Is it worth pursuing? In my opinion, at this time, based on the authors financial and time constraints, no.

Whats wrong with one of these?

90C discharge rate , thats 360 amps , and weighs 360 G .
The flywheel in the demo weighed 1 KG and was only able to light up some small leds.

I think the most important argument was the short time needed to speed up the wheel. If you could fly some minutes and recharge within some seconds, you would be flying much longer than with a battery with which you could fly for 20minutes but need 3hours to recharge.

With the battery that mauried mention you can charge with 10C, thats about 6 minutes.

With 2 batterys you can charge while flying, and keep going until forever

Of course you're all correct. At 10C you would have a very short cycle life.

Just another thought -

If the flywheel idea was really practical, don't you think that we would have already seen it in use? The problem with a flywheel is that it requires mass and rotational velocity. the bigger the diameter, the more energy stored, but mass and rotational velocity are still going to be a problem. The less mass, the more rotational velocity required for a given amount of output. The more rotational velocity, the more losses do to friction, no matter how little friction you have. Below a certain speed you will get no usable energy out of the flywheel - that is a problem of efficiency...

Its not only the flywheel that requires mass.
Flywheels dont produce any energy at all unless they are mechanically coupled to an electrical generator, which also adds mass.
Adding mass to a helicopter is the last thing you want to do.