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### Topic: Flywheel as quadcopter power source (Read 4766 times)previous topic - next topic

#### Dr_Freeman

##### May 01, 2013, 11:15 pmLast Edit: May 01, 2013, 11:19 pm by Dr_Freeman Reason: 1
I stumbled upon this interesting concept:http://en.wikipedia.org/wiki/Flywheel_energy_storage 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:http://www.youtube.com/watch?v=mV_b5oMqc2MThe 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?

#### jasonvanwyk

#1
##### May 01, 2013, 11:31 pm
Cool demonstration!

#### MarkT

#2
##### May 02, 2013, 01:53 am
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
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#### mauried

#3
##### May 02, 2013, 10:03 am
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.

#### MarkT

#4
##### May 02, 2013, 01:22 pm
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!
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#### Dr_Freeman

#5
##### May 02, 2013, 04:34 pm
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 ?

#### kf2qd

#6
##### May 02, 2013, 05:58 pm
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.

#### MarkT

#7
##### May 02, 2013, 06:25 pm
Probably 3 orders of magnitude out?
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#### APSDesEng

#8
##### May 02, 2013, 06:30 pm

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

No

#### Chagrin

#9
##### May 03, 2013, 05:22 am
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

#### FooTheBar

#10
##### May 05, 2013, 12:18 pm
"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
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)

#### sbright33

#11
##### May 05, 2013, 03:06 pm
It would be impossible to maneuver QUICKLY.  Maybe it would be more stable in theory?

#### APSDesEng

#12
##### May 07, 2013, 03:40 pm

"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
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?

#### FooTheBar

#13
##### May 07, 2013, 09:40 pm
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.

#### APSDesEng

#14
##### May 07, 2013, 09:56 pm

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.

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