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Old 12-29-2006, 10:18 PM   #1
Striker
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Default A123 ideas!

Hey Guys,
There are a couple of threads going around about A123. The main problems I see are weight and voltage.

This got me thinking about different configurations besides 4s.

For example:
Why not make a 2S pack which is 4600 mAh 6.6v 30C. This would only weigh 140 Grams which is as light as the 2100 prolites from thunder power.
This set-up would still get you 6-7 minute flights. (Cryofix gets 12 mins on 4s and he is flying much more weight around)

It would also only be 130MM in length which would fit in the same place as the lipo with no modification.

You would just need to change the motor/gearing a bit. For example on a 430L you could run a 21T motor pinion. (Not sure if that is possible or is manufactured)

OR just run a 6000 Kv motor with the 13T Motor Pinion. Such as this motor:
It's the exact same size and has the same mounting holes and everything.
http://www.allerc.com/y22s.htm

The other option is a 3s 9.9v using a 15T on the 430L OR a 4000Kv on 13T.
This would give you 9-10 minutes of flight time. The weight would be 210 grams which is really not bad. Only 54g (0.1lbs) heavier than an Apex 2200.

I'm all for trying this on my bird unless someone can tell me why this wouldn't work.

Thanks,
Eric James

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Old 12-29-2006, 10:27 PM   #2
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Eric,

I like your thinking, but I worry about how efficiently the motor will run at the lower voltage. If you could find a motor with the right KV and the right "design voltage" I think that would work OK. I plan to do a 4S A123 pack just as soon as I can. I'll certainly report how it works out.
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Old 12-29-2006, 10:41 PM   #3
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2s pack would either be 6.6V 2300 mAh or 3.3 4600mAh
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Old 12-29-2006, 10:54 PM   #4
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Quote:
Originally Posted by Cryofix
2s pack would either be 6.6V 2300 mAh or 3.3 4600mAh
I think 2S would be 6.6V 2300 mAh, while 1S2P would be 3.3V 4600 mAh. Right?
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Old 12-29-2006, 11:17 PM   #5
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That's right spork. you can't get 4600mah out of 2s. At such low voltage, it would require more amperage to get enough speed? That's where the a123s are weak, current draw. perhaps a 2s2p and use a really high kv motor with a pinion with more tooth count. 2s2p will give you insane amount of amperage draw.

In the end though, aren't lifting the same amount of weight? So no matter how you play with the configuration, you draw the same amount of wattage?
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Old 12-29-2006, 11:42 PM   #6
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Hey Guys,
Just did some math. Turns out that lipos are much better in terms of watt hours per gram.

So the REAL advantages to A123: Safety, Charging time, Battery lifetime.

mah x voltage = watt hours
to find: watt hours per gram

TP ProLite Lipos are: 168-174 Watt Hours per Gram (3s vs. 4s)
Apex 2200's are 148 Watt Hours per Gram

A123's are only: 101.2 Watt Hours per Gram

2300 x 6.6v = 15,180 Watt Hours / 150 grams = 101.2 Watt Hours per Gram
2100 x 11.1v = 23,310 Watt Hours / 138 grams = 168 Watt Hours per Gram
2100 x 14.8v = 31,143 Watt Hours / 178 grams = 174 Watt Hours per Gram
2200 x 11.1v = 24,420WH / 165g = 148 WHPG

Having charging time cut down to 15 mins sure would be nice!!

So let's look at a couple real world examples:
My current prolites: 23,310 Watt Hours
3s A123 9.9v: 22,770 Watt Hours

So for a 3s pack I would have LESS time and carry 87 more grams!


My current prolites: 23,310 Watt Hours
4s A123 13.2v: 30,360 Watt Hours

For 4s you have 7,000 more Watt Hours(30% more) BUT you carry 162 more grams!


I think the 12 minute flight times from Cryo may give some people the wrong idea.

Let's say with your current flying style you get 6 minutes of flying time. That would mean if the A123's weighed the same you would get flight times of 7:48. Now since they do not weigh the same amount you need to take some time off for this factor. Let's say 30 sec off. That leaves us with a flight time of 7:18

So all of that for a flight time increase of 1:18. That sounds a lot different than the idea of doubling flight times.

Judging this by these numbers I think the only major gain your getting is the recharge rate. But your losing some of the acrobatic abilities of the helicopter in exchange.


Let me know what you think of all of this.

Thanks,
Eric James

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Old 12-30-2006, 12:18 AM   #7
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I think your analysis is generally accurate, but I'm hoping there are a couple of other upsides. It's my understanding that the A123's can deliver a solid 30C, and maintain that performance with less babying than LiPo's. To me that's a big upside. I have some LiPo's now that have probably 80 flights each. Their capacity isn't down all that far, but their ability to put out real current is WAY down (unless there's some other problem). I'm looking for robust packs that will continue to give respectable performance with less care. I'm hoping that by the time I've gone through a couple of A123 packs we'll all be using ultracapacitors that give us 30 minutes of hard 3D and a 20 second charge! :mrgreen:
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Old 12-30-2006, 12:18 AM   #8
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I think Cryo is basing it on similar voltage set up. So he compared a 3S lipo to a 4S a123. 12.6v of 3s lipo to 13.2v of a123. Yes with a 4s lipo pack you'll get more flight time than a 4s a123. What he's trying to say is, the most optimal pack configuration for a 450 is a 4S a123, which gave him 12 min of flight time. Does not matter how much it weighs, how much the capacity. Bottom line, to use a123 on a 450, 4s is recommended and he gets 12min out of it.
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Old 12-30-2006, 07:02 PM   #9
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“I'm hoping that by the time I've gone through a couple of A123 packs we'll all be using ultracapacitors that give us 30 minutes of hard 3D and a 20 second charge! Mr. Green “

I Can't get the "Quote" to work?

Anyway touché to ultracapacitors :wink:
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