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Battery technology leaps ahead again with the introduction of these new Generation 4 packs. The current ratings are impressive at 45C continuous and 90C burst.
Check them out here: http://www.cheapbatterypacks.com/?menu=2B94921193&sid=63025
I think the pack sizes best suited for free flight (under 90 grams) are:
325 mah 2S 21 grams
325 mah 3S 31 grams
850 mah 2S 50 grams
850 mah 3S 74 grams
1250 mah 2S 76 gramsFor our short duration, free flight motor runs we could conservativley load these packs to say, 50C. As an example, this would put the output power capability of the 850 3S pack at an awesome 430 watts. Of course the motor and controller would have to be up to the task of absorbing all that power, and ya better build those wings strong. No, I have not tried any of these packs yet.
There probably will be other vendors offering similar hi-C batteries soon.
The technology just keeps getting better and better. This is a perfect example of why we cannot put limits into our rules structure that will become out dated before the next rules cycle. It it nice to see that the technology is not more expensive too. The day will soon arrive when EPFF models will be able to compete with gas models. If only we could eject the battery after the climb 😆 .
Dick, Thanks for the new battery reference!
The Thunder Power batteries cited have a 90 C burst. Even at 60 C, a 1250 mAh battery supplies about 75 Amps at about 6 Volts or 450 Watts. Motors that handle this burst amperage weigh about 180-200 grams. With a 75 gram battery, the power train will weigh 255-275 grams. F1C geared engines weigh about 250 grams and use over a horse power (~750 Watts). So the new auto-surface F1Q are likely to resemble F1Cs with about 60% of their performance. These are definitely exciting times!
Hummmm…. Five-seven seconds motor runs for auto surface F1Q seem likely. We may end up with rules that cap the motor’s weight, thus limiting the amperage and indirectly the model’s size as well. In addition, there seems to be a rational for granting the locked surface F1Q models longer motor runs – creating parity between locked and auto-surface models.
Another issue related to batteries that can supply more power (45C cruise, up to 90C burst) is the issue of a suitable controller. I happen to use Castle Creation controllers and on their web site http://www.castlecreations.com I found recently released controllers called Little Ice 50 and 75 (corresponding to 50 and 75 Amperes respectively). These ontrolers can track the following variables, sampling between twice and ten times a second:
– Battery Voltage
– Battery Ripple (Voltage drop)
– Battery Current
– Controller Temperature
– Controller Input Throttle (0-100%)
– Controller Motor Power Output (Watts)
– Motor RPMThese variables can be downloaded and viewed on a PC. At the moment, the interface is a bit awkward, requiring to disconnect the e-timer and connect the three-line plug to the PC through an interface. However, they have a new version that will be released in late January ’10 that will have a dedicated plug for the PC (without the need to disconnect the e-timer). Also, cleaning out the controller’s memory is a rather kludgy. Other oddities like starting to record as soon at the power is turned on, instead of when the motor powers up, will be fixed with future software updates.
I suggested including an altimeter to the technical support person, and to plot the altitude with the other variables. (This way the time dimension is synchronized.) This will allow deriving the actual climb rates and prop optimization. It’s something Castle Creations has been considering, but it might take awhile to implement and ship out. Currently, one can rig up a separate altimeter, like RAM3, and view the plots separately on a PC.
There is no doubt that these in-flight tools will accelerate the development of electric powered free flight models.
BTW, The ICE Lite 50 and 75 controllers are at least 20% cheaper than earlier Phoenix models due to improved manufacturing techniques.
Yes, we have seen big improvements in batteries, motors, and controllers. However, our knowledge of aerodynamics is still lacking. Despite numerous Sympo articles, technical papers, etc. we still cannot make high powered electric models track straight on a steep climb.
With 250 Watts “F1J” electric models could climb straight, but on the boundary of instability. Doubling the power implies larger and heavier F1C sized models with faster climbs. A faster climb is stabler, as the model is no longer on the cusp of velocity instability. These models have less power (50-60%) than F1Cs.
One can use “hot” outrunners with high RPM/Volt turning small props running at high RPMs (25-30K) emulating conventional F1C, or select “cooler” outrunners with lower RPM/Volt turning larger props running at lower RPMs (7-9K), resembling geared F1Cs. In either case, the prop/RPM conbination will have to force the motor to draw a lot of power from the new batteries, to utilize their high C rates. The appropriate battery (2S, 3S and 4S Lipos), controller and wiring should match the Amperage flowing through the system.
A nice conventionally built bunter, published in the July 2009 Model Aviation is the Super Marval 560 by Marvin Mace. (Kudos to Larry Bagalini!) With minimum adjustments, making a two part wing and replacing the mechanical timer with a e-timer plus a servo, it can be made into a hot F1Q. I’m offering to help spec the systems for those who might be interested.
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