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In a world where nightly e-threads leapfrog RC Electrics further into the IC's main living room, all that most of us can do is wish we could keep pace with the ever-advancing technology and our receding credit line. Charlie Wang's Thunder Power Lipo's have irreversibly changed the landscape of Electric Flight in ways we have yet to fully absorb from the front lines. Pushed at internet speeds, the ESC, Motor and Frame manufacturers scramble to catch up with the pioneers who are making it happen with hi voltages in video after video. |
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As an old greybeard Mechanical Engineer who has spent lots of time working on energy transfer in all kinds of things, this push for more Voltage had my vote from the start. Initially, like most, I bought my LOGO 10 with 12 x 2400 cell packs and an 18 cell 40 amp ESC. After the hovering and Morty Meekle phase was over, I boosted my voltage to 14 x 2400 cells, but found that the benefits of the extra power were somewhat offset by the extra weight, so the overall gain was not what a sports car enthusiast would look for. I ended up compromising at 13 cells. Extra voltage, less mass and more stored energy are the compelling reasons that LiPo's are so attractive. All that wattage and lower battery mass to accelerate your 3D is a seductive combination, for sure. Since Power is the product of Voltage * Current, if you double the voltage, you halve the current for the same wattage output, and generate only one quarter of the motor heat by the process of the resistance-current-squared law. The not-so-seductive part of the existing LiPo's is the high unit cost and increased risk of fire for all seasons and reasons. Still, I hungered to test my LOGO at the limits of it's ESC and motor without having to go to the Lipo Lending Institution. Thus, the search for 18 conventional technology cells that I could stuff into the LOGO 10 came about, without turning the PVC frame into a lead sled in the process. I reasoned that if it worked out, I would have a personal 'hands on' understanding of what Higher Voltage could do, and then make the intelligent (ahem ?) choice for LiPo's based on actual experience in my LOGO. The search ended up with 3 x 6 (18 cells - the max for the ESC, a Schulze 18.46K ), Type HR-4/5FAUP at 1950 mah and an internal IR of 5 milliohms, capable of pulling hi amps also. Best of all, the all-up weight of the pack is in the 720 gram range, verses 840 grams for a conventional 14 cell setup. This is a full 120 grams less than 14 sub C cells, and even 60 grams under the 13 cells I typically fly! Using the Hacker 13L, it puts the top RPM at 2280 or so, on the 13T, at shaft speeds the little hacker thrives on. The pack sells for less than a hundred bucks, which lowers the per crash battery replacement risk to a reasonable pucker factor. In building the packs, I ran the return wire from cell 18 back to the front via the valley in the centre of the pack, letting the batteries act as the shielding for the long wire. The pack fits the LOGO 10 perfectly; exactly in the spot you would put a 12 cell (6x2) sub C pack. I also added the third O-ring to tie down the pack for the extra power/acceleration loading it would experience. I also have the CF battery plate installed. To further prepare the LOGO 10 for HV, I installed the new style flybar frame and the improved tail slider links. Unfortunately, I left the old 2mm tail belt in place, as it "seemed" OK at the time. Don't do that, unless you have your finger close to the throttle hold. Get the newer wide belt, as the load on the tail goes up a lot. Trust me on that one. I added an in line plug resistor for the cooling fan that I can pop in and out to allow both the 13 cell and 18 cells to operate on the same fan. For the initial flight, I didn't have the cooling fins on the Hacker, but the fan was operating. Upon plugging in the pack, the first thing I noticed was a much snappier spark across the plug. When fired up, there is no doubt that an unbelievable surplus grunt resides in that little pack.. I settled on 1800 rpm governed. This set-up (wide open) is capable of 2285 rpm under load, way too high for my liking on that tail gearing. The power is incredible. There is no noticeable drop in governed rpm at full climb out, even halfway through the pack. I've never had such instant response from the LOGO before: flips in place, transition from hover to fast forward, rolls, inverted long climbs, anything I throw at it, and the rpm stays absolutely stable. It does run hotter: the Hacker
motor core was in the 150F degree range, and the
ESC was 102F when the flight finished. The pack
temp was 135F. I didn't have the cooling fins on
the Hacker. The flight time is the same as for the
13 cell sub C 2600's. Also, there is no sagging up
to the point where the pack runs out, and then it
collapses very quickly. I've since switched back to my favourite motor, the Kontronik 600-18 with third party cooling fins. Typical 3D flying gives a temp of about 135F on the core, which is fine for the torture it gets. The case is about 85F. The ESC is about 80F. (This is with the fan running, and OAT in the mid 60's) I am governing at 1750. At the 4:00 mark in the pack, when I give it full collective, there is no sign of RPM drop and the heli climbs like a scared banshee. The pack finishes at 6:00 +. And I do mean finishes!. It drops off a cliff. Only 0.1 AH left to full discharge as measured on the charger afterwards. If you fly down to the wire, you'll get lots of auto practice for real. Nonetheless, the packs are very consistent on time, so leave yourself 20 seconds or so and you'll be fine. The packs now have over 40 cycles each, and are still taking their usual 2000 mah charge. For a kinder gentler flying, you can squeeze over 7 minutes out of the pack. There doesn't seem to be a problem running in governed mode, either for the motor or the ESC combination I'm using. If you do the same flight profile as the 13 cells can do, the temps end up similar, perhaps a bit higher overall. The performance benefit is the weight savings and the power in reserve to the end of the pack. There is no sagging until the pack quits. Then there is nothing, as the Zen Master points out as you auto down.. Using KC's Spreadheet for the 4/5ths verses 5s3p Lipo's here is a comparison on the Kontronik 600-18 and Schulze 18.46K:
Power
Density: Max
Power: Max RPM@peak
power: Flight
time: Performance-wise (not duration), the outputs are strikingly similar. Of course, you get what you pay for: The LiPo's hang in for much longer. If you're not going to Lipo's on your LOGO 10 anytime soon, I would recommend you keep one or two of these packs around just for fun. If you do, I would also recommend that you add cooling fins and a fan for the Motor and ESC, especially for the summer. The only problem I have now is the 24-26-3000 sub C packs I have seem, well.. soooo pedestrian by comparison. Note: I will try to find someone who will take a short video of the L18 to add to this at a future time...... |
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