t-rex battery

[RC-MAN-4eva]

Hey,

What battery do u recommed for the t-rex? I want something that has a very long run time. Can u tell me what the battery's name and the charger?

Thanks

[martinic]

Thunder Power ProLite 2100 3S is an excellent pack for the Trex. I am using both a an Apache 2500 (nice, cheap ($50) simple, 1-4S li-po only charger) and a Shulze Chamaleon isl 6-330d (powerful, expensive ($250), complicated, multi charger (does everything)).

I time my flights to 8 minutes and only use 1600 of 2100 mAh. I can go longer, but I want to go easy on my expensive batteries (I burned out 3 G2 TP 21000s running them too long, 60 Celcius 11 minutes, 1800 of 2100 mAh). By limiting the flights to 8 minutes, my packs end up at 35 Celcius. I'm using a Just Go Fly 450TH on 13T using a CC35 ESC with 1.51 firmware, separate BEC (MR Potentia 6V).

What motor and ESC? That will matter for pack selection.

[RC-MAN-4eva]

i might buy this heli http://rccanada.ca/bb/viewtopic.php?t=23704 but i think i needa buy a battery pack and i dunno which one to get... is it better to buy an expensive pack with a long runtime or multiple cheap packs with shorter runs?

THanks

[martinic]

It's not the runtime that counts, but rather the pack's ability to cope with the power demands placed on it by the motor/pinion/ESC combo. Cheap packs will not cope with the high discharge rates that this setup will demand. If you're constantly drawing 15 Amps out of a pack that can only handle 10 constant, then the packs will die.

Flight times are determined by the pack's capacity and the disharge rate.. Cost is linked to both of these. Cheaper packs will not hold voltage as well which means the motor will draw more current, this will burn out the pack if it's excessive and/or constant.

For this heli, look for 15-20 C 11.1 V (3S) packs in the 2000 mAh size. The discharge rate is proportional to the mAh - for example, a TP1350 mAH 13C 3S ProLite pack can handle constant loads of 17A with bursts of 27A, while the 2100 mAH 15C ProLite pack can handle 31.5A concstant and 50A burst. Manufacturers over rate their packs, so assume 25-50% less load capability than they say (we also don't fly with constant loads). The physical size also matters since it has to fit in the heli properly.

You will also want at least two packs (I fly with 4) to provide a reasonable amount of flying. You can field charge, but remember that it will take about an hour (at a 1C charge rate) to recharge one pack.

You also don't want to overdischarge your packs otherwise you may damage them. If the per cell voltage at rest is less than 3V (e.g. 9V in a 3Cell, 11.1V pack), the cells will be destroyed.

So, for the Trex buy 2100 mAh packs with high discharge capability (15-20C continuous). Nothing less will do, really. For 3S 2100 mAh packs in this category, you will generally pay ~$100 per pack.

There are cheaper packs, but they will not last in this application.

Read up on lipo battery care in order to protect your investment. The $50 Apache 2500 charger is a good, basic, safe LiPo charger. You'll also need a 12VDC 5A (or more) power supply if you want to be able to charge without a car battery.

[RC-MAN-4eva]

ok which battery u recomend?

http://www.zoomsheli.com/ProductDetails.aspx?productID=9136

http://www.zoomsheli.com/ProductDetails.aspx?productID=8718

http://www.zoomsheli.com/ProductDetails.aspx?productID=8741


Would a 14.8 V work on my heli?

[martinic]

With that motor you will want 11.1V. These are good:

http://www.maxairrc.com/estore/index.php?action=item&id=7&prevaction=category&previd=2&prevstart=0
http://www.flyhighhobbies.com/product_info.php?products_id=1018
http://www.rcflightstore.com/product_info.php?cPath=29&products_id=248
http://www.rcflightstore.com/index.php?cPath=29&osCsid=dd7412df626af62f11406385d8354b9a

None of the batteries you specified will physically fit (at least easily) in that Trex and all of them would be too light duty for this application. The 34mm width of the TP2100 fits perfectly (some others do as well, all 34 mm or less, max. 27mm high, ~100mm long).

You will not go wrong with the TP2100 PL 3S. There are other good choices as well, but they're all around the same price.

[wheelman]

Ok I saw this post and decided to do an amp pull on the heli that is in question. I used this heli to learn to fly with and used 2200mAh 9C and 12C batteries. I also used it to test 1800mAh 10C batteries. I used the packs for 4 months and never saw a drop in performance from the batteries. The current motor is new and so is the ESC. Given the numbers being thrown around I got curious and did test this afternoon. I used the heli for sale, a Poly-Quest PQ-1800XP-3S pack. It is rated for 20C continous, I don't know the burst rating. I used this pack so there would be plenty of reserve to try to get an accurate reading. I thought the numbers being thrown around looked high and the test confirmed that. The motor has a 12T pinion I believe. I used a Medusa Power Analyzer Plus for the test.
The results showed that arround the hover point @70% throttle which is how I was flying it, it pulled 13~14 amps. At full pitch and 80% throttle it pulled about16~17 amps. The flight times on this bird were 11~12 min. using a 2200mAh 9C LiPo I usually stopped flying @10 min. On a 2200mAh pack it would usually take about 1900mAh back in the pack to charge.
The reason I'm doing this is because I thought that this young man was just starting to fly helicopters. My opinion differed from the other posts in that I think he would not require an "expensive" battery given his particular needs and the current draw for this heli. He's a young man on a budget. I think he can get away with using the "cheaper" packs until he becomes more proficient at flying helicopters. I know the 2200mAh 9C batteries I used with this heli are still perfectly fine after well over 100 cycles and 4 months of flying them every day. I say that he can get away with something in the 2200mAh 12C range and still have plenty of "headroom" as long as he does not over dis-charge from flying too long. The amp draw and burst would not harm such a pack on this heli anyway. Maybe if he changed to a hotter motor or went up a few teeth on the pinion, then I could see a requirement for more juice.
Just my 2 cents worth, I know everyone has a different opinion, and I respect that.

[can773]

The results showed that arround the hover point @70% throttle which is how I was flying it, it pulled 13~14 amps. At full pitch and 80% throttle it pulled about16~17 amps. The flight times on this bird were 11~12 min. using a 2200mAh 9C LiPo I usually stopped flying @10 min. On a 2200mAh pack it would usually take about 1900mAh back in the pack to charge.


Looks to me like your packs cant hold voltage well under load....without knowing either watts or volts the test has little value.

Once you loaded the pack if the voltage dropped off the amps would not go up....packs like the TP Prolites hold voltage so well that the amp draw goes way up.

My Trex with 2100's, 2100 rpm headspeed and about 10 degrees pitch will hit mid-high 20A's statically at full pitch. Packs with limited ability to hold voltage under high loads will got get the same amp readings.

[hillmanr2]

My Trex .

WTF? I thought you pattern guys looked down your noses at helis? :lol: :lol: :lol:

[can773]

My Trex .

WTF? I thought you pattern guys looked down your noses at helis? :lol: :lol: :lol:

Many pattern guys fly helis...Ivan flew them for a long time, Chip flies helis...I know Jesky has a Trex...for a few mentionables....I know tons of others that fly them as well.

Good practise for the fingers :) I am not any good, but improving :)

[hillmanr2]

just givin' you the gears. Sorry for yet again hijacking a thread

[martinic]

I have personally killed three TP2100 G2 (12C) 3S packs through cooking the middle cell by running them too long (to 60 Celcius, ~10-11 minutes, 1600mAH, ~11V finish voltage at rest, ~30-40 cycles per pack, 2400 RPM). I now have the prolites and time my flights to 8 minutes, 2700 RPM and temps are 45 Celcius (I may even run a minute less - just doing setup).

The Prolites hold their voltage really well. I have graphs to show the difference between the TP prolites and the PQ1800 XPs - for this application, the 1800s were too small and couldn't hold the voltage (dropped to under 9V under load, still at ~12V static once I stopped).

He may get by with the cheaper packs, but then again, he may not. There's a learning curve to runing Lipos - and it can be expensive if you run them too hard. Burning your way through cheaper packs can quickly add up (so can burning expensive ones :wink: ). I personally feel it is better to get the better packs up front - but it's up to the individual pilot. I spent my $300 learning my lessons.