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-   -   first airboat w/questions (http://www.rcuniverse.com/forum/rc-airboats-246/9635143-first-airboat-w-questions.html)

t3prongcoolness 04-03-2010 07:35 PM

first airboat w/questions
I just finished my first airboat (well still needs some cosmetic work) and test ran it a few times. i know most of you on here are gassers and nitro, but i am running a 1900 kv brush less motor with a 7.2V 3000mah battary. Im not getting a very long run time. im can only run for 5 minutes at the most. when i put these batteries in my rc sub they run for 20 min or more. what would be the reason for the fast draining? im new to brushless motors is that just how fast they eat up juice? i wil post some pictures up here in the next day or so..........got to show it off alittle bit.

ISIRC10 04-04-2010 11:32 AM

RE: first airboat w/questions
Welcome to the wild world of electric airboats! LOL
Okay, here are my 2c:
I went through a similar "upgrade" process about two years ago, switching from brushed to brushless... and then that dragged me into switching from NiCd/NiMH to Lipo. It was the natural progression. Now I have some questions for you: How big is the airboat? (the smaller the size, the higher the kv you can get away with running - it is cheaper) Also, what prop are you using? That dictates how many amps your setup will draw, and therefore your run time. As you have experienced allready, Brushless motors are far more efficient than brushed ones (Now you are thinking that doesn't make sense!) But the thing is, your motor may be more efficient, but it is also capable of drawing more current. This explains your drasticaly shortened run times. The batteries that you are using have a low discharge rating (I am guessing they are NiMH from the voltage you posted), somewhere between 10-15c. This would have been acceptable with a brushed motor, and your sub proves that. However, with your brushless motor, you need some more punch from your batteries. This would mean switching to lipo. If you go that route, your best bet would be to stay in the 4000-5000mAh and 20-40c range.

So in short, the answer to your question is, yes, the brushless motor is draining your batteries faster than the one in your sub. Now that you are into brushless motors, the logical progression is getting better batteries (lipo/lion/life) They don't have to be expensive brand name batteries either, as that will burn a hole in your wallet.

t3prongcoolness 04-04-2010 01:41 PM

RE: first airboat w/questions
i see what your saying about the battariesi think that is my issue i think i might also need a bigger motor it is not as fast as i hoped it would be. so i guess im going to go to the hobby shop and order some goodies.............

t3prongcoolness 04-04-2010 02:52 PM

RE: first airboat w/questions
1 Attachment(s)
here are some pictures..............i need to sand down some spots and paint and then i think she will be done. i am also thinking about making a splash gaurd on the bow to keep the water from flowing right into the battary compartment. i will put more pictures up after i finish. maybe a video if i can convince the girlfriend to go with me to the pond.

ISIRC10 04-04-2010 09:49 PM

RE: first airboat w/questions
I think 1900kv is a bit low to be running on 7.2 volts...
I am running 1100kv on a 4s lipo (14.8 nominal voltage) turning a 9x7ish prop with good speed...
the right person to ask would be CLASERdesigns... his mini airboat seems to be the same size as yours and runs very well... see what setup he is running, and build up from there to suite you needs.

Oh, and nice boat btw! http://www.rcuniverse.com/forum/js/f.../thumbs_up.gif

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