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sobamaflyer
12-14-2005, 05:48 PM
I have a foamie trainer (STC) weighing approximately 15oz (AUW).

I have been flying it with what I call success now for a few weeks using 2 differnet power systems, a few different batteries and a few different props, please 'splain to me what I may or may not be doing wrong.

1st system:
GWS 350d gearbox, has 66 tooth gear. Running on 7.4v 2 cell Lipo, 1100mah battery, and a 8.4v NiMh 650mah battery. I've tried 9x7, 10x4.7, 10x80, 11x4.7 props, the 11x4.7 & 10x80 seem "sluggish" but have no problems staying aloft, the 9x7 seems to stall a lot more doesn't fly well at all, the 10x4.7 seems to work the best giving nice, predictable flight. I seem to get 10-15 minutes of flight out of my Lipo, only a few out of my NiMH. I have to fly this at 2/3+ throttle to get it to stay straight, full to do more.

2nd system:
15amp ebay outrunner brushless and matching ESC, (direct drive) pretty much exactly in the way of performance and time of above, it "stutters" and doesn't go really any faster at more than half throttle. NiMh pack time is probably a minute or less.

So....are my batteries too small for the brushless, not enough power? I expected from my research for the brushless combo to have at least doubled the performance of my plane and/or extended my flight times. No I haven't discounted that my little combo may not be the greatest I could have purchased.

Are my prop choices making the above situations worse? Have I chosen props poorly in general for what I'm running and trying to accomplish?

Thanks for the help, Travis

sobamaflyer
12-14-2005, 06:43 PM
I believe I may have just answered part of my question, I believe I found my brushless motor elsewhere on-line and seems to list 12.3oz of thrust w/ my battery & prop combo. Which would make it operable on my plane but slow.

watt_the?!
12-14-2005, 09:06 PM
1st system:
GWS 350d gearbox, has 66 tooth gear. Running on 7.4v 2 cell Lipo, 1100mah battery, and a 8.4v NiMh 650mah battery. I've tried 9x7, 10x4.7, 10x80, 11x4.7 props, the 11x4.7 & 10x80 seem "sluggish" but have no problems staying aloft, the 9x7 seems to stall a lot more doesn't fly well at all, the 10x4.7 seems to work the best giving nice, predictable flight. I seem to get 10-15 minutes of flight out of my Lipo, only a few out of my NiMH. I have to fly this at 2/3+ throttle to get it to stay straight, full to do more.


2nd system:
15amp ebay outrunner brushless and matching ESC, (direct drive) pretty much exactly in the way of performance and time of above, it "stutters" and doesn't go really any faster at more than half throttle. NiMh pack time is probably a minute or less.

So....are my batteries too small for the brushless, not enough power? I expected from my research for the brushless combo to have at least doubled the performance of my plane and/or extended my flight times. No I haven't discounted that my little combo may not be the greatest I could have purchased.

Are my prop choices making the above situations worse? Have I chosen props poorly in general for what I'm running and trying to accomplish?

Thanks for the help, Travis

Your first setup is using a gearbox, which will reduce rpm significantly and therefore amps- allowing you to use a larger prop and get longer flight times.

The second setup is difficult to assess as you havent shown what kv the motor you purchased. From what you are saying though, and without knowing this, i'd guess that the kv is too high on the brushless causing it to draw too many amps and cutting out accordingly. under 1 min for the nimh also points to high amp draw.

please find out what kv the motor is and that'd shed more light on the issue.

Tim.

sobamaflyer
12-14-2005, 09:31 PM
Thanks Tim, I'll see if I can find the kv rating, it's not listed.

Do my prop sizes sound "normal" for what I'm running? The brushless says for use w/...and 8x4 prop is the largest.

I'm going to put the geared motor back on for the moment and continue my experimenting.

watt_the?!
12-14-2005, 09:33 PM
the props sound fine for the geared setup...but without the kv i wouldnt have a clue about the BL setup. That number is vital.

Tim.

sobamaflyer
12-14-2005, 09:49 PM
I have emailed the seller and I hope to get actual data but the link below appears to very closely match what I have, It's kv rating is 1260. Mine does supposedly have a 15amp draw and an 18amp max though.

http://slofly.com/cart/product_info.php?cPath=0_23_45_135&products_id=892

Forgive my newbie status, not sure what to make of the kv rating (I know it's Kilo-volt, but not sure of it's affect)

Travis

watt_the?!
12-14-2005, 10:21 PM
thats ok...it should be pulling 6A, so you should be good to go..even with the nimh pack...it must be something else.

your lipo should be fine...have you programmed your ESC correctly for battery type and number of cells?

i know its a pain, but i'd be asking the seller for a complete replacement of ESC and motor..that should eliminate those two as possibilities.

now, kv is turns per volt per minute. the higher the kv, the higher the power draw for a given prop.

Tim.

ps...love your Bueller sig!

sobamaflyer
12-14-2005, 10:50 PM
I'll email him and explain what I'm experiencing, cross your fingers :)

Programming - the only options available to me are a jumper to set 2 cell lipo or 3 cell (which I made sure was right, at 2) and a brake function (which I haven't messed with). I assume you are telling me under my current circumstances this power cut-out at full throttle isn't "normal"?!

Thanks for the diagnosing help so far

"Bueller Sig" - I'm feeling older and older, there's a whole set of folks that have never heard of one of my favorite movies of all time, glad some still get it :D

watt_the?!
12-14-2005, 10:51 PM
save ferris...

''oh you know him?''

lol.