few questions about my power plant - RC Groups
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Apr 17, 2005, 04:16 AM
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few questions about my power plant

Hi again. I've posted similiar questions in the past, but was long ago, and slightly different, so searching for that old thread wont answer my questions.
Gear i have:
mega 16/15/5
pheonix 25 esc.
kan 1050 nihm

My first question is, what prop should i use with this set-up? One problem with that question is i cant go to abything bigger than 7 inches, this setup is going in(and is already installed) a foam glider conversion i made into an rc pusher, the tail booms are made from some carbon fiber arrow shafts (i bought at a local archery range out of his "broken arrows" bucket for 1$ each), and are only 8 inches appart. the reason i placed them at 8 inches is because teh motocalc calculations i made long ago came up with an 8 inch prop pulling too many amps. well, now moto calc wants money for me to use it, and i just dont have the money to spend, so i used p-calc, i think its called, and its telling me 8 inches isnt too much for that motor/battery. Did i do something wrong calculating it last time? or this time? at any rate, what prop would be the best to use here? I currently have a 7x4 on there, don't expect it will pull too many amps, p-calc says around 18. I do understand i'm not getting the best out of this motor with only 8 cells, but 8-cell packs are what i have, and like i said, i just dont have money. I'm thinking the plane is a little heavier than the normal FF conversion, but still not too heavy i hope. one thing that adds to the weight of the aircraft is the four standard size, futaba s3004 servos, which leads to my next question...are 4 of those servos to much for the bec on the phx 25? the documentation says 8-cells, 3 high torque servos, or 4 micro servos, useing the 4 s3004s gonna be too much for it?
Hope i've given enough info to get my questions answered, looking forward to hearing what you more experianced people have to say.
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Apr 17, 2005, 05:50 AM
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vintage1's Avatar
probably the best you can do is an APC 7x5E actually.

My Motocalc suggests this is only 13A, not 18....so its well below what the motor can soak up.

Short of a bigger diameter or more cells, thats all you can do I aam afraid.
Apr 17, 2005, 06:17 AM
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thanks for the answer. i can maiden in the morning(whether permiting) with the security to believe im not gonna burn up my motor.
Apr 17, 2005, 07:13 AM
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vintage1's Avatar
Try and get some cooling on the ESC if you have 4 large servos.

Ebay ios your friend when flying on a tight budget, too.
Apr 17, 2005, 06:39 PM
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Thanks again, teh esc is taped to the side of the fuse, shoudl get plenty of airflow, actually, the motor battery and esc are all exposed, was just concerned that 4 full size servos may be too much load. Pretty sure i've flown this esc with 4 servos b4, and never had a problem, just couldnt remember for sure.
The sun rose a little late this morning, or maybe i just went to bed a little early, couldnt stay up that late. a little windy atm, gonna wait til this evening when the winds should be lighter, then i'll try my maiden.
As for e-bay, probably is a good place to find enexpensive equipment, for someone on a budget, but my budget is $0.00, really, but i'll keep it in mind next time i come up with some hobby cash.
Thanks for the help, wil let you know how the maiden goes.
Apr 17, 2005, 08:06 PM
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Well, maiden didn't go so well. Had enough power, just not enough hands i guess. First, i had to fly from the other side of my field than normal, cuz the light winds were from the wrong direction. Normaly i launch downhill, but due to the wind direction, i had to launch flat. because i handlaunch, i have no control over the plane for the first second or two after launch. so anyways, against my better judgement, i powered up for the launcch, threw the plane, and immediately the right wing dipped a bit. when i reached for the sticks, i missed, and barely caught the right gimbal with the back of my thumb. Ever try flying with the back of your thumb only? anyways got the wings mostly level, and cut the power, but was already too close to the ground,tumbled a bit and twisted the fuse into three pieces, it broke right where i expected to. A small cut in the foam, and a hot glued bamboo skewer into the foam, should fix it right up. but as i said, i think i got plenty of power, when i powered up it tried to launch itself right outta my hand, not sure if i threw it wierd, or if the wind cuaght it, or if my flaperons werent properly alligned. at any rate, about half hour of work and i can try again. thanks again for the help.

Apr 17, 2005, 08:11 PM
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vintage1's Avatar

I use a neck strap when hand launching.
Apr 17, 2005, 08:21 PM
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yeah i use the neckstrap, just dont know if i threw it funny or what, but when i reached for the stick i missed. not all too bummed about it, as i said easy enough to repair. And at around 10 dollars to replace, even had it been totaled wouldnt have been all bad. of course after i repair it, i need to try again, think i'll call a friend over to help me throw it so i dont have the stick problem again.


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