kevka

My Feedback: (7)

I am converting a Laser 3D kit to electric (like the U-Can-Do .46) and looking for the best setup motor to batteries. SkyShark RC has some great prices of lipos [link]http://www.skysharkrc.com/shop/?shop=1&cart=137602&cat=24&noCookiePassThrough=Y&PHPSESSID=04412437ea5d9bd1fe1561ef58533fc5[/link] but they are 15C. I want to do 3D with this plane. Do I need 20C or will 15C do? I am looking at eh 11.1v 4000-5000mah packs. Anyone using these? Will they last?

Thanks
Kevin

Fliprob17

The C rating depends entirely on the motor draw in amps, and how may amps you need to get the power required to allow the plane to perform. A little more information about the motor would help.

kevka

My Feedback: (7)

Sorry about that. I am looking at using the setup that is on Skyshark RC using the Lightning 75 Brushless Outrunner with the following info:

Lightning 75
Type: Brushless Outrunner
Li-Poly Cells: 6 - 8
Voltage Range: 8-36
RPM per volt: 380
Max. efficiency: 80%
Max. efficiency current: 30 - 60amps
Max current capacity: 70 amps
Watts: 725 - 1700
Weight: 14.4 oz.
Dimensions (DxL): 1.94” x 2.55”
Shaft diameter: 8 mm
Lead wires: (3) 12 ga.

click [link=http://www.skysharkrc.com/PDF/L75-instruct.pdf]here[/link] for more info on the motor

I will more than likly use the 4cell 5000mah (X2) lipos with it and the [link=http://www.skysharkrc.com/PDF/ultra80.pdf]Ultra 80[/link] speed control. Or would I be better using two 11.1v 5000mah. If the two 3cells would do the hard 3D that I want, it would save some weight and $$$. Also, do I still need a BEC? The ESC does not include one. Should I run the servos off a seperate pack like a 6V? I have done the math and the plane should weight 6-6.5lb depending on the battery selection. The 11.1v weights 13.1oz and the 14.8V is 17.2 so there is only a 8oz difference.

Thanks
Kevin

Fliprob17

The 15C pack should be fine, the 4000mah can handle 60 amps continuous, the 5000mah could handle 75 amps continuous

If the ESC does not have a BEC then you are going to need the receiver pack, or purchase a separate BEC.

If you go with the 11.1 volt pack, you are looking around 500 total watts if you are constantly drawing 45 amps, with the weight of that plane you are going to need about 700-750 total watts. With the 14.8 volt pack drawing 45 amps, you will get around 660 watts. The motor can handle just about anything judging by the specs., so at a minimum I would go with the 4 cell 14.8 volt pack.

Again, this will all change a little depending on what you system actually draws based on the prop used. But it should be a decent general ballpark

kevka

My Feedback: (7)

Thanks so much for your help. Let me get a few things straight. If I use a seperate pack for receiver, then I do not need a BEC. If I am using the lipos to run the servos, I do need a BEC. That would make sence!!! But when I hook up the ESC to the trottle channel, will it not automaticly be using the lipos? Someone said to cut the red wire from the ESC and the power will not go through the receiver. Is this all I have to do? There are 4 digital servos, so would it be best to use a receiver pack? Also as far as the watts, I would be using two packs in parallel, so two 11.1v would be 22.2 and/or two 14.8's would be 29.6volts. If I read corectly to get watts, it is amps X Volts, right? So 22.2 volts X 45 amps= 999watts. And 29.6v X 45amp=1332. Am I doing this right? I also heard or read somewhere for 3D electrics you need about 150watts per pound of airplane. If that is correct, then a 6.25lb plane should 3D on about 938watts. Boy....am glad I paid attention in math class, and someone said "but we'll never use this in the real world."

Again thanks for your help
Kevin

Fliprob17

I am not a big fan of cutting wires So someone else may field that question better, if you do not want to use the BEC. Which with 4 digital servos, you may need to use the receiver pack anyway. Just for clarification, using the BEC means the LiPo runs the receiver and servos.

If you connect the (2) 11.1volt packs in parallel, you double the capacity, not voltage, you would have to connect them in series to double the voltage.

Forgot you are looking for 3D, for some reason I remembered sport. Anywhere from 130-150 watts per pound for 3D. 130 watts per pound would not quite be unlimited 3D.

mrasmm

I dunno about the current draw on the digital servo's or what esc you are using and how much the BEC can handle, but yeah to get rid of it, I would just take the center connector out on the throttle and heat shrink it instead of cutting it off if you wanted to use a seperate receiver pack. If you want to use the lipo's make sure the the BEC has enough juice to run all your servo's and your receiver ect.

About the plane... if you want to run the 11.1v, by the time you add the extra weight of the batteries in there, you're probably going to want 1000watts or so, or about 90 amps, sounds pretty high for that motor, 11.1v the max watt output you could get with that motor is 777.

The 14.8v 4s lipo might be a better choice, which would give you 67.6A for 1000w of power. If you were running WOT on a 4Ah pack at 67.6A it would last about 2 min and 50 sec =P, and you would have to have a 20c pack, or if you had 2 10c's in series that would also work, and would double your battery weight and roughly your flight time. That is also assuming only 80% draw on the lipo's for longevity.

if you had a 4s2p setup with 5Ah cells you'd get 7 min and 6 seconds WOT also assuming only 80% draw on the lipo's for longevity.

basically if you go with a 3s1p setup you'll need a 20c, a 4s1p setup you can barely squeak by with a 15c, but it will be hard on the pack. With a 3s2p setup you could get by with a 10c, but 15 would be better, and also the same with a 4s2p. I don't think the 3s is going to get you into full 3d flying though, because at the absolute max you're talking 124watts per pound without the additional battery weight factored in.