olds455

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hello, Im looking for some insight on batteries for this dash. I also have a few other questions. A little info, the air craft specs are
Wingspan: 72''
Wing area: 582 sq in.
Length: 63''
weight: 5.5-7 lbs
Im building custom retracts so I think it will weigh between 7 and 8.5 lbs. I have two AXI 2820-12 and to Jeti 40 advance plus controllers. Ive removed the switches and the red wire. I will not be using the becs. Here is my confusion. I test ran the one motor thats set up and it doenst feel powerful enough for the plane to fly. I could only test it with the 3s 2100 10c pack. thats the biggest I have. I tried the two apc electric props I had laying around, One 11x7 and 12x6. Ive used motor calc demo and another(maybe the first motor calc) and it doesnt give me the power (watts) that I need for it to fly. To have 75w per lb I need 600 total and i havent found that. Ive ben planning to run a 3s2p 3500 to 4200mah. Ive been reading about the watt meter and will probaly buy one here shortly. Any help, tips or ideas would be greatly appreciated.Here are the questions

1.The jeti plus controller says only 2 to 3lipo, the opto even more lipos. I believe its because of the bec. Since Im not using it could I run a 4s pack if needed?
2.Will ,should this fly on 3s2p lipos?
3.I may have went overboard but I just put 10gauge wire through the wing for the esc. Is that to much? Is thier going to be a problem with long battery leads from the fuse to the nacelle? About 3ft

Ive read the C-160 conversion thread and continue to follw it. I refer back into it all the time. the pics are ove the wing currently and the plane from rt models. Thanks again.

normgoyer

Hi if this info will help, have you used the programming card to get the ESC to operate properly with Lipos? Very important. I have two AXi 2826-12 and run 14.8 volts all the time. They haul up a 6.5 pound Cub in seconds. Two of them should pull the wings off, if they are the same power range as your motors. Getting more amps will not increase the power just the running time unless you are really going very small. I run 3200 ma and it runs it for 15 to 20 mins at reduced throttle, 10 mins wide open. Norm

olds455

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i do have the program card and they have both been programed. i ran that 2100 battery at full power for a min and variable power until the esc shut down. The motor slowed and slowed until it finally shut off. The Axi specs say the motor is rated for 25 amps continuos and 35 peak so I wasnt sure if the 4s bat would over power it.

normgoyer

Hi, Iust checked the HL catalog and that motor can be run with 3 to 5 lipos, so you should have no problem. Norm

algutkin

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Nice plane,

However I don't think it will fly well on 3s, not enough rpm. If you are flying from grass, you need to overpower the plane.

If you use small props, 9s, 10s and some 11s, you really need to get more than 7000 rpm per motor. Don't forget that what we are doing is converting a nitro plane to electric. The distance from the center of the motor to the fuse could limit the size of the prop. So, what good would a motor be that could swing a 15 inch prop, if you only had clearance for a 9 inch. That 9 inch prop has to turn 9,000 rpm to get a 8 lb twin moving.

OK, so prop size is one limiting factor. The other is rpm. The nitro motor can spin those small props way more than 10,000 rpm, so that is what we have to emulate. I use a rule of thumb of 9,000 rpm, with the correct size prop, has worked to make any of my twins fly really good. Perhaps not advanced aerobatics, but good. By the way, I always prove my assumptions with Motocalc. I have found Motocalc to be very conservatice and I alway found that Motocalc is very wrong with the heat warnings on ESCs or motors. In almost every situation, Motocalc warned on 483 degrees, in a real test, the ESC didn't even get warm.

Al

olds455

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So it looks like Ive made a bad motor selection, or do I need to run a 4s battery? I do have room for a 13 inch prop. I dont have motor calc any more. My demo has expired. i do have this one though - http://brantuas.com/ezcalc/dma1.asp
The battery in my tach was dead so I couldnt get an rpm the last time I ran it. Ive been comparing my set up to others and Ive only found one twin that used the -12.

olds455

My Feedback: (1)

So it looks like Ive made a bad motor selection, or do I need to run a 4s battery? I do have room for a 13 inch prop. I dont have motor calc any more. My demo has expired. i do have this one though - http://brantuas.com/ezcalc/dma1.asp
The battery in my tach was dead so I couldnt get an rpm the last time I ran it. Ive been comparing my set up to others and Ive only found one twin that used the -12.

CAn I delete this post?

olds455

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Here is what I just done. I wired my two 1320tp and the one 2100 3s batteries together and made some pulls. It turns out the 12x6 prop was acually a 12x8. It got 8200rpm at max power. Then I had a choice of 11x7 or 10x5 so I put on the 10x5. It made 95 to 9600rpm. It felt more powerful with the 10x5 than the 12inch. As for real specs ill have to get a watt meter and check it. Can I charge this pack wired together? I hope this adds some insight. Anyone else have some input I gladly take what you got.

algutkin

My Feedback: (1)

Great, you are getting the rpm, and thats fantastic. However, you just can't stick different size batteries together. It looks like 5S will do the trick, but, the combination has to be the same mah. In other words, you can put a 2000mah 2S together with a 2000mah 3S, to make 5S but they all need to be the same mah. You can't mix a 1500mah with a 3000mah.

On the twin, in order to get any decent flying time, you will need a total of 8,000 mah, 4,000 per motor. I don't think you will have any problem with watts, you most likely are drawing around 30 watts per motor at wide open throttle. Motocalc will will most likely report that the plane can do aerobatics and flight should be attempted by an experienced pilot.

Converting nitro to electric is a research and development project. After you get your batteries setup, you should run the batteries down by running the motors on the ground at close to max rpm and see how long the run time is. Also, you should shut down the motors a few times during this run and feel the ESCs, the batteries, and the motors. In your case, heating should not be a problem, everything should be warm to the touch.

That plane is going to fly on less than 50% throttle once you get it in the air, so, if you get the batteries matched and installed, you should be good to go as far as the power plant is concerned.

Al

olds455

My Feedback: (1)

algutkin,
All the batteries are 3s 11.1 volt. I wired them in parrallel to get 4600mah at 11.1v. Those numbers are what came from that set up. Im aware of not mixing series batteries, ie, 2s and 3s that arent the same rating. Should I not have put the two 3s 1320s and the one 3s 2100 together? I thought you could mix say a 3000 mah bat and a 2500mah bat for a total of 5500mah. Anyhow if those rpm numbers are good then after I get a wattmeter Ill plan on a 3s2p or 3s 4000mah range battery. Times that buy two for 8000mah. Now for the last question, Should I leave them seperate (one for each motor) or parallel the two batteries and feed both motors off the one large battery? ( 8000mah 3s4p running both motors), Thanks

algutkin

My Feedback: (1)

They souldn't be put in parallel either. There will be an uneven amp draw after the smaller mah batteries run down.

Al

olds455

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Ok, this is for testing purposes, Im not running this on the aircraft nor is it being ran for more than a min or two. I have a wattmeter on the way. Any others with input? Answers to any of the other questions put forward? Thanks

Team Fine Design

Just curious.I am learning so for give me for butting in but could he go to 3 or 4 blade props to get the power needed.i know that effeciancy may suffer a bit but it would solve the ground clearance problem.Nice plane though, I will be watching and learning on this one.

olds455

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good luck, Team Fine Design, Not to many have an opinion. I do have a watt meter on the way. When it gets here Ill post some actual numbers from the test battery. I did call hobby lobby yesterday and told them about the plane and these motors and controllers. They recommended a 3cell bat around 4000mah. They even recommended using only a single battery to save weight. It would have to be big to power both motors for any period of time. They also said the most efficent setup would be a 12x6 prop and yeld about 6.5 lds of thrust. I figrue the plane will weigh between 6 and 9lbs. Im shooting for 8lbs. It will probaly have more than enough power. I have room for a 13 inch prop if needed.

olds455

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Hello,
I have a few questions about twin setups and power numbers Ive gotten from the astroflight wattmetter.Here is what I got. Two Axi 2820-12s with jeti 40 amp plus controllers and thunder power 3s 4000mah prolites.
1. What is the best way to hook up the alierons and two speed controls. Y-connector or seperate channel?
The #'s from this morning test are,
Motor #1 Left
10x5 apc electric
12.35v before start
At 100% 20 amps
200w and 10.2v under load,
Test 2 12x8 apc elec, 12.3v before At 100% 35amps 320w and 9.1v under load. While testing the #2 moter I left the #1 running and retested the initail #s. It pulled 37 amps and 360watts at 100%.The test are on brand new batteries freshly charged this morning but never ran more than 30 seconds. I talked to hobby lobby about my set up and they recommended a 12x6 prop as the best to use. Ive read about pitch speed and would like some help in that aspect. The plane should come in right at 8lbs. The wing area is 582 sq in. Thanks for any input or help that may come my way.

Motor #2 right
11x7 Apc electric
12.3v before
At 100%
27 amps
255w and 9.4 under load

olds455

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After a suggestion to warm to batteries I got these #s. I topped the batteries and warmed them with a water bottle. I ran each motor 1min continuous and got those #s as well.
#1 motor (left) 12x8 apc
12.35v start
10.4 under load
42 amps
420w
At 1min 9.99v, 38amps,and 385w

#2 motor (right) 11x7
12.42v
35amps
375w
10.45v under load
at 1min 31amps, 320w, and 10.3volts

I like these #s much better. tha batteries were just getting warm to the touch at the 1min mark. Any help, comments or suggestions, send them over, Thanks

drksyd

Sorry, had to read through fast. First, you would definitely want to run your packs in parallel. In parallel, you need to have the same identical packs, with series you can have different voltage but same capacity and of course brand.
Test #2 looks not bad. What kind of packs do you have?
As for battery placement, if there's room in the nacelle I would put them there. It would be a lot cleaner and easier not having so many connections and all the wire running through the wing and fuse. If there's no room in the nacelle or you need the weight to balance then put them in the fuse.

olds455

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The batteries are 3s thunder power 4000mah. Not the 3s2p battery. theres not enough room in the nacelle so they will go in the fuse. I will parrallel the two packs for flight. The initial test packs were before I bought these two. Im going to test the 11x7 test #2 fist when its ready.My nose retract just arrived so I can continue the build. Once its rigged and set I can finsh the fuse sheeting and sanding before coverig.

drksyd

I'm quite sure the numbers will go up with your new packs. I'm thinking an 11x6 or 10x7 would be about right.

olds455

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here it sit as of now. I still have some small items to attend to. Im thimking of putting in a naca vent on both sides of the cadin for ventilation with two exit holes in the rear of the fuse. Air can get in from around the nose retract, then up under the cokpit area and then down the fuse. At its current state it weighs 8lbs 1oz. I just need to come up with a way to mount the batteries. im thinking of laying them down longways in the fuse. at the area with the marker scrible. It balanced 1/8th behind the cg from the plan with the batteries there. other than the lose ends and covering its ready for taxi and run time test. Im either going to try the batteries there or put them forward of the sterring pushrod support which is where the rx was going to be. here are the pics. If anyone has an idea on mounting these batteries please let me know. Im thinking of velcro or a tie strap. Also, which way would these batteries cool better, flat or vertical. I think vertical would be better. thanks

drksyd

I like to use trays, that way you can velcro and strap the packs. A piece of ply joining the formers surrounding your planned location would work well.

olds455

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heres what I came up with. I doubled the balsa sheeting with I believe 3/32. then I placed velcro on that and the batteries edge. there are two vertical supports to help hold them upright. then thier is a rubber band thet holds the batteries from moving and biouncing around. It looks to work ok when I shake the fuse around and even when upside down. I started to cover the wing last night but I had to work late today. Ill post updates as I progress.

drksyd

You sheeted the inside of the fuse? The only problem I see is a hard landing could possible break the stringers.

olds455

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It has been test flown. It flies well and has plenty of power. I weighs 8lb 1 oz rtf. here Are some pics and a link to some video.Ive flown it 4 times. on the last flight I had a radio lockout or some thing and almost lost it. Then on landing I stalled it and ripped out the gear boxes. Its been fixed but it still needs the covering patched.

http://www.rcgroups.com/forums/show...800#post7286478

normgoyer

Hi First that is a very good looking model. Second I have a 455 in my restored 1974 Buick LeSabre Luxus convertible. Great engine, but at $3.50 a gallon for gas down here I prefer my 1974 Karmann Ghia convertible with 27 mpg. Norm

bet there aren't too many convertibles in Alaska