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Old 01-27-2011, 07:32 PM   #1
KnowAceHere
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Default Tri-Motor setup question

I'm setting up a Ford Tri-motor using 3 cf2812 motors (with a prop range of 5"-7"), 3- 20A ESC's, 3-gws 7x3.8 props running on a 2200mAh 3s 25c battery.

Ok running these 3 motors using my watt meter I am getting a reading of 27A 305 watts when hooked up to all 3 motors. The problem is this is more than the esc's can handle. The question is do I divide these numbers by 3, since I have 3 motors? I ran the motors hooked up separately and got 13A at 125 watts, so I'm thinking that the first numbers are divided by all 3 motors but I want to be sure. Any help would be appreciated.

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Old 01-27-2011, 07:37 PM   #2
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Yep you are good. 27amps is the total. If you have twenty amp ESC's per motor you are good since each is only seeing 9 amps.
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Old 01-27-2011, 08:13 PM   #3
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Thats a neat Tri-Motor.

You would be doing that model justice finding new props for it, them orange glow-sticks are fugly!

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Old 01-27-2011, 08:23 PM   #4
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Originally Posted by Nitro Blast View Post
Thats a neat Tri-Motor.

You would be doing that model justice finding new props for it, them orange glow-sticks are fugly!
Black spray paint and leave the tips orange covered with tape, will make them look a whole lot better, I agree!
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Old 01-27-2011, 08:27 PM   #5
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Thanks for the quick replies, yes the orange props are ugly. I'll be switching to apc props, most likely 7x4's now that I'm sure my esc's wont overload.
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Old 01-28-2011, 03:44 PM   #6
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Originally Posted by KnowAceHere View Post
I'm setting up a Ford Tri-motor using 3 cf2812 motors (with a prop range of 5"-7"), 3- 20A ESC's, 3-gws 7x3.8 props running on a 2200mAh 3s 25c battery.

Ok running these 3 motors using my watt meter I am getting a reading of 27A 305 watts when hooked up to all 3 motors. The problem is this is more than the esc's can handle. The question is do I divide these numbers by 3, since I have 3 motors? I ran the motors hooked up separately and got 13A at 125 watts, so I'm thinking that the first numbers are divided by all 3 motors but I want to be sure. Any help would be appreciated.

Attachment 142445

Something here isn't making sense. You are getting 27 amps with three motors, yet you read 13 amps on a single?

Sounds like the pack isn't holding up to the load.

What are your voltage readings? I bet the pack is sagging which would drop the amp draw as amps are related to volts to watts.

Notice how your total watts lost 70 vs what you had on the single set up x 3.


Maybe hook up a larger 3 cell or double your smaller ones to get another reading. As it sounds like the motors are starving for power.

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Old 01-29-2011, 12:47 PM   #7
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Glacier Girl makes a good point - the clear inference is that the voltage of the pack is indeed dropping under the greater current draw, yet the 2200mah 25C pack SHOULD be able to hold its voltage pretty much rock steady up to 50A.

Sounds to me like you may have a very bad cell in the pack.
Are you testing on a fully charged pack which had been balance charged?

I suggest you need to sort out this question before you start changing the props.
Balance charging is essential to ensure that you don't overcharge the good cells and risk a fire.

Nice try - but no cigar!
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Old 01-29-2011, 05:08 PM   #8
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ok I've run the numbers again. This time I made sure to use a fully balanced charged 2200mAh 3c 25c battery. Reading 12.60v when pluged in. I used the same battey for all the tests.

3 motors test
344.6W
29.94A
11.39V

2nd 3 motors test (Battery @ 12.40V)
349.1W
30.15A
11.35V

2 motors test (Battery @ 12.44V)
234W
19.75A
11.64V

1 motor test (Battery @ 12.34V)
111.4W
9.12A
11.99V

I believe that I had a different prop on the first motor test I did. I only have 2 APC 7x4 props, but I had 3 GWS 7x3.8 props so I switched them out. I believe that is why I had different readings. Thanks everyone for you input.
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Old 01-29-2011, 05:44 PM   #9
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So let me check... You changed the props between the first 3-motor test and the second 3-motor test to account for the otherwise unexpected rise of power while running on a lesser voltage?
If so that's looking good.
I looked up the CF2812 and see that it has a 1600 rev/v (Kv) so the slender pitch of the props should give you enough pitch speed for flight.
Normally taking 60W per pound a 300W power input should fly a 5 pound model so you should be good to go.

I wish you a happy maiden flight and safe return to Earth for the model.
And welcome to the forum!

Let us know how it goes.

Nice try - but no cigar!
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Old 02-08-2011, 08:39 PM   #10
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Default Kit information

I am interested in the plane itself. Was it a purchased kit or a scratch built from plans? I want to build a Tri-Motor myself and have been looking for a set of plans. A kit would be OK, but I prefer to scratch build for the fun of it.
What are the specs on your Tri-Motor? Thanks

HEBFLYER
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