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Question about motor specs

Old 07-27-2022, 12:14 PM
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Walkerbob
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Specifications:
kV: 560kV
Power: 1800W (180 seconds)
Peak Current: 80A (180 seconds)
Rated Voltage: 6S 22.2V
LiPoWire Leads: 100mm Enameled Wire
Idle Current: 2.4A / 10V
Internal Resistance: 16 mOhms
Weight: 300g
Configuration: 12N14P
These are the specs for my T-motor AT4120-7 KV:550, I am unsure how to use this information to buy an esc and lipo battery. Does peak current mean the level of current needed for an esc and battery?

Old 07-27-2022, 01:23 PM
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speedracerntrixie
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Not really. The motor has a maximum rating of 80 amps, however if you choose a prop that keeps the motor at 40 amps then all you would need is a 50 amp ESC. The C rating of the battery works much the same way. Pulling 40 amps out of a 1000 mah battery will require a C rating of 40 or better. A 2000 mah battery would only require a C rating of 20.
Old 07-27-2022, 05:00 PM
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Originally Posted by speedracerntrixie View Post
Not really. The motor has a maximum rating of 80 amps, however if you choose a prop that keeps the motor at 40 amps then all you would need is a 50 amp ESC. The C rating of the battery works much the same way. Pulling 40 amps out of a 1000 mah battery will require a C rating of 40 or better. A 2000 mah battery would only require a C rating of 20.
How do I know what effect the propeller will have? Is it a weight thing?
Old 07-27-2022, 06:10 PM
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The prop length and pitch create a majority of the load the motor must deal with, the weight is a minor factor. For example:
  • a 10" prop will have less drag, and therefore load, than a 14" prop IF THE BLADES HAD THE SAME TWIST(pitch) TO THEM
  • a prop with a 3" pitch(theoretical distance the prop will move forward for each full 360 degree rotation) will have less drag than a prop with an 8" pitch IF THE PROPS ARE THE SAME LENGTH
  • Now is where things get fun. An 8" prop with an 8" pitch could have less drag than a 14" prop with a 3" pitch.
Thus, it is the drag of the prop that determines how much of an effect there will be on the motor. More drag means more power is needed to turn the prop at a given RPM. To get that increase in power to turn a higher pitch or longer prop, you need to increase the watts(volts times amps) to keep the RPM the same. If you want to turn a prop with less pitch or shorter blades, you can reduce the watts in the same way to keep the RPM the same. The only way to find out how much a prop will affect the motor, ESC and battery pack(s) is to test the combination and see

Last edited by Hydro Junkie; 07-27-2022 at 06:19 PM.
Old 07-27-2022, 06:20 PM
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Not a weight thing but a diameter and pitch thing. The specs on that motor say it will spin a 15x8. With that prop you will come close to the max amperage. Depending on the airplane that may be too much power. In that case you will want to drop down in prop size. A14x7 would pull less amps and give you longer flight times. Of course these are all very generalized answers. To be more specific I would need to know more about your particular airplane.
Old 07-27-2022, 06:34 PM
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Originally Posted by speedracerntrixie View Post
Not a weight thing but a diameter and pitch thing. The specs on that motor say it will spin a 15x8. With that prop you will come close to the max amperage. Depending on the airplane that may be too much power. In that case you will want to drop down in prop size. A14x7 would pull less amps and give you longer flight times. Of course these are all very generalized answers. To be more specific I would need to know more about your particular airplane.
It's a Hobbistar 60 MKIII that was converted into an electric plane by attaching the above motor to the nose.
Old 07-27-2022, 06:53 PM
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Ok so at 22V on a 550KV motor gives you 12,100 RPM. That is equal to a healthy .61 glow engine. I would go with an APC 13x6 E prop. That should put you close to 50 amps. For a battery, a 6 cell 4000 mah 25-35C would do nicely. This would be quite spirited performance.
Old 07-27-2022, 06:58 PM
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Walkerbob
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Originally Posted by speedracerntrixie View Post
Ok so at 22V on a 550KV motor gives you 12,100 RPM. That is equal to a healthy .61 glow engine. I would go with an APC 13x6 E prop. That should put you close to 50 amps. For a battery, a 6 cell 4000 mah 25-35C would do nicely. This would be quite spirited performance.
Alright I will look into that, thank you for the detailed advice!
Old 07-28-2022, 06:30 PM
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Originally Posted by Walkerbob View Post
Specifications:
kV: 560kV
Power: 1800W (180 seconds)
Peak Current: 80A (180 seconds)
Rated Voltage: 6S 22.2V
LiPoWire Leads: 100mm Enameled Wire
Idle Current: 2.4A / 10V
Internal Resistance: 16 mOhms
Weight: 300g
Configuration: 12N14P
These are the specs for my T-motor AT4120-7 KV:550, I am unsure how to use this information to buy an esc and lipo battery. Does peak current mean the level of current needed for an esc and battery?
For this size of motor you are better off getting minimum 80 or 100 Amp ESC. Battery wise, 4 to 6Ah capacity with the highest C rating to get the most out of it. E-meter will also come handy to check your current draws with use of various size props.
What size and weight of the model you intend to use?
Old 07-28-2022, 06:53 PM
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Walkerbob
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Originally Posted by Joseph Frost View Post
For this size of motor you are better off getting minimum 80 or 100 Amp ESC. Battery wise, 4 to 6Ah capacity with the highest C rating to get the most out of it. E-meter will also come handy to check your current draws with use of various size props.
What size and weight of the model you intend to use?
these are the specs for the size and weight of the model:
Wingspan: 71" (1805mm)
Wing Area: 888" (57 dm2)
Wing Chord: 12.5"
Weight: 7-8lb (3175-3629g)
Wing Loading: 18-21 oz/sq ft (55-64 g/dm2)
Length: 55" (1400mm)
Width- 3 3/8"
Old 07-28-2022, 07:16 PM
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It all depends what type model it is and what you expect to do with it, not just the size specs. (sounds like it is extremely light wing loaded)

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