What is KV in Motor

What is KV of motor?

When a motor is given 1V (one volt) without any load (such as a propeller attached to the motor), the number of revolutions per minute (rpm) that the motor rotates is “KV”. For instance, without propellers installed, a 2300kv brushless motor running on a 3S LiPo battery (12.6V) will rotate at about 28,980 RPM (2300 x 12.6). Usually, the motor manufacturer specifies motor KV as a preliminary estimate. 2400kv brushless motor running on a 3S LiPo battery (12.6V) will rotate at about 30,240 RPM (2400 x 12.6).

kV=RPM per 1 Volt

k= The kV rating of the motor e.g, 2300

V = Voltage input e.g. 12.6v

Example: 2300(kV rating) X 12.6(Voltage) = 28,980(Revolutions Per Minute)

Motor KV vs. Winding Turns

The strength of the magnetic field at the stator and the coil’s number of turns determine the motor’s kv. Motor KV is often increased by a lower number of turns and decreased by a higher number of winding turns. The motor KV value can also be influenced by the magnets’ magnetic strength, with stronger magnets having a higher motor KV.

The-strength-of-the- magnetic-field-at-the-stator-and-the- coil's-number-of-turns-determine-the- motor's-kv

Multi-Stranded vs. Single Stranded Windings

Single-stranded and multi-stranded motor windings are the two main types available. Multi-stranded windings use several smaller wires in favor of a single, bigger wire. Each has a unique set of benefits and limitations that make them appropriate for various uses. Multi-standed winding can increases motor kv value and Single Stranded Windings decreases motor kv value.

Single Stranded winding

  • Advantages:

Thick wires used in single stranded windings are better at handling heat, which makes them perfect for high-stress flights (such as racing, acro, freestyle, etc.) that require a lot of amps.

  • Drawbacks:

The number of wires that can be wrapped around the stator is limited, though, because the thicker wires have bigger gaps between them.

Multi stranded winding

  • Drawbacks:

These thinner wires are more likely to physically break and don’t transmit heat as well.

  • Advantages:
  1. Multistranded windings may perform better than single stranded windings because of their tighter packing around the stator and smaller wire gaps, which strengthen the magnetic field. Improvements in power and efficiency may come from this.
  2. The advantages listed above may be countered by the fact that multi-stranded wire is typically more difficult to obtain the same neatness as single-stranded wires.
  3. Additionally, because there are more insulating layers between multi-stranded coils, there are more air spaces between the wires.

Motor KV vs. Torque Constant

Although motor KV has an effect on the torque constant, it does not directly alter torque. The amount of current needed to generate a specific amount of torque is determined by a motor’s torque constant. The real torque produced is unaffected by motor KV; coil resistance, air gap, and magnet strength all have a far greater impact on torque generation.

In comparison to lower KV motors, higher KV motors require more current to produce the same amount of torque due to their greater torque constant. The higher KV motor needs more current to produce the same amount of torque, which causes extra losses in the battery, ESC, and cables. Furthermore, less magnetic flux is produced and the motor becomes hotter as a result of the increased current. In general, if you were to fly at the same speed as the lower KV engine, the higher KV motor would be less efficient.

As a result, it’s wise to strive to keep KV reasonable rather than excessive. This is particularly crucial when constructing a long-range rig when efficiency and flight time are given first priority.

How to choose kv of motor for different size of propeller?

Smaller, lighter props are better suited for high KV motors, while larger props are usually used with low KV motors. The air resistance caused by a propeller installed on the motor causes a sharp drop in RPM. In an attempt to spin the propeller more quickly, higher KV motors will produce more thrust and power (but requiring more current).

More torque will be needed to spin faster if a higher KV motor and a larger propeller are combined. It will take longer to provide the necessary torque and produce too much heat. Your motor may also be harmed by this overheating.

Further reading: Tutorial Propellers: Choose Best Suitable Propellers for Your FPV

propeller-for-different-kv -motor

What is the best motor kv for 4S FPV?

For your 5 inch freestyle, if you decide to go with 4S, pick a motor kv at the range of approximately 2300 to 2700.

What is the best motor kv for 6S FPV?

Select a 5 inch fpv drone motor with a voltage range of 1600 kv to 1800 kv if you decide to use 6S. Take MEPS 2207 for example.

For the 6s FPV, if you want to fly more distace, the 1750kv motor is the best motor kv, because when the throttle reaches to 100%, the current is 36.5A, which is lower than 46A. This may cause lower heat generation and more far way.

meps-2207-motor-kv-1750-for-6s-fpv-to-fly-long-distance

For the 6s FPV, if you want to keep your fpv drone carry more things, the 1950kv is the best motor kv, because when the throttle reaches to 100%, the thrust is 1769.8g, which is higher than 1641.2g.

meps-2207-motor-kv-1950-for-6s-fpv-to-carry-more-things

meps 2207

Is higher KV better?

It is evident that greater Kv does not necessarily equate to better. All that is shown is the motor’s RPM in relation to a 1V voltage constant. Increased voltage results in increased current as well as higher RPM.

If the current is too high, your motor will overheat. In the gollowing chart, it reveals the relationship between motor kv and pro size, cell, motor size and lipo battery in detail.

Pro Style Cell brushless motor sizes Motor Size Motor kv LiPo Battery (mAh)
31mm Whoop 1S 0603, 0802 18000-25000 300-450
2S 0802 12000 300
40mm Whoop 1S 0802, 1102 15000-18000 450
2S 0802, 0806, 1103 10000-16000 300-450
3S 1102, 1103 8000-11000 300-450
2″ Triblade 2S 1103, 1105, 1106 6000-11000 300-450
3S 1104, 1105, 1106 5500-7500 300-450
4S 1105, 1106 5000-6000 450-650
2.5″ Triblade 2S 1104 5000-6000 300
3S 1106 4500 650
4S 1304, 1404 4500-5000 450-850
2.5″ Two-Blade (65mm) Ultralight 1S 1102 13500 300
Ultralight 2S 1103, 1104 7000-10000 450-520
Ultralight 3S 1104, 1105, 1106, 1203, 1204 6000-8000 300-650
Ultralight 4S 1104, 1105, 1106, 1203, 1204 4000-4500 450
3″ Triblade Freestyle 2S 1404 4500-5000
Freestyle 3S 1407, 1408, 1507 3500-4500 550-850
Freestyle 4S 1306, 1407, 1408, 1507, 1606 3000-4200 450-1000
Freestyle 6S 1408, 1507, 1606 2800-3000 550-650
3″ Two-Blade Long Range 1S 1103, 1202 11000 Li-Ion 2500-3000mAh
Ultralight 1S 1103, 1202, 1202.5 11000-14000 450
Ultralight 2S 1105, 1106, 1203, 1204, 1303 6000-8000 450
Ultralight 3S 1105, 1106, 1108, 1203, 1204, 1207, 1303, 1304, 1404 4500-6500 300-450
Ultralight 4S 1105, 1106, 1108, 1203, 1204, 1207, 1303, 1304, 1404 3500-5000 450-550
3″ Cinewhoop 4S 1404, 1408, 1507, 2203, 2204 3800-4600 850-1300
6S 1507, 2203, 2204 2800 850
4″ Triblade Freestyle 3S
Freestyle 4S 1407, 1507, 1606 3000-4000 850-1000
Freestyle 6S 1606 2000-3000 600-850
4″ Two-Blade Ultralight 3S 1306, 1404, 1406, 1408, 1504, 1505 3500-4500 650-850
Ultralight 4S 1306, 1404, 1406, 1408, 1504, 1505 2500-3000 450-650
Long Range 3S 1404 3500-4000 Li-Ion 2500-3000mAh
Long Range 4S 1404 2500-3000 Li-Ion 2500-3000mAh
5″ Triblade Freestyle 4S 2306, 2207, 2306.5, 2207.5 2300 – 2700 1300-1500
Freestyle 6S 2207, 2207.5, 2208, 2308 1700 – 1950 1000-1300
5″ Two-Blade Ultralight 4S 1606, 1806, 2004, 2204, 2205 2300-3000 750-1000
Ultralight 6S 1606, 1806, 2004, 2204, 2205 1600-2300 450-700
6″ Freestyle 4S 2207, 2207.5, 2208, 2405, 2407, 2408 2100 – 2500 1300-1800
Freestyle 6S 2207, 2207.5, 2208, 2405, 2407, 2408 1500-1800 1000-1500
7″ Freestyle 6S 2510, 2806, 2806.5, 2808, 3106.5 980-1450 2200
Long Range 4S 2408, 2507, 2508, 2806, 2806.5 1700-1900 Li-ion 2500-3000mAh
Long Range 6S 2408, 2507, 2508, 2806, 2806.5 980-1450 Li-ion 2500-3000mAh
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