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.
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
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.
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
These thinner wires are more likely to physically break and don’t transmit heat as well.
- 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.
- 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.
- 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
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.
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.
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|
|40mm Whoop||1S||0802, 1102||15000-18000||450|
|2S||0802, 0806, 1103||10000-16000||300-450|
|2″ Triblade||2S||1103, 1105, 1106||6000-11000||300-450|
|3S||1104, 1105, 1106||5500-7500||300-450|
|2.5″ Two-Blade (65mm)||Ultralight||1S||1102||13500||300|
|Ultralight||3S||1104, 1105, 1106, 1203, 1204||6000-8000||300-650|
|Ultralight||4S||1104, 1105, 1106, 1203, 1204||4000-4500||450|
|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|
|Freestyle||4S||1407, 1507, 1606||3000-4000||850-1000|
|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|