<span style="font-size: medium">Here is a controlled, objective test of the Turnigy SK3 2118-2250Kv motor:
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<u><span style="font-size: medium">MOTOR TEST: Turnigy SK3 2118-2250kv</span></u><span style="font-size: medium"> </span><span style="font-size: x-small">-Supplied by: HobbyKing (HK) <span style="font-size: small">PRICE: $13.07</span>
</span><div style="margin-bottom: 0cm">Motor Weight: 17g (HKdata)</div><div style="margin-bottom: 0cm">Rated Kv: 2250 (HK data)</div><div style="margin-bottom: 0cm">Max current: 4A; Max power: 36W; Motor internal resistance (Rm): 290 milliohm (HK data)</div><div style="margin-bottom: 0cm">External dimensions: diam 21mm, length 18mm (-<span style="font-size: small">the reason it is called a "2118" motor</span>)</div><div style="margin-bottom: 0cm">Stator size: diam 17mm, length 5mm (i.e. 1705 stator)</div><div style="margin-bottom: 0cm">Number wire turns: 11 (11T); Stator arms:9; Magnet poles: 12; Length of magnets: 5mm</div><div style="margin-bottom: 0cm">Shaft diam: 2mm</div><div style="margin-bottom: 0cm">X-Mount (black) weight: 0.8g;

MANUFACTURED BY: SUNRAY TECHNOLOGY: http://sunraytechnology.com/</div><div style="margin-bottom: 0cm">Retailer website: http://www.hobbyking.com/hobbyking/s...ner_Motor.html</div><div style="margin-bottom: 0cm"><span style="font-size: xx-small">
Measuring equipment used: Eagle Tree V4 data logger with brushless RPM sensor and micro-thermistor temperature sensors (for measuring voltage, current, motor RPM and motor temperature); Additional optical tachometer; Additional infra-red thermometer; ABCON Digital scales for measuring thrust.
I used a GT-Power Watt Meter to check the current readings on the Eagle Tree data logger, especially for low currents &lt;1A. A </span><span style="font-size: xx-small">GT-Power Servo tester device was used to control a ZTW 70A S-BEC speed controller, which was connected to motor.</span></div><div style="margin-bottom: 0cm"><span style="font-size: xx-small">I used fully charged, 30C to 45C, 2S and 3S LiPo packs as the power source.</span></div><div style="margin-bottom: 0cm"><span style="font-size: xx-small">On the Motor Thrust test stand used, the lower horizontal arm pushes on the scales to measure grams of thrust (see photo). The props are therefore mounted on motor so that thrust is generated in a direction away from motor and stand (i.e. with front face of prop facing the motor and test stand). </span></div><div style="margin-bottom: 0cm">
Description of motor:The Turnigy SK3 2118 2250kv motor, with wires and 2mm connectors, weighed 16.9g. The motor has a 9-arm stator (manuf states: wound with 11T turns) and 12 magnet poles. Externally, it is 21mm diameter; the motor main body is 20mm long, and adding the small nut on the rear housing makes it 22mm long. Motor came fitted with 2mm male connectors.</div><div style="margin-bottom: 0cm">The motor has an in-built prop saver on the front housing. The prop saver suits 3.9mm and 5.5mm prop hubs, and a supplied collar allows for props with 8mm bore. 2 phillips bolts are placed either side of the prop saver, for fixing the O-rings which hold the prop on the saver. The motor came with four O-rings in two sizes. It also came with a small black aluminium X-mount, and two fiberglass X-mounts. There were also two 2mm phillips screws for fixing the X-mount to the rear housing. The rear housing has 4 threaded holes at 14mm centers, although only 2 screws were supplied.</div><div style="margin-bottom: 0cm">
<span style="font-size: small">Standard motor test procedure:</span></div><div style="margin-bottom: 0cm">I mounted this motor using its black aluminium X-mount (which I bolted to the rear motor housing) onto the 8mm plywood plate of my motor test stand (see photo).</div><div style="margin-bottom: 0cm">I then attempted to fix props onto the prop saver with the O-rings.</div><div style="margin-bottom: 0cm">-And this is where I had my first problem -the gap between the back of the black screws and the front motor housing was very narrow -&lt;1mm -and I had difficulty getting the O-ring on and off the screws. I ended up using my Dremel to remove the back of each screw, to widen the gap. After this, I had no problem quickly changing props. (I did not, however, have this same problem with a Turnigy 2122 motor, which has exactly the same front housing).</div><div style="margin-bottom: 0cm">There was also another small issue -there were only 2 screws supplied for fixing the X-mount to the rear motor housing. I wanted the motor to be secure, and found another 2 screws to use in addition.</div><div style="margin-bottom: 0cm">
Test procedure: First, I ran no-loads at 7.4V (2S Li-Po) and at 11.1V (3S Li-Po), at full speed, and measured current (I), voltage (V) and RPM.</div><div style="margin-bottom: 0cm">I then ran 6 different props at full speed, in ascending order of size, using both 2S LiPo and 3S LiPo (3S LiPo for at least some props), and measured I, V, RPM and Thrust.</div><div style="margin-bottom: 0cm">After charging the LiPo's back up again, I then ran the same 6 props, now in descending order of size, to check that the results were reproducible. The second run gave almost identical values.</div><div style="margin-bottom: 0cm">
<span style="font-size: medium">Results:</span></div><div style="margin-bottom: 0cm">This little motor ran very smoothly indeed, and seemed well engineered. It sounded very nice and had a nice &ldquo;whistle&rdquo; sound when it ran. It also ran smoothly with all the props tested. It did, a few times, stutter to start with the largest props used, and to get it running I just spun the prop before starting.</div><div style="margin-bottom: 0cm">Results are shown on the attached data sheet.</div><div style="margin-bottom: 0cm">
Kv: I used two methods for calculating Kv. First, I used www.peakeff.com to calculate Rm ("static" motor resistance) and Kv (I used the 2S LiPo data values for smallest and largest props, to give the largest difference in load).</div><div style="margin-bottom: 0cm">Second, I used DriveCalc to calculate Rd ("dynamic" motor resistance) and ns ("real world no load speed"). -DriveCalc also gives a Kv value when data is entered for a new motor (For DriveCalc, I used 2S LiPo test values for 3 different props, at different loads).</div><div style="margin-bottom: 0cm">PeakEff gave a Kv of 2170 RPM/V; DriveCalc gave a Kv of 2197 RPM/V, and also an ns value of 2138. All these values were very close. PeakEff and DriveCalc also gave similar values for Rm and Rd, of 331 and 337 milliohm respectively.</div><div style="margin-bottom: 0cm">
Current and Power: This motor has a max current rating of 4A given by HobbyKing <span style="font-size: small">-And yet NONE of the props I tested, even when using a 2S LiPo pack, gave a current of less than 4A ...!</span></div><div style="margin-bottom: 0cm">The 2 smallest props - 4.5x4.1 and 5x3 -with 2S LiPo gave currents of 5.8A and 4.7A. With a 3S LiPo pack, the current draw was 7.8A and 9.4A, and power input for these was 90W and 109W<span style="font-size: small"> -well above the max manuf. rating of 36W ...!</span></div><div style="margin-bottom: 0cm">I could not run the other 4 larger props with 3S LiPo, because it may have drawn too much current and melted this lovely little motor. So I only ran these larger props with 2S LiPo. Current increased with prop size, up to a max of 12.6A (i.e. 3 times the manuf max rating). The 2 largest props - 7x4 and 8x3.8 -produced an input power of 83 and 88W -again 2.5 times the manuf max rating.</div><div style="margin-bottom: 0cm">
RPM: In general, RPM reduced as prop size became larger. However it is notable that the GWS 5x3 prop had a higher RPM than the APC 4.5x4.1 prop (and also gave more thrust for a lower current). You can also see that the GWS 6x5 prop gave the same RPM as APC 7x4, whilst at the same time drawing more current and producing larger thrust.</div><div style="margin-bottom: 0cm">
Thrust: This small 17g motor was capable of generating more than 300g thrust -and this is impressive. It gave 334g thrust when the GWS 5x3 prop was used with 3S LiPo. And 312g thrust when the 8x3.8 prop was driven with 2S LiPo.</div><div style="margin-bottom: 0cm">For the 2 smallest props, thrust with a 3S LiPo pack was roughly twice as large compared to 2S LiPo.</div><div style="margin-bottom: 0cm">It is also notable that the GWS 6x3 prop generated larger thrust than the 6x5 prop, whist drawing a smaller current.</div><div style="margin-bottom: 0cm">
g of Thrust per Watt of input power: In general, the values for this motor were relatively low. Using 2S LiPo, the GWS 5x3 and 6x3 props gave values around 5. The APC 4.5x4.1 prop gave vales between 2.2 and 3. The 3 largest props, when driven by 2S LiPo, gave values between 2.9 and 3.5.</div><div style="margin-bottom: 0cm">Some brushless motors gives values of 7 or more for g thrust produced per W. With the props tested, this motor produced relatively low thrust per W of input power. Low values between 2 and 4 suggest that the prop might have been overloading the motor.</div><div style="margin-bottom: 0cm">
RPM as % of Kv x V: Values for the 3 smallest props were between 64% and 74%. For the 3 largest props, the values were low, between 40% and 49%, suggesting that these large props may have been overloading the motor.</div><div style="margin-bottom: 0cm">
Efficiency: This was calculated as Power OUT (i.e. power produced by motor, taking into account internal Rm losses) divided by POWER IN (Vin x Iin =Watts in).</div><div style="margin-bottom: 0cm">The 3 smallest props showed an efficiency between 63% and of 70%. The 3 largest props tested had very low efficiencies, between 38% and 50% -again indicating they might have been overloading the motor.


Pics show: 1, The Motor Test Stand used (Can accomodate motors up to 60-size motors, and measure up to 20kg thrust); 2, 3,Turnigy 2118 motor and box; 4, Turnigy SK3 2118 2250kv motor with accessories; 5, 6,Turnigy2118 Motor mounted on test stand;7,Results of the test -the original datasheet, with original readings; 8, Props used for test
































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