This article was originally published in RC Heli Pilot February/March 2016 issue.
Story & Photos By Dan Goldstein
KDE Direct has been evolving their motor lineup on a regular basis, refining and improving an already premium product. The XF line offers motors to cover the gamut of 450-800 size helis. I obtained their latest KDE700XF-535-G3 to try in my MD7/8 helicopter setup as a 700-size.
The motor came nestled in dense foam inside of a printed cardboard box. KDE went more upscale with the packaging since I last reviewed one of their G2 series of motors. The motor itself, like its predecessor, is a piece of industrial art. It has a weighty feel in hand. It doesn’t sparkle, but instead the end bell and mounting plate have a matte silver finish and the end bell has a black, ribbed surface. The cog effect is noticeably less than the G2; the bell spins more smoothly when spun by hand.
The motor has two mounting bolt circles, one for 3mm screws on 25mm spacing and 4mm screws on 30mm spacing. The output shaft is supported by four radial bearings that insure smooth operation under heavy side loading. Power is fed through high- temp 13 AWG multi-strand silicone insulat- ed wire that comes with 6.5mm 24k gold plated bullet connectors soldered on. The mounting plate also features a custom formed rubber grommet that protects the power wires.
While slightly refined from the G2, this generation utilizes the same stator construction made up of ultra-thin, high grade, silicon steel laminations that are wound with revised, high-temperature, 16-strand 0.38mm pure copper wire. The stator is wound in a YY pattern to yield high performance levels. Despite this pattern winding being more difficult and time consuming compared to competitors’ windings, KDE felt the increased yield in power output was worth the additional manufacturing cost.
The timing suggested is a range from 5*-15* and a pulse width rate of 8 KHz – 12 KHz. Depending on the performance desired, more timing and higher pulse width will increase power output, but at the expense of higher current draw and increased internal ESC temperature. I opted for low timing and 8 KHz PW to keep the Talon 90 ESC I used on the cooler side. If you were to use this with a Talon 120, Edge 100, Edge 130 or equivalent ESC, you should be able to more safely experiment with higher timings and pulse width settings if the lower settings don’t produce the performance you’re looking for.
Kv: 1,200 RPM/V
Maximum Current: 205+ A (2 sec)
Maximum Power: 4,550+ W (2 sec)
Continuous Current: 125+ A
Continuous Power: 2,785+ W
Maximum Efficiency: 92%
Voltage Range: 22.2 V (6S) – 29.6 V (8S)
Io (@10V): 3.3 A
Rm (Wind Resistance): 0.007 ?
Magnetic Poles: 10 (12S10P)
Bearings: Quad, 696ZZ/MR106ZZ
Mount Pattern: M4 x 30mm, M3 x 25mm
STATOR CLASS: 3528, 3T+3T, YY
Stator Windings*: 16-Strand, 0.38 mm
Shaft Diameter: 6mm (6mm Internal)
Shaft Length: 40.5mm
Motor Dimension: 46mm x 52mm
Motor Weight: 300g (325g with Wire Leads)
Motor Leads: 13 AWG, 200°C
Cooling System: High-Volume Centrifugal Fan
Motor Timing: 5° – 15°
ESC PWM Rate: 8 – 12 kHz
Finish: Clear anodize, matte finish CNC end bells, Black electroplate, CNC gloss central core (flux ring)
*Equivalent Stator Winding: 1-Strand, 1.55mm solid-core
Like the G2 series, the motor bell utilizes N45UH neodymium magnets with machined slots that are bonded around the entire perimeter with high temperature epoxy. A high volume end bell fan maximizes cooling airflow to help keep operating temps lower during periods of increased load. The small blue dollop of hard material in the bell is high temp epoxy used for bal- ancing. The completed motor assembly is held together with an E-clip.
The model I used to test this motor is a customized Mikado Logo 600 that swings 550mm blades. The boom was cut down to accommodate a Thunder Tiger Raptor 30 belt. I also installed Logo 600 Mod 1 gearing. I’ve equipped it with the following gear:
Motor: KDE 550XF-1200-G3
Pinion: Mod 1, 11T
Main Gear: Mod 1, 106T
ESC: Castle Creations Talon 90 (SetRPM Governor mode, BEC @ 6VDC)
Cyclic Servos: MKS BLS-970
Tail Servo: MKS BLS-980
Gyro: Spektrum AR7200BX MicroBeast
Transmitter: Spektrum DX9
Receiver: 1 DSMX Satellite & AR7200BX internal receiver
Main Rotor Blades: Align 550mm
Carbon Fiber Tail Blades: KBDD Plastic 84.5mm
Battery: GensAce 6s 5300mAh 60C LiPo
Model Weight (no batteries): 4 lbs, 15.5 oz.
Model Ready To Fly weight: 6 lbs, 11.5 oz.
To test the motor, I flew a set routine to evalu- ate the performance and electrical characteris- tics during each segment of model flight. The repeated routine consisted of hovering for 10 seconds, positive pitch pull for five seconds, negative pitch for five seconds, then return to a hover for 10 seconds, then forward flight for 20 seconds and then repeat the sequence. This made it easier to produce repeatable, quality data. I started out by lifting the Logo into a hover and switching into my idle-up mode where I was turning 2,300 RPM on the head.
Forward flight causes the current and watt- age to drop slightly due to unloading of the disc. When the model moves ahead through the air, it provides additional lift through the rotor blades. Consequently, the motor’s cur- rent draw dipped slightly to around 29 amps from 32 amps in a hover with wattage falling and fluctuating around 646 watts, down from 700 watts during hovering. The motor was running super efficiently since 100 watts/lb is typically required to hover a model. Given the model AUW of 6 lbs. 11.5 oz., the ~104 watts/lb performance was decent!
Upright full pitch pulls produced peaks of 1783 watts with no signs of bogging or sag. Peak current draw during the session was a mere 70.7 amps! After running through the routine, I switched packs and performed some 3D. Every maneuver was well supported and spirited. Continuous tic- tocs didn’t cause any perceivable sag and it just kept going until my battery neared my cut-off. The motor and ESC were warm to the touch with ambient temps in the mid 40’s (F). Overall, the current and wattage draw readings for this size model were modest given the performance output.
I was really pleased with the performance results from this new motor. It provided solid power to the model and only moderate demands on the ESC and battery while being somewhat petite in size. Flying this new gen motor made it clear that the XF line is fully matured and should be taken into consideration by anyone looking for a new powerplant.