LRK 195.03 BRUSHLESS MOTOR BIG POWER FOR SMALL MODELS

Model Airplane News, Jul 2005 by Stennard, John

THE DREAMS OF MICRO MODELERS EVERYWHERE seem to have come true with the arrival of the readyto-use LRK 195.03 brushless motor from WES-Technik. This little 12-gram (0.48-ounce!) gem of a motor is accompanied by a 4-gram YG4-BL micro speed control.

Looking at important developments that have given micro indoor flying a performance boost, I would put the arrival of small Li-poly cells first, followed closely by reasonably priced micro-RC gear. Next is foam and carbon-fiber construction, followed by a micro-size brushless motor and speed control. Combined, these advances foretell 2- to 3-ounce planes with full 3D performance! So let's first take a look at the motor and its speed control.

THE MOTOR

Despite its really solid look and its diameter of 0.92 inch-close to the size of many micro outrunners-the LRK 195.03 weighs a mere 0.48 ounce! The motor uses "star" winding on the stator and has a speed of 1,500rpm per volt. The free-running speed is just 0.2 amp with a maximum of 4 amps if cooled. The maximum recommended input power is 35 watts, and although it could be used with other cells, it's obviously designed with 2 to 3 Li-poly cells in mind.

The motor has two, 2.5mm threaded holes on the front face and, as usual, the distance the bolt extends into the motor is critical and must not exceed 2mm. No bolts are supplied with the motor, and I had cut down the ones I bought. This needs to be done very carefully to avoid damaging the threads on both the bolt and the motor housing.

The motor has a 2mm shaft with two flats on it for securing a prop with grub screws. The performance figures are shown with the motor fitted with GWS 6x3 and 7x3.5 props. To use these props, you need a prop driver with a 2mm bore. I found it quite easy to buy three different types-two that use a collet and one that uses a grub screwbut any of these will add between 3 and 5 grams of weight. A GWS 6x3 prop weighs 6 grams, and the 7x3.5 weighs 7 grams. So the lightest prop and driver weigh in at 9 grams (0.32 ounce), while the new WES-Technik 6-inch carbon-fiber prop, specifically designed for the LRK motor, weighs only 2 grams (0.07 ounce) and fits perfectly on the 2mm shaft. These props are expensive, but they work extremely well with this motor.

The three motor wires terminate in a micro JST connector that matches the motor connector on the controller. So far, all my flying has been using a 2S1P 310mAh Li-poly pack, and this has given ample power for a 3-ounce model.

YGE4-BL MICRO SPEED CONTROL

In addition to its incredibly light weight of just 0.14 ounce, the YGE4-BL is very small and can be programmed to suit its application. The controller comes with a micro JST connector for both the receiver and the power supply. I exchanged the power-supply connector for the micro type I use on my battery packs. (Note that some micro JST connectors have the polarity reversed, and these can cause severe damage!)

The first time you use the YG4-BL, the controller can be programmed for timing, brake and cutoff. You can also make changes later by following the same programming procedures.

The timing can be varied from O to 30 degrees, the EMK brake can be set from off to 100 percent in five steps, and the cutoff can be set at low-voltage detection off, Ni-Cd/NiMH, or Li-poly mode.

The controller also includes an overload protection that cuts power to the motor at 4.5 amps. There is no reverse-polarity protection, and an incorrect connection will damage the controller. The warranty does not cover this type of damage but does cover malfunction and breakage for 24 months.

When connected to my JMP receiver, the controller worked perfectly and was very easy to program.

Although you could also use the less expensive Jeti JES 4A with this motor, keep in mind that it weighs about S grams more.

THE REAL TEST

My own-design Micro 3D was the obvious model in which to test-fly the LRK 195.03/YG4-BL combo, so I didn't waste any time in modifying the motor mount to suit the LRK. I had originally used a 2S1P 145mAh Li-poly pack with this model, but these cells have a maximum current draw of 1 amp. A 360mAh Li-poly pack would obviously provide plenty of power, but it's just a bit too large for the model. I found that the ideal cell was the WES-Technik 310mAh. These cells are the same width as the 145mAh ones but are twice as long and can provide up to 3 amps. Although this would prevent the LRK from using its maximum of 4 amps, I was sure there would be enough to fly the Micro 3D.

The Micro 3D is designed for minimum weight and maximum performance, so it uses 2.4-gram WES-Technik linear servos. The motor/controller change added about 0.7 ounce, so the model was bound to fly faster. First flights showed that the motor had plenty of power, but the linear servos-particularly the aileron servo-were struggling to provide fast and accurate control. Although it would further increase the all-up weight, I decided to replace the aileron linear servo with a rotary 3.6-gram (0.14-ounce) servo. This improved the control and flying qualities so much that 1 decided to replace the rudder and elevator linear servos with rotary servos, too.