Brushless motors.

Introduction:

Electric fly has made huge progress since the last few years on both the motor's and battery's sides and the achieved performances are now comparable to the performances of glow motors (to say nothing of bringing it easily into operation).

Motorwise, brushless motors represent a large advancement on performance and reliability. Today, their main drawback is their price which is significantly higher than the price of a standard brushed motor. However, brushless motor technology is much simpler than the standard motor one ( there is no commutator) and, at the end, for the same quality and manufacturing quantity levels, there is no reason for a brushless motor to be more expensive than a standard motor. As far as ESCs for brushless motors are concerned, they are also more expensive but they cost in fact the same price as the standard ESCs few years ago and therefore their price should also decrease in the near future.

In order to contribute to develop this technology ( development which should result in price decrease by mass effect and therefore make this technology affordable by most of the RC model fans ), you will find below the results of few tests I made on brushless motors.

Brushless motor tests published on model magazines are often oriented towards contests. Here, we will stay within the week-end flier's area : starting from market models equipped with standard motors, we will see the benefit we can get, with model's performances unchanged (or even slightly better), from a brushless motor in terms of weight, flight duration, reliability, etc... In my mind, it is this mass market which is the key of future brushless motor's development.

Small motors available:

If we only consider the small size brushless motors (equivalent to the Speed 400 or less) for Park-Fliers and Indoor planes, the following motors are easily available today:

Tests on Multiplex Pico-Jet.

The Pico-Jet by Multiplex is a foam flying wing which comes with a standard Permax 400 motor (equivalent to Speed 400), powered on 7 cells and with a Günther 4,7" x 4,3" propeller on a direct drive.

Motor type			Prop.	Prop speed (rpm)	Cell Nbre	Voltage (V)	Current (A)	Weight (motor, ESC, Prop.)
Permax 400 - 6 V - ESC JETI 10			4,7x 4,3	12100	7	7,3	11	100 g
Hacker B20 26 L - ESC Schulze Future 18be			4,7x 4,3	12300	7	7,3	8,2	90 g
Hacker B20 26 L - ESC Schulze Future 18be			4,7x 4,3	13400	8	8,2	9,4	90 g

As you can see on the table above, using a brushless Hacker B20 26 L motor instead of the original motor set-up not only allows for a reduction on size and weight (10 grams less ) but also reduces the current (and therefore increases the flight time) by about 25 % with slightly better performances. The motor can also be used with a 8 cell battery without any problem.

The Hacker B20 26 L motor has a velocity constant of 2077 rpm/V. Any brushless motor with the same quality level, the same size and with a similar velocity constant should give the same results. For information, the original Permax 400 6 Volt motor provided with the Pico-Jet has a velocity constant of 3026 rpm/V. This reflects the higher efficiency of the brushless motor.

Note:

The Twin-Star by Multiplex is a bi-motor plane also in foam and equipped with the same motor set-up (twice). One could also equipped the Twin-Star with two Hacker B20 26 L motors. The current would decrease from 23 A to 16,5 A thus increasing the flight time accordingly. On top of that, with such a 16 A current, you can efficiently use Ni-Mh batteries with larger capacity (3000 mAh or more) instead of standard Cd-Ni cells ( be careful moneywise, you would need an ESC per each motor ! ).

To Be Continued ...