Print Page - Does BRUSHLESS give more efficiency at low voltages.???

Hi Tejas

Welcome to the forum. My name is Saju. Well on to your query:

"since i have used brushed motor in my first design n supplied 12 volts .
but if i use BRUSHLESS motor at 6 volts instead of it then will the motor produce same pull
sufficient for the take off ? "

In a brushed system, there is a mechanical commutator which aids in changing poles for the rotor (coils) to rotate in the magnetic field created by a set of permanent magnets (which forms the stator). In a brushless motor, the coils are stationary (stator) and the magnets are rotating (rotor). The commutation is acheived by electronic means (the Electronic speed control... or ESC in short). The freqeuency of changing poles determines the rpm of the motor in both cases. The mechanical system of commutation is less efficient because as the brushes rub over the commutator there are sparks generated and also because of contact resistance of the brush on the commutator not being consistant since there is mechanical movement. There is also erosion of the brushes and the commutator and therefore performance deteriorates from time to time... leading to maintenance requirements in the form of replacement of brushes and cleaning of the commutator. All this is avoided in electronic commutation and therefore makes it more efficient. Moreover the speed is determined by the electronics and therefore is more consistant. Hence even at low voltages a brushless motor will give better performance than a brushed motor.

When it comes to RC planes, we have other factors as well to take care-of. In a small model to reduce weight we will generally have one battery which has the duty of powering the BLDC (brushless dc) motor, the radio (requires only 4.8v to 5v), and servo actuators (one for each control function... generally elevator, rudder, and throttle) besides other optional devices one may load on the model. The batterries used are nowadays, what we call as LIPOS (Lithium ion polymer), which have the same chemistry as the cells used in mobile phones and laptops. You would do well to search the internet for a complete understanding of LIPOS. To cut the story short, the ESC will get connected directly to the LIPO (either 7.4v or 11.1 v etc multiples of 3.7v) and the ESC in turn will reduce and supply 4.8v to power the radio and thru the radio the servos. It is generally not a good idea to reduce the voltage below 7.4v at which point the esc will stop operating the motor and will give you sufficient power to land the plane.

I said too much... please excuse me for the long explanation... but I thought atleast this much is in order.

Any further doubts are welcome

Saju

RC India

RC Equipments => Electric Power => Topic started by: TEJASCOOL007 on August 07, 2009, 10:44:58 AM