This guide aims to give you a basic understanding of brushless motors.
Brushless motors are made up of an outer "can" that holds a number of magnets.
The can rotates around a centre unit that holds a number of metal bars with coil-windings
called Stators. Electric pulses, controlled by the Electronic Speed Controller (ESC), are passed through the stators that
in turn attract the magnets at different times and cause the can to rotate.
The can also has a metal rod running through its centre called the shaft. Ball bearings are normally used to create a smooth rotation of the can and shaft.
The majority of brushless motors for model aircraft are three phase motors using DC power sources, commonly Li-Po batteries.
Motors come in various sizes and have different performance characteristics so work best for different models.
Some manufacturers use the dimensions of the motor in their naming, e.g. for a Power HD HD5055/06 motor it has a diameter of 50mm, a length of 55mm and 6 turns on the stators. Some manufacturers have the same naming format, but the first four digits relate to the stator sizes instead of the motor dimensions.
If in doubt it is always best to verify the schematic of the motor to double check which they are refering to.
Kv is the number of revolutions per minute (rpm) per Volt. A 270Kv motor supplied with 22
Volts will rotate 5940 times per minute or 5940rpm. There is a relationship between Kv and torque - as the Kv value increases the amount of torque reduces.
When comparing motors, a motor with a lower Kv rating will turn slower, but produce more torque than a higher rated Kv motor.
For larger models, a lower Kv is preferred as a larger propellor is used and requires more torque to turn the propeller and create the needed thrust.
For smaller models, a high Kv is preferred as a smaller propellor is used so less torque is required to turn the propeller, but
it needs to spin faster to create more airflow.
The number of magnetic poles (magnets) fixed to the can in the motor.
Turns are the number of coil wire windings used on the stator. Commonly the higher the number of turns on a stator, the lower the Kv so less rpm, but higher torque output. The lower number of turns allows for a thicker wire to be used which can carry more current. Some manufacturers use this number in their motor names.
Outrunner motors can be mounted to a model in a couple of ways:
X-Mount
This method fixes the back of the motor to an X-mount (see right) so the can is free to rotate. The X-mount is then attached to the model. Motors are normally supplied with the X-mount and the screws to attach the motor to the mount.
Firewall Mounted
This method fixes the static part of the motor directly to the model firewall. In this configuration the shaft then passes forward through the firewall
in order to attach the propellor.
The prefered method is normally outlined in the model assembly manual.
Propellers can be mounted in several ways, but this is normally dictated by the mounting of the motor and the direction of the motor shaft:
Shaft Driven
This method uses a Prop Adaptor to hold the propeller, which is then slotted onto the motor shaft and held by a grub screw or collect (see right) on the Prop Adaptor.
Can Driven
This method uses a Prop Adaptor supplied with the motor, which is bolted onto the motor can. The propellor is then slotted on to the Prop Adapator and held in place with a washer and nut.
Have a browse of our brushless outrunner motors by clicking here. If you need any help, just call us on 0845 539 2103 (local rate) or email us at Shop@TopProps.co.uk where we'll be glad to advise you.
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