RC Motor Basics

Posted:  Wednesday, March 14, 2012
Written By:  Gary Katzer
Copyright:© 2012 Horizon Hobby, Inc.

      It's amazing to see how far electric motor technology has come over the years. From closed end bell 540-size Johnson or Mabuchi motors to open end bell hand-wound modified motors, and now brushless motors, it's amazing to see just how far motor technology has come. With all the different types of motors and technologies in use, things can get quite confusing. We're here to help demystify motor tech and provide the answers you'll need in understanding your electric motor system. In addition, we've also put together a comprehensive list of terms below to help you better understand the different technologies out there, how they work and what this all means to you.

540 Motor—The most common motor size for 1/12- and 1/10-scale electric vehicles.

550 Motor—A slightly longer version of the 540 motor, a 550 motor is capable of delivering more torque and power without suffering from power loss. 550 motors tend to be less susceptible to damage from heat, overgearing or other similar issues.

Adjustable Timing—The ability to change the timing allows you to alter how the motor fires as the armature or rotor rotates through the magnetic field. Advancing the timing of a brushed or brushless motor will yield more RPM at a cost of torque, while less timing will provide more torque but reduced RPM. Excessive timing in brushed motors can cause premature motor wear. Also, excessive timing in brushed or brushless motors can cause a motor to overheat if the gearing is not adjusted accordingly.

Armature—The central component in a brushed motor. The commutator, stack and windings are all mounted to the armature.

Brushed Motor—An electric motor that utilizes brushes rubbing against a commutator to transfer electrical current to create rotation. Brushed motors are inexpensive to produce, but require frequent maintenance to ensure the motor will continue to perform at a high level.

Brushless Motor—An electric motor that utilizes a permanent magnet on the rotor and a series of coils in the can (referred to as the stator) to generate rotation. Brushless motors are much more efficient than brushed motors and have no designed wear components.

Brush(es)—Small, normally rectangular, components used in a brushed motor to transfer electrical energy to the commutator. Brushes can feature many chemicals in their construction, including copper, carbon, silver and graphite. The size, shape and orientation of a brush can be altered to change the overall performance of a motor.

Brush Hoods—An opening in the end bell of a brushed motor that houses the brushes themselves and maintains their position relative to the commutator. Brush hoods can feature a laydown, stand-up or angled orientation, just to name a few.

Brush Shunt—A small braided wire, often copper or silver in color, that connects the brush to the brush hood. Brush shunts can have a small eyelet on the end, allowing users to install it by screwing it into the brush hoods. While convenient, this isn't efficient and many performance enthusiasts opt to solder their brush shunts to the brush hoods.

Brush Springs—Brushed motors use small heat-treated springs to apply pressure to the back of the brush and prevent it from bouncing or losing electrical contact with the commutator. Varying the tension on the springs will alter the performance of the motor.

Can—The main "body" of an electric motor. The can houses the magnets in a brushed motor and the stator in a brushless motor.

Closed End Bell Motor—A brushed motor that is not designed to be readily serviced. Closed end bell motors tend to have shorter life spans compared to open end bell motors due to the fact that the commutators and brushes cannot be easily cleaned or replaced.

Cogging—A shuttering or stuttering when throttle is applied to a sensorless, brushless motor.

Commutator (A.K.A. Comm)—A rotary electrical switch in brushed motors. The commutator is copper in color, mounted to the top of the armature and features three segments. The brushes ride against the commutator and transfer current to generate rotation.

End Bell—The top-most portion of a motor. On a brushed motor, the end bell houses the brushes, brush springs, a bearing or bushing and, often, some sort of capacitor.

Fixed Timing—A motor that has been designed to prevent the user from adjusting the timing. This is done to reduce costs and keep motor performance on a level playing field.

Hand-Wound Modified Motor—A motor that features an armature that has the windings wound around the stack by hand. This generally provides a much tighter, more consistent and more efficient armature than machine winding and provides better overall performance.

Kv—A rating of performance for brushless motors. While Kv ratings are occasionally applied to sensored motors, sensorless brushless motors are almost always rated by Kv. The higher the Kv rating of a motor the faster it will be. Kv refers to the number of RPM a motor will produce for each volt of power input to it For example a 1,000Kv motor would produce roughly 7,400 RPM at 7.4 volts.

Laydown Brushes—Brushes that are wider than they are tall. Laydown brushes provide exceptional performance advantages in stock motors; however, they can cause excessive wear and heat in modified motors.

Machine-Wound Modified Motor—A motor that features an armature that has had its windings wound by a machine. While more efficient and less expensive to produce than hand-winding, a machine-wound armature generally does not have the same performance level as a hand-wound armature.

Modified Motor—A motor without limitations on the number of turns or wire gauge on the motor. Generally any brushed motor with fewer than 27 turns or a sensored brushless motor with fewer than 17.5 turns is considered to be a modified motor. Modified brushed motors also feature adjustable timing and ball bearings to support the armature/rotor compared to stock brushed motors that have locked timing and Oilite bushings.

Oilite Bushing—Bushings made of a bronze alloy used in 27-turn brushed stock motors and some machine-wound modified motors. Oilite bushings are less expensive to produce than ball bearings, but increase the friction dramatically.

Open End Bell Motor—A brushed motor that has been designed in a way to allow you to service and clean the commutator, replace the brushes and the springs. Some open end bell motors, known as rebuildable, also allow you to completely remove the end bell, making it possible to completely remove armature from the can for easier maintenance or replacement.

ROAR (Remotely Operated Auto Racers)— The main sanctioning body for RC racing in the USA and Canada. ROAR is a member bloc of IFMAR, the international federation that governs World Championship Racing around the world. ROAR establishes guidelines for manufactures to follow to ensure races are run as fairly and equally as possible. When it comes to RC motors, ROAR is responsible for determining whether stock and modified motors meet the criteria to be legal for use in competition.

Sensored Brushless Motor—A type of brushless motor that utilizes special sensors, called Hall Effect Sensor, to connect the motor to the Electronic Speed Controller. The purpose of this sensor wire is to allow the Electronic Speed Controller (ESC) to better monitor the position of the rotor in relation to the stator to provide smooth and consistent throttle response. Sensored motors are used for sanctioned racing and are rated in turns.

Sensorless Brushless Motors—A type of brushless motor that does not use any sort of Hall Effect Sensors to connect the motor to the Electronic Speed Controller (ESC). Due to the simpler construction and design, sensorless brushless motors are less expensive. Sensorless motors are generally rated in Kv. The higher the Kv rating, the faster the motor will be.

Stack—The main "core" of a brushed motor's armature. Each of the three stacks are constructed of laminated steel, typically green in color. The stack can be full-length or have material removed to alter the motor's performance in relation to the magnetic field. Each stack has a length of wire wrapped around it, creating the electromagnetic field of the motor.

Stand-Up Brushes—Brushes that are taller than they are wide. Stand-up brushes tend to work best in modified motors.

Stator—The "can" of a brushless motor. The stator is the part of a brushless motor that houses the windings.

Stock/Spec Motor—In recent years, the term "Stock" has taken on many different meanings. Stock motors are generally referred to as brushed motors that feature armatures with 27 turns of wire with the timing locked at 24 degrees. Brushed stock motors also utilize Oilite bushings to support the armature. This was done to keep costs down. In more recent years withthe advent of brushless motors many tracks and organizations have replaced the term "stock" with "spec" and has evolved to include 10.5T, 13.5T, 17.5T,21.5T and 25.5T sensored brushless motors.

Turn (A.K.A. Wind)—The number of times a length of wire is wrapped around a stack in a brushed motor or the stator in a brushless motor. The more turns a motor has, the more wire was used in its construction. Having more wire not only increases the rotating mass of a brushed motor's armature, but also increases the resistance, reduces efficiency and slows the motor down. The lower the turn of the motor (generally speaking) the faster it will be.