science

Outrunner

Outrunner is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Outrunner rather than just read about it. In short: An outrunner is an electric motor having the rotor outside the stator, as though the motor were turned inside out. They are often used in radio-controlled model aircraft.

Key takeaways

Outrunner belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Outrunner to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Outrunner from memory before moving on to harder problems.

Reference excerpt

An outrunner is an electric motor having the rotor outside the stator, as though the motor were turned inside out. They are often used in radio-controlled model aircraft. This type of motor spins its outer shell around its windings, much like motors found in ordinary CD-ROM computer drives. In fact, CD-ROM motors are frequently rewound into brushless outrunner motors for small park flyer aircraft. Parts to aid in converting CD-ROM motors to aircraft use are commercially available. Usually, outrunners have more poles, so they spin much slower than their inrunner counterparts with their more traditional layout (though still considerably faster than ferrite motors, when compared with motors that use neodymium magnets) while producing far more torque. This makes an outrunner an excellent choice for directly driving electric aircraft propellers since they eliminate the extra weight, complexity, inefficiency and noise of a gearbox. Some front loading direct-drive washing machines use an outrunner motor. Outrunner motors have quickly become popular and are now available in many sizes. They have also become popular in personal, electric transportation applications such as electric bikes and scooters due to their compact size and high efficiency.

Stator and magnetic pole count The stationary (stator) windings of an outrunner motor are excited by conventional DC brushless motor controllers. A direct current (switched on and off at high frequency for voltage modulation) is typically passed through three or more non-adjacent windings together, and the group so energized is alternated electronically based upon rotor position feedback. The number of permanent magnets in the rotor does not match the number of stator poles, however. This is to reduce cogging torque and create a sinusoidal back emf. The number of magnet poles divided by 2 gives the ratio of magnetic field frequency to motor rotation frequency.

Common stator pole/magnet pole configurations N denotes number of stator "wire wound" poles, P denotes number of rotor "permanent magnet" poles.

9N,12P - very common to many small outrunners. This is also the most common CD-ROM motor configuration. Winding Pattern is ABCABCABC 9N, 6P - Common for helicopter motor, EDFs, and other high speed applications. The winding pattern is ABCABCABC 12N, 14P (DLRK) - Common for higher torque applications. Noted commonly for its smooth and quiet operation. Winding Pattern is AabBCcaABbcC (lowercase implies reverse in winding direction).

Other configurations 9N, 8P - Magnetically imbalanced motor configuration occasionally found in high speed applications. This configuration is best terminated as WYE to minimize vibration. 9N, 10P - Highly magnetically imbalanced motor that often makes for noisy running. This configuration is usually only built by do it yourself motor builders. This motor is best terminated WYE. Winding pattern is AaABbBCcC 12N, 16P - A not so common but still used style. It has been overshadowed by the 12N, 14P. Winding pattern is ABCABCABCABC 12N, 10P - Higher speed variant of the DLRK motor. Occasionally found in helicopter motors. Winding Pattern is AabBCcaABbcC (lowercase implies reverse in winding direction). 12N, 8P - Even higher speed than the 12N, 10P. Winding pattern is ABCABCABCABC

Illustrations

Worked examples

Example 1 — a first encounter with Outrunner

Start with the simplest possible case. Write down what Outrunner claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Outrunner before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Outrunner ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Outrunner

In research: Outrunner appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Outrunner in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Outrunner is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electric aircraft, Electric motors, Radio-controlled aircraft, so understanding it makes those chapters shorter.
In everyday life: Look for Outrunner outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Outrunner in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Outrunner means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Outrunner out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Outrunner in simple terms?

An outrunner is an electric motor having the rotor outside the stator, as though the motor were turned inside out. They are often used in radio-controlled model aircraft.

Why does Outrunner matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Outrunner?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Outrunner.