Brushless Motors heresy

by Renato
(Europe)

"The quickest way to tell the difference between a canned motor and a brushless motor is to count the number of wire leads. All brushless RC motors have 3 wires. Canned motors have 2 wires. The third wire is used for feedback. Switching any two of these wires will change the rotation of the motor."

Are you aware how inaccurate is the following: "The third wire is used for feedback". Please, read at least wikipedia and make corrections

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Brushless Motors heresy

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Thanks for the feedback Renato
by: Matt

Renato,

The information you quoted from my content is not inaccurate, but maybe it could use some more explanation.

In a DC motor the electromagnets spin and the permanent magnets are stationary. The brushes of of a DC motor make contact with the commutator of the spinning armature supplying current to each elector magnet. As the motor turns, the brushes switch the polarity as it passes by each commutator.

Since a brushless motor doesn't have brushes, how does it now when to switch the polarity? It needs feedback.

A brushless motor has three wires. Only two of the wires are conducting electricity to 1/3 of the windings at any giving time.

The windings attached to the third wire actually generate a small amount of current for that split second that it is not receiving current from the ESC.

The ESC uses this current from the third wire as feedback to determine the position of the motor.

Please take another look at
wiki. It explains this under the paragraph titled "Controller Implementations" when it describes measuring the back EMF of the undriven coils.

Perhaps I should have explained in more detail that all three wires supply the windings with current, but only 2 are energized at a time while the third provides feed back for that instant.

I do appreciate you taking the time to point this out. Perhaps I do need to rewrite this paragraph so it is more clear and stated more accurately.

Thanks again, I appreciate it!

Matt

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Submitted by: Matt

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Renato, The information you quoted from my content is not inaccurate, but maybe it could use some more explanation. In a DC motor the electromagnets spin and the permanent magnets are stationary. The brushes of of a DC motor make contact with the commutator of the spinning armature supplying current to each elector magnet. As the motor turns, the brushes switch the polarity as it passes by each commutator. Since a brushless motor doesn't have brushes, how does it now when to switch the polarity? It needs feedback. A brushless motor has three wires. Only two of the wires are conducting electricity to 1/3 of the windings at any giving time. The windings attached to the third wire actually generate a small amount of current for that split second that it is not receiving current from the ESC. The ESC uses this current from the third wire as feedback to determine the position of the motor. Please take another look at <a href="http://en.wikipedia.org/wiki/Brushless_DC_electric_motor" rel="nofollow" target="_new">wiki</a>. It explains this under the paragraph titled "Controller Implementations" when it describes measuring the back EMF of the undriven coils. Perhaps I should have explained in more detail that all three wires supply the windings with current, but only 2 are energized at a time while the third provides feed back for that instant. I do appreciate you taking the time to point this out. Perhaps I do need to rewrite this paragraph so it is more clear and stated more accurately. Thanks again, I appreciate it! Matt

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