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Stepper Motor and a Brushless DC Motor......Difference?

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eem2am

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What is the difference between a Stepper Motor (Bipolar drive stepper motor with 2 coils) and a Brushless DC Motor?
 
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Both are in principle permanent magnet synchronous motors, but with different characteristics and intended mode of operation. Steppers are mainly used for low-power, discontinuous drives when precise positioning without feedback is intended. Brushless DC can have up to several kW power, is mostly designed for three-phase operation controlled by position sensors. For some applications fields, e.g. servo drives, both motor types are applicable.
 
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    eem2am

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I'd like to think that Brushless DC Motors (BDM for now) is more suitable for high rpm.

A brushless DC Motor would typically be lighter in weight than a stepper that can provide same amount of output power.

I'd guess that if you make a stepper and a BDM drive a fan (or other object that require high rpm), then if the motors get out of phase, a BDM would cause less vibrations than the stepper. Also I think that it's a little easier to regain phase control over the BDM.

I have many guesses here, but they won't put a stepper in an electrical car. A BDM will do better.
 
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Brushless motors can rotate to any angle. Steppers are designed to do just that, they move in fixed angular steps.

Brian.
 
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By utilizing micro steps, stepper motors also can rotate to "any angle". From a general view, both motors are just PMSMs, as already mentioned. This shows also in individual properties.
 
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thankyou, these are all excellent responses.

betwixt:- "Brushless motors can rotate to any angle"
...i agree, but i am not sure if a Brushless DC Motor can be static at any angle and have a lot of torque to hold it at that angle(?)

It seems to me that BDCM'S and steppers are extremely similar from your answers.

...but that BDCM's can manage larger power, and higher speeds.

...there must be some very intricate way in which the windings are wound on the stator of a BDCM...such that torque is smooth as the motor rotates(?)
...this is presumably what makes BDCM's more expensive than steppers.

I also hear of the requirement to know the rotor position for a BDCM.

I dont think this applies to all BDCM's?

...i am sure a MWD (remote exploratory drills for oil discovery) Engineer was telling me his BDCM's dont have angular position feedback, because they are used in drilling, and at the end of the day, put some signals into the stator coils , and the rotor will follow them round like a "dog on a lead".....and so he said his BDCMs dont need position feedback.

It also seems to me that BDCMs are always 3-phase?
 

but i am not sure if a Brushless DC Motor can be static at any angle and have a lot of torque to hold it at that angle
a "lot of torque" is of course relative. But basically a synchronous motor can deliver full torque at zero speed. Furthermore, the torque of a three phase motor driven by sine currents is constant in time (or "smooth" in your words). At least almost constant, because this depends on the motor design details to some extent. But the feature doesn't require a special design, you'll find it with most three phase AC motors.

It should be noted, that BLDC motors are often driven by square waves, and then the torque has a considerable ripple.

To achieve maximum torque, the drive current must be generated with a defined phase relation to the rotor position. Using a position encoder is the easiest way. There are also sensorless drive methods, but they don't work well down to zero speed.
 
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