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My general question is why brushless DC motors seem to be much more expensive than similarly sized brushed permanent magnet motors, especially considering that the construction of the latter is more complicated?

In my concrete application, I'm looking for a brushless DC motor with a 10-15W max power rating. I was first looking for an alternator of that range, but this kind of product practically doesn't exist, I believe because a BLDC fills this role pretty well. Using a BLDC as a generator is a very attractive idea - since you're not driving it, you don't need to worry about ESCs, you just throw in a 3-phase rectifier and you're done (also, it's much easier to detect the running speed by detecting the zero crossings on one of the phases. And some BLDCs have Hall sensors as well, which makes it even easier). Comparing an in-runner BLDC to a brushed DC of similar size, you'd expect them to be practically the same in terms of construction, with the latter adding the brushes and the commutator - you'd expect it to be slightly more expensive. My research indicates that the reverse is true: a decent BLDC fetches upwards of $100 in most reputable electronics shops (e.g. Electrocraft in the UK), even in Alibaba they are $30+ (the price break for 100 units), and even RC-craft units optimized for onesies from eBay are $15-$20. Then you can definitely buy s very well machined japanese brushed motor (e.g., Mitsumi) for a few bucks.

Why is that? Are BLDCs still considered a novelty and economies of scale do not yet apply to them? Or am I missing some technical detail?

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closed as primarily opinion-based by Chris Stratton, Leon Heller, Wesley Lee, laptop2d, ThreePhaseEel Feb 28 '17 at 2:07

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ This question isn't really a fit here. Likely many factors are involved - economies of scale as comparatively few products use them, perhaps better construction and more expensive materials given that those tend to be higher value products expecting high performance (more likely to be ball bearing, more expensive magnet material, etc), and also that your pricing numbers for brushless motors seem inflated compared to what is actually available. \$\endgroup\$ – Chris Stratton Feb 27 '17 at 16:16
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Brushless DC motors typically use strong permanent magnets on the rotor. This does some nice things, like alleviate the need to get any electrical power across the rotating interface. It also allows for Hall effect sensors to determine the position of the rotor.

However, these strong permanent magnets currently require rare-earth metals, such as neodymium. Being rare but in demand makes them expensive.

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  • \$\begingroup\$ Then the obvious follow-up comes to mind, which is why BLDC manufacturers don't use normal (cheap) magnets, in order to fill the "cheap BLDC" niche. But I kind of grasp what the answer to that might be as well. Thank you for the answer! \$\endgroup\$ – anrieff Feb 27 '17 at 17:45
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    \$\begingroup\$ @anr: Cheaper permanent magnets are less strong and less permanent. That means the motor has to be larger and heavier for the same torque, which also increases cost. However, there are probably some BLDCs out there that are lower cost and lower performance by avoiding expensive materials in the permanent magnets. \$\endgroup\$ – Olin Lathrop Feb 27 '17 at 17:57
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Depends on which bldc motors you are talking about. Those bldc motors used in computers are quite inexpensive.

Those ones used for drones are expensive due to their ability to handle large current and complexity / numerous windings but most importantly the lack of economy of scale.

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  • \$\begingroup\$ Yep - bldc motors have been in used as spindle motors in computer fans and floppy drives since the 1980s, CDROM drives since the 1990s, and they still are. \$\endgroup\$ – rackandboneman May 1 '18 at 21:59
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My company once had a project to quote a high volume system based on stepper motors or bldc. So on high enough quantities the only remaining difference is encoder, which in some cases isn't even required. But the best part is that performance and closed loop itself sometimes allow even cost reduction compared to steppers, as the motor may be precisely selected for application, while stepper often tequired wide margins. Bottom line, since the appearance of modern electronics bldc are not more expensive to drive and not more expensive per same performance.

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    \$\begingroup\$ This does not answer the question which was actually asked, which was about the costs of BDLC motors vs brushed motors, not about the cost of the electronics or about steppers. Also note that steppers and BLDC motors are similar machines that have been heavily optimized for very distinct purposes, but still have enough commonality that they may be expensive for the same reasons - magnets, bearings, overall quality, and small volume compared to brushed motors. \$\endgroup\$ – Chris Stratton Feb 27 '17 at 17:10
  • \$\begingroup\$ @chrisstratton you are right about every word. If you think this answer is useless- cool. I think it is as useful as any other answer. Since you can't guess it by yourself, the last not sentence, ome that normally is not said loudly, is "go recheck your facts". \$\endgroup\$ – Gregory Kornblum Feb 27 '17 at 18:08
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I suspect that the brushless DC motors use neodymium magnets while the brushed ones use less expensive magnets. Also the brushed motors are manufactured in very large quantities for all kinds of inexpensive products. Even though the Mitsumi motors are good quality, the brushless motors sold for quadcopter etc. may be better quality. There also may be less vigorous competition in the consumer market for brushless motors.

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Comparing an in-runner BLDC to a brushed DC of similar size, you'd expect them to be practically the same in terms of construction, with the latter adding the brushes and the commutator - you'd expect it to be slightly more expensive

The construction of an 'in-runner' BLDC is quite different to a conventional brushed motor. Instead of an armature it has coils arranged around the inside of the stator. Due to the restricted space, the windings on most small in-runners have to be installed by hand. This is a difficult and time-consuming and job, which makes them more expensive than machine wound brushed motors.

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you can definitely buy a very well machined Japanese brushed motor (e.g., Mitsumi) for a few bucks.

Well machined perhaps, but not in the same league as a good brushless in-runner. Even cheap rc hobby inrunners have neodymium magnets, ball bearings and cnc machined aluminum cases. Peak efficiency is typically over 80% (compared to 60-65% for small brushed motors) which translates to lower loss and much higher power for the same size. And they can spin at up to 60,000rpm, whereas brushed motors are limited by brush bounce and excessive wear at high rpm.

The biggest cost advantage of a brushed motor is often the controller, which can be made much simpler if bi-directional operation is not required.

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  • \$\begingroup\$ Could a commutator-less motor which used brushes and slip rings but electronic commutation offer advantages relative to a commutated-brush motor, but with less added cost than a BLDC? Could the cost of rare-earth magnets be avoided by using an electomagnet instead (somewhat like a universal motor or alternator)? \$\endgroup\$ – supercat May 23 '17 at 16:33
  • \$\begingroup\$ Brushes with slip rings reduce performance and wear out. You need 3 slip rings for 3 phases, which increases the size of the motor. And you still need a 'brushless' controller, so the cost advantage would be minimal. Electromagnets are used in very large brushless motors where they are cheaper than rare-earth magnets, but there is a performance loss - and they need slip rings! A BLDC motor can use cheap Ferrite magnets, pressed metal rotor and bushings instead of ball bearings to keep the cost down. This is how most CDROM drive motors were constructed. \$\endgroup\$ – Bruce Abbott May 23 '17 at 21:08
  • \$\begingroup\$ How strong are the ball bearings in hobby BLDC motors? Could they withstand 20 lb of radial force? \$\endgroup\$ – techSultan Jul 20 '17 at 16:37
  • \$\begingroup\$ Bearing 'strength' is mostly determined by the ball size and material. A motor with larger diameter shaft needs larger bearings which should have higher loading capability. Cheap 'hobby' motors often use cheap bearings which don't last long when subjected to high loading. These can usually be replaced with better quality bearings. 20lb is ~9kg or 89N. The NMB DDRI-418ZZ (3.17mm ID) is an example of a good quality bearing. It has a static rating of 97N. \$\endgroup\$ – Bruce Abbott Jul 20 '17 at 20:53

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