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Non wearing brushed motor

A modification to brushed motors that retains their simplicity while eliminating brush wear
  [vote for,

This idea stems from one common problem associated with brushed dc motors, brush wear. These brushes push against the sides of the rotor and deliver power to specific contacts thereon thus switching electromagnets on the rotor on and off. My proposed alternative system would use a mostly plastic ball bearing to both support the end of the rotor in the motor and to provide power to the electromagnets thereon. essentially the rolling elements inside the bearing transmit electrical energy from the stator to the rotor without the two rubbing against one another. The conductive balls have plastic ones between them so as to prevent current from short circuiting from one end to the other. this would eliminate brush wear and thus make the motor far more reliable. its doubling as a bearing would decrease the complexity of larger motors.

Ball bearings would decrease the size of the contact area to a single point. roller bearings might be better for high power applications.

[edit] after doing some more research it would appear that some people have m=been looking into using liquid metal conductors for exactly this purpose. Also carbon brushes are one of the more expensive components in electric motors. This might actually work [/edit]

RichardT, Mar 09 2010

How electric dc motors work http://electronics....orks.com/motor2.htm
Explanation + Pictures [RichardT, Mar 09 2010]

Dc motor wear http://ecmweb.com/m...ntaining_dc_motors/
This article deals exclusively with rotor wear as high end motors treat brushes as consumables [RichardT, Mar 09 2010]

http://en.wikipedia...d_DC_electric_motor Wikipedias article on brushed DC motors [RichardT, Mar 09 2010]

US 530,717 https://patents.goo...en?oq=US+530%2c717+
[xaviergisz, Mar 09 2010, last modified Feb 18 2018]

US patent 5,714,825 https://patents.goo...en?oq=5%2c714%2c825
motor with "ball-point pen" type brush [xaviergisz, Mar 09 2010, last modified Feb 18 2018]

The homopolar motor https://en.wikipedi...icity_and_magnetism
WKTE [8th of 7, Feb 13 2018]


       Strangely (gut feeling), I thought the opposite was the way to go; fast wearing brushes that are easily replaceable. Somehow use the disintegration of the metal brushes to supply free electrons to the circuit.
wjt, Mar 09 2010

       I like it, there could be potential for reduced friction, but if it works better totally depends on execution. Forget the plastic stuff, that is trouble. Plan on these not conducting quite as well, on account of a smaller contact area than a seated brush and because bearings are made of harder metal that doesn't conduct as well. The roller bearing would probably have to be larger than the brush version to compensate for this. It will also run hotter and perhaps need lubrication, which could be a can of worms. Deterioration due to arc pitting is not too big of an issue for brushes because it happens at the corners, and the face is renewed as the brush wears. For your bearing this may be a much more significant issue. An advantage the bearing has in this area is the lack of dust generated, which causes nearby bearings to wear faster and can even cause shorts/arcs on the commutator. I assume this is why liquid metal was tried as it does not suffer from arc pitting, but most all of those designs suffer from gravity constraints.   

       As for as maintainance life goes, I'm not sure if it would be extended or not considering these other factors. In those cases going for max life, the increased complexity of magnetically transmitting power to the rotor fields without physical contact is worth the increased cost. Depending on application it really isn't too substantial.
AutoMcDonough, Mar 09 2010

       for roller versions, you could distort the contacts slightly like herringbone gears so that one end of the roller contacts the contact first.In addition to this that end of the roller could include materials that increase resistance to current flow along with a thin coating of a conductor like tungsten. This resistant roller end would act to lessen spark voltage and to wear less from sparks.
RichardT, Mar 09 2010

       Hold on. The rotor is rotating, but the wires feeding the motor are not. So there has to be a sliding contact somewhere. The roller can transfer that motion nearer an axis of rotation, but I wonder at the cost/benefit trade-off.
afinehowdoyoudo, Mar 09 2010

       You do realize, [RichardT], that the balls in a ball bearing travel around at one half the speed of the borne rotating part?
lurch, Mar 09 2010

       Elimination, or at least reduction of sliding friction is the entire principle behind this idea. basically you are using the rolling elements in the end bearing to transfer electricity between the two contacts.   

       The rolling elements will be traveling slower than the rotor but the idea is to have enough of them that when one stops connecting two contacts another moves into place. You would need at least four conducting rollers for a three contact motor, five for a four contact motor and so on. That ensures all rotor contacts are connected to the stator contacts by rollers. There would of course be some variability to the motor timing. the rolling elements would slip a little every turn, but overall it should work.
RichardT, Mar 10 2010

       Ball bearings wear out eventually, but they should last longer than carbon brushes, I think, and they won't add as much friction. A motor already has two bearings, so just replace one with one of these commutative bearings, and that's a friction advantage over two bearings plus brushes.   

       Ceramic ball bearings exist. Those should be used for the insulating ones rather than plastic, because they'll last longer.   

       // You do realize, [RichardT], that the balls in a ball bearing travel around at one half the speed of the borne rotating part? //   

       If they have the same diameter as the borne rotating part. They work exactly like planetary gears.
notexactly, Feb 13 2018

       // replace one with one of these commutative bearings //   

       No, because then you need some sort of external switching to achieve the polarity reversal.   

       The point about opposed brushes on a segmented commutator is that they automatically switch current polarity with rotation. It makes the whole system extremely simple.   

       Now, if you use slip rings and sense the armature position, you can switch the polarity externally and have lower brush erosion, but then you might as well build a stepper motor - no brushes at all - or use a PWM controller to synthesize an AC drive waveform, which is of course what brushless motors do.   

       Synchronous motors are great, but they're constant-speed devices.   

       When it comes to converting electrical energy into mechanical rotation, it's all been tried before.   

       // using liquid metal conductors for exactly this purpose. //   

       There was this bloke called Michael Faraday, he used mercury as the conducting element, about two hundred of your Earth years ago ... <link>   

       Brushed DC motors are very, very cheap to make. That's why, for all their faults, they're still around.
8th of 7, Feb 13 2018

       I thought the point of this idea was that the bearing would act as a commutator, not just as a slip ring. That's why it has both conductive and insulative parts, right?
notexactly, Feb 14 2018


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