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Brushless motor enigma — Parallax Forums

Brushless motor enigma

science_geekscience_geek Posts: 247
edited 2009-02-21 19:00 in General Discussion
im am looking for a brushless motor that i can play with, in other words, i have a ton of ideas, but no motors that i can use as i have no brushless motors. i need a motor that can do various thing that doesnt cost an arm and a leg and also looks elegent, because my friends and family doesnt understand the awesome stuff that a machine can do looks mean everything to them, i need a motor that can be used as a high speed rotary tool like a dremel that i can use by making a motor mount that is hand held and can be attached to something in case i want to build a cnc machine. the motor will also be used for spinning a tesla turbine, i do a lot of work with tesla turbines, and i have some test that need to be done with the turbine spinning at 20,000+ rpm,

also, is it possible to turn a brushless motor "backwards" like a brushed motor and make it make electricity, if it does, is it dc ( i ask cause i have heard of it producing ac and am not sure), how does rpm affect the voltage output,

questions comments concerns or anxieties are welcome

Comments

  • icepuckicepuck Posts: 466
    edited 2009-02-19 01:15
    A brushless DC motor is really an AC motor with a built-in inverter.
    http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXSSK6&P=0
    using the above link as an example you will notice that the motor has three wires, thats because it is a three phase AC motor.
    The electric speed controller(ESC) that it requires is a DC to AC three phase inverter.

    Using a brushless motor as generator wouldn't work because of the on board electronics doesn't have a rectifier to convert the AC into DC. You could remove the inverter and use it as an AC generator, but you wouldn't be able to use it as motor any more.

    The Toyota prius hybrid is a good example of using motors as generators, but it is so complex the transaxle and inverter is run by a 32bit computer. The engine is run by a 32bit computer and so is the NiMh battery pack.
    -dan
  • rjo_rjo_ Posts: 1,825
    edited 2009-02-19 03:38
    Science-geek,

    For hacking around, you can't beat Walmart.

    Walmart carries a hand blender... the kind you put into a glass to make a smoothy. The kind that doesn't break immediately costs about $25 dollars. But the kind you are looking for is about $9. I don't know how many rpms it gets but it is nice little unit... which breaks after about a week leaving you a beautiful motor, which can operated off of a wall outlet... or will run at a slow speed by just hooking up +5V and ground to the motor terminals, which can be accessed by removing 4 screws. I wouldn't try this with a protoboard... I used a power supply from SpinStudio and a breadboard. Nothing blew up or started smoking.

    I also like the motors from ultra-cheap hand held vacuum cleaners.

    You can make a nice motor controller with a 5 volt relay from RadioShack(SPST Reed Relay part 275-0232)

    Although these relays are rated as 5 Volt (and .5Amps at 120VAC), in reality you can control the relay directly from a Prop pin. You should probably use a diode in between the prop and the relay. Since you will be using DC, the .5Amps spec doesn't really count. My guess is that using DC, the relay will probably handle higher amps, but I don't know how to do the conversion(but I would like to know[noparse]:)[/noparse]

    To do it correctly... you have to do it the way Parallax does... get yourself an HB-25 motor controller, it is easy to use and just begs to be held[noparse]:)[/noparse] This way your motor and your prop are protected from each other.

    http://www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/List/1/ProductID/64/Default.aspx?txtSearch=motor+controller&SortField=ProductName,ProductName

    Rich
  • science_geekscience_geek Posts: 247
    edited 2009-02-19 04:25
    ok, since it cant be used for a generator, is there a type of clutch that someone knows of that can be electrically activeted, meant for a small shaft, that i can rig up to a brushed motor
  • science_geekscience_geek Posts: 247
    edited 2009-02-19 19:26
    another thought, would it be possible to use a bridge rectifire(spelling?) and a couple/1 cap to smooth out the ripple
  • science_geekscience_geek Posts: 247
    edited 2009-02-19 21:00
    ok, forget about the generator portion of it, i came up with a better idea for doing something like that, new criteria for a brushless motor is... one that is good to play with that has good torque, high rpm, just a good all around motor to play with.
  • $WMc%$WMc% Posts: 1,884
    edited 2009-02-20 01:51
    science_geek

    Take a look at an automotive alternator. They are 3 phase AC generators with a simple 1/2 wave rectifier to convert to DC.




    ___________$WMc%__________

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    The Truth is out there············································ BoogerWoods, FL. USA
  • Carl HayesCarl Hayes Posts: 841
    edited 2009-02-20 07:25
    Automotive alternators have brushes.

    If you've got an old PC cooling fan lying around, it is almost certainly a brushless DC motor. Not powerful enough for some of the things you want to do, but OK for learning how to control one. Cheap, too -- usually free.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    · -- Carl, nn5i@arrl.net

    Post Edited (Carl Hayes) : 2/20/2009 5:52:49 PM GMT
  • JasonDorieJasonDorie Posts: 1,930
    edited 2009-02-20 08:34
    Hard disk motors are also brushless, as are cd or DVD drive motors. If you have a dead one, usually the laser goes before the motor does. If you don't have any of those, try NitroPlanes.com, or BPHobbies.com - both sell cheap Chinese motors that you can play with to get used to them. A big one will likely not be cheap, nor will the circuit to drive it.

    Jason
  • PhilldapillPhilldapill Posts: 1,283
    edited 2009-02-20 21:06
    Carl, what kind of automotive alternators have brushes??? I believe you are talking about old-time "generators" which are essentially just brushed DC motors. Vehicles switched to Alternators a good while back because there are less parts that wear out - at least that's my understanding.
  • FireHopperFireHopper Posts: 180
    edited 2009-02-20 22:17
    most car alternators have brushes due to the way they are made.. an alternator has a coil as the stator and rotor.

    there are no magnets in standard alternators..
  • kwinnkwinn Posts: 8,697
    edited 2009-02-21 03:53
    Alternators have 2 brushes that contact slip rings to provide current to the rotor coil. The rotor coil produces the magnetic field that generates the output voltage in the stator coils when the rotor turns. The output voltage is regulated by varying the current to the rotor coil. I have seen an alternator used as a motor to start a small propane fueled motor which in turn powers the alternator and generates electricity.
  • icepuckicepuck Posts: 466
    edited 2009-02-21 03:56
    Have a look at http://auto.howstuffworks.com/alternator1.htm
    They do a pretty good job of explaining things.
    -dan
  • science_geekscience_geek Posts: 247
    edited 2009-02-21 19:00
    ok, thanks for the suggestions, i have found a dead drive from something(looks like vcr) one last question though, how hard is it to rewrap a brushless motor so that you can change from torque to rpm
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