Inrunner vs. Outrunner

Discussion in 'Scratchbuild Talk' started by jcrankshaw, Jul 29, 2010.

  1. jcrankshaw

    jcrankshaw Ace Pilot

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    What's the difference and when is one prefered over the other?
     
  2. Threedee

    Threedee Cadet

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    From what I know, not 100%
    Outrunners generaly have more torque, run cooler and can swing a bigger prop, and inrunners have higher rpm and normaly run a small prop or use a gearbox. Internally outrunners the magnets are on the outside while the coils are in the inside, and inrunners the coils are on the outside while the magnets are in the inside.

    For preference its really whether you want to swing a smaller prop on a fast plane, or swing a big prop on a slower plane.
     
  3. JettaManDan

    JettaManDan Administrator

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    also can refer to how it is mounted....and that is usually the description given...a "back" mount so the motor sticks all the way outside of the plane for an outrunner..and inrunner has the mouting holes up front so the motor is behind a firewall and the shaft just sticks through...
     
  4. jcrankshaw

    jcrankshaw Ace Pilot

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    Then I need an inrunner motor if I ever want to fly my cessna 182 skylane. The crappy 380 brushed motor is too weak for this 16oz hog of a plane.
     
  5. JettaManDan

    JettaManDan Administrator

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    if it has a firewall with just the shaft sticking out then yes....make sure you measure the shaft length of the stock motor to match to whatever you buy...
     
  6. kevinm

    kevinm Rookie

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    most generally when an inrunners pulling a plane it is mounted on a gearbox for torque for the largish diameter prop -but a torquey outrunner can be put on thatll do the same thing -equal or better the torque of a geared down inrunner , with less to smash, and sound very cool, instead of the gear whine ( i wonder why they dont put on heli-"cut" gear sets, famous for being nearly silent )-straight "cut" gears are really loud
     
  7. JettaManDan

    JettaManDan Administrator

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    because they are more expensive to make for a hobby where everyone wants to be as cheap as possible...
     
  8. Argonath

    Argonath Top Gun

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    We'll back up a step and look at the motors first.

    Brushed motors spin the coil around inside a case with fixed magnets mounted around the outside of the casing.

    Brushless motors do the opposite. The coils are fixed either to the outer casing or inside the casing while the magnets are spun.

    Outrunner motors have the magnets mounted on the outer casing and the outer casing is spun around the fixed coils in the center of the motor casing, hence the term "Outrunner"

    Inrunner motors have the fixed coils mounted to the outer casing and the magnets are mounted to the armature shaft and this spins inside the casing, hence the term "Inrunner"

    EDF's are typically all Inrunner style motors because you cannot spin the outer shell of an EDF when mounted in a plane.

    Inrunners as previously mentioned here also get used on planes that have a firewall and you need to make sure the shaft length is adequate to pass through the firewall and connect to the gearbox or prop.

    Brushless motors have a great number of advantages / applications over brushed motors. For example, you cannot use a brushed motor system under water with having some kind of linkage between the motor and propellers that is sealed. An Inrunner style brushless motor is the basis for a Magneto-Hydrodynamic drive on a Submarine as the coils are mounted in a fixed position around a tube and the magnets are mounted on the impeller ( typically in a cork-screw style shape) in the tube. Water is sucked in via the forward intake and pushed out the rear to propel the craft.

    Problem is, the amount of resistance to get it spinning faster enough to be efficient requires a HUGE electromagnetic field to run it.....
     
  9. kevinm

    kevinm Rookie

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    true - only redeeming value of a gearbox is its ability to power a plane that otherwise would need a better motor , why do the gearbox good/right- just do it
     
  10. JettaManDan

    JettaManDan Administrator

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    a good/simple way to look at the inrunner/outrunner question is this...any brushed motor..the old "540" from an RC car..or the 370/380 motors in most small helis now are inrunner..or a fixed can that the armature spins inside of...and an outrunner the casing spins on the outside...on an inrunner you are fixed with the shaft length ornetation and other specs..on an outrunner you can actually change which way the shaft sticks out of the motor but pulling it apart and pushing it to the other side...kinda cool to do :)
     
  11. Chase

    Chase Cadet

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    That's what Id do in your case with the Cessna.:D
     
  12. Scrapdaddy

    Scrapdaddy Rookie

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    Would a Comparision of an inline engine and a radial engine be a good comparison?
     
  13. MoTheG

    MoTheG Airman

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    It is simply the available kv-ratings.
    inrunners have higher kv-ratings.
     
  14. DJRubberCow

    DJRubberCow Cadet

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    What's also important is:
    Inrunner equals brushed
    Outrunner equals Brushless


    However, not all outrunners have a rotating outer shell.
    Called "Hybrid Outrunners" by HobbyKing (kudos for the most friggin confusing description ever!), they have a line of motors that are technically outrunners but have a static outer shell around them to make them look like they're inrunners.
    However what I am missing here is that outrunners and inrunners are working totally differen.
    The inrunner(brushed) motors have self-regulating rotation. Since the brushes change polarity at the speed of the motor, you simply can hook up a brushed motor directly to a battery (or any other direct current source) and it will spin up.
    The outrunner(brushless) on the contrary needs rotary AC (3 phases, 120° apart, just like your average electric oven). Here, you need a Speed control that measures the internal resistance of the three motor leads to each other and adjusts the amount of electricity it sends through each wire accordingly. So you need much smarter electronic to use an outrunner than you need for an inrunner.

    One more interesting difference is that, due to the technique, brushless motors can be prevented from frying by the ESC if they are suddendly blocked. brushed motor ESCs don't have that feature afaik.
     
  15. rodrigo

    rodrigo Ace Pilot

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    both are brushless...only in terms of form inrunner are similar to brushed motors.... inrunner advantage is the case don´t spin.... but all other aspect are worst than outrunners: heat, torque, not good for direct drive, etc

    I checked it is not so at all ....
    http://www.rcpowers.com/forum/showthread.php?t=5851

    there are some outrunners with reversible shaft... my GWS motor has this feature

    http://www.gwsus.com/english/product/motor/gwblm002.htm
     
  16. MoTheG

    MoTheG Airman

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    That is incorrect, there is no correlation.
    I do not know of any brushed outrunners though.

    You could implement something like that for any type of ESC.
     
  17. vltchkr8477

    vltchkr8477 Rookie

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  18. ajromano2011

    ajromano2011 Rookie

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    thanks vltchkr
     
  19. BarryMartin

    BarryMartin Cadet

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    Outrunners have more torque and inrunners are better for high speeds. Thats why in planks you see outrunners turning props directly and inrunners used either with very small direct drive props or in gearboxes, in a outrunner the outside of the motor turns an in runner is as the name applys, and the advantage to outrunner is they seem to run cooler.
     
  20. Andy4568

    Andy4568 Cadet

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    Inrunner - The armature spins inside the case.
    Outrunner - The armature stands still and the case spins around it (like an old rotary engine if you know what that is).
    In general the advantage of an outrunner is that it can convert a given level of input power into rotary motion at a lower RPM than an inrunner. Thus an outrunner will take you towards the same types of benefits acheived by using a gearbox with an inrunner. Usually that means turning a larger prop more efficiently.

    Regards.
    Andy.
     
    squishy likes this.
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