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  1. #1
    RC Qualifier
    Join Date
    Apr 2001
    Location
    Neuhaus
    Posts
    677

    pro and cons of brushless summary

    i have written that to post somewhere else, but the thread was closed before i could click the send-button:

    hmm... i have so much time...
    so:

    pros and cons of brushelss vs normal motors in my eyes:


    PROS brushless:

    1.) power
    its not possible with non-brushless-motors to reach the same poweroutput at same size
    2.) weight
    a brushed motor is always heavier at same powerlevel than a brushless
    3.) size
    brushless does not have comm and brushes, for that smaller
    4.) no brush-replacement, no maintance
    maybe the biggest PRO: brushless-motors do not need any maintance (until every year oil for the bearings)
    (have not oiled my brushless for 6years now and it runs nevertheless)
    5.) timing through controller
    timing is changable through the controller...
    on new controller its changed automatically depending on the load which is on the motor...
    so always best efficience and poweroutput !
    this feature i know only from the GRaupner/Plettenberg-BRUSHED-motors, the big one with over 600g...
    there the ring around the motor moves on different current, so the timing is also changing...
    on normal (car)motors: timing is fix, have to be changed by a screwdriver
    6.) no "right" direction
    its unimportant in which direction the motor turns, brushless works in both directions absolut same way with best efficience
    on normal motors this is not true...
    when going into revesre the wear on the brushes is bigger, more radio-intereference, less power.....
    for reverse the motor needs a extra-timing-setup and the brushess have to be run-in sepearatly
    7.) efficience
    thing about:
    90% of a brushless-motor: so 10% heat
    70% of a brushed-cheap motor: so 30% heat...
    thats 3 times more heat at a cheap brushed-motor at same poweroutput !!!!
    ok: not all bls reach 90%, some are only between 80 and 85%
    and there are brushed-motors which reach over 75%...
    but nevertheless: over the whole band of rpms the brushless has MUCH higher rpms..
    8.) very high efficience on low rpms
    with the new good controllers the motors work also at very low rpms with very good efficience, so they are even used in solar-flyers !!
    9.) some of the BLs benefit triangle/Star - configuration
    with that you have two motors in one:
    resoldering the endplate of the motor:
    the rpm goes down by factor 1.7 at same voltage, for that
    torque goes up by factor 1.7
    so: you have two motors in one for different applications !!
    10.) costs
    brushless is meanwhile cheaper...
    you canīt compare a brushless with a cheap 540-brushed-motor..
    when you want to compare a brushless-motor you have to compare it with a about-same-powerfull brushed motor...
    example:
    a Mega brushless AC22/20/2 costs about 80 US$
    a Ultra BRUSHED 930 with about same power costs about 170 US$
    the Ultra costs more than twice as much, has about same poweroutput and about same efficience, BUT: weigths 260g compared to 160g of the little MEGA brushless !!!
    11.) rpm-limit
    because of the fact, that at most brushless-motors the magnets are on the shaft and in one-piece, these motors are very rpm-robust...
    100.000rpm and more are possible without damage !
    12.) the "Outrunner"-configuration
    only possible with brushless...
    these Outrunner-motors have about 7times more torque (of course lower rpms for that) than normal brushless or brushed motors !!!
    the selfbuild-motors i spoke about before are such motors...
    13.) runtime
    because of the great efficience runtime is higher too...


    Cons of brushless:
    1.) COGGING !!
    a very big problem, most noticable in rc-cars...
    you can avoid that by the right gearing, but in some cases its not avoidable (old controllers, wrong controllersoftware, kind of application)
    the cogging is something, there is no way around..
    thats why: brushless is not good for trucks like TXT1, Juggernaut2, ... so trucks you want to use for rock-crawling..
    if you want to use it for rock-crawling you have to put a realy oversized motor into the truck, so the cogging is not noticable
    also gearing is a big isue to provide cogging
    2.) gforward/backward-problem
    thats a problem which is related to the controller-software...
    for example some controllers:
    when the truck rolles backwards down a slope the controller will not let the motor power forward..
    first it will brake until the truck stands and than it will go forward..
    here there can be another problem: when the truck stands, the controller releases brakes, and when it will give forward-power the truck is already running backwards again, which starts the whole thing again..
    not all controllers, but some have these problem..
    3.) forward/backward - delay
    donīt know if these is realy a problem...
    have often read about people with brushed-setup with the opposite problem: problem, the controller changes too fast between forward and reverse...
    some brushless-controller have a delay of 4sec !! some only a half second..
    4.) not smooth enough
    these is not realy true for all controllers...
    some people have reported that there controller-setup (for example Lehner-1860 car-controller) is smoother on the throttle controll, than there competition-car-controllers..
    and these people were racing at competitions, so i think they know what they say..
    so these point is also only true for some few controllers (no modern controllers anymore are not smooth)
    5.) falling out of phase
    the controller-software can be the reason or the motor does not fit excactly to the controller..
    i have these problem with one controller/motor-combination, that when i shift from 1st to 2nd-gear the motor gets out of phase which means some shuttering for half-second to one second..


    i hope i was fair on that comparison...

    you did not find "price" at the CONS for brushless, because as i said:
    a brushed-motor with about same power (but more weight) costs more !
    so price is a pro for the brushless becaue they are cheaper..


    i had 30-40 cheap-caned 280, 300, 400 and 540-motors over the years
    around 10 high-end-brushed-motors (up to 300 US$ !!!! in price)
    and now 7 brushless-motors (from 49 US$ up to 150 US$ the most expensive)
    so i think i can compare a little bit


    if something is wrong or something missing, please add...
    my homepage:
    www.my-page.at/portal

  2. #2
    pioneer
    Guest
    I found this information here http://www.allegromicro.com/techpub2...mot/a17a19.pdf which I think is another pro of brushless motors that they have constant torque since brushed motors have sinusoidal torque. This means that with the same current and magnetic field the motor generates more torque.

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