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  1. #1
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    Speed control: brushless vs stock

    I had a debate last night about any differences between the slash stock brushed speed control and the slash brushless speed control in brushed mode. My track requires stock speed control to race. I only had a brushless so argued that there is no difference in brushed mode. The counter argument was made that the internals were much better and the MOSFETS would be much better and smoother. Ultimately I lost, but I'm trying to do my research for future rules changes. Can anybody help?

  2. #2
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    I didn't know that the VXL could go into brushed mode. i know it has a LiPo mode but thats all i know about

    Quote Originally Posted by Hardeight View Post
    I had a debate last night about any differences between the slash stock brushed speed control and the slash brushless speed control in brushed mode. My track requires stock speed control to race. I only had a brushless so argued that there is no difference in brushed mode. The counter argument was made that the internals were much better and the MOSFETS would be much better and smoother. Ultimately I lost, but I'm trying to do my research for future rules changes. Can anybody help?


    Wow Auto Detect for Brushed motor just went and did the look up on it hummmmm
    Last edited by skye; 08-25-2013 at 07:38 PM.
    Anza Slash & a pile of Parts

  3. #3
    RC Turnbuckle Jr. Greatscott's Avatar
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    Page 26 tells you how to do it:

    http://traxxas.com/sites/default/fil...X_manual_1.pdf

    Don't really know how much better the VXL would be compared to a XL5, this is certainly engineering level stuff. But, it really is up to your local track, as if they allow it or not.
    Submarine Qualified, Chief Inducted, Navy Retired

  4. #4
    RC Turnbuckle Jr. billy-bones's Avatar
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    I've never run a brushed motor on the vxl-3 nor am I an electronics expert.
    However it would seem a motor can only achieve so many rpm's, no matter what quality the mosfet(metal-oxide-semicondutor feild-effect transistor) is.
    But again,I am no authority on the mater.
    There is a gentle man who's son runs a titan in a losi brushed,brush less esc rig, and it is noticeably faster,but I presumed this is a result of losi vs traxxas gearing.
    But now I'm going to do a bit more research.
    Built Ford Tuff With Chevy Stuff.

  5. #5
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    yes the VXL-3s can run Brushed Motors. It even has a sensor port for sensored BL Motors. Many people don't no this either.

    I once used the VXL-3s even for my trail rig with a 27 Turn and 55 Turn Brushed Motor for crawling.

    But one esc can never make a motor run faster then another

    At max throttle is just lets the entire current pass through to the motor, as if the batteries are plugged directly into the motor.

  6. #6
    RC Turnbuckle Jr. billy-bones's Avatar
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    At max throttle is just lets the entire current pass through to the motor, as if the batteries are plugged directly into the motor.
    If this statement is correct your saying that a velineon system that pulls about 65 amps will tolerate the full discharge of a 6500mah 65c capable lipo(422 amps), seems a little extreme.
    I've always been told the esc will limit the current to what ever the motor asks for, and only that.
    One wouldn't try running a 110 motor on 220.
    But then again volts and amps are two different things.

    Found this to be interesting.
    Apparently there can be a difference.
    When choosing MOSFETs, pay attention to the highest "source to drain"
    voltage (normal R/C equipment uses up to 20V, but because of inductive
    spikes and such you want at least 60V); maximal continuous current (as
    much as you can get! 10A is the least for a rather small motor); gate
    "on" voltage (only "logic level" FETs will turn fully on at the 5V or
    so at which a typical ESC operates - with other types you must play
    various voltage doubling tricks); and the "on" resistance: the lower
    the better, and you can decrease it by wiring several FETs in
    parallel.

    But this is still "on and off", not proportional. You want the motor
    to run slower or faster, not to hiccup on and off. So most ESC's take
    this small voltage (remember, the one that comes from the comparator),
    and chop it up into pieces -- they apply the control voltage to the
    MOSFET on and off but very fast: a thousand times a second or more.
    Depending on how high the control voltage is, they keep the MOSFET
    turned on for a shorter or longer period of time. The motor keeps
    turning (no motor can stop and start 1000 times a second), but it
    gets less or more power, so it turns more slowly or faster. This is
    exactly the way the dimmer in your living room works -- it sends
    power in short spurts to the bulb, but you don't see it blink, only
    get dimmer or brighter:

    +-+ +-+ +-+ +-----+ +-----+ +-----+
    | | | | | | | | | | | |
    | | | | | | | | | | | |
    --+ +-------+ +-------+ +-- --+ +---+ +---+ +--
    not much power coming in lots of power, motor turns fast

    For various rather obscure reasons this method of pulse driving
    power equipment is very good and efficient compared with the old
    fashioned "huge variable resistor which sinks loads of energy"; it
    makes motors and friends start with higher torque and eat up less
    power than they normally would.
    Last edited by billy-bones; 08-26-2013 at 09:01 AM.
    Built Ford Tuff With Chevy Stuff.

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