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motor faster in reverse

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  • motor faster in reverse

    last night i noticed that one of my scx nascar motors (rx42B) is much faster in reverse. i had the car on my tire cleaning station, and running in the reverse directions the sound from the motor was noticeably smoother and it sounded like it was spinning faster as well. i don't know how much faster, but i'd guess about 10%.

    is there anything i can do to make it faster in the forward direction? it isn't a "dud" in the forward direction, but it would be a total ringer if i could get it to run forward like it does in reverse.

    i suppose i could hardwire the motor to the opposing braids and flip the axle so the crown is on the other side, but that would require taking a dremel to the chassis to accomodate the crown gear. i'd prefer to open the motor and make the corrections internally if at all possible.

  • #2
    Have you got another car you could flip the rear end to see if it was any faster one way or the other
    It could just be the way the brushes are worn makes it sound different when it spins the other way

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    • #3
      SCX motors are spec'd at zero-timing, but production variation ensures that some will be noticeably faster forward (advanced timing), or faster in reverse (retarded timing). The fix is to twist the commutator on the shaft just a little bit. The slots in the commutator should be exactly centered on the steel pole pieces. Of course, you have to accomplish the twist without breaking those fine winding-wires where they attach to the commutator plates.

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      • #4
        Motor faster in reverse

        Hi boopiejones, I just love my SCX motors! There are a few things you can do to fix your problem!

        Now and then you will get a set of brushes in a motor that are a bit softer than the norm! With normal running the soft brushes have worn down a bit and retarded the timing of your motor just a bit!
        If your carefully remove 1 brush, don't remove both at the same time, carefully taking note of the rotation of the brush, you will notice a difference between the leading and trailing edge of the brush! If you look at the brush side on, the leading edge will be shorter that the trailing edge! I have measured up to 3degrees retard in a motor like this!

        Here's the trick, simply rotate the brush 180 degrees and pop it back into the brush holder! If you have a good magnifier glass, you could also very slightly cut the very sharp edges of the brush away before you re-install! This will reduce if not remove arching between the brush and comm resulting in a cooler and electrically quieter running motor!

        Once you have done the first brush go ahead and do the second brush!

        Having done this you may have advanced the motor by as much as 3 degrees!

        I have 2 x RS42B motors that out-perform both Speed Pro and Double Rally motors! I set these babies aside for those special championship events, they are always sure winners!

        You need to check them more frequently than the rest of your SCX motors!

        I have been playing with "Open End-Bell" motors since 1961!

        Hope this helps

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        • #5
          that makes sense. i'll have to try flipping the brushes and possibly rounding off the edges.

          thanks for the info

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