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  • Parma 500 motors

    Hi Dave,
    Man I have been reading almost all of you posts. Even though I do not
    race slot cars my R/C car is almost as small and utilize some slot parts.
    I am trying to get as much power production from my Parma motors as possible.
    I would love to build a car dyno for testing my motor & gearing set ups, it would be
    great. What would you need from me in the way of information to get me started?

    The 1/18 scale cars that I race use the STOCK Parma green endbell motors (non adjustable)
    timming, I believe they are the Parma 500 series. We use 4 AA batterys @ 4.8 - 5.2 Vdc
    for power and it is metered out through a electronic speed control. My application is Oval
    racing of which we have 20' straight aways and 8' turns. Since we use a standard gear
    ratio of 5.77 and rear tires of 1.29 dia. What could I do to these motors othe than changing
    arms out to derive more punch out of them?

    The armature has to be a stock wind and the gearing is the same for all cars.

    any help would be appreciated.

  • #2
    Mike

    I think the ideal chassis dyno would be constructed around a roller about 3 times the diameter of the rear tires. The housing would be just a simple box about one and a half times the size of the car.

    The roller would need to be perfectly true in run-out and balance to be able to run the car at full speed.

    If this isn’t possible, you could build one like mine using a drive train from a R/C car mounted under a flat plate.



    The most critical part of the dyno is the load brake, it will have to absorb all of the power created by the race car without burning up.

    The brake can be mechanical, hydraulic, or electrical. The electrical brake could be a R/C motor of greater power than the race car motor.

    An adjustable stop mounted to the running surface is needed to restrain the car and keep the rear wheels of the car on the center of the dyno roller. This adjustable stop is used for breaking in the car or other testing.



    To measure the power created at the drive wheels you will need a scale and a tachometer.

    The scale needs to be mounted in front of the car at a distance where an adjustable push bar can be inserted. The push bar has to be free of any force in any direction other than pushing against the scale.



    To calculate the rear wheel power of the car, the free running rpm (maximum rpm) of the rear wheels needs to be measured (off the dyno ).

    The car is then placed on the dyno and run at full speed, make sure the scale is operating properly, then apply the braking force until the drive wheels of the car are running at one half the maximum rpm. When the car is running at one half the maximum rpm, the load on the scale is read. This reading is used to calculate the maximum power.

    To calculate the maximum power, multiply the force ( scale reading) X ˝ maximum rpm, divided by 5250 = maximum power.

    With this amount of a load on an electric motor, the torque and max rpm will change very rapidly.

    Each time you test the car you will get some variations in the maximum power created by the car.

    From the amount of changes that you can make to your cars, it seems like you are limited to fine tuning. I am not sure if the chassis dyno will be capable of measuring these small changes because of the variation in measuring the maximum power of the car.

    Dave
    Last edited by davejr; 01-25-2009, 01:53 PM.

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    • #3
      Mike

      A few things can be done to the motor, clean and polish the commutator, adjust the brush tension, balance the armature, and shim the magnets closer to the armature. File and polish the armature plates to true them up, while spinning the armature in a Dremel. This will allow closer placement of the magnets.

      Shimming the magnets will increase the stall torque and lower the maximum rpm. This will also lower the maximum power, but with the gear restrictions, the higher torque might help.

      Dave

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      • #4
        One of the biggest things to do when working with stock parts, is to center the arm in the magnetic field, so, that when at rest, with no brushes/springs installed, that the armature touches neither the front or rear bearing. Once this is achieved, add spacers at both ends as needed so the arm doesn't magnetically "Lean" on either end of the can setup. This causes added internal motor friction. Not much, but, certainly enough to be a factor when added to all the other little drive train frictions.

        Also, when running stock moderate powered motors, you can make most of your power gains elsewhere in the chassis/drive train, that, don't actually include the motor itself. Remember, Friction is the Enemy of power.

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