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Parma ho controller

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  • #16
    Originally posted by Maddman View Post
    One thing I discovered when recently building a 90 Ohm Turbo controller is the fact that the three plates on the resistor barrel are much higher than the wire. This gives a very poor action and feel. Sanded down the three plates using a diamond sharpening stone. They are now only a few thousandths taller than the wires and it feels like butter. I can also sand the trigger button flat which gives a better contact patch than the stock button.
    Yep, not all resistors are created equal. There is definitely a lot to do on a Parma to get it feeling and working nicely. The plates always need to be fixed a bit.

    However, sanding the trigger button flat is the opposite of what you want to do with it. You want a nice, clean, convex (or even conical) surface on the button, so it only hits 1-2 resistor coils at a time. With a flat trigger button, you're potentially bridging three or more resistor coils, so the button is not getting the actual ohm value of that particular spot on the coil but a combination of multiple values, which could cause erratic behavior.
    Last edited by el gecko; 06-25-2019, 08:07 AM.


    • #17
      Let us agree to disagree. My DVM shows that when the button contacts three or more coils it gives the lowest ohm value. Its does not provide a combination of values. Rounding the button as you suggest increases wear on the resistor wire and can give a rough feel. Don't want either of those.


      • #18
        Generally, the increased wear and rougher feel are only a function of how tightly the button arm presses against the resistor or how misaligned it is. This can be tuned out of any controller by bending the button arm slightly and tweaking the pressure of the button. One of the things I have been doing to rehab old Parmas is to sand the buttons back to convex because most of them have been ruined by misalignment or over-pressured arms. The alignment of the resistor in the frame can have a huge effect too, even if everything is ship-shape with the button/arm.

        The other issue with sanding the buttons flat is that the outermost edges could catch more easily on the coils. With a slight convex shape, the button just glides right over. Conical is obviously overkill, I just mentioned it to aid the imagination.

        I'd be curious to see an actual scientific test on this--try a button with a "normal" convex shape, as well as one after you've sanded it flat, to see if there is actually any measurable improvement.

        Electrically, you say that the voltmeter is only seeing the ohm value of the lowest coil the button is currently contacting. Which I take to mean that every coil AFTER the contact is electrically "dead", so I just can't see how more connections to dead coils would make it work any better.