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  • slowpok
    started a topic Parma ho controller

    Parma ho controller

    I know it's out here somewhere, I'm looking for recommend ohm rating on ho parma controller ?
    I run stock life like, afx,and wizard,viper cars .No hot mods yet

  • el gecko
    replied
    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.

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  • Maddman
    replied
    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.

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  • el gecko
    replied
    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.

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  • Maddman
    replied
    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.

    Leave a comment:


  • el gecko
    replied
    Originally posted by RichD View Post
    Have you compared regular straight 120, 90 and 60 ohm controllers with the switchable one?
    Yes, and I should revise my previous statement: The DS actually has LESS fine control than a true resistor controller, not more.

    With the DS, the contact patches on the wiper board are around 4mm wide, and there's only like 15-20 of them (sorry, don't have it right in front of me to confirm). This is because each "segment" of the wiper board has a specific ohm value determined by the electronics in the controller, and to have as many "steps" as a resistor would mean the controller head would have to be a LOT bigger and more complex.

    On a normal resistor controller, each coil of the resistor wire is around 1mm wide, which means there are easily twice the amount of steps, giving the resistor controller much more granular control than the DS, which is why I keep my Parmas around still (my 90ohm with custom adjustable brakes will always be one of my favorites).

    The switchable nature of the DS still makes it more versatile than a resistor, and when I'm just out to run some fun laps (not pushing the ragged edge) it's perfect for any old car I should decide to plop on the track. But when I get down in the nitty gritty and really start pushing a chassis to the limit (or driving with a particular style, or racing), it's Parma (and resistors) all the way.
    Last edited by el gecko; 06-24-2019, 08:18 AM.

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  • RichD
    replied
    Have you compared regular straight 120, 90 and 60 ohm controllers with the switchable one?

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  • Wicker Bill
    replied
    I, too, have the DS 120/90/60 controllers. The only thing semi-negative Iíve found is I have to clean the contacts off occasionally, but thatís no big deal. Handles come in various colors so you can match to lane colors.

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  • tbuck
    replied
    Originally posted by el gecko View Post
    Tim, I have one of the DS 120/90/60 switchables and it's been solid so far, going on 2 years I think now. The power delivery across the trigger pull is a bit more "progressive" than a Parma, there seems to be less of a jolt at the beginning of the trigger travel, so low speed control is very good, especially with the higher ohm settings. Very easy to drive the new can motor Mega G cars on 120ohms, even at 20+ volts.

    I use the 90ohm setting for HP7s and Tycopros (works good for Tjets/Magnatraction too), and flip it to 60 for just about all my other magnet cars, all at 19.5V. I still prefer my good old Parma 45 resistor controller for the really fast modified cars, but the DS can handle such a wide range that it's become my go-to controller for the vast majority of my track time these days.
    Great information...Thanks bunches el gecko!!!!

    Leave a comment:


  • el gecko
    replied
    Tim, I have one of the DS 120/90/60 switchables and it's been solid so far, going on 2 years I think now. The power delivery across the trigger pull is a bit more "progressive" than a Parma, there seems to be less of a jolt at the beginning of the trigger travel, so low speed control is very good, especially with the higher ohm settings. Very easy to drive the new can motor Mega G cars on 120ohms, even at 20+ volts.

    I use the 90ohm setting for HP7s and Tycopros (works good for Tjets/Magnatraction too), and flip it to 60 for just about all my other magnet cars, all at 19.5V. I still prefer my good old Parma 45 resistor controller for the really fast modified cars, but the DS can handle such a wide range that it's become my go-to controller for the vast majority of my track time these days.

    Leave a comment:


  • RichD
    replied
    In order to have a variable resistor controller you need to use several resistors. One scheme is to have one regular resistor that the wiper makes contact with and with a fixed resistor wired in parallel with that. You could also use two fixed resistors with a switch to select one or the other or take both of the fixed resistors out of the circuit. with this method the wiped resistor has the highest ohm value, switching in the parallel resistors can only lower the effective ohm value. Another method puts the fixed resistor across the wiper and the low end of the wiped resistor.



    With either method you end up with 60 ohms using the resistors that I show, 60 ohms is as low as you can go with the second method, adding a resistor will make the effective resistance higher. Neither method will give you the same response as a regular 60 ohm controller. Blame it on Ohms Law. A controller with a parallel resistor will only act like the effective value at the beginning of the trigger pull, as you pull the trigger further the controller acts more like the wiped resistor alone, so the controller will have a non-linear response. The effect gets more pronounced the more you try to lower the effective ohm value.
    Years ago I did a controller using the first scheme, only instead of a fixed resistor I used a rheostat with a switch to take that out of the circuit.



    The wiped resistor is 45 ohms and the rheostat is 500 ohms. I took readings and determined where the rheostat needed to be set to get 40, 38, 33 and 25 ohms. I did not like the way that controller felt and it is normally used as a straight 45 ohm controller with the rheostat bypassed. If I remember correctly the second method may work somewhat better than the first one. In any case there could be an advantage to using a controller that has a fast initial response then transitions to a slower response. If you do get a variable controller let us know how you like it. I have never seen a report on the DS variable controller.
    Last edited by RichD; 06-19-2019, 08:06 AM.

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  • tbuck
    replied
    This place has several models of DS controllers that are very similar to the Parmas. http://njhobby.net/home/online-catalog/controllers/
    They also have 120/90/60 ohm and 35/45/55 ohm switchable DS controllers. I purchased the 120/90/60 ohm because I currently have AFX Meg G+ cars, but also want to be able to run other cars. I also have a variable voltage power supply so I should be able to find the right combination for a lot of cars.
    I have not yet been able to test the controllers because my track build has been delayed. Has anyone else tried them and have comments for myself and the OP?

    Thanks,
    Tim

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  • RichD
    replied
    One problem that you get if you are using too high of an ohm value controller with a car that really needs a low ohm one is that you have to pull the trigger part way before the car will even start to move. That means that the useful trigger travel will be reduced and the car might be more difficult to control. Years ago when i started to run modern high downforce cars I was using old 85 ohm Atlas controllers. With Life-Like, Tyco 440X-2s and Tomy Super G+ cars I had that problem, so I bought some Parma 45 ohm controllers. Then I started to upgrade my cars and also buy aftermarket cars like Wizzard Patriots and BSRT G3s, so I needed 35 and even 25 ohm controllers for those. Before I knew it I had 25, 35, 45, 60 and 90 ohm controllers.

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  • ScooterMcCoy
    replied
    Good point Rich, a 60 is a good compromise. For the stock Tyco, LifeLIke, AFX, etc. they might feel a touch sluggish on the acceleration curve with the 60 and Thunderjets that like a higher ohm controller will feel a little "touchy" accelerating too quick and not having as much low end throttle. You can learn to compensate and get used to it though.

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  • RichD
    replied
    Most people would use a 90 ohm controller with T-Jet type cars. Parma does not sell a 120 ohm controller, One Stop Slot Shop has straight 100 ohm and 120 ohm Nitro resistors with a taper. If your track voltage is not too high you can use a 90 ohm controller with an AFX Mega G+ car. As you can see many different ohm value controllers are used with HO cars. If you only want to buy a single controller you could shoot for a compromise value like 60 ohms, if you get too far away from the ideal resistance the car may be more difficult to control. People that race tend to be fussy about that and often use an adjustable electronic controller rather than several resistor based controllers.

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