[Grandcheapskate]

As I have gotten better at cleaning and tuning pancake chassis, I now seem to be running into an issue. The cars are getting too responsive. Let me s'plain.

I am running on Mattel track using old Aurora 20-22v power packs. The controllers are 60 Ohm Russkits.

As I work on a (Aurora stock) pancake chassis, I can get them better and better. Eventually some of them get so responsive that the slightest touch on the controller gets them going near full speed. There is no slow speed, so negotiating 6" (and 9") curves is often a matter of letting off the trigger completely and then "jerking" the car around the turn.

So I am starting to wonder whether 20 volts is too high to run cars once you get them tuned up, or maybe the 60 ohm controller is not high enough at the 20 volt level. I know when the JL cars came out, the general advice was to get a 90 to 120 ohm controller, but these are not "hot" armatures or high performance parts. In almost all cases, it's the original 40+ year old parts with the standard gearing.

Opinions?

Thanks...Joe

 

[ParkRNDL]

As I understand it...

You probably DO want a 90 or 120 ohm controller. Cars with "hot" armatures don't like high-ohm controllers such as 90s or 120s. My original Aurora Tuff Ones with Mean Green armatures, which at around 6 ohms are considered "hot" compared to old Thunderjet arms at around 15 ohms, don't work well with a 90-ohm controller. Using that car with a high-ohm controller, I have to pull the trigger 2/3 to 3/4 of the way just to get the car rolling. At anything below half throttle, the car stalls and dies. So I have to do all my throttle modulation in that last 1/4 of the throttle travel. It's kinda like the problem you're having in reverse... pull the trigger slowly and get nothing, nothing, nothing... oh crap that's like full throttle. My cars with low ohm (read "hot") armatures do well with 45 or 60 ohm controllers.

I haven't played with my ohm meter in quite a while, but if I recall correctly, JL/AW arms ohm out significantly higher... is it 15? 18? Something like that... My smoothest AW/JL cars really benefit from the 90 or 120 ohm controllers. Lots of throttle modulation available starting at a steady crawl. I think the rule of thumb is that cars with higher ohm arms are smoother with higher ohm controllers...

Feel free to correct me if I'm wrong. Just throwing that out from what I think I know.

--rick

 

[cwbam]

Great job Rick
Lower Ohm cars need Lower Ohm controllers
and maybe try lower voltage (tri power pack)
http://www.scaleauto.com/parma/recommnd.htm
and test hookups so you are not connecting (+- poles ) wrong and getting an ON OFF feel (I wonder how I know that)

I know a sweet spot on my track is 45 ohm controllers @ 14 volts using Lifelike T chassis.

 

[beast1624]

Rick/'Bam: I think ya'll hit the nail n the head. If I try to use anything less than 90-120 ohm on either J/L or Aurora T-Jets I have the same problems Joe mentions...either 'on' or 'off'.

 

[brownie374]

Running at 18 volts helps alot

 

[smalltime]

As I have gotten better at cleaning and tuning pancake chassis, I now seem to be running into an issue. The cars are getting too responsive. Let me s'plain.

I am running on Mattel track using old Aurora 20-22v power packs. The controllers are 60 Ohm Russkits.

As I work on a (Aurora stock) pancake chassis, I can get them better and better. Eventually some of them get so responsive that the slightest touch on the controller gets them going near full speed. There is no slow speed, so negotiating 6" (and 9") curves is often a matter of letting off the trigger completely and then "jerking" the car around the turn.

So I am starting to wonder whether 20 volts is too high to run cars once you get them tuned up, or maybe the 60 ohm controller is not high enough at the 20 volt level. I know when the JL cars came out, the general advice was to get a 90 to 120 ohm controller, but these are not "hot" armatures or high performance parts. In almost all cases, it's the original 40+ year old parts with the standard gearing.

Opinions?

Thanks...Joe

+1 on the controller advice. Professor motor controller are also a good bet. But the real deal is the armature choice.

When I was racing Magna tractions, the mean greens were for the ovals, the road courses is where I broke out the stock magna traction arms or even a T-Jet arm. Stayin' in was paramount. That was allot easier with a detuned chassis.

 

[Grandcheapskate]

When I was racing Magna tractions, the mean greens were for the ovals, the road courses is where I broke out the stock magna traction arms or even a T-Jet arm. Stayin' in was paramount. That was allot easier with a detuned chassis.

Hey guys, thanks for the input. I had figured my problem was the combination of a 60 ohm controller, 20 volt power source and high ohm armature, and you guys pretty much confirmed that. I may try to lower the power using the Harbor Freight Router Speed Control and see how the cars react. And maybe try to find replacement resistors.

Smalltime - are you saying above that you purposely "detune" some pancake cars so you can control them better, or just a general statement that a detuned car is easier to control?

Here's a question I always wanted to ask. I know there is a relationship between the resistance of the controller and the ohmage of the armature, but isn't there also a relationship between the voltage output of your power source and the resistance of your controller for a given ohm armature? For example, would my 60 ohm controllers be a better fit if I were running at say 16-18 volts? It seems to me that the resistance required in your controller would be somewhat dependant on the voltage output of your power source. Right?

Thanks...Joe

 

[dlw]

Yes, 14-16 volts will allow you good control with a 60ohm controller.

 

[smalltime]

Smalltime - are you saying above that you purposely "detune" some pancake cars so you can control them better, or just a general statement that a detuned car is easier to control?

Yes, I detuned regularly.

I tuned for throttle response. I hate an all or nothing feel, and worked hard to get away from it.

There are numerous things you can do: (in order)

#1 get the shoes right first. If you have too little tension, you get blackening, too much and you walk out.

#2 If your controller is set in stone, it's time to change arms. If you have a 60 ohm controller, you will probably need a t-jet arm in the thing to get thru the tight stuff.

#3 set your brush spring tension relative to the coast in your chassis. If you have a ton of coast, then tighten up the spring pressure, if there's not enough coast, lighten up a little.

Hope this helps.

 

[slotking]

this is why the 90 to 120ohm controllers are selling!

best bet, is the BRP stage III (compared to other electronic controllers)
low cost but lets you run all the cars.

 

[Bill Hall]

Take a baby step

Joe,

60 ohms just aint gonna cut it for t-jet and t-jet modified.

Dump the toy/set controllers. You wont regret it! Get yourself a Parma econo with a 90 resistor fer cheap so you can actually appreciate what a properly rated controller has to offer. It's night and day.

Once yer convinced and wanna upgrade to an electronic cuisine art the econos are easy to get rid of. I'll take it it fer the kids. :thumbsup:

 

[slotking]

I went to the 90ohm parma and my cars are still a little to touchy with it!

That's why I suggested the BRP stage III, it will fit any pancake car you are driving as well as some inlines.

I do own 1, but had to borrow them a few times!, Will get 1 as soon as i can

 

[mikeponiatowski]

BRP 120 Ohm Resistors

I went to the 90ohm parma and my cars are still a little to touchy with it!

That's why I suggested the BRP stage III, it will fit any pancake car you are driving as well as some inlines.

I do own 1, but had to borrow them a few times!, Will get 1 as soon as i can

BRP also has 120 ohm resistors for Parma Controllers. They are called "Nitro" Resistors, apparently they are wound differenctly from stock resistors for smoother action. They work great for the touchiest cars and cost $20.00 each.

 

[slotking]

do they fit the parma 90ohm?

I have to debate the fix ohm controller vs the I can fine tune the ohms for almost anything BRP III??

 

[beast1624]

do they fit the parma 90ohm?

I have to debate the fix ohm controller vs the I can fine tune the ohms for almost anything BRP III??

I can verify that they do. Had an old Parma Econo 45 with a busted resistor and bought one of Jerry's 120's. Been using it for the last year and love it. Just bolted right in. Exact same size as the Econo and Pluss resistors that Parma uses.

 

[beast1624]

...then again that has gotten me to thinking if a $20 resistor can transform a Parma Econo, how much better would one of his Stage II or Stage III controlers be?

 

[AfxToo]

Here's a question I always wanted to ask. I know there is a relationship between the resistance of the controller and the ohmage of the armature, but isn't there also a relationship between the voltage output of your power source and the resistance of your controller for a given ohm armature? For example, would my 60 ohm controllers be a better fit if I were running at say 16-18 volts? It seems to me that the resistance required in your controller would be somewhat dependant on the voltage output of your power source. Right?

<edited: try to answer the question more directly>

The question is about the relationship between 1) power supply voltage, 2) controller resistor size, and 3) armature winding resistance.

1) First, the power supply voltage directly effects the maximum RPM the motor can run at. A 24V power supply will allow you to achieve higher RPM than an 18V power supply regardless of the controller or the armature winding resistance. Motor speed is directly proportional to the applied voltage and motor torque is directly proportional to motor current.

2) The controller resistor (rheostat) is simply a voltage divider. At one extreme it provides 0V to the motor and at the other extreme it provides the full power supply voltage to the motor. As you move the controller wiper the voltage applied to the motor varies over this zero to maximum voltage range. If all the controller was doing is supplying a variable voltage across the arc of the resistor wiper arm then all resistors would have the same exact behavior. The voltage at the 50% point on a 45 ohm resistor would be the same as the voltage at the 50% point on a 90 ohm resistor. With zero load on the controller this is the case.

3) Where the motor winding resistance and all other things like traction magnets come into play is on the load side. With a load attached to the controller the differences between the 45 ohm resistor and the 90 ohm resistor come into play. The resistor/rheostat is still a voltage divider but the difference is that the 45 ohm resistor will be able to supply twice as much current to the motor at any given point in the wiper arc of the resistor other than at minimum and maximum throttle where they are both equal. Since motor current determines motor torque and a motor with lower winding resistance requires more current to start the point in the controller arc where the motor starts spinning will be different between the 45 ohm and 90 ohm resistors.

The end result is that the usable arc of control for a resistor based controller is dependent on the point in the controller wiper movement that the motor starts turning, which in turn depends on the current requirements of the car. While DC motors are speed controlled through voltage the variable factor between resistor controllers of different sizes, say 45 ohm versus 90 ohm, is one of controlling the current availability at a given point in the controller's arc of motion.

Finally, this all assumes the power supply can supply enough current to start the motor. The controller can only make available the current provided by the power supply.

 

[Hornet]

Joe,what kind of controller hook-ups do you use.
If you've converted to the standard 3 wire hook-up
You can experiment with an old school homebuilt choke.
The real old school chokes were nothing more then a length of solid core light duty wire (18 to 20G usually) wrapped around a piece of pipe,or even a soda can.
This you just hook in line with the power out (black wire on most 3 wire tracks) from your controller.
Where you hook up on the coiled wire determines the amount of extra resistance.
My old track used kit bashed Tyco resistors as chokes,and you could just alligator clip onto the resistor,where you wanted.
It's not perfect,but it's cheap,and usually something you can build with parts on hand.
Rick

 

[alpink]

AFXToo, what category does that Jerry Shmoyer stage II and stage III controllers fall into, please.
thank you, al

 

[slotcarman12078]

One other suggestion Joe. Check the ohms of those super touchy armed chassis. It sounds like a low ohm arm to me. I have a few in the 6 ohm range that are plenty fast (read too fast) with barely a click of a 90 ohm Parma controller.