Digital controllers are adjustable emulating a range of "ohms".
Have a look at greg gaub's "mister flippant" youtube explainations of the slot it scp to get an idea of the possibilities
AlanW

 

Digital controllers are adjustable emulating a range of "ohms".
Have a look at greg gaub's "mister flippant" youtube explainations of the slot it scp to get an idea of the possibilities
AlanW

He had one, and also has other adjustable controllers. For some reason, he wants a fixed ohm controller that makes his car behave differently than his 25Ohm controller, and does't know which way to go. We talked about this privately, but my understanding of ohms is incomplete at best.

One thing I realize I don't understand is whether the ohm resistor is choking amps, or volts. If it's choking amps, then that would explain why a high torque motor (as per his example) might need a bit more trigger to get going, but then go quite quickly. He wants it to start moving sooner, but at a lower speed.

 

Ohm’s Law:

V = I/R

where V = volts, I = current in amps and R = resistance in ohms.

 

Ohm’s Law:
V = I/R
where V = volts, I = current in amps and R = resistance in ohms.

I was just trucking through this thread, saw the equation, hunted through my grey cells back to O-Level physics 55 years ago and thought it was wrong. I checked it to be sure and I was right - it's actually

V = IR

This may explain some of the worrying in this thread!

Andy

 

But, that says that the same input voltage through the same controller would deliver higher volts to the car if the power supply simply has more amps. If I toss a car battery on the floor as my power supply, which is effectively unlimited amps, shouldn't the car take off like a rocket no matter what the Ohms are? Clearly, I'm missing something important.

 

Most set resistor controllers will be between 30 and 60 ohms with the average being 45 ohms. At 1% throttle the resistance will be 45% in this case and at full throttle 0%. With the correct ohm controller the car will start to move with little throttle and almost reach top speed just before full throttle. If the car reaches top speed at part throttle the the ohms are to low and if the car needs quite a bit of throttle to start then it is to high. Although not completely accurate try reducing or increasing the ohms but the throttle percentage needed or not needed.

 

The other way is R=V/I

In Marks formula the amps can be considered the fixed value as this is dictated by the motor and as the ohms change so will the available voltage.

 

In Charles's case lower ohms are required. Finding the correct value is where the problem comes with resistance controllers. Using my guide above I would say if the car starts at 1/4 throttle try 20 ohms, 1/2 try 15 or 10 ohms, 3/4 try 5 ohm if almost full throttle is needed then maybe 2.5 ohms.

It may still be a trade off between start and full speed but I'd be looking for a smooth transition at full speed.

One reason why controllers with changeable resistors were popular.

 

I agree with Beardy56. If half throttle is required to gently the car moving on 25 ohms then a lower value is required.

All my NSR and Scaleauto cars perform well with a 35 ohm controller but that is at 13.8 volts. I see you are running 9 to 10 volts which is unknown territory for me and clearly has a big impact on these higher performance motors.

Go low!

 

Greg this is a can of worms (edited to fix an autocorrect thing)

To get the car moving with less throw, a lower resistance is required.
But lower resistance means less control through the throttle sweep.
In the end resistor controllers behave differently depending on the load which explains why they behave differently with different motors.
It's possible to build a resistor controller that felt right for a motor but it would not feel right for any other motor type.

I can imagine setting up a rheostat instead of the hand controller, twisting it 'till the car just started to move, then disconnecting it And measuring the resistance. That would give you the ohms required to to get the car moving as soon as the throttle is touched for that motor. So if the test showed that a (for example) 21.7ohm controller was "right", a controller would have to be built to that spec.

The better control through the trigger sweep would have to be achieved by changing the resistors in the controller, using higher then lower ohms (or vice versa) in the throw,
A DS type controller with individual resistors (as opposed to a wire wound ) could emulate "curve mode"

But why do this when a good digital controller can adjust this in the fly for every car you put on the track?
For all of the reasons above I abandoned my old throttle set (15ohm, 25 ohm, 35 ohm and 50 ohm) and bought an scp2.
AlanW

 

To get the car moving with less throw, a lower resistance is required.
But lower resistance means less control through the throttle sweep.

This is my concern. I only lost a few bucks selling the 25 OHM guys so I'm not against a guess but I'd prefer it to be educated.

But why do this when a good digital controller can adjust this in the fly for every car you put on the track?

Two fixed OHMs controllers are roughly 1/2 the cost of one of my Difalco controllers. And it seems overkill to have four sitting around. Plus beyond logic I just like the aspect... plug it in and go. Back to the old school days I remember along with a "forced" different experience. I'm not trying to beat anyone rather simply enjoy the session.

 

If the controllers are just for your fun then just buy one probably at 15 ohm to see how it goes, you can then decide if you need another 15 ohm or something lower.

If you not in a rush then wait until a good value older controller becomes available.

Nearly all my resistor controllers are vintage. Most came with vintage sets and were 45 ohm with the odd 30 ohm. These worked with most of my cars but as you've found were almost on/off switches with some cars. I finally found a 10 ohm vintage controller at a very good price. I only use this occasionally, most of my driving is done at 10 volts with a 30 ohm controller same as the vintage one but made around the turn of the century.Most of my cars including my Slot.It NSR, Scaleauto and other modern performance bands work ok with this controller. Some of my vintage cars require the 10 ohm but not that many. Some of my older set cars require a 60/70 ohm controller and again I have vintage ones and now another bargain buy turn of the century made one.

You can see why adjustable controller became popular as you can have every controller you want in your hand at once.

With the old big commercial circuits used for racing you would probably have be looking at using a 2.5 ohm at most, possible even as low as 0.5 ohm. Back in the '70s at the track I went to my 2.5 ohm was a high resistance controller. By then I was behind the times as transistors were already in wide use.

 

It looks like many people do not understand how a resistor controller does what it does. The voltage drop across a resistor depends on the ohm value of the resistor and the amps that the car wants to draw. You also need to remember that you will be dropping the power supply voltage. If you run your track at 18 volts and the average draw is 0.25 amps (a common value for inline magnet cars with a 6 ohm armature) the car would see 18 - 11.25 = 6.75 volts at the beginning of the pull with a 45 ohm controller. That is the theory, but most people have no idea how many amps their cars are using.
If you need to pull the trigger too far just to get the car moving, you need a lower ohm value controller and if the car wants to go too fast at the beginning of the trigger pull you need a higher ohm value controller.

 

Many folks find it easier to understand electricity by using a water analogy.

Think of the power supply as a pump. In our hobby that pump, ideally, supplies a constant pressure -- analogous to voltage. How much water flows out of the pump -- analogous to amps -- is determined by what restrictions -- analogous to ohms -- there are downstream.

If you vary how much the flow is restricted the flow increases or decreases. Again the pump output pressure -- volts -- is constant. Double the resistance -- ohms -- the flow is cut in half. Cut the resistance in half the flow -- amps -- doubles.

Now one more concept -- flow times pressure is power. Once more, pressure is constant. Very little flow -- amps -- due to high restriction -- ohms -- means very little power. Lots of flow due to low restriction means lots of power.

Your controller provides variable restriction. The motor also provides restriction, but that gets more complicated because some of its restriction varies with speed.

I won't take this any deeper. If you want to better understand electricity, well, some people make a whole career out of it. I've given you a very, very basic start.

 

Easy question, easy answer.

If you have to move the controller trigger half way before the car starts to move then the controller needs to be lower Ohms.

If the car sets off like a rocket as soon as the trigger is moved then the controller needs to be higher Ohms.

This does mean that a number of different controllers need to be bought and lugged around though.

 

If you have to move the controller trigger half way before the car starts to move then the controller needs to be lower Ohms.

If the car sets off like a rocket as soon as the trigger is moved then the controller needs to be higher Ohms.

This is my issue. As far as I remember it took roughly half throttle for the car to move (suggesting a lower OHMs) and as soon as it moved it took off like a rocket (suggesting a higher OHM)... which has me believing I can't get the car to take off sooner without turning it into an on/off switch. Now 25 OHM lap time wise was very good. Again I'm trying to simply detune the car a bit... a slower response across the entire throttle range. Sounds like two Difalco controllers without Traction Control (DD301) is the answer. I'll be sure to tell guests to bring theirs.

 

What you're wanting is something as cheap as a fixed ohm but as versatile as a DD301.
Good luck!

 

What you're wanting is something as cheap as a fixed ohm but as versatile as a DD301.
Good luck!

Sort of... to some extent price doesn't matter. Not having the ability to tweak the controller is appealing and I'm happy with zero versatile as long as the one way it performs is close to what I want! Maybe I could adjust the DD301 and then pull off the knobs... that just might work. Only problem is I would have to ensure they perform differently than my DD302s or I'd be back to square one. The same experience...

 

What is the difference between using an adjustable controller, adjusting it to suit the car and your driving style, or using a fixed ohm controller chosen from a variety available, in order to suit that car and your driving style?

 

Good question beyond the obvious more than likely cost. For me there is some value in knowing I can't adjust the controller. As silly as it sounds... pick it up and use it which goes back to old school memories... plus there is never the should I try this or that setting and to a minor degree if I try this or that my previous track times will be null and void. And since I'm not chasing speed and want a different experience than the Difalco they would serve a simple purpose. As such something as "fancy" as a Difalco feels overkill and out of place - to the point of being wasteful. At the same time I'd want something that I enjoyed using. The 25 OHM controllers were very nice, enjoyable and perfect if I was only trying to turn fast laps - I guessed rather well. They just didn't offer the "casual" lap I have been migrating into of late. By definition I'm not looking for something to duplicate the Difalco experience as when I pick it up I want to have to drive differently. Something simple and fixed I have to adjust to, not it adjusting to me or my car.

I understand it doesn't make sense. In my head there is a proper tool for every job and this job doesn't call for something so complex.

 

You claim you get no response out of a car until the controller is halfway depressed, but then it takes off like a rocket?

Sounds to me like your issue isn't the wrong ohm controller. I'd suspect something is wrong with the car.

Or does this happen with all your cars? In that case its the controller.

I'm wondering if the wiper on your controller isn't actually making contact with the resistor block until it is halfway depressed. That would explain the all-or-nothing response.

I'd recommend opening up your controller and manually pushing the wiper up against the resistor block, wiping up and back to see how the car responds. My guess is the wiper needs to be tweaked so it makes good contact throughout its entire sweep.

If the wiper is the issue you also shouldn't have brakes. That can be easily tested. Hold the rear of the car off the track and give it full power. Then let go of the trigger. The rear tires should stop spinning almost instantly. Now try maintaining full power and lift the car off the track. There should be noticeably more 'coast'.

If you see no difference then you don't have brakes. Another indication that the wiper is not making contact.

In very rare cases the resistor block itself may be damaged. No fix for that except to replace it.

 

Or does this happen with all your cars? In that case its the controller.

Yes it did.

I'm wondering if the wiper on your controller isn't actually making contact with the resistor block until it is halfway depressed.

Acted the same way on two brand new controllers and both wipers were inspected.

My pure guess is at the low voltage (9.5 - 10) it takes a lot for them to get started and there isn't much "left" afterward.

 

What cars are they?

As I've said I'm running at 10 volts on my Policar layout with a 45 ohm controller and get good response from nearly all my modern cars. My track is fairly small with no long straights, longest is only 5 long, and if I didn't have good control it would be undriveable. In standard form, out the box setup, I run Slot.It, NSR, Scaleauto, Black Arrow, SRC, Team Slot, Avant Slot and others with no real lag and fairly smooth control across the full resistor range. A few motors in the 35k and above range need a lower value controller, but that's a different story. There is the odd motor need needs a few volts to get running but most of these are rated for more than 12 volts and are fairly high torque.

If the controller ohms are to high then the car should only start after some amount of throttle has been applied but then will work as normal to full throttle, just with short stroke. If the ohms are to low the car will start very quickly and reach maximum speed before full throttle is reached, but again you should have control in the limited range. You shouldn't be getting both effects at the same time, so something isn't right. Is the power supply really giving 9.5-10 volts? If you can adjust the amps are they set high enough? If you place the cat on the track and with the controller at full throttle starting from zero volts when does the car start?

 

What cars are they?

As I've said I'm running at 10 volts on my Policar layout with a 45 ohm controller and get good response from nearly all my modern cars. My track is fairly small with no long straights, longest is only 5 long, and if I didn't have good control it would be undriveable.

NSR and Scaleauto. The controllers performed great and were actually faster (lap times) than my tweaked Difalco controllers. Simply looking to increase the range of acceleration and reduce braking.

If the controller ohms are to high then the car should only start after some amount of throttle has been applied but then will work as normal to full throttle, just with short stroke.

I think that pretty well describes it.

Is the power supply really giving 9.5-10 volts? If you can adjust the amps are they set high enough? If you place the cat on the track and with the controller at full throttle starting from zero volts when does the car start?

I have no way of knowing if the voltage is accurate beyond "common sense" as to how it performs and it's set for 10 amps. The controllers are long gone... I remember one time I placed the car on the track and slowly pulled the trigger and it appeared to be well past halfway before the car moved and when it did it shot off. Hard to tell actually how close to full speed since I had to let up before it flew off the track.

 

Do you have traction magnets in your cars? They could contribute to your all-or-nothing response. Most especially if they have warped the chassis.

There are power supplies that limit the current as well as regulate the voltage. I'm not sure how that would affect things. Could get complicated.

You probably should check things out using a different power supply. Possibly even a battery. A big, dumb, wet-cell battery would be best if you want rock-solid voltage output and ampacity out the wazoo. But it ain't no plaything -- heavy and arc-welder powerful.

 

Do you have traction magnets in your cars?

Magnet free.

You probably should check things out using a different power supply.

It has performed perfectly with a dozen different controllers and endless cars.

 

No wonder I failed Physics! 😬

Apologies 🙏

 

385148[/ATTACH]Coides, post: 2655112, member: 1291"]
I was just trucking through this thread, saw the equation, hunted through my grey cells back to O-Level physics 55 years ago and thought it was wrong. I checked it to be sure and I was right - it's actually

V = IR

This may explain some of the worrying in this thread!

Andy

 

Simply looking to increase the range of acceleration and reduce braking.

With a resistor only controller you will not be able to do anything about the braking as this will be purely down to each motor and the back voltage it generates. Any motor difference you can dial out with an adjustable controller will be only too apparent with a plain resistor controller. One of the reasons people started to add adjustable brakes to their controllers.

The controllers are long gone...

I did read above that you had sold them but I thought a few ideas for next time might help 😁

When you have your next go it might pay to try a different make of controller. The only thing I can really thing off that would explain your experience is if the controllers ohms where to high and the resistor had a variable winding with most of the resistance at the beginning. You can normally tell by looking at the resistor winding, if the spacing opens up across the winding's or at some point on the resistor then it's not what you're looking for or need.

 

I guess the takeaway is... I'm out of luck. The 25 OHM controllers worked great for lap times. And if I want simple and save a few bucks I'll probably go back to 25 OHM. Who knows how less or more will perform. In reality I can adjust my Diflaco controllers to perform differently so it's more of a mindset thing outside of having four controllers for a few occasions. Which certainly wouldn't require tweaking... rather endless putting the cars back on the track. Come to think of it I have different Networks for my Difalco controllers as I "upgraded" to more sensitive ones so if I get two Difalco DD301s they won't be the same as my DD302s anyway.

 

Could the resistor in your 25 ohm controller be shunted with a fixed 37 (or thereabouts) resistor to give you a 15 ohm approx. unit. Simple and easily changed to alter the resulting value?

 

Hi Charles, I think the best explanation was from RichD. I believe what you are seeing is due to the lower track voltage and potentially motors needing a bit more to get started. Think of the resistor as a flow restrictor and the motor struggling to get going until you have enough flow then wham takes off. I see a very similar occurrence one 1 car SCX which almost pulls 75% before it going leaving you with only top 25% of the wiper to run. I hate it