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Controllers and “ohm” lesson needed


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#1 JewelryMonk

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Posted 25 October 2018 - 09:06 AM

Hey everyone,
I am fairly new to this obsession of slot car madness and need a lesson on controllers, to be more specific:
What is the difference in controller ohms and how do the different ohm controllers affect the car, for example, 60, 90, 120. How do the different resistors apply? ( by the way, I race tjets and AFX)
Thanks in advance, also I am a visual thinker, so illustrations will help.
Doug
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#2 garyvmachines

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Posted 25 October 2018 - 12:18 PM

Hi Doug

 

We Love Newbees hear .....!!

 

I am not an electrician , I am a machinist..... so I wont get all tecky on you.

The guys that run on commercial tracks ( BIG TRACKS ) use 1.5 ohm or 2 ohm controllers.

If the track is tight & twisty they use 4 ohm .........On these ( Big Tracks) you don't need much throttle response ....

All on or all off.

 On HO you need lots of throttle response to stay on...... So bigger #### resistor .

The 120 will give you a softer gas peddle than the 60 or 90.

 

GAV        


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#3 Randy Tragni

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Posted 25 October 2018 - 01:32 PM

For HO you can buy one, great controller such as DiFalco, Lucky Bob or OS3. Make sure it has a choke, besides sensitivity and brake.

If you want to go cheaper you can go with multiple resistive types such as Parma. It is often cheaper to buy one great controller rather than carry around 3 or 4 resistive types but this is a matter of personal taste.

Typically:

Pro 10 and faster cars (built up Slotech, Viper, Wizzard, BSRT) will work best with 5-10 ohm control.

Pro 4 (stock Viper, BSRT, Wizzard) will work with 15-30 ohms

Mega G, SRT, Lifelike and Tyco work with 30-45 ohms.

T-Jets work with 60-90 ohms (many like to add a secondary resistor to provide slight fine adjustment).

Mega G+ need 120 ohms for effective control.

As you can see, it might be cheaper to buy a great controller depending on how many of these you plan to race.

In our club (SJSCC) most are using OS3 and DiFalco.


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#4 Ramcatlarry

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Posted 25 October 2018 - 02:56 PM

controller 101:

 

Slot cars use three very different electrical circuits to get the same job done - namely to get the car to go slow, quick, and stop.  The mid-range speed is the drivability part.  A door bell switch does meet the basic goal except fot the drivability part.

 

1) Resistor controllers.  Cheapest to make and has a wide range of resistor  OHM values to find the drivability part.  A resistor controls the car by varying the amperage to the car.  The voltage is constant.  The Wattage value defines how much overall LOAD the controller can handle.  OHMs Law:  volts X amps = wattage.  An HO car usually runs on 18 VDC and less than 2 amps, so a 36 (minimum) wattage controller  resistor is fine.  This is what a Parma two barrel Turbo contrioller is designed for.  Many lighter duty T-jets use less current and therefore the single barrel 25 watt Sebring type controller is also fine.  The ohm value comes back to drivability.  The same car will drive differently on a tight twisty track than on a long straights and wide corner track with only one controller resistor value.  Every track is somewhat unique and testing is the only sure proof.  If the controller overheats, it is due to too low a wattage and driving with the throttle in the mid range too much.

 

2) Transistor Controllers.  Polarity sensitive (has to match the track wiring) , actually uses a resistor group as part of the wiper band, but all of the amperage goes through the power transistor to make the whole controller more robust AND adjustable to different driving conditions.  Many are fitted with other gadget circuits like choke and coast features for more advanced race cars and tracks

 

3) Diode Controllers.  Polarity sensitive also.  Instead of resistors to control the amperage, these controllers use diodes to STEP Voltage to the track.  Several brands have been made over the past 20 years, with Prof Motor most common to HO and other home type racing.  Look for units that have THREE rows of diodes in order to work best with the 18 volt systems.  Low voltage is considered 12-13 volts and hve only two rows of diodes


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Larry D. Kelley, MA
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#5 JewelryMonk

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Posted 27 October 2018 - 06:18 PM

Thanks everyone for the info.

So, is the difference between a 60 ohm and a 120 ohm the sensitivity and drivability of the controller in the middle, and Wide open is the same voltage?

I had a couple of lower ohm controllers and they were like a toggle switch for my t-jets, so I got rid of them.

Doug


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#6 Eddie Fleming

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Posted 27 October 2018 - 06:30 PM

All controllers are the same at full throttle, In theory.

 

Full throttle is 0 ohms.

 

Higher ohms makes the lowest possible speed lower and therefore makes it easier to control touchy cars. 

 

So you are looking for a ohm value just high enough to give you a slow enough speed that you can drive the car effectively.

 

Each scale car and type track may require a different ohm value to be driven well.

 

Electronic controllers have adjusts to make them usable on a verity of tracks and cars, but they may not cover every possible combination of car and track.


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#7 Randy Tragni

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Posted 30 October 2018 - 02:53 PM

"Electronic controllers have adjusts to make them usable on a verity of tracks and cars, but they may not cover every possible combination of car and track."

 

As I mentioned in an earlier post, OS3 and DiFalco controllers make up the majority of controllers used in our club. I have yet to see anyone pull out a car that could not be controlled with one of these controllers.

If that were the case, DiFalco makes different resistor packs that can be insert to specifically profile car and track requirements (different mid-band, etc.). 


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#8 Ramcatlarry

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Posted 31 October 2018 - 10:45 PM

I use my difalco 30 band for most 1/24 races and have the plug-ins from 78 to 180 ohms - and use them all on different tracks and classes.  You should be able to make the racecar creep slowly at the first band off of brakes.The 'standard' plug-in is 148 ohms.  For HO, the board could be closer to 180 ohm for the standard.  Get one or two either higher or lower for different tracks


Larry D. Kelley, MA
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#9 Paul Lindewall

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Posted 09 November 2018 - 08:34 PM

For HO you can buy one, great controller such as DiFalco, Lucky Bob or OS3. Make sure it has a choke, besides sensitivity and brake.

If you want to go cheaper you can go with multiple resistive types such as Parma. It is often cheaper to buy one great controller rather than carry around 3 or 4 resistive types but this is a matter of personal taste.

Typically:

Pro 10 and faster cars (built up Slotech, Viper, Wizzard, BSRT) will work best with 5-10 ohm control.

Pro 4 (stock Viper, BSRT, Wizzard) will work with 15-30 ohms

Mega G, SRT, Lifelike and Tyco work with 30-45 ohms.

T-Jets work with 60-90 ohms (many like to add a secondary resistor to provide slight fine adjustment).

Mega G+ need 120 ohms for effective control.

As you can see, it might be cheaper to buy a great controller depending on how many of these you plan to race.

In our club (SJSCC) most are using OS3 and DiFalco.

 

Will the DiFalco handle different cars, like a Mega G+ and a Viper V1 "Club Stock" with the standard 290 ohm network installed?



#10 Randy Tragni

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Posted 11 November 2018 - 07:22 PM

"Will the DiFalco handle different cars, like a Mega G+ and a Viper V1 "Club Stock" with the standard 290 ohm network installed?"

Very likely. I'm using 15 band DiFalco's with all the bells and whistles and these work just fine with those cars. I would imagine your best course of action would be to call Jim DiFalco and ask his recommendation. Jim has always been very helpful to me when I had questions or needed suggestions.



#11 Paul Lindewall

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Posted 12 November 2018 - 08:48 AM

Does anyone have any feedback regarding the DS controllers? Specifically, I'm considering the 120 ohm units for use exclusively with Mega G+ cars. 



#12 Ramcatlarry

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Posted 12 November 2018 - 01:22 PM

Each of the newer transistor controllers use different ohm packages to make them work properly with different car and track situation.  When only a old style resistor controller ohm numbers are discussed, the values are much different.

GENERALLY:

commercial track 1/32 - 1/24 modern cars use 3 - 4 ohm; drag racing use 1 - 2 ohm

home set 1/32 plastic cars and pre-1975 production antiques -  4 - 25 ohm.  More curves, higher the ohm rating.

HO T-jet - up to 60 ohm.  Newer one part motors can go lower.

 

The goal of testing is to find which one ON YOUR TRACK, allows a slow speed at the first power band that will drive around the tightest corner.  Full speed is the same for all controllers.


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#13 drrufo

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Posted 17 May 2019 - 08:07 PM

This may not be the thread for this but Buena Park Raceway has a Ruddock HO controller in their counter.

 

John Andersen


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#14 Ecurie Martini

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Posted 17 May 2019 - 09:32 PM

 

1) Resistor controllers.  Cheapest to make and has a wide range of resistor  OHM values to find the drivability part.  A resistor controls the car by varying the amperage to the car.  The voltage is constant.  The Wattage value defines how much overall LOAD the controller can handle.  OHMs Law:  volts X amps = wattage.  An HO car usually runs on 18 VDC and less than 2 amps, so a 36 (minimum) wattage controller  resistor is fine.  This is what a Parma two barrel Turbo contrioller is designed for.  Many lighter duty T-jets use less current and therefore the single barrel 25 watt Sebring type controller is also fine.  The ohm value comes back to drivability.  The same car will drive differently on a tight twisty track than on a long straights and wide corner track with only one controller resistor value.  Every track is somewhat unique and testing is the only sure proof.  If the controller overheats, it is due to too low a wattage and driving with the throttle in the mid range too much.

 

 

 

 

 

Well....sort of.....The basic equation, Ohm's law is  Volts (E) = Current (I) X Resistance ®  This tells us a couple of things:  The current in a circuit will be equal to the voltage divided by the resistance so, the current in a 12 volt circuit through a 12 ohm resistor will be 1 amp, through a 6 ohm resistor will be 2 amps etc.  If we put two resistors in series (nose to tail), the current will be (volts)/ (R1 + R2) and the voltage drop across each resistor will be proportional to the resistance.  For example, in a 12 volt circuit with two identical resistors in series, the drop across each will be 6 volts.  If one resistor has twice the value of the second, the drop across the first will be 8 volts and, across the second, 4 volts.

 

Now, lets apply this to slot cars.  In this case, there are two "resistors" - the controller - a variable resistor and the motor, a complicated resistor.  It is complicated because motor resistance is not a fixed quantity but is variable due to a variety of things including inductance and "back EMF" the latter accounting for the fact that a rotating motor is also a generator, producing a current that opposes the current being fed to it. This, in effect, increases the effective resistance of a motor!

 

Don't give up.  We can simply things a bit and still end up with useful guiding principles.  Concept # 1 The effictive resistance of all motors increases as the motor speed increases.  It is a minimum just before the motor starts to turn and increases as the motor revs up.  Now let's divide motors into two groups - "small", low current motors and "large", high current motors (this grouping is predicated on current draw, not physical size)

 

Looking at the motor + controller combinations: A small motor might have a static resistance of a few ohms increasing to a full speed figure of 30-50 ohms.  Let's assume that the low speed effective resistance is about 15 ohms.  If we want our controller to be effective down to 3 volts at the motor, the controller must have a resistance 3X that of the motor or 45 ohms.  Well, we're OK here - why not use this controller everywhere?  We could, but, on a large motor with perhaps  a fraction of an ohm static resistance and a full speed figure of 3 ohms, we wouldn't get to even 50% power until the controller was nearly 90% of the way from "off" to "full" so, no modulation - a short travel "on -off" switch.  The mirror image of this would apply if we used a 3 ohm controller with a small motor - as soon as the wiper moved from "off" to the beginning of the winding, the motor would be at near full speed - another on-off switch.

 

Diode controller are a horse of a different color.  Diodes are not resistors and do not follow Ohm's law.  The voltage drop across a diode is a pretty consistent 0.6 volts, independent of current (not to exceed the current capacity of the diode) so, for example, a string of 20 diodes with a pick-up point between each will give you 0-12 volts in 1/2 volt steps.

 

EM


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#15 Ecurie Martini

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Posted 18 May 2019 - 08:42 AM

Diode controller are a horse of a different color.  Diodes are not resistors and do not follow Ohm's law.  The voltage drop across a diode is a pretty consistent 0.6 volts, independent of current (not to exceed the current capacity of the diode) so, for example, a string of 20 diodes with a pick-up point between each will give you 0-12 volts in 1/2 volt steps.

 

EM

 

correction - 0.6V steps


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#16 MattD

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Posted 18 May 2019 - 10:13 AM

Whew!


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#17 Ecurie Martini

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Posted 18 May 2019 - 11:28 AM

Another way to think about it:  Ohm's Law:  E=IR - one equation thus one independent variable.  In this case,

 

E (a constant) = I (dependent variable) X R (independent variable, i.e. the factor that is controlled)

This is the equation that governs the function of resistor controllers. They operate by controlling the division of the total voltage drop (which must equal the power supply voltage) between the motor and the resistor.

 

Diode controllers e.g. Cidex operate similarly but are essentially independent of current.

 

"Transistor" controllers fall into two main categories - typical transistor control and PWM - pulse width modulation.

Transistor controllers operate by controlling the current that flows through the circuit.  Because of this current management, transistor controllers for high power applications will typically need heat sinks.

 

PWM controllers operate by switching full power on and off rapidly.  The ratio of "on" time to "off" time determines the effective power available.  They are more efficient than any of the above but questions of "feel" and the effect on motor longevity are subjects for debate.

 

My own experience (limited to "small" motors)? I abandoned resistor controllers for a Cidex controller for traveling and fitted my home track with Prof. Motor diode controllers when they became available.  I no longer have a home track and my traveling controller is PWM.

 

EM


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#18 mdiv

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Posted 24 May 2019 - 11:49 PM

Doug, I've tried a variety of different controllers, including the resistor DS controller with the 60, 90 and 120 ohm setting toggle switch for T-jets.  It is not a bad controller and you can't blow it up because it is just some resistors, I.E. no fuses or active devices (diodes or transistors/FETs).  I think I paid about $80 for mine.

 

Most of the guys I've raced with prefer the more expensive professor motor Diode controller with adjustable brakes and sensitivity potentiometers.  This lets you "dial in" for any car.  If memory serves these run between $130 to $160.  

 

My go-to controller that I've had for the past ten years is my third-eye fet-1.  It has adjustable sensitivity and brakes, a control for how the trigger response curve is shaped as well as a voltage choke function.  It was just under $500.  It runs any car I've raced:  T-jet, life-like, mega G+ in HO on 18 to 20 volts, 1/32 and 1/24 vintage 60's cars i've put together for use on a commercial wood track (16D motors, 36D 26D all the pittmans etc).  I've run flexis with falcon motors hawk motors, parma S16D Deathstars, wing cars with falcons and all the way up to international 15s on a fast king track.  what else?  Group 10 16d motors, i've even farted around with eurosports and weird motors from the 70s and 80s in crazy cars I've put together.  The controller can handle anything, and the only thing that has failed for me on it is the bolts holding the plastic handle together (it's all taped up now)!  Granted, I'm not much of a racer but it handles anything I've ever thrown at it.

 

I would recommend the prof. motor controller overall for HO though as it is great for price and adjustability.  I will give some observations that I've made in slot car racing - practice practice practice practice.  get your laps in.  learn the hardest lanes on the track.  if you can drive junk, you can drive anything.  how much time and prep you put in the car, learning how to get it to handle, the motor to go fast (the right way to oil it, holy crap i screwed up my first thunderjet with oil on the brushes lol), body choice and mounting [given this isn't as critical for HO....] ...95% is the car and how to drive it.  probably more than that, very little is what you use to control it...that's like icing on the cake.

 

/soapbox off!

 

welcome to the forums, ask those questions!


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