Slick 7 Magnets - Competition Manual
By Rudy Garriga
Updated July 2003
This manual is a summary of all of the knowledge compiled through 30 years of racing and by consulting the world's best and fastest racers and builders.
We would like to specially thank:
Craig Landry of Zap Racing Products, and 1993 World Record Holder for his thoughts on this subject and his partnership in car development.
Bob Green, previously of Mura Products, for sharing his insights in Motor design.
Joel Montague of Camen Enterprises, for the collaboration and correspondence over the years, on the subject.
Csaba Zekelihidy - 1984 National Champion, for his many contributions to the sport and his technical conversations during the early days of Cobalt motor development.
Fred Hood - devoted racer and friend for the many years of help and testing that developed the understanding of the slot car mechanism.
Tracy Chin for his testing and sharing his unique and innovative views on Eurosport car designs.
Lee Gilbert for sharing his many innovations during our many after the race dinner talks.
Lee Roberts, builder of some of the fastest motors in modern times. For his trust and sharing his findings in development of some of our magnet designs.
Don Perko, for his collaboration during the development of the "P" magnet that launched our magnet projects.
Mike Aceves for his devotion to our company and his testing and development of the world's fastest dragsters. This has allowed us to develop our understanding of the Slot Car drag racing motor.
Dennis Kurshner for sharing his findings during his developments of some of the fastest eurosport motors (used by winner of the 1994, 1995, 1996 and 1997 USRA Nats).
And in memory of:
Ivan Jenkins: Who shared his many findings with us and in his tinkering has developed some very fast motors.
Of course, there are many that have shared with me race results, testing results and effect of changes that they have done. The people, listed have been most influential during my long study of the Slot Car Motor design.
What Is A Magnet
Magnet theory is a very complicated subject, which is covered in many graduate school text books with a great level of detail. For slot car racing, some important fundamentals will be covered here in common terms. I hope that this guide will help the average racer with motor and magnet selection and provide guide with what to do in the development of the racing program.
There are only a few common materials, which are magnetic; these are Iron, Nickel and Chromium. Traditionally all magnetic materials were made from alloys of these materials. In addition, Ferro-magnetic materials exist in two forms. These are soft and hard magnetic materials. A hard magnetic material is one that can be magnetized permanently, where a "soft" magnetic material is magnetized in a presence of a magnetic field, and then reverts to near zero magnetic field, when the field is removed. The armature material is a perfect example of a soft magnetic material.
Another type of material is Para-magnetic material. This is typically a material that is a good electrical conductors, which when subjected to a fluctuating magnetic field allow currents (Eddy Currents) to flow. Eddy Currents counter-act the electro-magnetic field and act to reduce its strength. Examples of these materials are aluminum, copper, brass and similar good conductors that are otherwise non-magnetic. A paramagnetic material acts to reduce the magnetic field strength, instead of increasing it, and is one reason why they are not used for armatures or can material.
A material becomes magnetized because polarized molecules or groups of molecules called domains become aligned in a magnetic field. These domains are little magnets themselves with a "North" and "South" Pole.
In soft magnetic material, these domains are free to move, and when a magnetic field is applied, they line up and form a magnet, but once the field is removed, the material becomes non-magnetic again. This type of material is used on motor "cans" or armature blanks, where the polarity needs to change.
The other parameter to consider in can and armature materials is the para-magnetic effects, due to induced currents. As previously, mentioned, non-magnetic materials decrease magnetic fields due to good conductivity of eddy currents. This same effect will reduce the performance of a magnetic material. Addition of alloys like silicon to iron alloys will increase resistivity and decrease the induced currents to improve magnetic performance as well as reduce heat from the induced currents in soft magnetic materials (makes them better for armature blanks and cans!).
Silicon bearing alloys are chosen for Armature laminations and sometimes for can materials to reduce the induced Eddy Currents. Another method used to reduce the Eddy Currents is the use of laminated armature stacks. The thin laminations act like a small diameter wire and increase resistance to these currents.
For a permanent magnet, a "hard" magnetic material is used, where these domains are trapped and not free to move. With a very strong magnetic field, these domains are rotated and trapped in an aligned orientation, so when the field is removed, the material remains magnetized.
Now yow know some basics of magnetic materials, and what a permanent magnet is. It's a material with small magnetic domains, which are trapped in the lattice of the material and are aligned to form a magnet with a very strong magnetic field.
With this knowledge, we go into a more refined definition of magnets and magnetic materials:
Early magnets were no more than high carbon steel, magnetized by an electro-magnet, but with advances in material science, alloys with very strong dipoles have been designed.
The first of these alloys were the Alnico magnets, where iron was heavily alloyed and cast to form a magnets with very high flux densities.
Modern materials have been made for many applications.
Modern Magnet Materials:
Since the early days there has been many developments in magnet materials, modern materials can be summarized into five different types:
Neodymium and Samarium-Cobalt are referred to as Rare Earth Magnets because they contain Rare Earth Elements Neodymium or Samarium and are the strongest of the magnets available.
Ceramic magnets have good coercive properties, and are low cost.
Alnico magnets were commercialized in the 30's and are still used today, especially in areas where very high operating temperatures are required.
Plastic magnets are simply magnet powder bonded by a plastic or rubber binder. Because of the binder, the strength is never the same as a magnet made out of the powder by itself. The plastic magnet, however is lower cost, and can be made into different shapes easily, and of course can be made as a flexible magnet.
Magnets for Slot Car Motors
The Slot car motor requires the strongest and lightest magnet possible, so when one looks at what is needed the conclusion that the magnet needs the following:
If only one of these properties is considered, like energy product, which has received a lot of discussion among slot car racers, you could decide that the magnet to use is Neodymium-Iron Boron. You can get these magnets with energy products in excess of 50MGO.
The problem is the maximum operating temperature is 200 degrees or below, and the temperature coefficient is around .1/degree.
Compare this to Samarium Cobalt with BH less than 32MGO, but with operating temperatures of 300-400 degrees and temperature coefficients of under .03/degree that explains to great extent why Neodymium slot car motors don't work.
Slick 7 Samarium Cobalt magnets have the right balance of properties, which have made them superior for slot car applications. The material we use is so stable, that we have never seen a change in properties after several races in a Gr-7 motor. Therefore the need for re-magnetizing is eliminated, and motors don't heat up because of loss in magnet properties during racing.
Have you ever wonder why motor have 6 or 12 clicks per revolution, and why some motors feel like they have dead magnets, yet other feel super strong?
In slot car Cobalt motors, this has to do mostly with magnet geometry, tip strength and tip position. Below is an example of a 12 "click" motor, using .400" tall magnets on a .459 diameter armature. Note the position of stack labeled "1" during each 30 degree click.
You have the primary click whenever the face of a pole is aligned with the face of the magnet; this gives you six clicks. You have a secondary click when the pole is between tips. As you will notice, the tips are covering the ends of the pole when it's between tips and the center web is always about 50% in the magnet face when one web is in the opposite magnet. That means you have a centering pull on the opposite poles when the primary pole is in the field.
12 click motor - .400 tall magnets in a .459 armature.
When the magnets are not so tall, then you can see that when the primary pole is aligned, the center of the web on the other two poles are further away from the tips. This means that the poles are too far away for the tips to apply a strong counter pull, so the clicks are primarily due to the one pole aligned with the magnet.
Armature rotation- 30° increments .360 tall magnets on a .459 armature
When the magnets are tall, like .450 tall in the example, the tips overlap the web in the first photo, where pole 1 is aligned with the top magnet; this provides a very strong centering force. This causes a very strong primary "click" followed by a weaker secondary click, and an armature that is hard to turn in the field due to the condition of all 3 webs being within the magnet at once.
.450 tall magnets with a .459 diameter armature
It is believed and argued that a hard clicking motor is "unbalanced" and makes the motor run as if it's out of balance. This is not true, of course, because one is relating the static magnet coercive attraction to an un-charged coil to that of an operating armature where the poles attract and repel from the magnets. The operating conditions are quite different from the "feel" of a motor when turned by hand.
When one tests performance, motors with very heavy cog and real tall magnets may have very high torque, but may sacrifice top speed. On the other hand, a small magnet motor also with heavy cog may have lot's of top end. The point is heavy cog in both cases, but much different motor performance.
Commutator Timing and Magnets:
Timing affects the performance of the motor;
More timing generally gives top end and less torque. As you can see from the following picture, when the armature pole is coming into the magnet, the commutator contacts the brush and energizes the pole, causing it to attract to the middle of the magnet.
Bob Green always told me that the performance of the motor was based on the tips, and this is the reason why, the armature is turned off when the poles get to the middle of the magnet. The real work is done when the poles are closer to the magnet tips.
In fact, when the pole is entering the tip of the magnet, this is the point when the armature is turned on by the commutator.
It is seen in the drawing, that the more timing a motor has the more of the pole is out of the magnet and the following holds true:
It is for these reasons, that I believe that higher timed armature are improved with taller magnets (More torque and less heat).
Another factor to notice is the position of the tips relative to the center webs during commutation. The thicker web armatures have more metal into the magnet as well as more metal to produce stronger fields, these armatures prefer magnets that are not as tall, or angle tipped magnets. Note that armatures produced in the end of the 1990's to today, with thin webs (27's and C-12's) like increasingly taller magnets than older armatures. The newer armatures have thinner webs!
The Armatures that have smaller webs can produce more torque without loss of RPM, and because they run hotter, the taller magnets improve reliability of these armatures.
Horizontal Vs Vertical Brushes:
In the picture below, you can see the two contact points of vertical and horizontal brushes.
Which is better?
38° timed armature in .400 tall magnets, with vertical and horizontal motor brushes superimposed.
Here are some facts:
1: There is an orientation with horizontal brushes where the poles are in direct short, luckily the contact area where the short occurs, called overlap is small and motor still runs. However, this short out condition is eliminated with vertical brushes unless the commutator gets very small.
2: Commutation takes place sooner in the rotation with horizontal brushes, so you have the effect of more timing with horizontal brushes, which may account why in some conditions, the horizontal brushes give more top end.
3. Because, for the same armature, vertical brushes produce an effect of less timing, you can expect more brakes and bottom end torque on vertical brushed motor.
4. The amount of time the poles are on; is less with a vertical brush, this can account for cooler running motor, and better throttle response to a motor (important in Eurosport racing)
5. Vertical brushes have more contact area with the brush hoods.
6. You have more wrap around with a horizontal brush, and therefore more contact area against the brush.
My conclusion is that vertical brushes should be better for open motors or motors or high power racing, but only because you eliminate the short-out condition on the commutator. I have seen a lot of horizontal brush motor work better, particularly in group racing, where there is more timing given and more time allowed for the coils to charge, since there are a lot of turns of small wire. So horizontal brushes work best on restricted motor classes like Gr-27 and C-12 or boxstock ect..
Wing Car Motors:
Wing car motors are the most refined of all of the motors used for slot cars, because they have been in development for over 40 years.
The basic requirement for the wing car motor is good power at high RPM, strong mid-range and medium low-end torque.
Other characteristics desired or enhanced are:
Gr-7 "Open" class motors:
Open class motors are complicated but give the motor builder the most tools to work with. The ability to change timing, armature length, winds, and blank dimensions allow the manufacturer great flexibility to make a good motor.
For the racer, the same applies by using a particular manufacturer's armature (blank design) and selecting timing as well as wire size and number of turns.
When planning your motor, you need to decide, what armature you will be using, diameter, can type, power conditions and how much timing the arm has.
Since I wrote this article, there has been some new developments - The introduction of our 6, 8 and 10 magnets sets give the builder some new choices.
One can characterize multi-mag motors as even number segments for smooth bottom end and more top end and odd number segments for more bottom end.
The more segments you use, the more efficient the motor, and you get a cooler running motor, as well as a motor less prone to power drops or voltage changes.
Motors for qualifying need to be built for lightweight and top end power. In qualifying there will be typically a lot of glue and power so you don't want to over power the car with low end torque or draw too much current to arc the braid.
The magnets to pick for qualifying Gr-7 will usually be Multi-magnet types
- Traditional .459 qualifiers -
For .459 armatures picked in order of heavier, more mid range and bottom end torque.
S7-360 - .400 tall x .360Long x .073 thick flat tip quads
S7-352 - .400 tall x .380 long x .073 thick flat tip quads
S7-304 - .430 tall x .380 long x .072 angle tip magnets
S7-306 - .430 tall x .380 long x .072 thick - flat tip magnets (Proslots like these)
For .480 Armatures pick in order of heavier and more mid range and bottom end torque:
S7-360 - .400 tall x .360 long x .073 thick - is so light they work for qualifying.
S7-352 - .400 tall x .380 long x .073 thick flat tip quads
S7-303 - .450 tall x .380 long x .073 thick angle tips
S7-306 - .430 tall x .380 long x .072 thick, flat tips - Will give more top end than 305's
- New .480 arm qualifiers -
For .480 arms you have to kill their brutal bottom end to hook-up your car for qualifying, now you do this with our introduction of 8 magnet motors. 8 magnets give you smoother bottom end, and more top end.
Use .360 long 8 mags for high power qualifying - S7-500 with S7-482 center segments for a .450 tall 8 mag
There are many combinations you an do, if you use S7-503 - 10 mag outer segments and S7-479 center segments you can make a wicked .480 tall 8 mag
Use .360 long 6 mag for high power qualifying - use S7-360 and S7-482 center segment.
Other combinations are S7-500 and S7-479 center segment for a .420 tall six mag qualifying motor - light and Fast!
For racing, you need to consider reliability, operating temperature and crash resistance. Quads are best for reducing operating temperature and high power racing, whereas singles have the advantage in that they are more durable, and run best in low power, specially low volts operation.
Quad Magnets for .459 armatures:
S7-352 - .400T x .380L x .073T. Flat Tips
S7-365 - .400T x .400L x .073T Flat Tips
S7-304 - .430T x .380L x .073 T -Angle tips
S7-380 - .400T x .440L x .073 T -Flat Tips
S7-306 - .430T x .385L x .073T Flat Tips
Single magnets for .459's
S7-366 - .400T x .400L x .073T Flat Tips
S7-312 - .430T x .380L x .073 T angle Tip
S7-314 - .430T x .380L x .073T Flat Tips
S7-317 - .400T x .440L x .073 Angle Tips (creates impressive horsepower!)
Quad Magnets for .480 Motors:
S7-303 - .450T x .380L x .073T Angle Tips. (Works bets with Camen and PK arms)
S7-365 - .400Tall x .400L x .073T flat tips, this is a popular size for both .459 and .480's
S7-380 - .400T x .440L x .073 Flat Tip Quads
Single Magnets for .480's
S7-311 - .450T x .380L x.073T Angle Tip
S7-313 - .450T x .380L x .073 flat tips
S7-427 - .450T x .360L x .065 These magnets work well on low power open racing with big air gaps
S7-429 - .480T x .360L x .073 These are good single mags, plenty thick for all open motor applications and high power racing.
Six Magnets Sets:
S7-350 and S7-407 center - Makes a ..450T x .380L x .073T 6-mag, The original six mag. configuration, use this as the baseline.
S7-350 and S7-480 center - Makes a .470T x .380L x .073T - 6mag. These were developed during the 2000 Nats, and provide more bottom end and reliability than the thin center segment 6 mag configuration. Better on high power tracks, more reliable.
S7-304 and S7-407 center - Gives a big .490T x .380L x .073T 6-mag - Really big horsepower, and rpm from angle tips!
S7-360 and s7-407 center - makes a .450 tall x .360L x .073 6-mag - good on med to low power shorter magnet gets more RPM, and is lighter then using the .380L sets.
S7-360 and S7-480center - Makes a .470T x .360L x .073T - 6mag. These are lighter than the .380L brothers, but are more prone to heat. so they will be better for med to low power tracks. The shorter magnets will also give you more RPM.
Eight Magnet Sets :
Eight magnet sets are characterized by more RPM, less Bottom end, and Cooler running motors.
S7-445 (S7-439 and 2 sets of S7-407) These are our original 8 mag sets, .450T x .380L x .073T- These are super reliable, have smooth bottom end, and lot's of top end! Good on any type of power.
S7-500 and 2 sets of S7-407- .450 T x .360L x .073T - Makes a real high revving motor, perfect for qualifying or really hot power!
S7-504 and 2 sets of S7-478 - .480T x .380L x .073T - Makes a real animal! More bottom end, than the .450 T motors, just what the 8mag needs.
S7-503 ad 2 sets of S7-479 - .480T x .360L x .073T - Light weight and more bottom end, makes a very good, light motor for all types of power
Ten Magnet Sets:
Then magnet sets are characterized as stronger bottom end than 8 mag, the motor will run more like a 6 mag motor with more reliability. Because of the improved efficiency, the motor will usually have more top end than a 6 mag motor as well.
S7-504 and (3) S7-407 - .450T x .380L x .073 - 10 mag - The baseline 10 mag motor.
S7-504 and (1) S7-478 and (2) S7-407 - .470T x .380L x .073 - More bottom end.
S7-504 and (2) S7-478 and (1) S7-407 - .490T x .380L x .073 - More bottom end and top end.
S7-503 and (3) S7-482 - .450T x .360L x .073T - Lighter and more top end than baseline
S7-503 and (1) S7-479 and (2) S7-482 - .470T x .360L x .073 - More bottom end but about the same weight as the baseline
S7-503 and (2) s7-479 and (1) S7-482 - .490T x .380L x .073 - This is the preferred configuration for a .490 tall 10 mag, a magnet this tall needs to be short to save on weight.
There are more configurations to make up; here are the guidelines to decide on your motor:
Gr-27 Class Wing Car Motors:
Restricted class motors are tricky, because you don't have as many parameters to change. Therefore, you can only pick magnets for different arm brands and power conditions.
S7-306 - .430T x .385L x .073T Flat Tips - High power qualifying
S7-366 - .400T x .400L x .073T Singles - Med-High power qual.
S7-307 - .400T x .440L x .068 T Singles - Baseline magnet, works everywhere
S7-381 - .400T x .400L x .064 angle tips quads for .480 arms in big .459 set-ups
S7-382 - .400T x .400L x .073 angle tips quads for .459 arms or .480 arms in .480 set-ups
S7-365 - .400T x .400L x .073T- Quads For high power qualifying
S7-415 - .430T x .400L x .073T - Improved qualifying magnet for .490 arms
S7-471 - .430T x .440L x .065T - Great qualifying Singles for .490 arms.
For multi-magnets - see Gr-27 multi-mag section below.
S7-366/367 .400t x .400L x .073 for 366 and .064T for 367. Depending on set-up, and arm diameter, using #s7-367 for lowest power conditions.
S7-307 .400t x .440L x .068T flat tip magnet - A very popular Gr-27 magnets for med-high power.
S7-381 - .400T x .400L x .064T angle tip quads for .480 arms in .459 set-ups, a thin magnet.
S7-382 - .400T x .400L x .073T angle tip quads for high power racing
S7-317 .400t x .440L x .073 Flat tip single magnet. Lots of torque with this one.
S7-321 - .450T x .440L x .073 angle tip single - Big magnet,. But motor runs cool! works well on low power.
S7-380 - .400T x .440L x .073 flat tip quad for real high power conditions
S7-415 .430T x .400L x .073T - One of my favorites for High power racing or qualifying
S7-471 .430T x .440L x .065T - Single mag. designed for .490 arms - really fast!
MULTI SEGMENT MAGNETS:
Multi-segment magnets are characterized by having good power, even when the power dips. The magnets used are 6 and 10 mag configurations. 8 mag configurations give more RPM, but in Gr-27 you need torque.
S7-382 + S7-483 - .450T x .400L x .073 - The first of our 6 mags for 27's produces great bottom end, and is immune to power drop during the race.
S7-381 + S7-483 - .450T x .400L x .064T - Same as above, but for .490 arm. You don't have to hone as much.
S7-382 + S7-480 - .470T x .400L x .073T - Taller six mag for more torque and higher power tracks.
S7-505 + (3) S7-483 - .450T x .400L x .073T - Makes awsome 10 mags
S7-505 + (2) S7-483 + (1) S7-480 - .480T x .400L x .073 - Makes the secret 10 mags used by Beuf.
S7-506 + (3) S7-484 - .450T x .440L x .073T - 10 mags for lower power tracks.
C-12 Wing Car Motors:
Because these armatures have many turns of small gage wire, we need a magnet that does not overpower the arm, and allows it to rev. This can be accomplished by a tall, short magnet.
S7-350 - .400T x .285L x .064 thick singles for C-12 set-ups - very light
S7-351 - .400T x .285L x .071T flat tip singles for C-12 arms, more magnet for more power.
S7-427 - .450T x .360L x .065T - Designed for C-12 racing, this is the baseline magnet for C-12
S7-429 - .480T x .360L x .073T - Gives improved bottom end over S7-427
S7-468 - .430T x .360L x .065T - Code name "AL" magnets (Al Chuck built a motor with S7-314 magnets that were cut to .360 by mistake) These magnets were responsible for several world records!
S7-411 - .430T x .360L x .063T - Quad versions of "AL" magnets, holder of several world records. Good for qualifying and high power racing.
S7-500 + S7-479 - .430T x .360L x .073T - The 6 mags Benny Justice used to blow everybody away at the 2001 Nats
S7-503 + (3) S7-482 - .450T x .360L x .073T - Killer 10-mag C-12 motor, lot's of bottom end, and runs cool!
Drag Racing Motors:
Just as Eurosports are the finesse motor in slot cars, Drag motors are the brutes on the sport.
The drag motor requires a strong, but not overpowering bottom end torque, but a HUGE! Mid-range, the Dragster motor is operating most of the time within the middle RPM range of the motor and does not need to have the high top end RPM performance of a Wing Car Motor. This is because the dragster is at top end for a very short time, and spends most of the time getting off the line and up to 60ft speeds.
The important attributes to consider on a drag motor are:
Dragster Gr-7 Motors Magnet Selection:
The objective in drag racing is Low end and Mid range power, the motor is operating at top end for so short a time, top end seems to not matter as much.
The Key here is a small diameter arm for low inertia, and milder bottom end, then boost the bottom end with magnet and can.
S7-303 -.450T x .380L x .073T angle tip quads These are useful for medium power tracks, which there are many. for bigger arms in small cans.
S7-305 - .450T x .380L x .083 T - The main drag magnet - In a .459 can you can run a .450 arm with these and you will get a light motor with good bottom end and mid range. If you use a larger .480 can, then you need a .465 diameter arm. We have set many world records with these.
S7-350 + S7-478 - .450T x .80L x .073T High power 6-mag motor for more bottom end in a small diameter can
Drag Racing Gr-27 Motors:
S7-318 - .450T x .440L x .075T - angle tip quads - For larger diameter arms on low power tracks
S7-319 - .450T x .440L x .085T - These are the main Gr-27 drag magnets - hard to beat!
S7-382 + S7-481 - .450T x .440L x .073T - Big 6-mag configuration for small diameter cans or big diameter arms. great on lower power configurations.
Eurosport motors are the finesse motors for slot racing; these motors are selected totally by power curve.
The Eurosport motor has to come on smooth, have good throttle control in the mid-range of the RPM curve and strong top end with brakes.
Magnets for Eurosport motors are typically short to kill bottom end torque and tall to provide the broad power curve desired.
Weight has been an attribute that has received a lot of attention lately among racers. The fact is, weight is not as nearly as important as a good power curve, too short of a motor will have poor mid range properties, and lack brakes.
Extensive testing at Slick 7 using armatures with stack lengths as short as .125" and magnets as short as .120" showed that stacks shorter than .200 loose throttle control in the mid range. Also, cause the motor to turn on abruptly during negotiation of esses where power is changing during partial throttle.
Magnets shorter than .280" affect the brakes significantly on a Eurosport motor, and lower than .400 affect the drivability.
Magnet Selection for Eurosports:
Motors for Eurosports are almost always .480 or bigger diameter armatures, the popular sizes are:
S7-310 - .400T x .330L x .064T for .480 arm in .459 set-ups - The popupar mag. for the Speed Inc. cars by Lee Gilbert
S7-308 - .380T x .330L x .068T lower bottom end than #310
S7-485 - .320T x .400L x .065T - Magnet for long arms for smooth bottom end 1/24 scale Eurosport cars
S7-486 - .320T x .380L x .065T - Magnet for regular and short arms for smooth bottom end 1/24 scale Eurosport cars
S7-485 - .320T x .330L x .065T - Magnet for 1/32 scale Eurosport cars
There are many combinations possible for multi-mag motors, but racers have not tried them;
I would suggest:
S7-503 + (2) S7-482 - .420T x .360L x .073T - 8 mag motor that should give smooth low end plus lot's of top end for today's 6-46 geared motors - I think the first guy to try this will have a big advantage!
Magnet Selection Chart