12 click motor - .400 tall magnets in a .459 armature.
Magnet Theory
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.
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 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.
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 the basics of what a 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.
Since the early days there has been many developments in magnet materials, modern materials can be summarized into four different types:
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.
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:
The problem is the maximum operating temperature is 200 degrees and 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.
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 °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.
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:
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.
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. 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: Comutation 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
have 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, but only because you eliminate the short-out condition on the commutator.
But I have seen a lot of horizontal brush motor work better, so I am of the
opinion that this is a preference item in motor building, and the difference, if
any, is very small.
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 30
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:
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.
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 Quads.
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
S7-305 -. 450 tall x .380long x .073 thick flat tips - for proslot blanks and High power.
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
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!)
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
S7-305 - .450T x .380 L x .073T Flat Tips (works best with Proslots)
S7-380 - .400T x .440L x .073 Flat Tip Quads
S7-311 - .450T x .380L x.073T Angle Tip
S7-313 - .450T x .380L x .073 flat tips
S7-366 - .400T x .400L x .073 flat tips
S7-317 - .400T x .440L x .073 Angle Tips
S7-321 - .450 T x .440L x .073 Angle tips (Great singles for high power, a little heavy, however)
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.
Qualifying is one of the only few times which Quads can be used, typically because the magnets are too strong for race conditions.
The Qualifying magnets to use in order of weight and bottom end:
S7-360 .400T x .360L x .073 thick Quads- High RPM magnets, can work in race conditions.
S7-352 .400 Tall x .380L x .073 Thick Quads - For medium power qualifying, more bottom end than S7-360.
S7-366 - .400T x .400L x .073 Singles
S7-307 - .400T x .440L x .068Thick Singles
S7-381 - .400T x .400L x .073 angle tips for .459 Group arms or .480 arms in big .480 set-ups
S7-382 - .400T x .400L x .073 angle tips for .480 arms in .459 set-ups
S7-365 - .400 L x .400 Tall x .073 Thick- For high power qualifying
S7-304 - .380L x .430Tall x .073T angle tip - For high timed arms and high power
Listed in order of power requirements, with low power first.
S7-309 .380L x .450 T x .064T - These are Eurosport magnets, but work well on low power Gr-27's, also try S7-308 which is shaped for .480 cans and S7-310 for .480 arms in .459 set-ups.
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.
S7-360- .400T x .360L x .073 quads - small enough for med. To high power race conditions.
S7-312 - .430T x .385L angle tip singles
S7-307 .400t x .440L x .068T flat tip magnet - A very popular Gr-27 magnets for med-high power.
S7-382 - .400T x .400L x .064T angle tip quads for .480 arms in .459 set-ups, a thin magnet.
S7-381 - .400T x .400L x .073thick angle tip quads
S7-317 .400t x .440L x .073 Flat tip magnet. Lots of torque with this one.
S7-321 - .450T x .440L x .073 angle tip single - Big magnet,. But motor runs cool!
S7-380 - .400T x .440L x .073 flat tip quad for real high power conditions
C-12 / C-15 Class Wing Car Motors:
Cobalt 15 is a class where you need less magnets for high revving motors.
Now with the introduction of X-12 arms into the class we also need smaller magnets for the short stacks, so we have lot's of choices.
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 or by a longer, but not as tall magnet.
S7-350 - .400T x .285L x .064 thick singles for X-12 set-ups - very light
S7-351 - .400T x .285L x .071T flat tip singles for X-12 arms, more magnet for more power.
S7-310 - 450T x .330L x .063T - Is a Eurosport magnet, but in a .459 can and with a .480 arm X-12 or I-15 arm run good in these.
S7-367 - .400T x .400L x .064T makes a good I-15 magnet
S7-316 - .450T x .380L x .060 T Tall magnet, but short enough for X-12 arms in good power.
S7-307 - .400T x.440L x .068T flat tip magnet - good for big power tracks
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:
Drag racing is still in its infancy, and although we have made great strides at Slick 7, we feel there's a long way to go.
The objective in drag racing is Low end and Mid range, the motor is operating at top end for so short a time, top end seems to not matter.
The Key here is a small diameter arm for low inertia, and milder bottom end, then boost the bottom end with magnet and can.
S7-306 - .430T x .380L x .073T - Not much testing with these, but we think they can be faster than 305's because they are lighter.
S7-303 -.450T x .380L x .073T angle tip quads These are useful for medium power tracks, which there are many. And for Camen arms.
S7-365 - .400T x .400L x .073T - Flat tip magnets for low - medium power tracks.
S7-305 - .450T x .380L x .073 T - 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.
S7-318 - .450T x .440L x .075T - For most bottom end with Camen of Koford Arms, these monster mags are great especially with .450Dia. Koford arms in .459 set-ups or .465 Camen arms in .480 Set-ups.
S7-319 - .450T x .440L x .075T - The largest magnets in slot racing, designed for the high revving proslot arms. Use a .450 dia Proslot Arm in a .459 Billet Set-up for a very crisp motor!
This is an area where great improvement is coming, because Gr-27's are more sensitive to magnet design than open motors.
For low power tracks, use the same magnets as described in Gr-27 qualifying.
For high power, use :
S7-382 - .400T x .400L x .073T angle tip quads
S7-365 - .400T x .400L x .073T Flat tip quads
S7-380 - .400T x .440L x .073T Flat tip quads
S7-318 - .450T x .440L x .075Thick angle tip quads
S7-319 - .450T x .440L x .075 Thick - Proslot arms can work with these, but you need high revving arms, with thin webs for a Gr-27 to work with these! The big magnets kill the top end and the upper mid range.
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 driveability.
Magnet Selection for
Eurosports:
This is a very fast moving area because of the introduction of the mini-motors. The mini-motors kill a lot of bottom end, unfortunally too much for competing with the world class racers catered to by Slick 7.
To regain the lost bottom end and "Save" the mini-motor Slick 7 has produced some .285L magnets, which give the mini-motor lots of desperately needed bottom end.
The only thing we can't fix, is the poor throttle control of the .459 diameter arm. So until we get .480 mini-arms, which should be coming soon from some manufacturers the off-the-shelf mini-motor will be a victim of the mid to fill size motor the top racers are running.
If you are to order custom arms, you can make .480 arms for the current mini-motors being sold and use the following magnets.
S7-350 - .400T x .285L x .064Thick for .480 arm in a .459 set-up
S7-351 - .400T x .285L x .071T for .459 arms in .459 set-ups (or for .480 arm in .480 set-up!)
S7-310 - .450T x .330L x .063T for .480 arm in .459 set-ups
S7-309 - .450T x .330L x .068T for .459 set-ups with .459 arms
S7-308 - .450T x .330L x .068T for .480 arms in .480 set-ups
S7-367 - .400T x .400L x .064T for .480 arms in .459 set-up - The choice for the 1997 World's and Nat's winner, using big wire, 23t-25!
S7-366 - .400T x .400L x .073T for .480 arm in .480 set-up
S7-307 - .400T x .440L x .068T for .480
arm in .459 set-up (almost too much in most cases)
Firing Point of a Motor
Each armature stack is energized twice per rotation in a sequential mode at
alternating points. The degrees at which the stack fires equals the timing
degrees of the armature. The stack and the magnet repel each other at the point
of fire. So by placing the strongest edge of the magnet at the point of
repulsion will increase torque. (See Note)
Note: The torque of the motor is in direct proportion to its
field strength and the armature current.
THANKS TO SLICK 7
The figure shows the deferent points of degrees, where the center of the stack
falls during the time of fire. This point of degrees depends on the timing of
the armature. The degree of time that a stack stays energized from start to end,
solely depends on the circumference of the commentator and the size of the brush
face.