Working With Slot Car Drive Shafts

By Bob Ward

 

Drive shafts are a feature of many slot cars in use today.  In this article you will learn what you need to know about them.

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The front-motor in-line motor/chassis arrangement has become fairly common since the slot car racing renaissance beginning in the 1990s but it really got started back in the 1960s. The purpose was the same then as now – to allow a deeper and more detailed interior than just a flat tray with a driver figure. Strombecker, a prominent manufacturer at the time, had front-motor cars as early as 1960, but these cars used a piece of rubber tubing to couple the motor to the drive shaft. Later versions used a very long one-piece motor shaft that ran all the way to the rear axle. Before long Strombecker moved to rear-motor inline designs and front-motor cars disappeared for decades. However, with the introduction of strong neodymium traction magnets in the 1990s they made a comeback and have been quite successful on cars for plastic sectional track with steel contact strips. Fly has used the arrangement in all its models of front-engine cars. Scalextric uses it in models of 2-seat front-engine sports cars to make possible the fitting of a full interior. Revell-Monogram and MRRC have also made extensive use of it. The chassis of two front-motor cars, a Fly Ferrari GTO and a Scalextric Dodge Viper, are shown above.

The front-motor arrangement seems at first to be an unlikely drive train configuration for a slot car, since it places the motor’s weight at the opposite end of the car from where it’s needed for maximum cornering grip.   That flies in the face of proper principles of weight distribution for optimum handling. But with a stout magnet at the rear providing downforce the arrangement becomes viable. If you want to race non-magnet, however, you will do better to run a rear-motor car or convert your front-motor car to a rear-motor configuration. That kind of conversion, by the way, is not hard to do on a plastic chassis. All it really takes is a few basic hobby tools, a piece of sheet styrene or ABS, and a bottle of CA glue.

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All the Fly, MRRC, and Scalextric front-motor cars use very much the same endbell-drive motor and drive shaft assembly. The difference from one car to another is only in having a longer or shorter drive shaft length and sometimes different connectors on the ends of the lead wires. The motor, shaft bushing, pinion gear, and spring coupler are interchangeable on all of them, as are the various mounting points in the chassis. (Drawing 1) Thus, if you have any Fly, MRRC, or Scalextric motor and drive shaft assembly you can use it in any of these manufacturers’ cars or in a scratchbuilt or kitbashed car using one of their front-motor chassis simply by lengthening or cutting the shaft as necessary. Since the shaft diameter on every motor currently being used in 1:32 scale front-motor home racing cars is .078” (2mm) you can easily and inexpensively make a longer shaft by getting a piece of .078” steel wire from the K&S metal rack at your local hobby shop and cutting a length to fit your car. In a Fly, MRRC, or Scalextric front-motor car you can use any endbell-drive Mabuchi S can (FC130) or other motors with the same external configuration. The motor will fit the chassis and the drive shaft and spring coupler will mate up with the motor’s shaft. In some cases, however, you may need to trim the motor shaft, either on the end that mates with the drive shaft or on the opposite end to clear parts of the chassis. This can be done easily with a Dremel Moto-tool equipped with a carbide cutoff wheel. Be sure not to let the motor shaft get too hot when cutting it, as this can damage the bushings.

Revell-Monogram uses the same arrangement but with a can-drive FC130 motor. R-M’s shaft bushing and pinion gear are compatible with Scalextric, Fly, and MRRC. Again, shaft length differences apply.

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Removing the drive shaft from the motor and reconnecting it is not difficult, but many people have trouble getting the spring off without stretching it. The key is always to push the spring off the motor shaft or the drive shaft, as shown in Drawing 2, rather than pulling it. Place the jaws of your needle-nose pliers on the motor shaft between the endbell bushing and the spring coupler. Slide them along the shaft, pushing the spring coupler as you go. The coupler will normally come right off with only light pressure. Use the same technique to remove the coupler from the drive shaft as shown in drawing 3.

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When it’s time to put the coupler spring back in place it just pushes onto the shaft. Fly and Scalextric motors have a splined shaft end to better grip the spring coupler. If you are installing a hopup motor from another manufacturer it may not have the splined shaft end and may not fit the coupler tightly.   In that case, use a drop of medium CA glue in the spring coupler to hold it tightly to the shaft (Drawing 4). Don’t use the thin CA, as it can easily run into the shaft bushing and lock up the motor. Before using any kind of CA on a motor shaft or a drive shaft be sure to put a drop of oil in the motor and drive shaft bushings.     Be careful not to get any oil where the CA glue will go.

You can use a gear puller to remove the pinion gear from a drive shaft assembly without removing the shaft from the motor, but you have to remove the shaft before you can press a pinion back on. Once the spring coupler is removed you can use a pinion press on the drive shaft exactly as if it had a motor around it. If you do a lot of gear changes you will save time by making up several shafts, each with a pinion gear with a different number of teeth. Whenever you put the shaft assembly back together don’t forget to put the shaft bushing back on before reattaching the drive shaft to the motor shaft.

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One of the biggest problems with some front-motor cars is the drive shaft bushing’s tendency to pop out of its mounting in a crash or even a hard spin. When this happens the pinion gear starts chewing teeth off the crown gear and after that the car never has a smooth, quiet gear mesh. We have heard from customers who have glued or wired the bushing in place, but we don’t recommend either of those measures because they make the bushing difficult to remove when you need to. There’s a better way, as shown above in Drawing 5.   All you have to do is cut a piece of styrene strip or basswood about 1/8” by ¼” and glue the end of it to the bottom of the car’s body, interior tray or tub so the end of it presses down on the shaft bushing when the body is in place on the chassis. It will take a bit of cutting and trying to get the exact location and length needed, but once you get it right it will permanently end all problems with the shaft bushing coming loose without making it hard to remove.   Some front-motor cars come with an arrangement like this already in place.

With this information you should now be equipped to repair, replace, or modify the drive shaft assemblies on any of your front-motor cars with the fewest possible problems. Good racing!

If you have questions or comments about this article we invite you to e-mail e-mail them to bob@victorylaphobbies.com or call at (insert phone number here). We’ll be glad to give you all the information and advice you need.

Copyright ©2014 Robert M. Ward. All rights reserved.

Aftermarket Tires for Slot Cars

This article provides essential knowledge about tires for your slot cars.  This isn’t everything you will ever need to know but it will enable you to avoid being confused by the misinformation about tires that abounds and will help you make the best tire choices for your needs.

Most home slot car racers want to do one of two things with their 1/32, 1/43, or 1/24 scale cars. Either they want to make each one go as fast as it possibly can or they want all their cars to have the same level of performance so they can be raced with each other. Either way, installing a set of aftermarket rear tires is one of the best things they can do. Only a more powerful traction magnet gives a bigger performance boost for less time and effort.

Aftermarket slot car tires are those tires made by manufacturers other than the car makers themselves. As with life-sized cars the wide range of aftermarket tires is intended to provide increased performance over the original equipment (OEM) tires that come on the cars and, in some cases, to provide tires in different diameters to fit both OEM and aftermarket wheels so they can be used with a wider range of cars requiring different tire diameters. A choice of tire diameters also makes it easier to adjust the height of a car’s traction magnet above the track to achieve desired downforce figures. Some aftermarket tire product lines also include tires for vintage slot cars made as far back as the early 60s. Since spare parts for these cars, including tires, went out of production long ago the aftermarket tire industry is vital to hobbyists who want to keep these old cars running and even improve their performance.

There are two kinds of aftermarket tires, those made from silicone compounds and those made from any of a variety of high-traction rubber compounds. The two most prominent rubber categories are neoprene and urethane. The major functional difference between silicone and rubber tires is in the way they develop grip. Silicone tires do this by cleaning the track and rubber tires by “rubbering up” the track, that is, by depositing a layer of rubber on the track surface.      It’s not hard to see that the two kinds of tires work at cross purposes, the rubber tires constantly laying down more rubber while the silicones constantly clean it off. Contrary to what many people still believe, silicones DO NOT leave some kind of deposit on the track that causes rubber tires to lose grip. They simply reverse the rubbering-up process on which the rubber tires depend for their effectiveness. In most, though not all cases this difference in the way the tires work eventually leads to one kind of tire or the other becoming the only kind in use. This may occur naturally, with one or the other gaining a preponderance of users and the rest having to fall into line to be competitive. In many cases it occurs by decree, with the rules makers mandating the use of one or the other.

Popular lines of silicone tires include Indy Grips and Maxxtrac, manufactured by Professor Motor, Quick Slicks, and some tires produced by Slot It. Rubber tire product lines include Paul Gage Tires and Slot It’s rubber tires. Slot It’s tires fit many other wheels besides their own, though it is often a matter of test-fitting to see if they fit particular OEM plastic wheels.

Most aftermarket tires fit the cars’ original equipment wheels in exactly the same way as the original tires. Silicone tires used to be tricky to install and remove, which involves stretching the tire over the wheel’s center rib that holds the tire in place. This was because they were prone to tearing due to the stresses involved. The introduction of more robust silicone compounds has largely eliminated tearing problems, not only during installation but also due to racing impacts. If you have heard about such problems in the past you no longer need to be concerned about them. Still, some tires are quite a tight fit on some wheels. Slipping them on and getting the properly seated is easier if you put soapy water on the wheel. If you don’t have soapy water available your own saliva will usually serve the purpose. Keep this in mind particularly when a project calls for installing a pair of tires on wheels that are a little too big for them.

As mentioned above, silicones work best on a clean track. If you put a car with silicones on a dirty or rubbered-up track the tires will immediately begin to try to clean off the dirt and/or rubber. You will be cleaning them every lap or two until they clean off the racing line all the way around the course. You will repeat the process on every lane of the track you run on. If you are running on a track where everybody else is using rubber tires you will never get the track surface clean enough for your silicones to work, and you may as well switch to whatever tires everybody else is using. In the same way, your rubber tires will never lay down enough rubber to develop good grip on a track where everybody is using silicones; they will clean it up faster than you can lay it down.

It has always appeared to me, though I have no data to back it up, that if the number of racers using silicones and rubber tires is somewhere near equal the silicones are more than likely to prevail eventually. I believe that what happens is that the silicones clean the track faster than the rubber tires lay rubber down. But until that happens nobody will have optimum traction and the grip on any given lane may vary drastically depending on what kind of tires the driver who preceded you on the lane was using. For this reason almost every organized race program sooner or later ends up with some kind of specified (commonly referred to as “spec”) tire rule under which only one kind of tire or only one brand of one kind of tire is allowed. A rule like this takes tire choice partially or entirely out of the performance equation. This reduces cost and complexity, as drivers do not have to spend money, time, and effort experimenting with every different tire type and compound on the market. Perhaps more important, it creates more consistent track conditions which leads to closer and more competitive racing. You won’t see a situation where one driver smokes the field just because he happened to guess right about or tested for hours to determine what tire to use that day. If you want the maximum participation in your program or in any particular class within it you want to keep things as simple as possible. The best racing classes are the ones where there are clear limits on what you can do to the cars and the people running the program make sure everybody knows how to do all the allowable modifications. A spec tire rule is a big part of bringing this about.

It’s worth noting that the silicone/rubber issue is not absolute. I ran a low-key racing program on my Scalextric Sport track for a while. There were three classes. One was for box-stock cars with OEM rubber tires and the other two had a silicone spec tire rule. We always started each race night with a scrupulously clean track. The OEM rubber tires worked well enough and no one ever noticed that they had any negative effect on the performance of the silicone tires. Of course, this was magnet racing in which tire grip was less critical than in non-magnet racing, and because we always started with a clean track there was scant opportunity for any rubbering-up to occur.

This points to another issue, consistency of track conditions. The ONLY way to have truly consistent track conditions is to keep the track completely clean from both dust and laid-down rubber. If anything is allowed to accumulate over time on the track surface it introduces changes in grip level that cannot be completely predicted or controlled. This does not mean that you can’t use rubber tires and let the rubber build up over time. In most cases the change from one race day to the next will be gradual enough that regular competitors will be able to deal with it. It does mean, however, that an infrequent competitor may encounter significant changes since his last race, especially if there has been a change in the types and compounds of tires being used, and newcomers will go through a longer process of discovering the winning combination. It also means that over periods of months or years lap times can’t really be compared accurately because there is no way of quantifying changes in track conditions.

In my case maximum consistency of track conditions is exceptionally vital because my track is used far more for testing and development work than for actual racing, but in any racing situation consistent grip conditions do make it easier and less expensive for the greatest number of participants to become and remain competitive.

If your track hasn’t been used for a while it will have a film of dust on it. Clean the surface by wiping it down with a soft, damp cloth before running your cars. The damp cloth also works on your tires. Rolling the tires over the sticky side of a piece of masking tape is another good way to clean them. If you are using rubber tires that have been sitting on the car for some time without being used you may find that sanding the tread surface makes a significant difference in grip even if the tires are already true and concentric. This is because over time chemicals evaporate from the rubber on the surface of the tire leaving a thin layer of “dead” rubber that does not grip the track. A light sanding gets rid of this layer and leaves a fresh tread surface with full grip. This is true of both stock and aftermarket tires.

Equalizing the performance of two or more cars is often as simple as installing higher-grip aftermarket tires on the slower car to give it more traction. If that doesn’t do the trick you can also install stronger or milder magnets or just adjust magnet heights in the cars you are trying to equalize. You may be able to equalize two cars while making them both faster by putting silicones on one and a stronger magnet in the other. A little trial-and-error with tires, different-strength magnets, and different magnet positions will teach you how to fix many basic handling problems and level the playing field for all your cars, generating close, even competition and more racing fun at minimal cost. Remember that equalizing cars means not just getting all of them to do equal lap times but also giving all of them a set of driving characteristics you and the people you race with enjoy. This can mean either increasing or reducing grip, however generated, to get the feel you want.

So, to the bottom line, what tires do I recommend? The answer, of course, depends on where you want to go with your racing.

If you are making the rules and you want to keep things a simple and inexpensive as possible the best approach, in my experience, is a silicone spec-tire rule in all classes and a frequently cleaned track. With this combination your fellow racers will always know what to expect when they come to compete on your track. The best tire brand for this is Indy Grips/Maxxtrac. This is because these brands come with the stock number molded into the inner sidewall, so it become a very simple matter to make sure all cars are running the legal tire. This rule works best, of course, along with rules specifying maximum tire width and, if you are running magnets, a hard limit on magnetic downforce. Another thing to take into account is that some tire manufacturers make tires in more than one diameter for some cars and some wheel types.   Generally speaking, you probably don’t want to be running the stock diameter tire if the rules allow a smaller diameter, which lowers the center of gravity and also moves the magnet closer to the track surface, increasing downforce. A useful advantage to a choice of diameters, of course, is that you can use these tires in kitbashing or scratchbuilding projects in whichever of the available diameters is right for the car you are modeling. Indy Grips/Maxxtrac tires only come in the stock diameter for the cars they are made to fit, eliminating tire diameter from the performance equation. Slot It also makes both silicone tires and rubber tires in a variety of compounds and more than one diameter to fit its aluminum wheels and similar ones from other manufacturers. These tires will also fit the original plastic wheels of some cars, but you will need to test-fit to identify specific applications.

If you are going into an unfamiliar situation where silicones are required but no brand is specified you are, unfortunately, on your own. All the aftermarket tire manufacturers make performance claims, but without knowing a lot more than the information any of them gives there is simply no way of evaluating them as they may apply to any specific situation. You’re just going to have to try the available options or see if the people doing the winning where you are going to race will tell you what they are using. The same is true with rubber tires only more so. We know that where silicones are required there is always going to be a more or less clean track. With rubber tires there is simply no way of knowing ahead of time what track conditions will be and, therefore, what works on any given track at any specific time unless you can get some inside information.

A final thing it’s interesting to know is that tire choices don’t necessarily follow any consistent logic. It is far from unheard of for two groups of racers running on exactly the same type of track surface or brand of plastic track to come to different conclusions about optimum tire selection. If you race enough in enough different places, sooner or later you will encounter a situation that seems to turn logic on its head. That’s part of what makes the hobby so challenging and keeps you learning new things.

If you have questions about tires that I haven’t covered above, please feel free to send them to bob@victorylaphobbies.com. I’ll do the best I can to answer them.

Copyright © 2005, 2014, Robert M. Ward. All rights reserved.