Tuning
Your Slot Car - Advice and Tips
by Mark Rampling - Dunton Slot Car Club
Many thanks for allowing us to use this on our site.
6.5 Lead Wires
Ninco cars come with a series inductor in the lead wire to absorb any electrical noise emitted from the motor. SCX and Scalextric/Hornby cars have a parallel ceramic disc capacitor across the motor terminals to do the same thing. Noel claims that they both affect braking performance, so I always remove them. Just break off the parallel capacitor, or remove the series inductor and attach the lead wire directly to the motor terminal using a small soldering iron.
Bend the lead wires to: (i) make sure that they don't hold the body away from the chassis; (ii) centre the guide in the straight ahead position when the car comes out of the slot, making the marshall's job easier and quicker; (iii) still allow full side-to-side movement of the guide. If the wires are being stubborn, I sometimes use a piece of tape or some glue to hold them in the right place.
6.6 Motor
Motor response plays a critical part towards the balance of the car when coming out of corners. The motor should be easily controllable; the power mustn't come in with too much of a 'bang' that will cause sliding, wheel spin, fish-tailing or judder. There needs to be a good balance between the motor response, controller resistance and rear end grip to give a smooth, progressive and easy to drive car.
According to the DSCC rules the motor cannot be opened, so there is very little that can be done to it. As I have a number of cars, I have selected the best performing motors (by trial and error) and put them in the best handling cars. Beware that the fastest-revving motor when the rear wheels are lifted clear of the track will not necessarily be the fastest motor round a lap! Lubricate the motor bearings with a small drop of oil every now and then -- don't over-lubricate, as the copper commutator/brushes inside the motor could become contaminated!
I like to glue the motor into the separate motor bracket or directly into the chassis. This has the benefit of preventing the motor rocking slightly and absorbing some power, or popping out in an accident. For the models without a separate motor bracket, a further benefit of gluing the motor to the chassis is to stiffen the chassis. Let me explain: With the body removed and the motor in the chassis, look at the chassis sideways on, put your thumbs under the centre and gently pull the front & rear of the chassis downwards. The chassis will flex, usually more so at the rear where it is narrow between the rear wheels. Formula Ones are bad because they are so narrow at the back, the SCX Formula Ones are worst of all because the chassis is made from particularly cheap, flexible plastic. This flexing can cause rear-end judder when accelerating hard out of corners or braking into them. As the chassis flexes, you will see the contrate gear moving relative to the pinion, and the front & rear mounting lugs splaying away from the motor. By gluing the motor at both ends into the chassis, I am effectively creating a structural member above the plane of the chassis, which will minimise any flexing. And sure enough, the motor lugs can no longer splay away from the motor, there is no movement between the pinion and the contrate, and the chassis feels much stiffer. The judder disappears.
The other thing you can do when gluing the motor in is to check that the motor shaft lines up with the centre of the rear axle, to enable a good gear mesh. It is possible to buy an alignment tool to help you with this, the trouble is that the alignment tool works best if there is no pinion on the motor shaft - but once you've glued the motor in, it could be difficult to fit the pinion!
Gluing the motor in is pretty drastic. If something goes wrong with the motor, then it is very difficult to remove it without damaging the motor bracket or the whole chassis. Because nominally identical motors have different performance (due to production tolerances & variations), I always try the car out before gluing the motor in, just to make sure that the motor isn't a duff one.
To ensure a good joint, I roughen the surfaces on the chassis and motor. With Ninco, SCX & Fly models where the lugs wrap round both the motor can and the end bell, I run Superglue down the gap. Scalextric models have two legs to grip the sides of the end bell - I've found Superglue to be not quite "man" enough for this joint, so I use a viscous adhesive (e.g. Araldite) around the legs and across the rear of the end bell.
When a motor is brand new, it will have tight bearings and poor brush contact. As the motor runs-in, the bearings will become a better fit to the motor shaft, the brushes will wear to the same curvature as the commutator and stop arcing, and any loose windings will settle and possibly improve the balance of the armature. A run in motor is generally quieter, it has smoother acceleration, more topend speed and better brakes.
So it is advantageous to run-in the motor before using it in anger. Some people run-in just the bare motor on a reduced voltage for ½-1 hour, until the brushes stop arcing. Others swear by running-in for 12 hours at 6V, a further 12 hours at 9V, and a final 12 hours at 12V (I'm told that this is of particular benefit to Ninco NC2 motors, after which they fly)! The choice is yours!
I prefer to run-in the motor in the car, so that I am also runningin the gears and the rear axle. Some running-in takes place during the tyre truing process (see 6.9). After tyre truing, I used to do further running-in with no load on the rear axle, but I've just acquired a Scalextric -based rolling road to experiment with. Early indications are that the rolling road demonstrates very clearly whether the rear axle is running true (see 6.9); a surprising number of my cars were jumping around which I could only cure with a quick re-true. I've also found that weight needs to be added on the rear of the car to load the drive-train whilst running-in. Watch this space for further observations!
In the Modified class, choice of motor is open. Having tried the Oz-Race, Slot It and ProSlot alternatives, I have settled on the Ninco 'CLK' NC2 as the best compromise for the DSCC track. The 'CLK' NC2 has more torque than the standard Ninco NC2, and is ideal for punching hard out of the slow corners and braking late for the next one. With a 10t pinion (see below) it is still competitive for top speed, and I find I can gain on most cars down each long straight!
6.7 Gears
Check first of all that the contrate runs true, by removing the motor and slowly rotating the rear axle. You should be able to see any 'wobble' quite clearly. If there is contrate 'wobble', you're going to have a noisy, power-robbing gear mesh. So throw the contrate away and find a good one.
Then check that the contrate sits centrally on the axle by seeing whether the rear wheels are equidistant from the rear axle bearings and/or the chassis. Quite often they aren't! If this is the case, remove the rear axle from the chassis. Then grip the axle on a nonbearing surface with a pair of long-nose pliers and gently rotate the contrate relative to the axle to centre it. Hold the contrate in place with a drop of Superglue. Make sure that an axle bearing doesn't slide against the contrate at this point, because the glue will run into the bearing by capillary action and ruin it - I use an elastic band wrapped tightly around the axle to prevent the bearing from slipping down.
Nincos and SCXs have a brass pinion that is a press-fit onto a smooth motor shaft; Scalextric/Hornby and Fly have a plastic pinion on a serrated motor shaft. With in-line motors, check that the pinion is in the right place on the motor shaft. It needs to fully mesh with the contrate teeth but not rub against the hub of the contrate.
To move, fit or remove a pinion, it is far better to use a specialist gear puller like the one supplied by Ninco. This avoids the risk of damaging other parts of the motor with the forces involved.
Pinions can move along the motor shaft and out of mesh with the contrate gear. When this happens, exchange the pinion for the same make but with a tighter fit (normal production tolerances). Alternatively hold the original pinion in place with a small amount of solder (brass pinions only!) or glue, making sure that none gets into the teeth.
It is very important to achieve a good, smooth, quiet gear mesh. A noisy gear mesh is robbing power, it can give uneven acceleration and braking, and it is a psychological disadvantage to have a car sounding like a bag of nails! With the motor and rear axle in place but the body removed, turn the rear axle very slowly and lightly by hand in the direction of normal wheel rotation. A good gear mesh gives a consistent feel for the complete rotation of the rear axle. A bad gear mesh will have one or more 'sticking' points, where there is an irregular resistance to rotation (don't confuse this with the normal cogging effect of the motor). Sometimes it is even possible to see the effect of these 'sticking' points, by looking closely at where the motor shaft engages into the hub of the contrate -- a 'sticking' point will make the contrate jump sideways relative to the motor shaft, then back again.
A 'sticking' point is caused when a tooth on the contrate binds against the pinion as it tries to come into mesh. To eliminate the 'sticking' point, you first need to determine which tooth on the contrate is at fault. At a sticking' point, mark with white Tippex correction fluid the contrate tooth that is just about to mesh with the pinion. Carry on rotating the rear axle, it is possible that there will be more than one 'sticking' point, and mark each one.
Then use a sharp scalpel to take off the tiniest sliver from the leading side of each marked tooth on the contrate. This is usually enough to remove the 'sticking' point, but check the gear mesh again and repeat as necessary until you have a smooth, consistent feel for the complete rotation of the rear axle.
Gears benefit from running-in to exactly match the contours of the pinion and contrate in that particular car. Only run the rear axle in the right direction, never in the wrong direction. To speed things up, I gently press the contrate in towards the pinion, and out away from the pinion, with the motor running fairly fast. This usually results immediately in a quieter mesh and an increase in motor revs - good news! I then apply a small amount of Vaseline to the contrate teeth prior to further running-in (see the last part of section 6.6).
The standard gear ratio is 27t (contrate) : 9t (pinion), i.e. 3:1. The gear ratio may be changed only in the Modified class. Ninco supplies a 24t contrate, which with the standard 9t pinion changes the ratio to 2.67:1 and can help to calm down a fast-accelerating, powerful motor. It is also possible to buy 8t, 10t & 11t pinions to change the ratio. Generally, a lower numeric gear ratio will give worse acceleration & brakes but a higher top speed; conversely, a higher numeric gear ratio will give better acceleration & brakes, but a slower top speed. Beware of mixing pinions and contrates from different manufacturers, as they won't always mesh together very well.
In my Modified cars with Ninco 'CLK' motors, I have changed the pinion to 10t to calm down the acceleration a little, and give me a little more top-end speed on the long straights. I've found this to be the best compromise so far!
6.8 Front Axle/Hubs/Tyres
Make sure that the front tyres are sitting properly on the hubs, so that they are relatively true when spinning the front axle. Don't forget that the front tyres support the front of the car when cornering and prevent it from tipping too easily. If there is a bulge in the tyre because it is not sitting properly on the hub, it could cause the front of the car to jump out of the slot!
Also check that the front axle rotates easily, with no snagging or snatching against the body or chassis.
For a good handling car, it is important that the front of the car is supported on the guide, not on the front wheels. Each front wheel should lift by only ½-¾mm off the track before the movement is restricted by the front axle 'stop' on the chassis (thus resisting the tendency to tip). Check that there is the same lift around the entire circumference of each front tyre. The type of braids you are using will set up the height of the front of the car above the track surface. The lift of the front wheels can be tuned by truing the front tyres down to a smaller diameter. This involves putting the front tyres onto a rear axle (of course!) and a bit of trial-and-error to true them down to the right diameter. It is even possible to compensate for a slightly twisted chassis (see 6.1) by making one front tyre a different size to the other. In the Modified class, you can mix different front hub sizes (e.g. Fly hubs and Ninco CLK hubs are larger than the standard Ninco front hub), or different front tyres (e.g. Pink Kar supply an ultra-low profile version) to get the front wheel lift just right.
If you are running a Ninco chassis in the Modified class, you can experiment to increase the front axle "stiffness". A "stiff" front axle seems to give better entry into a corner, but slightly less grip coming out; a "floppy" front axle is the opposite, with slightly more rear-end grip but slightly worse turn-in.
In a car with a "floppy" axle, the front axle can lift upwards so it cannot initially resist any tendency of the chassis to tip. A "stiff" front axle has no lift, the front wheels are locked in place relative to the chassis, and this helps to prevent the car tipping when going into a corner.
However for best grip coming out of a corner, the car needs to lean slightly, allowing the outside rear wheel to dig-in and provide maximum grip. Look at a well-used car on a set-up block. You will notice that the tread of the rear tyres is not sitting flat on the track surface. Instead the tread slopes upwards towards the outside of the wheel, indicating that the car is leaning in the corners. A "floppy" front axle allows a car to lean and generate rear-end grip, whereas a "stiff" front axle resists the lean, so the outside rear tyre cannot dig-in and instead slides over the track surface.
This tweak stiffens the front axle but is easily reversible, so you can try it and see if it suits your driving style and your car. If you don't like it you can always revert back to the standard "floppy" front axle, with no harm done! Remember though that it is legal only in the Modified class.
Remove the front axle, remove one front wheel, take a couple of rear axle bearings and slip them onto the front axle. If you are using the Scalextric/Hornby plastic bearing, you may have to open them out to fit onto the slightly larger diameter Ninco axle. Replace the wheel and refit the front axle to the chassis, ensuring that the bearings sit on top of the ridges moulded on the chassis right behind the guide. The bearings now restrict the downward movement of the axle, the lugs on the chassis restrict the upward lift, and the axle is effectively locked in height. You may have to tweak the braids a bit, as some of the weight of the front of the car may now be supported by the front wheels. To revert back to the standard "floppy" axle, just remove the bearings again.
It is possible to take the approach further for even greater front axle stiffness, by opening out the chassis lugs locating the front axle and gluing the axle bearings directly into the lugs. You'll have to be careful though, as the DSCC rules require the front wheels to touch and roll on the track surface, but you still want the guide to support the front of the car - a difficult balancing act!
Again only for the Modified class, I like to add small washers to centralise the front axle and stop it slopping around sideways in the chassis.
A tweak only for Fly cars in the Modified class - most of them have stub front axles, which are not a good fit and they allow the front wheels to wobble all over the place. Grab the inside end of the stub axle with a pair of pliers and rotate the wheel until it comes off. Now throw the stub axles away, and fit a conventional front axle instead. A Scalextric one seems to fit nicely - it is a slightly loose fit in the chassis, the hubs fit OK, but the axle will need narrowing. Now you have a front axle set-up giving much more consistent support to the front of the chassis during cornering.