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Jim Moyes
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Discussion Starter · #1 ·
I've seen a few people (not necessarily on SF) saying that the best setup for slot cars is tripod like. i.e. The car rests on it's rear wheels and the guide, and the front wheels are only for scale accuracy!

To be honest, I'm having trouble getting my head round this and wanted to put it up as a topic for discussion in the hope that someone could enlighten me further.

I could almost understand it on Formula 1/ Indy type cars and even low wide sports cars or lightweight bodied cars like vac forms (shudder). But surely as the centre of gravity gets higher there is more chance of the car just tipping over at the corners. Are these people saying that if you remove the front axle from a car it will go better. I understand that it will give better electrical contact with all the front weight on the guide, but surely a sprung guide like Ninco use gives the best of both worlds.

I know you can't always compare the handling of slot cars with 1:1 cars but would they say a Reliant Robin handles well? Next time I see a Reliant driver I'll ask, or better still, I'll step out in front of it and see what happens when it tries to swerve round me!

RSVP

Mr.M
 

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I have very mixed feelings about this and look forward to seeing reasoned explanations too. Most of the top North American racers subscribe to the tripod theory. BWAminispeed is one notable detractor - there may be others.

I would suggest the 'tripod' is really a tripod with front outriggers. ie the front wheels are set at such a height that they ONLY touch track when they are needed n order to to prevent the car fron leaning and eventually tipping, but not unless. There are slot cars that actually have little metal skids to carry out the same function. So, they only constitiute a true tripod when travelling in a straight line, or more controversially, when the back wheels are so far out of line on a curve that the front axle remains at the ideal 90 degrees in relation to the direction of the slot, all the way round the curve. It's hard to explain this concept in words but it is possible to make a mathematical argument that the two front wheels do not trace longer or shorter routes when traversing curves as long as the back axle maintains precisely the correct angle to the slot!
 

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Tripods are somewhat useful in racing as well. A slot car at it's best or worst as some insist is basicaly a tripod. Some basic things apply here if you think about it.

The slot cars effective working wheelbase is the distance from the center of the rear axle to the guide shoe pivot shaft a tripod shape. A longer length here makes the car handle smoother than a shorter one to a point. Too long and it is slower through tight corners. Much shorter and it is more twitchy through wider corners. The wheel base showing all four wheels is not the real one for slot cars.

Next a most electrically effective slot car should have the weight of the front of the car on the guide shoe braid or close to all the weight there. Good electrical contact is essential to getting the most out of the cars performance potential both in accelration and with EMF braking. Sprung guide shoes come close but it takes a perfect spring setup to work, with out bouncing or lifting the braids from the rails. Why add another varible. Keep it down with weight or fixed height adjustment. Now I know some claim it is too much friction. Well I will take that type friction any day when my car needs the power.

Next cornering suffers some say as the car tips with the front wheels off the ground.
We are not talking about much off the ground here, just enough to not influence the guide shoe ride height. .005 thousandths of an inch above at rest. Down a straight, why have them drag along. In cornering if the chassis tips a bit, the wheel only has to tip .005 to touch ground and stabilise the car. You want your body to do more than that in cornering to free the handling up thats why many loosen body mount screws. Weight transfer in the rear is essentail to get the out side rear wheel gripping better in cornering hard.

In addtion to being slighty above the track the front wheels should ideally be independantly turning from each other. As the arc each takes through the corner is not the same, why have one dragging the other along through the longest arc. Keep them free wheeling around corners but do not have a sloppy front wheel stub axle as fly had so it rubs the body.

Now that is the basics of tripod theory, it works for some quite well and others do well with their approach. It would have to be with identical cars and a well observed and clinical setup trials to prove which one works best. I have proved it to my self, time and time again over my 40 years in slots but to live and let live is good to. It's up to you what you like and can live with.
 

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As a addition to my tripod tale. I should add that this applies mainly to non magnet cars and less to out of the box euro car racing on plastic track with triple/quad magents, applying dampening effects to everything in sight including pacemakers in the area.


But the tripod effects to these as non magnet cars still apply to a great extent if done right. All the basic tuning tips need to be followed first and then set up for tripod style guide shoe applications.

Scratch built or modified cars benefit greatly from the tripod effect, especially to the faster types.

BWA mostly runs narrow wood cars that have a hard time not looking devoid of a lolly.

Just teasing Al. Al does all right on his own.
 

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Jim Moyes
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Discussion Starter · #5 ·
Thanks for the reply, Larry


So, we were never reallly talking true tripods, more like tripods with dual front outriggers. OK, I understand that better.

Couple of things that came up in your reply made me think of more questions.

BTW, I am more interested in the non mag side of things and I'm only interested in RTR plastic cars, on wood and plastic, but the basics must remain the same for these and scratchbuilds, surely. I am also very keen to have a car look realistic as it motors round the track. Even the small amount of clearance you state, means there is a fair chance that the front wheels will not actually go round. HMMM! Not for me I'm afraid, but, like you say, whatever you are prepared to live with is right for you. Plus, even that small amount of "tip" is going to lift the opposite rear wheel some, which must affect grip, mustn't it?

I was also interested in what you said about independently rotating front wheels because of the different distance travelled by each around corners. Why does this not affect the back wheels as well? They travel the same arc as the fronts, don't they?

I know sprung guides are a good fix for certain cars, the Fly Lancia being a good example, but on some the spring is too strong, the SCX Abarth Fiat rides around with a nose up attitude.

This is all good stuff, and an optimum set up is starting to appear ( for my tastes anyway).

Mr.M
 

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Scott Brownlee
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The tripod theory seems ideal for a car with a very low centre of gravity. For most RTR cars I think it would be debateable.

The Brownlee Theory of Slot Cars is that you are trying to make the guide go around in the groove as fast as possible using two variable and one controlled contact patches (the rear wheels and guide respectively). In a real car you are trying to make the centre of gravity of the car go around as fast as possible by employing four variable contact patches (all four wheels) hence the benefit, at least in the good old days, of four wheel drifting through corners.

By the way, I say variable because the path of the tyres is not controlled by the track or groove the way the guide blade is strictly limited to travelling around in the groove.

Electrical Contact

I'd say the least critical job of the guide's two jobs is keeping the braids in electrical contact with the rails.

Yes, you need contact, but before we get too hung up about it let's consider that the braids have a bit of movement, or droop. On the GT40 in front of me that amounts to about 3mm. Not sure how far a sprung guide moves, but not much more. More importantly, the braid droops to about 1-2mm above the bottom edge of the guide blade, meaning that you'd need to be able to corner with only that little bit of blade in the slot before the lack of electrical contact is your worry rather than de-slotting.

Where sprung guides might help is in hard acceleration as the car tends to rise up at the front, although of course the lack of contact is its own self regulating traction control so is not entirely undesirable. The potential penalty of sprung guides is that at the point where the car has little or no effective weight over the guide due to the action/momentum of the car, over a crest or bump say, the sprung guide is pushing the car higher. Better hope thsi doesn't coincide with a corner. No absolute right and wrong here since on some tracks with some cars a sprung guide would be better and vice versa.

Steering

The real hard work done by the guide is steering the car around. Here is where real car and slot car dynamics vary fundamentally.

I think all would agree that you want as much weight on the guide during cornering as you can get to ensure the front of the car will follow the line of the corner and not de-slot and plough on and off. Only when the front/guide is in the groove can you start to worry about controlling the rear axel (via throttle inputs) to make your time in the corner as short as possible.

Slot racers can however borrow an idea form the 1:1 boys who, on cars with no aerodynamic down force, use weight transfer under braking to increase the grip of the front tyres and hence raise the entry speed into a corner. Too much and they understeer. On a slot car understeer is technically impossible of course, so braking into a bend can only add weight to the guide giving more than enough front end bite. I say more than enough since the rear will spin around long before you chisel the groove into a new, wider arc.

Back to tripods - bet you thought I'd forgotten! The move from stable straight ahead to stable cornering requires the weight transfer from front to right or left. If we assume a slot car has no suspension (big assumption, I know) then when the car begins to turn the mass of the car will act through the centre of gravity (CG). This should be as low as possible, but it must have some height. If the car tips up when cornering - assuming the tyre retains grip - then the CG can only get higher. The car will tip more, assuming speed, radius etc remain unchanged.

This twisting/tipping force must be counteracted by the outside wheel. Assuming the rear tyre has grip, the resisting force is acting through the distance from the wheel to the centre line. Therefore the greater the width of the car the more twisting force it can resist. Hence what we all know: low, wide cars have more grip.

A pure tripod slot car assumes the vast majority of the mass of the car is at the rear and therefore the rear axle is taking the vast majority of the twisting action. Think Vanquish MG base chassis and you'll get the idea.

However, add a body, interior, driver and front axle - a pretty heavy cosmetic part on most RTR cars - and the mass is more forwards, pushing the CG towards the centre of the car.

In a tripod car the resistance to tipping is all at the rear, but with the CG in the middle the car tips towards the front outside corner. It is at this precise point that having a front wheel touching the track and capable of taking some weight will stop the cat tipping up higher and the guide lifting from the slot.

Ideally it will be instantly effective i.e. already supporting weight, but in the absence of working, tuneable 1/32 springs, roll bars (sway bars) and dampers, most RTR cars make do with an axle riding just off the track, but coming into action as soon as the car tips.

At this point it is worth mentioning that the tiny amount of roll that is needed to bring the front axle into play might, if the braids were very stiff, mean the inside braid lost contact with the rail, but the previously mentioned droop compensates for this.

Ninco are master of this stiff and low front axle ride height trick and new Scalextric cars are pretty good too (although old Scalextic so-called big wheel saloons - TR7, 911, Rover 3500 - are the worst). The only downside is you need a pretty smooth track or else the low riding, firm front axle will lift the guide out of the slot on bumps.

Anyway, bed time.

Scott
 

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Rich Dumas
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Here is a 1/24th Group 27 car of the sort that one might see on a commercial raceway in the US. It only has front wheels because the rules call for front wheels, they never touch the track. All of my wing body cars have front wheels that don't touch the track. They are very low and have air control to generate a lot of downforce. A car like this can turn a 150ft. King track in 1.5 seconds. You can feel a blast of air when they go by. Eight of them on the track at once is quite a sight. With non-wing bodies I prefer to use front wheels that touch and roll on the track.
 

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Gee! this topic got diverted a bit with steering, wing cars etc. Here is a graphic that sort of illustrates the guide shoe set up for a full tripod setup and the other versions used by many.

Anytime you get air space between the guide shoe braid and the track braid or rails you get a spring action at best. If the braid used is robust, it will stay in contact with the track contacts at best. At the worst it will ride up away from the contacts.. Many cars out of the box look like the bad braid illustration. So no wonder newbies wonder why the car runs in fits and spurts around the track if at all.



My choice is full contact of braid one to one and a full depth insertion of the guide blade in the slot for full contact with the slot sides. As in a tripodian setup This does not mean there is no up and down movement of the braid/guide shoe and track contact but it is kept to a minimum, that is what the guide shoe washer spacers are for, adustment.


Now to Mr materials questions about the front wheels not rotating all the time looking bad. If you can tell the front wheels are not rotating going around the track you are not paying enough attention to what you are doing or going so slow as to be a road block. In corners where more visible, they rotate at the slower speeds just from the vibrations etc..

As to the arc of the rear wheels not being equal you are right but both the rear tires are, in non magent conditions, sliding and trying for optimum grip on the outer rear tire to pull out of the corner. Now Vanquish claims to have the solution to this with their differential as in real cars, to help with this problem. I am not convinced it applies to the size car we race but then again it may.

Spring loaded guides are just a another problem you don't need to deal with when it is so simple to solve with proper guide height settings to start with. Another varible if thrown randomly in an equation is never a good solution to keep things simple.

Your mileage may vary and I wish you all good luck to keep it in the slot for the most fun in this hobby. Nuf said from this end!!!


Larry S.
 

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Always keep in mind the tremendous downforce relative to their weight these wing cars generate. Our scale cars produce nothing close. Add the glue and the smooth track, banked corners, etc, etc and you have a different ballgame entirely. Don't see much lead weight on the wing car. Plus my God they are butt ugly. I have driven them if you were wondering.
 

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1/32-cars are different!!!
..ever thought about the friction between the braid and the track? Try to keep your braid as short as possible, the front-wheels should carry load of the car, look that the front wheels have no grip and move free! Try that setup and compare it with your tripod-method - and then post your results. You'll be surprised!
 

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Jim Moyes
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Discussion Starter · #11 ·
Hmmm.... I think this topic may just be highlighting the wide spectrum of the hobby that can be called slot car racing


Those wing things may run in a slot and race against each other but cars? Still, I'm sure you guys have a blast racing each other and that's great.

So tripod is really only for machines of that ilk. Somebody had a real sense of humour putting those front wheels on sideways like that. But I bet the guy who insisted on that rule got hot under the collar when he first saw them. I think he was probably thinking maybe these are getting a little unlike "cars".

I agree with Thomas and Dennis, that those of us who prefer things a little more "scale" perhaps need different approaches to getting the best out of our chosen subject matter. I know what you're saying too, Thomas, I prefer to use front tyres that have as little grip as possible to help stop binding on the bends.

I suppose it's all just part of life's rich tapestry!
all, for all your contributions

Mr.M
 

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Graham Windle
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Over the years I have done extensive testing with the tripod v front wheels touching theory and at least on the tracks I race on the tripod wins hands down,However when I sent one of my cars to the us for Chris Briggs proxy race he found it better for him with the wheels touching,Chris track is very short and twisty and he likes his cars set this way, When Chris' cars came to the uk the tripod cars were quicker in most races, had chris been driving this might not have been the case or had I been driving in the US perhaps I would have lapped quicker with the tripod than he did ,The best set up is the one which you lap consistantly fastest with dont write off one in favour of the other both systems have there merits ,but as I have said the tripod works for me,
Graham
 

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I'm with Graham on this. The only exception to the tripod setup being better than the 4 wheel type on my track is on some of my narrow track width cars that have a high ground clearance such as some of the classics. On these cars I seem to get better lap times with slightly more weight on the front wheels. I assume this is because of the greater tendency for the chassis to "tip" though I'm not sure. Adding magnets then seems to make these cars work better in the tripod setup. This I would also assume is because the "precieved" CG is much lower.

Jimmy
 

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I have to agree with Jim and Graham....

I have seen and tried both set ups on my track... (keeping in mind that these are all 1/32 hard plastic bodied cars) And on my track having the front wheels rolling is the fastest way around the track...

In the Proxy race Graham mentioned I found that the cars sent in with the tripod set up ran poorly. and I had to do some work on a number of cars to get them running their best.....

I want the front wheels on the track, the car has less of a tendency to start to tip in the turns.. With the tripod set up once the car starts to tip in the turn it just keeps on going and you out of the slot.... The only way to stop this is to take the turn slower and that is not the fastest way around any track....

But I think it all boils down to the track you race on and the cars you use.... We are talking two different world with 1/32 scale cars and smaller home track and 1/24th cars on the big sweeping tracks..... Driving style and how you want your car to feel to you also play a major role in car set up..... not to mention that the 1/24 cars have a much wider track for more stability

And there is no comparing the winded wonders with our 1/32 hard plastic cars....

One set up is no better than the other...... It mostly depends on the car and the track being raced on......

I do know that I will have to give the tripod set up a try in the next Proxy race for the UK tracks..... Different horses for different courses..

Chris
 

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Alan Tadd
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Interesting Topic.

It was always a very firm rule in the ECRA that all four (or 6 !), wheels must be in contact with the track. I'm not sure what the case is now with this new organisation.

We did some tests, at my old Club, many years ago to see what effect, if any, running without front wheels would have on different types of slot car.

In 1/32 cars, (Lexan bodies, brass chassis), cars without front wheels were quicker and handled better, but tended to de-slot on banked curves.

1/24th cars vere much quicker without front wheels and tended to stay in the slot.

I wouldn't dream of running a modern (hard bodied)slot car without all four wheels touching the track, I'm more interested in appearence than outright speed.

Great Forum, keep up the good work.

Cheers
Alan
PS I'm glad so many of you seem to share my opinion of modern thin lexan cheese wedges that pass for racing slot cars.
 

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Graham Windle
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Re the ecra rule about 4 wheels must touch and roll I always used to set mine with just enough give in the braid so when the car was pushed over the tech block the presure caused the fronts to roll but under power the wheels would be lifted clear of the track giving a tripod effect ,not quite as good as the system I use now but effective.
Graham
 

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Hi. what a bag of fun this all is! Anybody mind if I throw in my twopennyworth? I love the look of that wing car, personally. Real Colin Chapman/Jim Hall engineering there. Maybe that's what real Can-Am cars would have looked like by now if the rule-mongers hadn't spoilt the fun (slight problem with steering, though). Anyway, since I don't have easy access to a 150 ft King track, I content myself by building models of favourite cars to run on my 20+ year old plexitrack. Seeing as how it is mostly bumps, the tripod theory is appropriate! My cars spend most of their time running on odd numbers of wheels. The best handling chassis I have found in these circumstances is a good old fashioned drop arm, or iso-type, with a magnet (or lead if you prefer) on the drop. My favourite model is actually a sort of monocoque (posh word for a cheap build) Lotus 40. It actually has a tripod; a sidewinder rear set up to the guide flag via a simple brass rod frame, which is fixed to the body with a piano wire hinge just behind the rear axle. The front axle is mounted direct to the resin body. With a neo magnet just in front of the motor and a very limited travel on the 'iso' this thing goes like the clappers, and there's even room for the whole of Jim Clark in a full cockpit. In a 1/32 Lotus. And Jim is not sitting up in the airstream like those daft Vanquish cars. Am I rambling on a bit now? But the main problem I have in building realistic looking cars that perform well is getting close clearances around the wheels/wheel arches, and a good low CG on the track. When the front wheels are fixed in position relative to the body rather than the chassis, you can get them tucked up really close without binding the bodywork, while the chassis soaks up track stresses. I hate seeing my cars sitting on the track with air under the front wheels, but I understand the importance of keeping the guide in the slot and keeping the front wheels out of the way as much as possible. It's important to have them there for the balance through the corners, though. Ciao for niao
 

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QUOTE If tripods are that good, how come Reliant Robins handle like a brick?
I'd take a quiet bet that they would handle very differently with a transverse motor BEHIND the driver. It would also make quite a difference if the single front wheel was running in a tramline inset into the road surface!
 
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