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Apologize for this infantile question, but, of what benefit is it to loosen the body mounting screws for a racing car? I would have imagined that "tight and quiet" was better.

Thanks

Maltese' Wife
 

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Loose body absorbs vibrations from the track, this helps to keep it floating along in the slot, rather than bouncing and potentially hopping.

The other advantage is that when you enter a corner just a bit too fast, instead of the whole car tipping, just the body will. This keeps both rear wheels on the track and the guide in the slot. It makes it tremndously more foregiving and is a worthwhile easy mod that you should perform on every car you buy... (even the shelf queens, lol).

Lotus
 

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Discussion Starter · #3 ·
Thank you, thank you ... from the bottom of my wife's heart. Of course I knew that, but she wanted to hear it from someone else (er..ermm)


Maltese
 

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It is true that loose body mouning can stop chassis vibration being magnified by the body, rather like the body of a guitar or other stringed instrument vibrating in sympathy with and magnifying the sound of the strings.
But there is severe doubt that the body tipping has any advantage. It certainly doesn't in a full size car, in fact anything but. So it is highly unilkely that it is anything but disadvantageous in a small model either. The trick is to loosen screws just enough to prevent transmitted vibration, without the body actually slopping around.
 

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That is a real possibility, depending on the particular design etc.
One must experiment and what works with one car might or might not work the same with another
 

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it definitely works on most cars, improving handling and lap times. I wish it didn't. cos i hate rattly bodies and loose screws
 

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Brian Ferguson
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Most people say that I always race with a screw loose.


The theory behind loose body mounting is easy to visualize. Picture those chrome ball doodads, where 5 steel balls hang on threads and, at rest, touch each other in a line. Pull back an end ball and let it go. When it strikes the stationary balls, the ball at the other end flies away. The 3 balls in the middle never move.

With a slot car, the track imparts shocks into the chassis. With a firmly mounted body, the chassis and body react to the shocks as a single unit and the entire car is affected - loss of traction/grip results. If the body is loose however, the shock passes through the chassis and it is the body that reacts to the shock - the chassis stays firmly planted to the track. Track = ball 1, chassis = balls 2-4, body = ball 5.

The body does not need to be flailing around. It merely needs to have a tiny degree of free play. Too much and it can impart negative weight transfer effects in the turns or may result in tire rub.

Loosening the body is also a guarantee that the chassis is not being warped/twisted by a tightly mounted but warped/twisted body. This is more common than you may realize.

Being a little loose is good.
 

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Fergy, good answer to an old question; in fact during our weekly race with Ninco's BMW, I lost the front screw, and since the rear was very loose, the body began to dance on the chassis and was very difficult to control; too much weight transfer I believe, so the main reason behind loosening screws is exactly to insulate the chassis from the track.
Ciao
 

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Graham Windle
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When you loosen the screws stick a bit of bluetack in the hole this will stop you loosing them and youll still get the movement
 

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While there is no doubt about the ability of a slightly loose body to reduce transmission and amplification of vibration, there are a couple of potential snags with the seductively simple 'chrome ball doodads' analogy - Newton's Cradle.

Old Isaacs's balls rely on being made of the same material, same shape, mass, orientation etc, which isn't the case with our complex little cars.

Secondly, I think we are missing one of the important basic factors - that first jolt of energy, without which, the balls can't bounce at all. This is usually provided by a human hand pulling one ball away from the others and then letting it swing back again to set the cycle in motion. I think that in our car/track situation, the equivalent of the hand grab is the track itself, or the irregularities in the track. Obviously the track can't actually move, so the chassis has to. In other words, the track isn't Ball 1, the chassis is. Now it looks as though the body is equivalent to all the other balls . . . or is it? Actually, it is not even as simple as that either, if we now take into account each stage of energy transmission via tyres, wheels, axles, bushings, chassis, screws and a very oddly shaped and non-rigid body (compared with a nice spherical steel ball)!

There, that thought should keep the ball rolling a little further.

It ain't quite as simple as it might seem!
 

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Don't want to start an arguement Tropi, but if you race on a perfectly smooth routed track (ie. no vibrations) you think you can run fully tightened up? I don't think so.

I am certain that letting the body rock side to side in a bend improves handling because I can see it happening. I take a corner with a tight car and I see the whole car tip and come out. I take the same corner again with a slightly looser body and the body tips and the chassis tips slightly. Loosen it off more and you can find the point where just the body tips. Unfortunaly loosening off too much has side effects like tyres rubbing on arches and the like...

Try this... set up about 3-4 lengths of that super smooth Carrera track that almost everyone has now, then a 60 degree corner then another couple of straights. Hook up a train transformer to the track instead of a controller.

Place your tightened up car with it's back wheels just over the end of the track and set the voltage to any value (reasonably low). When the wheels are spinning at a constant speed give the car a nudge so that it starts travelling toward the corner. If the car stays on round the corner, try again with a slightly higher voltage, if it comes off try it slightly slower. You basically want to find the voltage (or setting) where the car just comes off in the corner.

Now loosen the screws on your car just a little bit. Repeat experiment at the voltage/setting that you found earlier. Watch as you'r car trundles round the corner without coming out. Infact find the voltage/setting that your loose car runs at and tell us the percentage increase. That will mean that you can take that kind of corner X% faster or brake some other constant Y% later.

Now that's an advantage if ever I saw one.

Go on, try it... I dare ya.

Lotus
 

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Sprint
You are making it even more complicated than I did!
But . . . you are absolutely right that the motor is equivalent to yet another swinging ball, though I would hesitate to state exactly which number it should be! Similarly, ALL parts of the transmission can produce side effects too - it is VERY complex when we get into the detail. It is some combination of these other factors that is affecting Lotus's experiments. I maintain resolutely that a tilting body ALONE is actually disadvantageous, unless you can fit the car with miniaturised Trebron suspension and make it tilt IN to the corner instead of away from it! This is precisely why full size cars are fitted with anti-roll bars (anti-sway for the trans-Atlanteans!) - to stop the car from tilting outwards, or at least minimise it. Seeing a body tilt outwards and also seeing a faster speed through the corner doesn't make it follow that they are direct cause and effect. We can't casually forget that all-important vibration/resonance break that came along with the loosening of the screws.

Don't worry about 'starting an argument'!

We call it a spirited and intelligent discussion and we probably all learn something in the process. It's time that Mr Penrose, BWAmini, joined in I think!
Where the heck are you when we need you, Al?
 

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the vibrations and forces that the car have to deal with are:

uneven track causing bounce
rotational force of motor, especially when accelerating or braking - ie the force is changing
irregularities due to transmission imperfections - gear mesh, non straight cam shafts etc
cyclic problems due to non straight axles, slightly untrue fron or rear wheels etc
wheel size changing due to speed and weight transfer (rubber tyres expanding at high revs etc)
centripetal (or is it centrifugal) forces on curves, which will usually be variable due to braking into and accelerating out of the corner

(and possibly some other stuff too!)

All these things are putting different types of vibrations and forces on the car, and how they work is very different. I think loosening the body aids with a lot of these matters - and in different ways.

Overall, I have found the biggest performance difference to be on corners, so I suspect something along the lines of the process Lotus is suggesting must be at work
 

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QUOTE (Tropi @ 15 Apr 2004, 23:07)But there is severe doubt that the body tipping has any advantage. It certainly doesn't in a full size car, in fact anything but.
Funny you should mention that. I always felt that until this very week when the battery died on my MR-2 and I ended up tatting around in my sisters ancient 1.2 Clio. After a few miles of culture shock (whats wrong with this? Why isn't it accelerating? Where's the induction roar? etc. )
I discovered that by chucking the wheel around agressively and letting the soft springs rock the body, loading the weight over the outside front gave the car stacks more grip.

Of course, forgetting to stop doing this once the MR-2 had a new battery fitted on nearly killed me but that's neither here nor there.

To keep your screws once loosened, try putting a square of insulating or fibre-reinforced tape over the hole.

Coop
 

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Hi

The REASONS.....

In the midwest in 65, the guys started experimenting with rattle plates and flopping body mounts and floating platforms. All worked, but floppies worked best,. And flopping and tilting worked even better. Old news.
At the time a number of racers did some high speed photography of the cars in given corners and discovered that if the body moves in the corner, it eats some of the energy. Thus, faster.

Now, with most of the current plastic cars, the chassis is flexi/floppy too much and often needs the extra stiffness of the body. Frankly, I use the timer to tell me. I start buttoned up, do some laps, dial back the screws a half turn and time. Keep loosening until the times drop again.
If the car is immediately slower with the first turn of the screw, I pull the car apart and put in a couple bits of piano wire to stiffen, and repeat the above.

Fate
 

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Brian Ferguson
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Tropi.....


It was a loose (pardon the pun
) analogy, intended only to illustrate that adjacent bodies can transmit shocks without displaying any effect of the shock themselves.

There are a myriad of forces acting on a slotcar, some external and some created by the car itself. In essence, we want disruptive forces (such as those created when a car hits a bump on the track or during violent throttle changes) to be transferred away from the chassis. The loose body concept allows many such forces to be transferred to the body, thus keeping the chassis (tires!) in better contact with the track surface.

A textbook could probably be written on the dynamics displayed by a slot car, but the simple reality is that it works. Always has.

Body weight is a key factor, and not every method of "loosening" will work with every type of body. As Fate mentions, floppy pan systems date back to the mid-60s, but the bodies were so light that it was the pans that accomplished the desired effect. On today's RTRs, the chassis is pretty much a fixed item, and it is the heavy hardshell bodies than can be used to dissipate unwanted forces.

Specific bodies will also be better or worse at achieving the desired result. Total weight, and distribution of the weight, will make one body better or worse than another.

It isn't rocket science.... or is it?
 

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As regards the "tight & quiet" opinion expressed at the beginning of this thread, I'd just like to say that Loose & Loud can be good fun and works most of the time



Mark.
 
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