43 replies to this topic

[Pablo]

Why is flex good in a slot car chassis, and bad in a motorcycle chassis?

[Kevin Juliot]

Same reason it's good in a racing kart, the motorcycle has suspension the other two don't.

[Pablo]

That's kind of what I was thinking.
I'm curious to see what PdL and cheater have to say also.
Not to mention all the other smart guys

[Kevin Juliot]

So your saying I'm not a smart guy.

With out any flex it would be very hard to get any handling or traction. When I first started racing R/C cars they were 1/12 "Pan" cars made of flat fiberglass sheet. The flex of the pan and the cuts determined the handliing of the car. Then some added a shock to the flex point for the rear and springs on the spindles, now we had tuning but we needed to start making the chassis stiffer. Thats where carbon fiber plates came in to it. Now these cars are full suspension and a very stiff chassis.

Give me a brass and wire slot car chassis any day.

[Pablo]

Kevin, you can spell "chassis",
so that automatically makes you the smartest slotblogger awake at this hour of the night !

[MantaRay]

The question is......Can I use an "Mini Torch".....

[Russell Sheldon]

Detailed descriptions of different types of chassis can be confusing, especially as there is no proven best design and, indeed, many of the most successful chassis builders themselves find it difficult to analyse why a particular car handles better than another.

When entering a corner at speed, due to its momentum, a slot car tends to want to go straight. If the chassis is too stiff, it will react stiffly and resist the change in direction. Flex 'dampens' this to a degree, as well as enabling the tyres to generate more grip or traction.

The main approach used today is still the flexi-iso or flexi-board chassis design, pioneered by Ian Fisher with a 1/32nd scale chassis built for ECRA regulations in the late '70s or early '80s. It is a very good all-round design which works well on most tracks, both in 1/32nd ans 1/24th racing.



The "flexi-hinge" allows the front and back ends of the chassis to flex or twist independently by means of the central longitudinal pivot, called the "flexi hinge". This effectively absorbs some of the cornering forces, while the side rails dampen longitudinal twisting, helping to keep the guide blade vertical without being affected by what's happening at the rear, since the front end of the chassis remains relatively fixed.

The side rails contribute to the torsional stiffness of the chassis, controlling the degree to which the rear end can twist. Too much traction or 'grip' causes the car to want to tip over when cornering and adjusting the stiffness or degree of flex can be achieved by experimenting with different thicknesses of side rails. I've found 18 gauge piano wire works well.

The side rails, or "torsion bars" as they are sometimes referred to, do not contribute much to the beam stiffness of the chassis -- in fact if you press down the middle of the central spine, it doesn’t take much force to make it touch the track. To overcome this to some degree, I extend the central "spine" all the way to the front, as pictured below:-



The chassis is more effective if it has a degree of "plumber" movement. The more 'weight' or force on the guide under braking and during cornering, the harder it is for the guide to come out of the slot. "Plumber" movement allows the transfer of weight to the front of the chassis under braking, by allowing the rear of the pans and body to lift slightly. This is achieved through upwards hinging, to assist the weight transfer.

The "plumber" effect is best illustrated by the way that dragsters lift their front wheels off the ground when accelerating; the opposite torque effect - when decelerating - is not so obvious but it is there in a big way. The "flexi-iso" design is particularly good at transferring these forces.

Chassis can also be built so that the side-pans have a small amount of additional sliding motion, allowing the body to move slightly forwards and backwards in relation to the centre section, guide and rear wheels. This also has the effect, under braking, of transferring weight to the front and, under acceleration, towards the back, aiding traction.

Side-pans or "bat-pans" are hinged to aid the weight transfer of the body from one side of the chassis to the other, caused by cornering forces. If weight is transferred to the outside rear tyre while cornering, it will provide more traction and thereby reduce excessive sliding.

The relative movement of the various chassis parts is always very limited. The effect is to provide a degree of controlled isolation of the guide, motor/rear axle and body.

Modern Eurosport chassis are laser or EDM cut from spring steel, which does away with the need for piano wire and hinges to achieve dampening or flex. Current Eurosport chassis are also designed so that the motor-box/rear axle unit is free to move slightly from side to side. With this arrangement, often called "rear-end steering", the rear of the chassis and body is allowed to move out slightly, being pulled back into line as the car straightens up when accelerating out of the corner.

With kind regards,

Russell

[Marty Stanley]

What he said!

Actually Pablo I have ridden a motorcycle that had lots of 'flex' in the frame.

Kawasaki first brought them out in the early '70s. The Kawasaki H2! They were only three cyclinders and had a total displacement of 750cc. I forgot to mention that they were two-stroke motors - really narrow powerband, but oh what a sweet powerband! Back then it was faster then the chassis and tire designs and it was a very interesting motorcycle to ride at elevated speeds!

If you put it into a corner and really started to apply that sweet powerband, there was a feeling of impending doom that immediately swept over you as you realized the chassis was about as stiff as overcooked pasta!

Now, run it in a straight line and it was one awesome motorcycle!

[Hworth08]

Kevin's answer is correct. Since a 1:1 has a suspension that flexs it is best for the frame to stay constant and not change. No matter the materials or triangulation, a stock car frame still flexs some though.

A bit strange now, nearly all the asphalt stock cars now use very soft springs and large sway bars, known as the soft spring/big bar or SS/BB setup. This lets the suspension bottom on the stops and the car actually is just using the tires for the suspension.

Sort of make a person wonder, all the money that's spent on "handling" and the fastest way around a road course is to bounce the car off the curbs! Seems something in the design ain't quite right!

And Pablo, all chassis flex, it's the FRAME that's best not to flex.

[Prof. Fate]

Hi,

Ian and Pete Crane (Charlie Fitzpatric's son-in-law) were sending me drawings and chassis bits for that chassis design in '79. I immediately did it on one of my spring steel 1/32 monsters and it STILL puzzles me. It's big advantage is that is somehow "feels" more predictable. We were racing then at Jimbos with G15s and the hinge changed things for me!

But I still just accept it on faith.

With floppy and plumbers, in the day, we were doing high speed photography to see what the cars were doing in the corners, and you could watch!

Kawie Tripple. John Ford of SARN had one in the early '80s, a true monster. Oddly, Kawie solved their flexi flyer problem by doing an effective copy of the Norton featherbed chassis on the JP version of the Commando. I did some really irresponsible riding on that 750/4. Grin.

With bikes, you want stiff and use the suspension for the movement. But bikes don't need to keep the guide in the slot to keep the power flow. With slot cars, in the late '50s, all of us tried making working model cars that just happened to have a slot guide of some sort. It took a while to realize that we first had to keep the guide down hard on the braid, or nothing else mattered.

Fate

[Old pink can guy]

Pablo if you can read some of the stuff when Yamaha was making frames for King Kenny Roberts they tried to make them stiffer and due to tire girp the harmonic frequinces hope I spleed that right would wind up and have no place to go and cause the bike to be ill handling! some flex is required so those forces can disipate. its the yen and yang thing! too stiff is good only for one thing lol.

[endbelldrive]

OK...where's my mini torch? How are ya doing so far, Pablo? We're talking about cars with low to medium downforce cars...right?

I kinda look at the chassis as being basically a harmonic dampener... ... ... with the motor box acting like a weight at the end of a pendulum...like what Ken and others previously posted.

[Pablo]

Thanks Russell and everybody

That gives me some new ideas

I'll be firing up the minitorch here soon !

[Dennis David]

Basically in slot cars you want the chassis to work for you and in Formula 1 you want the chassis to have as little effect as possible letting the suspension and aero to do their work.

[TSR]

I wonder what JPVR thinks of the rigidity of a Belgian frite.

[Dennis David]

My best memory of Belgium was this place in Brussels called the Drug Opera. Besides their frittes they had great deserts. Oh and their gun laws are a lot looser than they are in Holland.

[Phil Irvin]

What he said!

Actually Pablo I have ridden a motorcycle that had lots of 'flex' in the frame.

Kawasaki first brought them out in the early '70s. The Kawasaki H2! They were only three cyclinders and had a total displacement of 750cc. I forgot to mention that they were two-stroke motors - really narrow powerband, but oh what a sweet powerband! Back then it was faster then the chassis and tire designs and it was a very interesting motorcycle to ride at elevated speeds!

If you put it into a corner and really started to apply that sweet powerband, there was a feeling of impending doom that immediately swept over you as you realized the chassis was about as stiff as overcooked pasta!

Now, run it in a straight line and it was one awesome motorcycle!

I had a 69 H1 saki. 500 CC. It went like stink in a straight line .....And would dump you on the corner before even coming close to the pegs.....Make that pipes. I had a set or Worges (sp) pipes on it too....Power band from 7500 to 9000.....And nothing below 3000.......But you could hear me coming 2 miles away ....

PHIL I.

[TSR]

My best memory of Belgium was this place in Brussels called the Drug Opera. Besides their frittes they had great deserts. Oh and their gun laws are a lot looser than they are in Holland.

Belgium is one of Europe's most screwed up countries, with so many issues, ours here look puny in comparison.
It is also a country where most of the fake racing cars "with 20-dollar history" such as Lola T70s, Chevron B19s and other desirable machinery for "vintage" racing are built, to be sold as "real" with utterly fabricated histories by unscrupulous British dealers (is there any other kind?).
It is also a country of multiple languages, multiple parties, in which the anarchist revolutionary party is considered as legit.
It is also a country where there are almost as many motorcycle thefts as in Italy, the country that beats all records.
Chassis rigidity in these places comes second to anti-theft devices in a vain search for any kind of protection.

[Duffy]

Gee, Philippe, I sense some veiled animosity. You should go with your feelings, let 'em out. Please don't hold back out of courtesy, we're all friends here.

And--
I dunno; when you put it that way, Europe sounds a lot like Brooklyn. But with frites.
Duffy

[Duffy]

And, AND--
If all that's going on, maybe Europeans are right to be fritened.

[TSR]

Good one Duffy!

And fear not, there is no anger in my words, I just prefer confronting reality as it really is, not as some would like you to believe. And Brussels is not the Bronx, but it can be as good and as bad, depending on which side of the knife one is. There are great (but very expensive) restaurants there, but most are just as bad as the dives found in the Bronx, with beef meat that would not be suitable for your dog.
The diff is that in the Bronx, the bill would be a LOT cheaper.

But back to chassis: why motorcycle chassis must NOT flex is a simple matter of tire-contact patch. The handling of a motorcycle greatly depends on a consistent patch, and changes to it make the motorcycle unstable. Hence it is ultimately important to maintain this consistency and increase chassis rigidity. But new factors have appeared as performance increased, that of chassis vibration frequency, that also disturbs other factors in the bike's handling. It is my opinion that telescopic front suspension is now obsolete and MUST be replaced by an adjustable dual A-arm, ball-jointed suspension system with a rigid upright that can include built-in braking acting directly on the wheel rim so as to save a massive amount of un-sprung weight.
Many moons ago, I worked on this issue with an Italian company, you can see some of the results HERE.
I believe that most of the theories also tested in practice are still valid today, a mere 32 years later.

As far as a slot car chassis, it is indeed correct to compare it somewhat to that of a go-kart. It NEEDS a certain amount of flex, in part to absorb track unevenness, in part to absorb frequencies due to motor vibration, in part to allow the tires to work properly. But in no case can it be compared to the issues of a full-size car or bike, even in its aerodynamic features.
1/24 scale air molecules are the same as 1/1 ail molecules, at least so far.

[Dennis David]

Philippe, I'm surprised you didn't mention Belgium's pedophile scandal.

[TSR]

Well, I try to keep an open mind, right?

[Phil Nyland]

Anyone who ever rode a late 60's early 70's Suzuki motocrosser would swear there's a hinge between the seat and gas tank

[TSR]

And yet, Joel Robert won several world championships aboard the beast...
No doubt that huge progress has been made since those days, but let's not forget that before the yellow Suzukis cleaned the clock of what was there, the British (Triumphs, BSA...)and Swedish bikes (Huskvarnas) were also blessed with twist-O-flex frames and LEARNED from the Japanese experience and... results as the Japanese did not sleep on their laurels and kept working at it until they utterly dominated.
Now things have changed as the Japanese became more complacent and lost ground on the best European machines.