10 replies to this topic

[mariner]

As I mentioned earlier Richard Mallock came to the 750 club one evening to tell the history of the Mallock U2 cars.

 

Before I expand on the question above some things that came out from Richard’s talk.

 

- They were one of the first constructors to use FEA on a spaceframe with impressive results. Apparently the original application was optimizing electricity pylon designs!

 

- As Mallocks mostly ran with an underbody tunnel once GE was understood it kept their solid axle design competitive. The unsprung weight ratio fell as downforce rose and the solid axle (especially the BMC one) allowed a big, single tunnel helped by the front/central engine location.

 

Once downforce was more regulation limited they went to a de Dion axle for the mark 36.

 

Like F1 pitch sensitivity was constant problem. sorted by a longer wheelbase and running 150kg of pre load plus "no droop" at the front. drivers didn’t like it at first but they did when they went quicker.

 

Mallock have now built 350 cars, many more than I thought.

 

Back to the question above. The FEA chassis has claimed 8,000 ft/lb/degree stiffness and it has just one removable tube to get engine out.

 

One idea was to remove the tube for wet races to reduce chassis stiffness to improve feel.

 

I have never heard of a twisty chassis helping in low grip conditions. I know you soften roll bars etc but I though that was to let the car roll more onto the tyre edges.

 

Can anybody think of why that less chassis stiffness for the wet idea might actually work?

 

 

[MatsNorway]

It does work but i can not explain it properly. I think it has to do with the car being more forgiving, gentle and smooth.

 

Its very common for RC cars to have adjustable flex. They also use different deck thicknesses if the chance needed is big.

http://www.teamxray....e58f65e16de9369

Rubber tire edition is 2.5mm vs the foam tire model being 3.5mm that is a significant difference.

 

Its not just flex either. They tuned how the flex is applied.

 

They even have suspension arm flex options. I assume it has something to it but its a fairly new thing in RC cars. At least for me.

http://www.teamxray.com/t4/

http://www.teamxray.com/xb4/

Edited by MatsNorway, 09 October 2014 - 18:14.

[gruntguru]

Reducing torsional rigidity without changing the springs or dampers will reduce the effective wheel rates for springing and damping in single-wheel-bump (kerb strike) without reducing stiffness and damping in roll, pitch or heave. One drawback is that depending on the distribution of roll inertia, the roll moment distribution and the roll damping distribution (front to rear) may change from the normal setup.  

[Lee Nicolle]

Karts use twisty frames, the only suspension they have.

In years past I have known of cars too stiff for class rules. Commodore Cup was one. Too stiff a cage made the cars very twitchy. Which really says something about allowed suspension packages!

Speedway midgets used to twist too.  An amount in the 80s was built in. Though I doubt they do now with their very offset nature. Not pretty to look at but can provide some very good racing at times.

[Greg Locock]

The ballpark figure for 'enough' torsional rigidity to stop affecting handling is somewhere between 2500 and 10000 ft lb/deg for a full size road car. A track car with stiffer shocks may benefit from more than that, there again it is likely to weigh less than 1.4 tons. There are various advantages even for a road car in going stiffer than 10000, but it won't show up in objective steering/handling data. I'd have thought any serious wet weather handling package would want to do more than just affect the stiffness coupling front to rear, but perhaps combined with adjustable shocks that is enough by itself to make a significant worthwhile difference.

[Fat Boy]

I've known people that dump chassis stiffness on purpose from time to time. To be honest, I've never seen much of an advantage to it. You're shifting the roll couple from a spring that is damped to one that is undamped. That's rarely a good thing. The only real advantage with it *might* be that it's a quick change which is easily repeatable.

 

Rain, being inherently mischievious, always waits until right before a session or race before showing itself. This causes all sorts of scrambling and lamentations from the crews while the engineer alternates his slack-jawed gaze between the sky and his smart phone (which, being in on the joke, will refuse to load the most recent radar sweep of the area. Besides that, the damn thing is stuck on Sheboygan, Wisconsin and you're in upstate New York!)

 

The real answer would be to soften the springs/bars/dampers, reduce cambers, increase tire pressure and max the aero.

 

What you'll probably end up doing is get the rain tires on the car (2 set to dry cold pressures, 1 set to wet cold pressure, and the one that just came back from mounter is at whatever pressure it took to set the bead.) Likely any other change you make will be in a rush and set wrong. 3 clicks softer compression invariably turns into 3 clicks stiffer rebound and if you were so optimistic as to change springs, then they were incorrect for sure and your corner weights are god-knows-where. Ride heights? "I thought Joey was checking that..." If you put a bigger gurney on the rear wing, that probably ended up OK, but the change to the front didn't happen, so who knows where the aero balance is at? Not me.

 

Invariably, the driver either likes the wet, ends up at the top of the sheet timing proclaiming the car brilliant or he doesn't care for the wet, is in the middle of the sheet declaring the car 'undriveable'. The last option is the guy who actively hates the rain. He comes back safe and sound in the tow-truck.

 

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We had a wet session at Petit a week ago. I didn't even have the guys warm the car up. We crowded in the office and watched a bit of _Talledega Nights_. I highly recommend this approach.

[Ross Stonefeld]

I heard, and was never able to confirm, that when they filmed some of the on-track bits at Talladega and introduced the French racing driver the real crowd booed.

[Fat Boy]

Damned straight we boo'd him....I mean, "they" boo'd him....

 

 

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Honestly, how happy would Sasha have been with that type of a reception? He would have been over the moon!

[Lee Nicolle]

I've known people that dump chassis stiffness on purpose from time to time. To be honest, I've never seen much of an advantage to it. You're shifting the roll couple from a spring that is damped to one that is undamped. That's rarely a good thing. The only real advantage with it *might* be that it's a quick change which is easily repeatable.

 

Rain, being inherently mischievious, always waits until right before a session or race before showing itself. This causes all sorts of scrambling and lamentations from the crews while the engineer alternates his slack-jawed gaze between the sky and his smart phone (which, being in on the joke, will refuse to load the most recent radar sweep of the area. Besides that, the damn thing is stuck on Sheboygan, Wisconsin and you're in upstate New York!)

 

The real answer would be to soften the springs/bars/dampers, reduce cambers, increase tire pressure and max the aero.

 

What you'll probably end up doing is get the rain tires on the car (2 set to dry cold pressures, 1 set to wet cold pressure, and the one that just came back from mounter is at whatever pressure it took to set the bead.) Likely any other change you make will be in a rush and set wrong. 3 clicks softer compression invariably turns into 3 clicks stiffer rebound and if you were so optimistic as to change springs, then they were incorrect for sure and your corner weights are god-knows-where. Ride heights? "I thought Joey was checking that..." If you put a bigger gurney on the rear wing, that probably ended up OK, but the change to the front didn't happen, so who knows where the aero balance is at? Not me.

 

Invariably, the driver either likes the wet, ends up at the top of the sheet timing proclaiming the car brilliant or he doesn't care for the wet, is in the middle of the sheet declaring the car 'undriveable'. The last option is the guy who actively hates the rain. He comes back safe and sound in the tow-truck.

 

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We had a wet session at Petit a week ago. I didn't even have the guys warm the car up. We crowded in the office and watched a bit of _Talledega Nights_. I highly recommend this approach.

Gee you sound organised. If there was a chance of rain I always had the wets ready to go and pressured. Then it was soften the bars and grit your teeth. I hate the rain, but generally seemed to go ok in it. Though good wets always make a difference and generally mine were not. Though I have raced in torrential rain on occasion and even then did ok. But slow and cautious,, and finish.

Changing springs is always ideal,, but by yourself or with one helper takes way too long. Often you make the call to change about 3 min before due on the track. So a real mad rush to change the wheels

[Fat Boy]

Gee you sound organised.

 

Gee, you sound like you have a stick in your ass.

 

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It's the off-season. I was having a little fun. I understand I'm not up to the writing standards of RDV, but I'm sure I'm not the only person to go through a pre-session rain scramble.

Edited by Fat Boy, 13 October 2014 - 22:43.

[Catalina Park]

I think Fat Boy just about covered it.

My idea of a wet set up was changing the tyres and hoping they still had pressure, knowing that two of the wheels were porous which was why those wheels had wets and not drys.

I have sent a car to the assembly area on two wets and two drys so that we could make the decision late and only have to change two wheels. (and we still made the wrong choice!)