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Old 08-21-2014, 04:28 PM   #31
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Originally Posted by CristianTabush View Post
I have an observation on this, which has always intrigued me. While the laws of Physics remain the same, I think the application might change a bit. I think where things get tricky is that Surface area increases ^2 and volume increases ^3.
That's the crux of the problem if one desires to get data from a scale model and accurately apply it to a full-scale model (or vice-versa).

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One example that stuck in my brain was the effect of down force at the slower speeds affected our cars.
Aerodynamics is one of the disciplines where scale models are used since large wind tunnels are expensive, but getting useful data that extrapolates back to 1:1 scale is difficult because the air itself isn't scaled; i.e. the distance between molecules doesn't shrink by a factor of 10 for a 1/10 scale model if the tests are run at normal atmospheric pressure and temperature. The general goal is to run the scale model in the wind tunnel at the same Reynolds number if one wants reasonable data to use on the full-scale vehicle. This value is dependent on many factors such as density and viscosity of the medium, and velocity. Also, the equations that describe aerodynamics well are wildly non-linear, which adds to the fun.

Aerodynamicists in both the aviation and automotive industry constantly yearn for ever-larger wind tunnels so that they can more accurately predict what will happen on the actual vehicle.

Small models are actually less aerodynamically efficient than one might guess, because they operate at lower Reynolds numbers. Small model airplanes don't generate lift as readily as real airplanes, and small model cars don't generate downforce as readily (though it can still be substantial). Imagine how good these things would stick to the track if the air were 10 times thicker!
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Old 08-22-2014, 12:11 AM   #32
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Originally Posted by inpuressa View Post
Differentials could be changed to LSD style ones, and again, it did come out for 1/8 off-road, but also never caught on. Not to mention expensive.
I'd love to have a Torsen limited slip in my little touring car. Did wonders compared to the open diff in my autocrosser. Just don't lift a tire.
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Old 08-22-2014, 12:45 AM   #33
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In RC cars , more flex means more grip ( better cornering ability, feeling more planted, higher cornering speed @ tight turns ).
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Old 08-22-2014, 01:56 AM   #34
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I'd love to have a Torsen limited slip in my little touring car. Did wonders compared to the open diff in my autocrosser. Just don't lift a tire.
What Torsen did you use?
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Old 08-22-2014, 03:51 AM   #35
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I see it this way:

1:1 scale cars mostly made of metal, bolted/welded together so when it flexes it doesn't snap back like plastic tub or carbon fiber chassis. I've seen a chassis/body alignment rig, basically it checks for tweaks then twists the whole car while being hoisted (without engine, tyres, etc) back to its specs. Maybe that's why race cars are reinforced not to tweak or flex because once it does, it stays thay way.

In my experience, a soft chassis is easier to drive but will be slow when pushed hard or driven aggressively, example is a TA05R, that kit feels like a rubber.
On the other hand, a stiff RC chassis is nervous to drive without downforce from let's say protoform body. But will be faster if driven aggressively and is sensitive to set up changes and surface conditions.
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Old 08-22-2014, 06:30 AM   #36
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Originally Posted by Airflow View Post
I see it this way:

1:1 scale cars mostly made of metal, bolted/welded together so when it flexes it doesn't snap back like plastic tub or carbon fiber chassis. I've seen a chassis/body alignment rig, basically it checks for tweaks then twists the whole car while being hoisted (without engine, tyres, etc) back to its specs. Maybe that's why race cars are reinforced not to tweak or flex because once it does, it stays thay way.

In my experience, a soft chassis is easier to drive but will be slow when pushed hard or driven aggressively, example is a TA05R, that kit feels like a rubber.
On the other hand, a stiff RC chassis is nervous to drive without downforce from let's say protoform body. But will be faster if driven aggressively and is sensitive to set up changes and surface conditions.
I use the carbon TA05R tub and I think it's the stiffest car I have seen.
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Old 08-22-2014, 12:52 PM   #37
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I use the carbon TA05R tub and I think it's the stiffest car I have seen.
second that. the carbon reinforced parts are the same material as the arms so they are pretty stiff. The stock one is pretty soft though. But I remember the original TA05 was easy to drive and it's probably due to that soft chassis.
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Old 08-22-2014, 07:25 PM   #38
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Flex in the 1:1 world depends on the construction of the car but adding stiffness to the car is always recommended as it makes the suspension work like it's supposed to. That being said some flex is still wanted as a completely solid car will be very hard on mounting and stress points. Too much flex though will make the car unpredictable as there's no way to control it
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Old 08-22-2014, 11:44 PM   #39
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Few points some of which have probably already been covered.

Shocks used in RC do not damp high frequency vibrations well. Flex in the chassi helps keep the car stable and damp out these vibrations. (With foam tyres the tyre damped out the vibrations and the chassis were designed to be very stiff)

Different roll centers front and rear, torsional flex helps to allow both ends of the car to roll different amounts slightly to optimise performance at both ends of the car.

Wider setup window which allows more margin for error.

Couple of other points, real cars flex too, standard production cars flex a lot more than a RC car.

In one class of race car the chassis are setup so that they have 10 times more redgidity of the suspension. Ie if the suspension compresses 20mm under load the chassi with flex 2mm.
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Old 08-22-2014, 11:51 PM   #40
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Originally Posted by howardcano View Post
I would stick with the basics (only one of which has to do with this thread):

1) Increase the torsional rigidity of the chassis.

2) Lower the CG by laying the dampers down, or using rotary (or other) dampers.

3) Make the bump spring rates, roll spring rates, and damping infinitely adjustable.

4) Make the bump springing and roll springing mechanisms independent from each other.

(Items 2 and 3 are already being done in the Awesomatix design.)

Then I would consider other, more esoteric items. For instance:

Active differential, so coupling can be varied in real-time depending on torque, velocity, or some other selectable parameters.

I'll stop here, since these items are best discussed (and have been discussed) in a different thread.
Well no matter how innovative or low cg the awesomatix is..one fact remains. It still requires flex. Look at the latest a700 evo. They use a rod to substitute the upper deck. Why ? They want the flex !
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Old 08-23-2014, 12:26 AM   #41
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Originally Posted by alcyon View Post
Well no matter how innovative or low cg the awesomatix is..one fact remains. It still requires flex. Look at the latest a700 evo. They use a rod to substitute the upper deck. Why ? They want the flex !
It's actually the other way around, they use that rod to keep the torque of the driveshaft from twisting the chassis and upsetting the handling.
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Old 08-23-2014, 03:35 AM   #42
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It's actually the other way around, they use that rod to keep the torque of the driveshaft from twisting the chassis and upsetting the handling.

Lol. Thats what the local awesokatix dealer told me when i asked him about the rod deck. Looks like he doesnt know his own product.
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Old 08-24-2014, 12:34 AM   #43
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Well I'm glad I asked! Been a lot of interesting points brought up. I'm wanting to pick up a used roller for 17.5 class and have been debating between the tc4 and the tc5. That's what spawned the question in case anyone was wondering. Thanks folks!
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Old 08-24-2014, 07:17 AM   #44
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Lol. Thats what the local awesokatix dealer told me when i asked him about the rod deck. Looks like he doesnt know his own product.
Awesomatix torque rod does two things, it acts like upperdeck and isolated the torque from the motor at the same time.
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Old 08-25-2014, 01:17 PM   #45
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(...for making me want a Yokomo)





http://www.eviltwinmotorsports.com/?page_id=204&page=3

Thanks for posting this. A great article!

Chassis flex will be around until every driver has a team of engineers and full data acquisition equipment on their car. RC Cars are unique machines that require unique design solutions.
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