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Old 10-12-2009, 09:00 PM   #166
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It's not. It's a little lighter in comparison to the older style batteries.
I think Robbie was comparing the electronics on one side wieghing about the same as a LiPo.
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Old 10-12-2009, 09:33 PM   #167
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The corally 1/12 mini tc had the arms through the bulkhead (I think.) The problem is you are adding more complexity and parts without having to. As for the diffs on the losi, the reason they are so wide is to run 2 belts instead of 3. You could try to invent something, but again, you are adding more parts and complexity without having to. The xray basic design is the national and world champion in every class.

Another thing, I've always thought that the biggest problem with the everything down the middle design is you don't get very much roll and the car self corrects very quickly. This is great on carpet, not so great on lower traction surfaces.

Anyway, to each their own. I've always liked the xray quality and the fact that you don't have to sand or modify anything and the car goes together perfectly. Plus the cars are very durable. I am sure the new one won't be any different.
Sure, any new design comes with its own trade-offs. Until we get motors inside each wheel I think not much is going to change. Pretty much all the possible layouts have been explored by the manufacturers and it looks like all they can do (with current technology) is little tweaks here and there, and/or specialise the cars for one surface/tire.

The problem with a car with the weight all down the middle is that is not actually self correcting. If you think of the jet fighters currently in use by various military you will see they are not dynamically stable (i.e. they can fly upside down, on the side or tail first). They are stabilised by computers but having their center of gravity pretty much in the center of the plane allows them to manouvre way beyond the limits of human endurance. Same applies here. If your car had all its weight concentrasted at one point in the CG and that was exactly in the middle of the 4 wheels' contact patch, your car would change direction faster than tire grip would be able to cope with. Making the car lighter reduces grip too, so there's a constraint to how light you can go, and my prediction is that at some point you will see that a heavier car is actually faster than a lighter one simply because you need some weight to get back some grip. Distributing a light weight car's weight at the corners helps. I am only curious where this tipping point is.
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Old 10-12-2009, 11:35 PM   #168
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I think its great that Xray are developing the T3, even if the differences are minimal, as long as it is positive then why not? I own a 009 and I don't feel 'jipped' by Xray with them releasing a new car for the next year. I bought the 009 knowing full well they update every year and for the people who don't like it or complain about a new model each year - you don't have to buy it if you don't want to.

Can't wait to see the final production pics.
+1

I cant wait for this car. The small updates and refinements will only make the car better. The pictures that are out now look almost like a foam car or stiffer car made for carpet. It dosent have many cutouts on the topdeck and has the stiffening posts available on either side. Im sure the final design will be very different and it will be a great car

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Old 10-13-2009, 12:01 AM   #169
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+1

I cant wait for this car. The small updates and refinements will only make the car better. The pictures that are out now look almost like a foam car or stiffer car made for carpet. It dosent have many cutouts on the topdeck and has the stiffening posts available on either side. Im sure the final design will be very different and it will be a great car

Antoni
Posts on side, as their is no bulkhead screw in front of the layshaft bearing anymore.

Broader top deck, perhaps to keep the stiffness at the front of the chassis, and generate the flex where every Xray needs it, at the rear end for predictable handling, and a wider setup window.
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Old 10-13-2009, 12:51 AM   #170
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Making the car lighter reduces grip too, so there's a constraint to how light you can go, and my prediction is that at some point you will see that a heavier car is actually faster than a lighter one simply because you need some weight to get back some grip.
That is when you can start running softer tyres and go even faster without overheating the tyres.
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Old 10-13-2009, 12:59 AM   #171
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Default Yeah I was thinking....

the same thing, but I'm sure they have explored it. I would rather have blocks like the TC4 or HPI pro 4. They were solid.

I love my 008, but it would be nice to have the motor moved in, electronics moved in and battery moved out. Xray has priced me out of any new car, so I only see a T3R in my future.

My guess, ball cups on the production? The machining looks a lot less detailed. Will be interesting to see the production car.


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IMHO, the Suspension mounts look like they may be a good place for tweek or bends. The HB/Tamiya mounts have a much more substantial "bridge" between the two sides, and they bend when hit hard enough. The inner front appears to have one screw, I would be concerned with the durability of that for average drivers. The Tamiya one piece mounts have two screws...

I am no engineer, so I am probably incorrect, but just kind of stood out to me.
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Old 10-13-2009, 03:57 AM   #172
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The problem with a car with the weight all down the middle is that is not actually self correcting. If you think of the jet fighters currently in use by various military you will see they are not dynamically stable (i.e. they can fly upside down, on the side or tail first). They are stabilised by computers but having their center of gravity pretty much in the center of the plane allows them to manouvre way beyond the limits of human endurance. Same applies here. If your car had all its weight concentrasted at one point in the CG and that was exactly in the middle of the 4 wheels' contact patch, your car would change direction faster than tire grip would be able to cope with. Making the car lighter reduces grip too, so there's a constraint to how light you can go, and my prediction is that at some point you will see that a heavier car is actually faster than a lighter one simply because you need some weight to get back some grip. Distributing a light weight car's weight at the corners helps. I am only curious where this tipping point is.
I don't think this is quite right from what i've studied. As long as the CG is far enough forward so the amount of rear grip can always generate a lateral force more than the turning force (moment) the car will always be stable in a corner (neutral or understeer). The only time a car can get unstable and oversteer is when the rear lateral grip is not enough to balance the rotating moment which depends mostly on the distance the CG is from the front track and not much to do with unsprung side-to-side weight distrbution which probably effects roll angle more than anything. I tend to look as F1 cars as an example, they have all the weight low and centered as much as possible and their chassis barely roll at all.

The only time i ever heard anyone want to make a light car heavier in any form of racing is if the rules specify it. we all want to be that 10 year old kid who can drive at the go kart track - i hate those kids (my son being one of them)
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Old 10-13-2009, 04:37 AM   #173
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I don't think this is quite right from what i've studied. As long as the CG is far enough forward so the amount of rear grip can always generate a lateral force more than the turning force (moment) the car will always be stable in a corner (neutral or understeer). The only time a car can get unstable and oversteer is when the rear lateral grip is not enough to balance the rotating moment which depends mostly on the distance the CG is from the front track and not much to do with unsprung side-to-side weight distrbution which probably effects roll angle more than anything. I tend to look as F1 cars as an example, they have all the weight low and centered as much as possible and their chassis barely roll at all.

The only time i ever heard anyone want to make a light car heavier in any form of racing is if the rules specify it. we all want to be that 10 year old kid who can drive at the go kart track - i hate those kids (my son being one of them)
I wasn't talking about unsprung weight.

I don't really understand your point otherwise.

I think if you're having problems with the rear coming loose you will find that having a rear-biased weight distribution is more helpful than the other way around (all else being equal).

Those forces you talk about depend on speed as well as mass (weight). Grip depends on weight alone. The lower the weight, the lower the grip, lateral or otherwise. Don't confuse yourself with complicated notions. Look at the basic principles. All the tuning and tweaking can only make the best possible use of the grip available, but not increase it. That is physically impossible just like a perpetuum mobile. Sure, you can tune the car to transfer the weight on the axle you need, or to keep the contact patch as large as you can and so on and on, but ultimately, the grip available is a given value and when you've done everything you can there are only two things left to do to get more grip: slow down or increase weight. And as the purpose of racing is to be fast, there is only one option left.

From experience I can tell you that a lot of the people in mod at our club think they need the sanctioned 1500gr weight limit and some go above that in order to increase grip. In lower classes you could probably get away with less weight (not allowed though) without losing grip, but when trying to carry higher corner speeds it is becoming a problem.

F1 cars are exactly an example up my alley. They have the weight as far forward as physically possible, but still most of it is on the rear axle (leave aside they use ballast distributed around the car to achieve the desired weight distribution). The reason they would like to have it all in the middle at one point is as I pointed out above, so they can be dynamically unstable (which is equal to unbiased). A good example of something biased and therefore very stable (so the exact opposite to an F1 car or a jet fighter) is an arrow. An arrow tends to go pointy end first, no matter what. You can shoot it with the wrong end first and it will try to turn the right way around. That makes an arrow very hard to steer (or blow off course), because they want to go head first and in a straight line. In opposition, a jet fighter or an F1 car are more manouverable the more dynamically unstable they are.

Back to F1 cars, they can't have all the weight in the center at one point. The engine and gearbox are almost entirely on the rear axle. So my guess is they try to distribute the ballast around such that they get close to probably 40:60 front/rear (no F1 team will tell us what their weight distribution is, but you can read here if you want: http://www.springerlink.com/content/e7213614284627w7/ click on the full text link at the top). Also, they have a lot of downforce (aerodynamic aids), and a lot of dynamic load (under acceleration) on the rear axle. That is what gives them grip beyond what their weight would lead us to believe. Just watch an F1 car that has lost its rear airfoil in a crash how clumsy and slow has to limp through corners.

That is not the case for us. Have a play. Get a F1 R/C car and see how light you can make it before it becomes undriveable.

Just realised you're in Australia. Get your nice big V8 ute and try going fast through a corner, find the max speed you can do and then try adding some weight on the back to see if you can go faster or not.
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Old 10-13-2009, 07:50 AM   #174
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I wasn't talking about unsprung weight.

I don't really understand your point otherwise.

I think if you're having problems with the rear coming loose you will find that having a rear-biased weight distribution is more helpful than the other way around (all else being equal).

Those forces you talk about depend on speed as well as mass (weight). Grip depends on weight alone. The lower the weight, the lower the grip, lateral or otherwise. Don't confuse yourself with complicated notions. Look at the basic principles. All the tuning and tweaking can only make the best possible use of the grip available, but not increase it. That is physically impossible just like a perpetuum mobile. Sure, you can tune the car to transfer the weight on the axle you need, or to keep the contact patch as large as you can and so on and on, but ultimately, the grip available is a given value and when you've done everything you can there are only two things left to do to get more grip: slow down or increase weight. And as the purpose of racing is to be fast, there is only one option left.

From experience I can tell you that a lot of the people in mod at our club think they need the sanctioned 1500gr weight limit and some go above that in order to increase grip. In lower classes you could probably get away with less weight (not allowed though) without losing grip, but when trying to carry higher corner speeds it is becoming a problem.

F1 cars are exactly an example up my alley. They have the weight as far forward as physically possible, but still most of it is on the rear axle (leave aside they use ballast distributed around the car to achieve the desired weight distribution). The reason they would like to have it all in the middle at one point is as I pointed out above, so they can be dynamically unstable (which is equal to unbiased). A good example of something biased and therefore very stable (so the exact opposite to an F1 car or a jet fighter) is an arrow. An arrow tends to go pointy end first, no matter what. You can shoot it with the wrong end first and it will try to turn the right way around. That makes an arrow very hard to steer (or blow off course), because they want to go head first and in a straight line. In opposition, a jet fighter or an F1 car are more manouverable the more dynamically unstable they are.

Back to F1 cars, they can't have all the weight in the center at one point. The engine and gearbox are almost entirely on the rear axle. So my guess is they try to distribute the ballast around such that they get close to probably 40:60 front/rear (no F1 team will tell us what their weight distribution is, but you can read here if you want: http://www.springerlink.com/content/e7213614284627w7/ click on the full text link at the top). Also, they have a lot of downforce (aerodynamic aids), and a lot of dynamic load (under acceleration) on the rear axle. That is what gives them grip beyond what their weight would lead us to believe. Just watch an F1 car that has lost its rear airfoil in a crash how clumsy and slow has to limp through corners.

That is not the case for us. Have a play. Get a F1 R/C car and see how light you can make it before it becomes undriveable.

Just realised you're in Australia. Get your nice big V8 ute and try going fast through a corner, find the max speed you can do and then try adding some weight on the back to see if you can go faster or not.
i didn't intend to create a technical debate in the thread here, but firstly yeah i typed unsprung instead of sprung sorry for that, doh! i read the rest of what you typed but to me it is backwards. Unless an RC tire generates more lateral force than the vertical force applied to it? (generally tires lose efficency as you load them up). More weight doesn't mean faster cornering (or higher cornering forces) unless the tire generates more grip than the force required to move the weight itself around the corner. My experience is that if i put a stiffer roll bar up front i get more understeer in a corner due to loading the outside front tire more which means that tire is losing efficiency as it is loaded more, not gaining.

Also, at our club track records are still being broken in the spec classes even though motors got slower but weight dropped 100g. less weight, less grip, slower motors, faster times it doesn't add up?

F1 car oversteers when it loses rear wing, this is because downforce is an external force not related to the weight of the car (for this discussion it is a free weight that you don't have to carry around the corner in the car with you). You have a situation where the front wing still provides downforce and of course overall front grip is higher and the rear is all over the place. A rear biased CG makes this worse becuase the heavy end of the pendulum just got outta control. Likewise if they lose the front wing they understeer like a dog, but they are not unstable like if they lose the rear wing.

utes understeer in corners, they break rear traction easy on power cos yeah they have no weight over the back and it easy to use up all the rear grip with the throttle and a V8

All i was trying to say is that having all the weight up the middle like a losi or TM E4 i don't think makes the car inherently unstable (oversteer) if the weight bias is to the front. If you meant something else by instabiliy or ability to correct itself then i apologise, we have our wires crossed

Us aussie's gotta get our stories straight, lol!

BTW: i like your sig, driver's skill is a definite upgrade worth having
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Old 10-13-2009, 09:36 AM   #175
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i read the rest of what you typed but to me it is backwards. Unless an RC tire generates more lateral force than the vertical force applied to it? (generally tires lose efficency as you load them up). More weight doesn't mean faster cornering (or higher cornering forces) unless the tire generates more grip than the force required to move the weight itself around the corner. My experience is that if i put a stiffer roll bar up front i get more understeer in a corner due to loading the outside front tire more which means that tire is losing efficiency as it is loaded more, not gaining.
No, completely untrue. It isn't that black and white, it actually varies with a curve. There is actually a grip "curve" if you will, when dealing with tire traction and load. The curve slowly ramps up, and then drops off sudenly. The drop off represents the point where the tire is overloaded, and you skid out. Up until that point, traction increases as load increases.

Now, a real full scale car, under normal driving conditions, operates pretty close to that drop off point on the curve. Too much roll, loading the outside tires too much, and vuala... you break traction. But an RC car doesn't operate there. tiny 1/10th scale cars operate at the very beginning of the curve, and it is difficult to get them to even REACH the curve fall off.

That is why in full scale cars, reducing roll and keeping traction across all 4 tires increases traction when driving the car hard, and why in 1/10th scale cars, you INCREASE roll and individual tire load to increase traction.

They are exact opposites, but work on the same principle if you understand the traction/load curve that a tire operates under.
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Old 10-13-2009, 09:38 AM   #176
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Don't worry about the thread. Banter is just to keep it going til the car is released.

I read your post again and I undestand better what you're trying to say. I agree of course, with the points you made.

100 grams is not much, and yes, you will get faster. Perhaps you can shave more than that again, and keep shaving, but my point is that eventually a point is achieved where further weight loss is detrimental rather than helpful. That is why I told you about the experience of the mod guys at our track.

Brushless motors are getting more powerful and escs are more and more capable of extracting this power while weight seems to be going down as batteries get ligther and electronics smaller. It follows then that at some point we will have so much power, the cars will just be too light. Sure, stickier tires can help but I am sure we will reach the point I was talking about.

And yes, swaybars will do that and it's normal. If you ever had a FWD car (real) you know the secret to tame understeer is to get a beefier rear swaybar.

Yeah, I think there is more gain in skill than upgrades. Sure, the global economy has other imperatives.
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Old 10-13-2009, 09:52 AM   #177
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Having owned or tinkered with virtually every TC on the market at some stage or another over the last 10 years I have a fair bit of knowledge about TC setup and design. I can assure you for a fact that this chassis is a MAJOR change from the T2 platform which I also have owned. I haven't been a big fan of xray since I owned a few of them but I am sure this car is a huge change and has much potential. If you don't understand why then you may explaining it would not help. I suggest you just try one when it comes out.

BTW I have been bagging XRAY for years so I am hardly biased.
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Old 10-13-2009, 10:02 AM   #178
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[...]
If you don't understand why then you may explaining it would not help. I suggest you just try one when it comes out.

BTW I have been bagging XRAY for years so I am hardly biased.
Can you please rephrase the first sentence above?

Judging by the past, the car will be expensive to buy for a try.

Aha! You sold out!

Capt'n, it would be interesting while we wait here for the car to arrive if you could point us to some literature. I am interested in the factors considered in building the curve you talk about. Common sense and basic physics would suggest grip vs load should be a linear variation, but I can imagine a number of things that could change that.
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Old 10-13-2009, 02:10 PM   #179
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Judging by the past, the car will be expensive to buy for a try.
Actually XRAY chassis hold their value very well so to resell it and recoupe most of your costs would be easy. I for one would be interested in playing with one for the 1st time in years but that said my current chassis has proven to make me faster than drivers who I think are better than me... Hard choice lol!
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Old 10-13-2009, 02:35 PM   #180
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No, completely untrue. It isn't that black and white, it actually varies with a curve. There is actually a grip "curve" if you will, when dealing with tire traction and load. The curve slowly ramps up, and then drops off sudenly. The drop off represents the point where the tire is overloaded, and you skid out. Up until that point, traction increases as load increases.

Now, a real full scale car, under normal driving conditions, operates pretty close to that drop off point on the curve. Too much roll, loading the outside tires too much, and vuala... you break traction. But an RC car doesn't operate there. tiny 1/10th scale cars operate at the very beginning of the curve, and it is difficult to get them to even REACH the curve fall off.

That is why in full scale cars, reducing roll and keeping traction across all 4 tires increases traction when driving the car hard, and why in 1/10th scale cars, you INCREASE roll and individual tire load to increase traction.

They are exact opposites, but work on the same principle if you understand the traction/load curve that a tire operates under.
I understand it is a curve i am familiar with them for full size chassis work. Seriously, now i am learning something new. Occasionally i have noticed that things don't work out the way i intended (the opposite) and i put it down to me not interpreting the result correctly or not being in touch with the feel of the car on that day or something. But it would seem if what you say is true then it all becomes clear. I still have some confusion on rollbars but it would seem maybe i still get understeer because of the less roll and less tire loading rather than tire overloading, possibly same result but for different reasons.

Do you have any RC tire data? I'd love to build an RC sized test rig to test it, i had some crazy idea's involving a belt sander and some strain gauges, lol!

Thanks for the tip, i need to get down to the track to try some of this out. I think you've just increased the fun factor for me by a million
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