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Mid-motor touring cars. Legit faster or fad?

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Mid-motor touring cars. Legit faster or fad?

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Old 09-09-2019, 07:54 AM
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Originally Posted by DavidNERODease View Post
The one thing I don't understand is the ridiculous flex in the front end of my Medius kit and there is no significant provision to adjust it. You can soften the rear but you can't stiffen the front
What is the distance between bulkheads?

You could use a tie rod to tie the bulkheads together at the bulkhead. We make a CF bulkhead stiffener that mounts on top of the top deck for the Gizmo/XRAY/AE car. Maybe try something like this to "close off" the front of the deck. Should help with front flex substantially. If you give me dimensions of the hole pattern for the top deck, I'll cut you a brace. Just pay for shipping.
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Old 09-09-2019, 08:10 AM
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It's hard to change your mind set when 'stiffest chassis and let the suspension do the work' was the 'Holy Grail' !!
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Old 09-09-2019, 09:15 AM
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Originally Posted by CristianTabush View Post
What is the distance between bulkheads?

You could use a tie rod to tie the bulkheads together at the bulkhead. We make a CF bulkhead stiffener that mounts on top of the top deck for the Gizmo/XRAY/AE car. Maybe try something like this to "close off" the front of the deck. Should help with front flex substantially. If you give me dimensions of the hole pattern for the top deck, I'll cut you a brace. Just pay for shipping.
I'll look into it tonight
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Old 09-09-2019, 10:22 AM
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Originally Posted by jag88 View Post
It's hard to change your mind set when 'stiffest chassis and let the suspension do the work' was the 'Holy Grail' !!

I'm always intrigued as to why chassis flex is important in RC but in full scale racing it's a big deal to get the chassis as stiff as possible. Flex in full scale racing is a bad word and essentially an un-sprung component that makes the vehicle unpredictable and difficult to tune and drive. There's some great mechanical engineering studies for chassis developers online that show how flex has a significant affect on performance by shifting load from the tires doing the work to tires that are not causing slip and understeer. I would see flex as good in something like karts with no suspension but in a typical car shouldn't we allow the suspension to do what it's designed to do? Asking for a friend...
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Old 09-09-2019, 12:37 PM
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Originally Posted by VegasHB View Post
I'm always intrigued as to why chassis flex is important in RC but in full scale racing it's a big deal to get the chassis as stiff as possible. Flex in full scale racing is a bad word and essentially an un-sprung component that makes the vehicle unpredictable and difficult to tune and drive. There's some great mechanical engineering studies for chassis developers online that show how flex has a significant affect on performance by shifting load from the tires doing the work to tires that are not causing slip and understeer. I would see flex as good in something like karts with no suspension but in a typical car shouldn't we allow the suspension to do what it's designed to do? Asking for a friend...
Big-budget full size race cars such as F1 probably use flex more than you think, and they will have a full understanding of where it's happening. Road cars normally have a lot of flex in the suspension bushes rather than the body, but road car bodies are also generally too bendy for racing which is why they get stiffened. Also there needs to be a really strong safety cell around the passenger which is something we don't have to deal with in RC.

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Old 09-09-2019, 12:56 PM
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Originally Posted by VegasHB View Post
I'm always intrigued as to why chassis flex is important in RC but in full scale racing it's a big deal to get the chassis as stiff as possible. Flex in full scale racing is a bad word and essentially an un-sprung component that makes the vehicle unpredictable and difficult to tune and drive. There's some great mechanical engineering studies for chassis developers online that show how flex has a significant affect on performance by shifting load from the tires doing the work to tires that are not causing slip and understeer. I would see flex as good in something like karts with no suspension but in a typical car shouldn't we allow the suspension to do what it's designed to do? Asking for a friend...

You are not in the car, and anything you "feel" is what your brain is making up in response to what the car does when you work the radio (shows you the power of your mind in a way). Our cars don't have the same shocks or tires like a full size car, along with much less weight and a lot more power. I think all this adds up to forgiving handling being the #1 aspect to making your car work. You need a wide window on setup, especially if you have only average talent, as most of us do. Not to mention, anything more than the most rudimentary data acquisition for rc cars is very rare. The flex is the fudge factor.
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Old 09-09-2019, 02:02 PM
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Mid or rear motor isn't the main performance focus.
Weight bias and mass centroid are, the Porsche 911 isn't hampered by its rear motor but it certainly needs fatter tyres on the rear end. It's a design choice that made sense back then and still does if you can use wider rear tyres.

​​​​Mid motor for us is just moving the motor closer to the middle of the car,getting rid of the pendulum effect by shifting the grip towards the rear end. You can't run away from physics,more weight on the tyres means they're closer to maximum grip and they produce less grip. But as mentioned above safe is fast. In the end if it's faster for you it's faster. Clock is supreme.

About flex it's complicated. You don't need it because you are introducing an undamped "spring" which is the last thing you need to do but then you are introducing another spring so the roll stiffness distribution you chose its void. That means you need larger swings in setup to change behavior. That's why 1:1 use less flex, because they can tune everything else in finer increments.
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Old 09-09-2019, 02:51 PM
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I like the idea. Even if it just resolves the dang electronic placement problem. lol
The funny thing is this is not a new idea or even innovative. A design that I am surprised that has not came up by another company is the Losi JRSR. I loved that car and true the timing of its release was bad because it was design was based on brush motor and Ni-Cd batteries. It was a more complex design and the standard design that we all run now is what is sticking. I am glad to see change and always like to try a different design.
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Old 09-09-2019, 03:45 PM
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Originally Posted by Brian10811 View Post
I like the idea. Even if it just resolves the dang electronic placement problem. lol
The funny thing is this is not a new idea or even innovative. A design that I am surprised that has not came up by another company is the Losi JRSR. I loved that car and true the timing of its release was bad because it was design was based on brush motor and Ni-Cd batteries. It was a more complex design and the standard design that we all run now is what is sticking. I am glad to see change and always like to try a different design.
I'll admit that I do like the new electrics layout even though it's more spread out. Mine isn't as pretty as some but not bad.

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Old 09-09-2019, 06:56 PM
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Originally Posted by VegasHB View Post
I'm always intrigued as to why chassis flex is important in RC but in full scale racing it's a big deal to get the chassis as stiff as possible. Flex in full scale racing is a bad word and essentially an un-sprung component that makes the vehicle unpredictable and difficult to tune and drive. There's some great mechanical engineering studies for chassis developers online that show how flex has a significant affect on performance by shifting load from the tires doing the work to tires that are not causing slip and understeer. I would see flex as good in something like karts with no suspension but in a typical car shouldn't we allow the suspension to do what it's designed to do? Asking for a friend...
I also struggle with why RC car designers like chassis flex so much. Here's my take on it:

I feel that the main tool for tuning a car is changing the roll stiffness of the front versus the rear. The end that is stiffer will transfer more weight. When you transfer more weight, the outside tire's traction does not go up as much as what you lose in traction from the inside tire. Therefore, the stiffer end will have less grip than the softer end. I stiffen or soften the roll stiffness of each end by changing out the corner springs and/or the anti-roll bars, not by changing the flex of the chassis.

Now if I make my chassis more flexible, it will lessen the effect that I get from softening one end and/or stiffening the other end. It makes my main tuning tool less effective. So that's why I've always run my chassis as stiff as I can make them. I believe that I can tune the car better and more accurately if I don't have a chassis that is not stiff.

One more way to look at it is how effective is chassis flex anyway? The anti roll bar and corner spring are two springs in parallel, so they add together. But this overall spring rate and the chassis flex are two springs in series. I'm guessing that the chassis flex is at least 10 times stiffer than the corner springs/anti-roll bars. In this case the chassis flex only lowers the roll stiffness by approximately 10%. And since it's much easier to control springs and anti-roll bars, I'll stick with them.
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Old 09-09-2019, 07:56 PM
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If you have to overcome the resistance that a gyroscope provides to turn flex or rotate I think it makes sense to have the resistance controlled and distributed evenly over more tires than less tires. I believe that placing the motor nearer to the intersect of flex that travels from front to rear corners is the place where the resistance the gyro produces will have the least impact on the flex but its just a guess.

Motogp was doing some testing where they rotated the brake rotors in the opposite direction of the wheel and the bikes transitioned much quicker. By the same logic 2 motors on an rc car rotating in opposite directions would remove the gyroscopic resistance. Or a mass of equal size to the motor rotor going in the opposite direction.
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Old 09-10-2019, 12:14 AM
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Originally Posted by glennhl View Post
I also struggle with why RC car designers like chassis flex so much. Here's my take on it:

I feel that the main tool for tuning a car is changing the roll stiffness of the front versus the rear. The end that is stiffer will transfer more weight. When you transfer more weight, the outside tire's traction does not go up as much as what you lose in traction from the inside tire. Therefore, the stiffer end will have less grip than the softer end. I stiffen or soften the roll stiffness of each end by changing out the corner springs and/or the anti-roll bars, not by changing the flex of the chassis.

Now if I make my chassis more flexible, it will lessen the effect that I get from softening one end and/or stiffening the other end. It makes my main tuning tool less effective. So that's why I've always run my chassis as stiff as I can make them. I believe that I can tune the car better and more accurately if I don't have a chassis that is not stiff.

One more way to look at it is how effective is chassis flex anyway? The anti roll bar and corner spring are two springs in parallel, so they add together. But this overall spring rate and the chassis flex are two springs in series. I'm guessing that the chassis flex is at least 10 times stiffer than the corner springs/anti-roll bars. In this case the chassis flex only lowers the roll stiffness by approximately 10%. And since it's much easier to control springs and anti-roll bars, I'll stick with them.
I used to come from the same school of (full size car tech) though, but there is something else more upstream anyway: flex is a "pure" spring - shock springs and roll bars are hydraulically damped.... A damper filters high-frequencies out - a spring doesn't. you cannot do the same thing with suspension as you can do with flex. All in all - I'm clueless about this stuff, I can't set it up, I'm not sure I can even put a name on how it "feels" on the track - but I believe it actually matters.
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Old 09-10-2019, 07:07 AM
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Originally Posted by DavidNERODease View Post
I'll admit that I do like the new electrics layout even though it's more spread out. Mine isn't as pretty as some but not bad.
Can I candidly ask what category you run this beast in? 10AH packs, structured tires - what class?

Thansk,
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Old 09-10-2019, 07:13 AM
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Originally Posted by Lonestar View Post
Can I candidly ask what category you run this beast in? 10AH packs, structured tires - what class?

Thansk,
Paul
i think USGT 21.5
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Old 09-10-2019, 07:22 AM
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Originally Posted by Lonestar View Post
Can I candidly ask what category you run this beast in? 10AH packs, structured tires - what class?

Thansk,
Paul
itís actually only like a 8500mah R1 rates there batteries That are HV are rated at there 8.7v discharge curve to 6v
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