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Old 09-01-2009, 12:04 AM   #31
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What are you going to run the car on?Road?Asphalt?Carpet?If you goin on asphalt tracks or something like that.Try Foam Tires.
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Old 09-01-2009, 08:28 AM   #32
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Hi speed attempts is better of with rubber tire i think.
The ballooning of the tire gives off a smaller footprint, and thus less roll resistance.
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Old 09-01-2009, 11:45 AM   #33
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Last week I would have agreed on the rubber tire theory, until a racer at our track took his TC off the track and gave it full throttle while holding it in his hand. The ESC ramped the timing to the point it sounded like a dentists drill and he exploded two Jaco blue tires. It sounded like a small caliber handgun had gone off...

wouldn't want that to happen under your car @ 100 MPH...
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Old 09-01-2009, 12:08 PM   #34
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Can anyone point me to some general information on tires? More importantly, what are best for top speed, but I'd really like information about road tires in general.

Try BSR tires for info. They made the tires for Nic Cases speed run car
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Old 09-01-2009, 01:33 PM   #35
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Last week I would have agreed on the rubber tire theory, until a racer at our track took his TC off the track and gave it full throttle while holding it in his hand. The ESC ramped the timing to the point it sounded like a dentists drill and he exploded two Jaco blue tires. It sounded like a small caliber handgun had gone off...

wouldn't want that to happen under your car @ 100 MPH...
A buddy did that at my track last week. Sounded more like a larg rubber band breaking. Pretty wild if you ask me. Thats with a 13.5 !!

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Old 09-01-2009, 03:24 PM   #36
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Default Chassis

I am on Austinitsua's team here at KU. I'm the chassis team member. I have very little to no knowledge of cars, full size or RC, or their components. If we're to build the chassis from scratch, either by machining it in our lab with a CNC, or by other means, can anybody lead me in the right direction as to what is the most desirable material for this build as to minimize overall deflection, increase strength, and decrease weight.

Also, where is the best position for the center of gravity?
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Old 09-01-2009, 03:36 PM   #37
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Also, where is the best position for the center of gravity?
Low. The lower the better!
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Old 09-01-2009, 03:37 PM   #38
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In positioning the c.g. is it better to have it directly over the rear wheels, or more centered in the body?
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Old 09-01-2009, 03:53 PM   #39
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CG should be slightly ahead of half way forward. If I remember correctly the tire stiffness times the moment arm to the CG has to be larger in ther rear to keep from going into a oversteer condition. So with a car with 50/50 weight distribution, the rear tires need to be stiffer (wider or more air pressure) to keep from spinning out at a critical speed. This is true oversteer, which the corvair could have if the rear tires were not inflated more than the front. See "unsafe at any speed" by ralph nader. You dont want this as any steering input above your critical speed will cause a crash. If the CG is toward the back, you need a lot bigger/stiffer tire in the rear to make it work. Ie gocarts.

Roll over is basically governed by 2X the track width/CG height. So make it wider or CG lower to keep from rolling over.

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Old 09-02-2009, 05:12 PM   #40
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What do you think the best material would be? Some kind of light weight aluminum, or carbon fiber, (that would have to be machined) or do you think finding a company to rapid prototype the chassis would be better?
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Old 09-02-2009, 06:18 PM   #41
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If you are going to machine it, aluminum is the quickest and easiers. Will also be relatively stiff. Carbon can work, but is not the easiest material to work with. You should realize that unless you do it in house, machining runs $90+ per hour and you will have a couple of hours in setup. If you are making more than one, this may be the way to go as the machining time will not be that long compared to setup.

If you have the capability to model in cad, the quickest and cheapest is probably to do it out of LS nylon for a rapid prototype house. Plastic is not the stiffest material, so you will need to optimize the structure for stiffness. You can probably mold a chassis for less than $500 and have it in 2 or 3 days using LS nylon. Local place I use is www.protogenics.com.

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Old 09-02-2009, 08:08 PM   #42
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If you are going to machine it, aluminum is the quickest and easiers. Will also be relatively stiff. Carbon can work, but is not the easiest material to work with. You should realize that unless you do it in house, machining runs $90+ per hour and you will have a couple of hours in setup. If you are making more than one, this may be the way to go as the machining time will not be that long compared to setup.

If you have the capability to model in cad, the quickest and cheapest is probably to do it out of LS nylon for a rapid prototype house. Plastic is not the stiffest material, so you will need to optimize the structure for stiffness. You can probably mold a chassis for less than $500 and have it in 2 or 3 days using LS nylon. Local place I use is www.protogenics.com.

John

We have access to a full machine shop (CNC included), so machining costs are reasonable. Aluminum is obviously going to be the easiest route (design in CAD, cut on CNC), but are the advantages of carbon fiber worth the extra work (I'm unfamiliar with precision machining of carbon fiber)? We also have access to Kevlar from the Aerospace department.
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Old 09-03-2009, 04:09 AM   #43
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We are definitely still in the brainstorming part of all this. We actually have until May to have a running RC car. There is still a lot of theory work to be done before anything is purchased or developed.

As far as efficiency goes, I know Castle CLAIMS the Neu-Castle motors are around 85% efficient and some of this most efficient in the world. This is definitely worth testing (and will be tested as soon as the dyno is complete). What other brushless motors are known as being the most efficient?

Is a 6 cell lipo going to be more than enough for what we are going for? or should we look towards more? Say 10 cell?
team losis xellorin series 3,5T has a claimed efficiency at 89% but that motor produces less than half the claimed power of the corally 3,5T. ^^

tread with all my gathered data.
http://forum.radiostyrt.no/vb/showthread.php?t=40575

edit: Dropp the carbon and Kevlar. high speed is not so much about light weight. At full scale speed racing like they do on Bonneville they don`t pay much attention to light weight due to the risk of getting airborne. some even add weight.
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Old 09-03-2009, 06:27 AM   #44
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team losis xellorin series 3,5T has a claimed efficiency at 89% but that motor produces less than half the claimed power of the corally 3,5T. ^^

tread with all my gathered data.
http://forum.radiostyrt.no/vb/showthread.php?t=40575

edit: Dropp the carbon and Kevlar. high speed is not so much about light weight. At full scale speed racing like they do on Bonneville they don`t pay much attention to light weight due to the risk of getting airborne. some even add weight.
I would rather be light than heavy though. Once the car is together it is much easier to add weight than take it away. By going light, if we get into a situation where the car is too light, we can simply add weight to the car and essentially perfect our cg.

Back to the motors. Are we going to be better off driving the rear end with belts or a direct gear driven setup?
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Old 09-03-2009, 08:04 AM   #45
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We have access to a full machine shop (CNC included), so machining costs are reasonable. Aluminum is obviously going to be the easiest route (design in CAD, cut on CNC), but are the advantages of carbon fiber worth the extra work (I'm unfamiliar with precision machining of carbon fiber)? We also have access to Kevlar from the Aerospace department.
Carbon is actually quite dense and heavy. The advantage is that you can create shapes that use very little of it and are still stiff. All the composites get stiffness from the shape. For ease of mfg and the ability to repair aluminum is much easier.

If you were making several cars, then the work of making molds for the carbon may be worth the effort. Kevlar is not as stiff as carbon, has lower compressive strength, but higher tensile. Really the best way to use the composites is to use both, carbon for you compressive loads and kevlar for the tensile loads. On the boat hulls that I make the best layup is carbon on the outside, then kevlar on the inside.

John
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