If you were to build an extremely fast car from scratch you would.....
#31
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.
#32
Tech Addict
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.
The ballooning of the tire gives off a smaller footprint, and thus less roll resistance.
#33
Tech Adept
iTrader: (6)
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...
wouldn't want that to happen under your car @ 100 MPH...
#35
Tech Master
iTrader: (10)
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...
wouldn't want that to happen under your car @ 100 MPH...
DK
#36
Tech Rookie
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?
Also, where is the best position for the center of gravity?
#37
Tech Elite
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Join Date: Mar 2007
Location: Bristol, England, United Kingdom
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#38
Tech Rookie
In positioning the c.g. is it better to have it directly over the rear wheels, or more centered in the body?
#39
Tech Adept
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.
John
Roll over is basically governed by 2X the track width/CG height. So make it wider or CG lower to keep from rolling over.
John
#40
Tech Rookie
Chassis Material
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?
#41
Tech Adept
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
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
#42
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
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.
#43
Tech Addict
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?
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?
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.
#44
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.
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.
Back to the motors. Are we going to be better off driving the rear end with belts or a direct gear driven setup?
#45
Tech Adept
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.
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