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Car Action World's Fastest RC Car Challenge! What car are you going to build to break the world speed record for RC cars?

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  #276  
Old 06-09-2004, 07:39 PM
Spoon37 Spoon37 is offline
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Mike keeny: that engine rules!!!

as for the nitro/electric thing....

2 points BL/brushed seems to make little difference, its just that the current breed of BL motors use rare earth magnets and are designed for very high voltages, so comapred to ROAR legal brushed motors then obviosuly the brushed will seem limited on performance, so yeah brushed can be built really fast. BL tends to be a bit more efficient tho, which is why it tends to be looked at as an eaiser route....

secondly nitro do not make very high RPM's, not compared to good BL motors(most of which can make 60,000-80,000RPM without breaking a sweat) making high speed easier, but if properly designed the gearing of a suitable nitro tranny should compensate for this and rely on the nitro engine having enough torque to pull higher gearing than would be needed for the electrics...

and weight is an issue, Grant Tokumi: you assume that more weight means more power, e.g. thrust SSC uses two jet engines and weighs over 8 tonnes but the thrust/weight ratio is stacked in its favour. one of the definitions of power is the ability to move a given weight to a given speed, so more power means more speed, but also less weight and the same power means more speed too. you must strike a balance between lightweight and powerful to acheive high speed.

thats why I dont think an MT will do it I am an electric MT nut, but I can't see any electric MT reaching 100mph or more, there is just too much weight even if it is grossly overpowered(as is the case of many dual BL maxxes). I reckon they would accelerate pretty well but probably top out on speed due to excess weight, drag or gearing limitations. heck I know its pretty hard to get most of My MT's anywhere near 40mph...lol

I do like that 8 wheeled chassis idea tho - it would spread the load more and may allow smaller wheels to be used for less aerodynamic drag......

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  #277  
Old 06-11-2004, 01:14 AM
Grant Tokumi Grant Tokumi is offline
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Quote:
I was amazed at how fast and stable the TC3 looked as it sailed down the backstretch at nearly 100mph. Cliff explained that the 4WD TC3 had more traction than his 2WD L3O, and that made the TC3 much easier to launch off the line and easier to drive. Ironically, Team Associated tested a 2WD TC3 speed-run car, but there wasn’t any noticeable speed advantage even with the savings in rotating weight.
I think this is a key point regarding rotating mass (inertia).
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  #278  
Old 06-11-2004, 01:26 AM
Interstate Interstate is offline
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Steve Pond said in his article that even with the sky high gearing, he still had traction problems getting off the line.
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  #279  
Old 06-11-2004, 12:59 PM
bhstall bhstall is offline
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I understand it has to be on an oval due to radio problems, but does it have to be an oval with a low degree of banking that makes downforce and handling an issue, where there are at least 2 high banked 1/2 mile ovals in the country that I know of that would take most of the handling issue out of the speed run contest. Bristol, TN and I think Salem, OH(?) have the fastest 1/2 mile tracks anywhere with a high degree of banking. Bristol Raceway I know has a ground down concrete surface that appears to be very smooth and with very tall grandstands around the track to get elevation to operate the radio without problems.

Maybe next time.


Its Salem Indiana, There is more info at their site /www.salemspeedway.com/
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  #280  
Old 06-11-2004, 01:01 PM
bhstall bhstall is offline
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Quote:
Originally Posted by Craps
I understand it has to be on an oval due to radio problems, but does it have to be an oval with a low degree of banking that makes downforce and handling an issue, where there are at least 2 high banked 1/2 mile ovals in the country that I know of that would take most of the handling issue out of the speed run contest. Bristol, TN and I think Salem, OH(?) have the fastest 1/2 mile tracks anywhere with a high degree of banking. Bristol Raceway I know has a ground down concrete surface that appears to be very smooth and with very tall grandstands around the track to get elevation to operate the radio without problems.

Maybe next time.

Its Salem Indiana, There is more info at their site /www.salemspeedway.com/
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  #281  
Old 06-12-2004, 01:31 AM
lerningdriver lerningdriver is offline
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anyone know what an estimated top speed is gonna be at this race? i'm guessing 120-140?? what do you guys think?
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  #282  
Old 06-12-2004, 02:08 AM
Grant Tokumi Grant Tokumi is offline
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I'm ballparking 150 mph.

Here's an interesting thought I came up with to put it into perspective since I can't visualize a 1/2 mile track, but I can a football field. 150 mph is 220 fps (feet per second). Converted, thats 300 ft (1 football field) in 1.36 seconds. So at 150 mph, you can travel a whole football field in 1.4 seconds. So you should be accelerating up to top speed by 1 football field. That allows 1.4 seconds of top speed (150 mph) through a 2nd length of a football field. Thats 200 yds, and on a 1/2 mile track, the straight is probably around 200 yds which means you will probably be entering the curve going at 150 mph. You'll most likely have to do some radical decceleration in the curves, otherwise the wall will deccelerate it for you....
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  #283  
Old 06-13-2004, 02:01 AM
crank throw wei crank throw wei is offline
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Like Grant,I think 150 will be the #,= or - a few MPH.I've been thinking about this very seriously,and I believe I have conceptualize a vehicle capable of that speed,but I keep coming back to tires as being the weak link in the equation.
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  #284  
Old 06-13-2004, 02:47 AM
Mike Keeney Mike Keeney is offline
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Quote:
Originally Posted by Grant Tokumi
I'm ballparking 150 mph.

...... You'll most likely have to do some radical decceleration in the curves, otherwise the wall will deccelerate it for you....
A problem made more serious for those of us with locked rear ends. Posi's don't like to turn.

Mike
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  #285  
Old 06-13-2004, 11:40 AM
Grant Tokumi Grant Tokumi is offline
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Someone can correct me if I'm wrong on the math, but based on this equation in another thread:
Fc = mv2/r
where Fc = centrifugal force, m = mass, v= speed, r= radius

I'm calculating that at 150 mph and a 6" diameter tire, the tire will be experiencing 6000g's of centrifugal acceleration.
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  #286  
Old 06-13-2004, 11:43 AM
KTRTS KTRTS is offline
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I wouldn't call it a tyre by then
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  #287  
Old 06-13-2004, 01:30 PM
lerningdriver lerningdriver is offline
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a balloon? ... but what are you plugging in for the mass grant?
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  #288  
Old 06-13-2004, 01:50 PM
Grant Tokumi Grant Tokumi is offline
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mass cancels out.
F=m*a
ma= mv2/r
a=v2/r

I thought factors of gravity (G) would be more relevant than some force value.

v=220 fps
r=.25 feet

a=220*220/0.25=193,600 ft/sec2
193,600/32.2 = 6012G

This still could be wrong. Its seems quite outrageously large. And thats for a 6" tire. A 2" tire (TC tire?) would be 18000 Gs!!!! I'm a bit suspicious that I'm assuming a linear acceleration ("a") value, when it might actually be some angular acceleration value.... Crank?

Last edited by Grant Tokumi; 06-13-2004 at 01:59 PM.
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  #289  
Old 06-13-2004, 05:10 PM
AudiTT-Quattro AudiTT-Quattro is offline
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Grant,

Your calculations are for centripetal accleration, NOT centrifugal acceleration. HUGE difference...
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  #290  
Old 06-13-2004, 06:57 PM
crank throw wei crank throw wei is offline
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I think this page can explain it better than I can. I do think a fully belted tire of as large of diameter as possible will be needed.One thing is for certain: No "standard" R/C tire will work for these types of speeds.
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  #291  
Old 06-14-2004, 01:09 AM
EddieWeeks EddieWeeks is offline
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Just get some of these... I use them on my Jets and they go 80 mph
with 30 lbs load all day long..

http://www.bvmjets.com/Accessories/wheels.htm

Eddie Weeks
http://www.corpcomp.com/weeks1/
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  #292  
Old 06-15-2004, 06:08 AM
MegaMe MegaMe is offline
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im still concerned about getting anywhere near 150mph on this track due to its tight corners...

this has come up a couple of times - but seems to have been ignored so far, i suppose because noone has any answers to the problem


but i just wanted to check the forces in the corners:
im from australia so i work in metres and stuff but the way i see it:

1/2 mile is about 800 metres, although i dont know what 1/2 mle actually refers to - is it the circumference of the inside of the track? im assuming it is... from the picture i would guess that the straights are about 150m long... leaving 800-300 = 500m in the corners

500 = 2 * pi * radius

so radius of the track is about 80 metres.

i found this: "Irwindale Speedway is a 1/2-mile paved oval with blended banking of six, nine and 12 degrees in the corners and banking of six degrees in the straights."

so say the banking is 9 degrees then after spending 20 minutes doing some nice geometry and then finding a page that had it all done for me:
http://hyperphysics.phy-astr.gsu.edu...arbank.html#c1

we see that if the coefficent of friction is 1 then we can go round at 73mph
if coefficent of friction is 2 then we can go round the corners at 111mph and of the coefficent of friction is 3 then we can go round at 153 mph

this coefficent of friction can kinda be equated to be the gforces the car is pulling - although its all screwy with the banking angle.

i dont know what gforces rc cars generally pull with the foam tyres and eveything but without downforce i would be surprised if they can pull much more than 1 g???

with that 111 mph run from cliff lett he said he had to slow down for the corners - its quoted earlier in this thread. if he was going say 95mph in the corners and the accelerated to 110 on the straights then his coefficent of friction was about 1.6, even with the body he was using that looks like it would produce a fair amount of downforce...

to me this kinda suggests 2 things: 1 is that you will need downforce and alot of it to win with this track, as well as fat tyres to provide lots of grip, or else you have a very fast accelerating car that can go from say 80mph to whatever speed you want in about 100 metres (as if the straight is say 150m long then you probably want about 50 metres to slow down for the corner )
i think something like those lola bodies that are everywhere would be good???

second thing this suggests is that you need a wide car or a low centre of gravity so that it dosent flip in the turns. that means those people who want to put on big gocart engines or want to run a monster truck or anything else with a high centre of gravity. or as before you could make something that will accelerate in the 100 metre or so straight. note that there arent any problems reported on the record attempt website with cliff lett's 96mph tc3, even though its not that wide and has 2 levels of batteries on it, so it should not be such a big problem for normal looking rc cars i think?


i really think that providing enough downforce will be essential to win this competition on this track, as if you are serious about winning then you probably want to pull at least 2 g's on the turns.


oh last thing i with that tc3 they commented that they had no extra speed even in 2wd mode... i dont think that having 4wd on these cars will effect the speed to much. generally a gear pair is between 95 and 99% efficent, and i dont know about universals or dogbone links but provided the suspension arms are pretty horizontal i dont think you would lose too much power... even if you lose say 10% power through 4wd or independent suspension it should only cost you 1 or 2 mph, and it may save you lots of money if its stops you spinning into a wall or something
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  #293  
Old 06-15-2004, 08:03 AM
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StevePond StevePond is offline
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Quote:
Originally Posted by crank throw wei
Like Grant,I think 150 will be the #,= or - a few MPH.I've been thinking about this very seriously,and I believe I have conceptualize a vehicle capable of that speed,but I keep coming back to tires as being the weak link in the equation.
The tires are going to be a big part of this. Most off-the-shelf touring tires shred at about 80, so something larger in diameter is certainly called for. I used the "Super" sized tires and wheels on my last car with sucess. They were Kevlar belted, but I think they would have easily survived with standard belting. Going faster... not sure how they'd hold up. ;-)
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  #294  
Old 06-15-2004, 09:36 AM
DualBL DualBL is offline
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steve, can you give us more info, or a link to the tires that you used?
-Nick
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  #295  
Old 06-15-2004, 12:21 PM
DaFF DaFF is offline
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Go to the HPI Website,

http://www.hpiracing.com

then click on "tires"

then "super size tires"

That is the kind of tires Steve is refering to.

Hope this help

DFF
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  #296  
Old 06-15-2004, 05:20 PM
racerrandy racerrandy is offline
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Man, my head hurts after that geometry lesson!

I really think everyone is over analizing this. If the track is 1/2 mile on the inside then the outside could be closer to 3/4. You won't drive a straight line around the track, if you go high in 3 on a rolling start then you can cut down low in turn 4 to straighten the track out kinda and gradually move up the track to go through the traps.

I really think the track is not going to be the issue. I think tires is the number one deal.
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  #297  
Old 06-15-2004, 10:39 PM
MegaMe MegaMe is offline
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yeah you can do that randy if you have a fast accelerating car... but at high speeds its much harder to accelerate as quickly as low speeds, both because of the wind resistance and the fact that it takes much much more energy to accelerate from say 0 - 20mph than from 100 - 120 mph...
when you think of cliff letts car - they said they had trouble getting it off the line because it had so much power - so its not a slow accelerating car by any means, but even going round the corner and then accelerating along the straight - they were in the 100mph range... they only broke 110mph because they didnt brake for the corner in time and wiped out - something that most entrants might try to avoid

you can ignore my calculations and stuff if you like - you dont need to understand them to understand the problem, because we already have a perfect example which demonstrates the issue quite clearly... from this article which uses the same track it says this:
"After the run, Cliff reported that the motor still had plenty of revs left and could have gone even faster if space had allowed."

the corners were a problem for him - and i think they will be a problem for anyone else who dosent take the cornering issue seriously...
having said that - the tyres he used did appear to be pretty narrow and not so grippy, and the body looked ok - but i think a lola body or similar would produce more downforce. So i think its not so hard to improve on his corner speeds, and hence hopefully improve on his top speed, so i think the problem can be avoided if you recognise it.
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  #298  
Old 06-16-2004, 03:45 PM
RC-scientist RC-scientist is offline
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Read my post on the new size forum.

150mph ha, with this new size thing I think it will be more like 200mph.. Also I think the L3o was running on just one section of the track, so if you open it up to the turns I think the sky is the limit.

As far as I have read there is not a engine size limitation so I think 1 liter or 1000cc's will be enough, for now. Well unless I hear of a 300hp bell helicopter engine being used and I guess I would just be back to the drawing board.

Steve needs to think long and hard about this. This change really moves the contest into less RC more real world mechanics. Not that RC car dont have them but now you are talking about full size engines. Gasoline, or alchohol top fuel engines. The sky is really the limit.

I bought a polar clutch and should have the ZX-10R apart by weekend. I will see if it will work then, if not I will just put it back in my bike, but if it does? I will be sure to tell that guy who was talkign about electrics to keep dreaming.

Steve, The whole track will be ours? What kind of time will we get to test our cars? I plan to bring at least 3 cars to the event 1 that is completed and 2 that I am building. It would have been 2 but the lenght changed and I was allready about 80% done with the design.

If this lenght stays and the engine size is not limited.. The number will be around 220mph I am sure of it.

RC-Scientist
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  #299  
Old 06-16-2004, 05:25 PM
Hz-R Hz-R is offline
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Just a question: is there any video footage of Cliff Letts run?? Would be intresting to watch how bumpy the track is for ride height etc.

For you guys interested in aerodynamics, I found this web page with lots of close-up pictures of Le Mans racecars:
http://www.mulsannescorner.com

Sounds like a lot of cool cars are being built! Lots of power is not going to be a problem, handling it is, that's for sure!

Anybody trying for a solar powered rc world speed record?
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  #300  
Old 06-16-2004, 05:38 PM
guver guver is offline
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Can anyone confirm this?
It takes 10 times the power to double the speed, especially at higher than 100. Is it a constant slope?
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