Re: World's Fastest R/C Car, anyone?
 

Matt you make it sound so easy. :) It will be quite difficult to make all those components work together but it can indeed be done. As for the horsepower of that engine, I've read sever articles claiming that the way manufacturers come up with that rating is different between each company and it is not a uniform system of measurement/testing. Your 6 step plan would make a pretty fast car. How fast? I don't know. One thing is that nitro engines can not run at WOT for too long or they'll break the con rod or sieze or blow a gasket or whatnot, not to mention possibly overheat. But it might be possible for just getting to top speed and back down really quick. It would depend on the gearing. Also, the speed and power you can get on them depends largely on several factors such as air temperature and humidity, fuel composition, etc. You would need some really good tires and a body and components because of the forces involved with such high speeds.

Even with all the challenges, I would like to try this.

What does everyone think of a dragster style car with just a really fast electric motor with a pinion, an axle with a spur and wheels, a _______ load of batteries?

Or would a pan car type car be better or would a sedan?

Is larger better or no?

So many questions.

Re: World's Fastest R/C Car, anyone?
 

needs to be under 2 ft long

Re: World's Fastest R/C Car, anyone?
 

Well, there is a really simple explanation to why you are almost definitley wrong in your reasoning. Unless the drill is much less efficient in (input/output and output/weight), then a direct drive configuration is probably precisely what you are looking for. If a motor, batteries, and chasis can go at 111 mph, then a motor with an output/weight ratio anywhere near the ones used in the 111 mph car would, in at least some configuration, be able to travel at 111 mph also. Using your calculations, we see that to achieve this with just a drill motor and a wheel, we need to actually use larger wheels and therefore less force at the wheel because that is using the free speed which is no where near the peak power output (and therefore a very bad output/weight ratio). Using the formula for drag in a non-compressing fluid:
D=(1/2)*CD*A*r*V2
we see that the drag force of such a car (assuming it is a sphere with radius 10cm)
= (1/2)*(0.5)*3.14*(0.1 m)2*(1.2 kg/m3)*(49.6m/s)^2 = 23.2 N or ~5lb.

The drill at max power is at ~10k rpm therefore requiring about 4" wheels and outputting about 7.9/(2*2) = ~2 lb. (divided by 4 because double size wheels and half stall torque). $@#$@#$@#$@#, maybe I should have made those calculations before starting to write this :). Seriously though, I think this result shows that is reasonable to have the drill motor going at 111 mph on direct drive, especially because of the highly overestimate drag (a sphere the size of a basketball?).

Re: World's Fastest R/C Car, anyone?
 

I somewhat screwed that up didn't I? :D :o Of course you can never get more power out of a motor and gearbox than you can out of just the motor itself. But what I was thinking is that the drill motor wouldn't have enough power to reach those kinds of speeds. But perhaps it is indeed possible. The RC motors spin at more like 28,000 rpm but the drill motor I believe has more torque.

Anywhoo, we can sit here and engineer this all day but I think untill one of us gets off our chair and starts making it we'll never know if its possible.

/me rummages through old RC parts :)

EDIT: /me kicks self for selling carbon fiber pan car chassis I once had.

Re: World's Fastest R/C Car, anyone?
 

Haha! Yes! That's the real engineer attitude! I wonder what sorta power source you can use that can give you such a high power/weight ratio (not energy/weight, lithium would suck in this case). Considering it runs for only a few seconds, maybe even capacitors?

Re: World's Fastest R/C Car, anyone?
 

Nah...it has to still be able to run afterward.

The 111 mph record run, IIRC, was done on about 24 sub-C cells, all wedged into an Associated L3O. So I don't think that using Sub-C cells is a death sentence...unless you're dealing with some insane high voltage (like a hybrid car's batteries).

Re: World's Fastest R/C Car, anyone?
 

I thought someone would bring that up.

If I really wanted to be picky, I'd point out that there was no (stated) restriction on how wide the thing was--so mount it in a transverse arrangement.

Also, if you slightly tilted a standard v-twin or a very compact 4 , you should be able to make it fit within 2'. Problem solved.

And if that's too big, use an 85 HP competition go-kart engine. (Uses 100 octane racing fuel, no less, so it's a little safer....)

Re: World's Fastest R/C Car, anyone?
 

I think that the speed record is for cars using the rc car race people sanctioned (im forgetting the acronymn) parts so I think go cart engines are out. The one that set this record if I recall correctly was build by Associated employers and could have gone much faster if it hadn't crashed into the wall at the track they were racing it on. :)....it would put my Kyosho Turbo Ultima (circa 1987ish) to shame.
Eric

Re: World's Fastest R/C Car, anyone?
 

You ever heard of a Panda Danny Thomson's Stadium Racer? Probably not. It has a little Thunder Tiger .10 engine adapted for the truck. It is the most POS RC car I have ever owned. Its brake is a piece of cork bonded to a brass strip that is bent over by the servo and rubs on the clutch bell. I bought it because it was only $50 brand new in the box and it was old and rare. It has a really cool body though...

Ah, I love RC cars. They are so much fun sometimes.

Just a quick story on the importance of failsafe mechanisms. I was once driving my Traxxas Nitro Stampede with my JR XR3 FM radio. The AA battery holder in the radio had a crack, but once it was put in the radio it all seemed to sandwhich together okay and it still worked fine. Well, this one particular day, I had the engine all tuned up for maximum performance. Just as I was making a full speed run dead center down my street, the craked part of the battery case in the remote breaks even further, the transmitter batteries lose contact with the terminals, the radio loses power, and the servos stay in their WOT and dead ahead positions and the truck takes off screaming dead down the middle of the street at 30+mph. It goes a full block until it comes to the intersection where it crosses the street and runs head on into a curb at full speed. But that is not all. It bounces off and makes a right and goes up the other street. At this point, I can't see it because it is no longer on my street but I can hear it's engine still screaming at WOT. After it goes up a block, it hits a curb again, somehow makes a U turn and starts heading back down the block it went up. Finally the front end is falling apart and it veers to the right back into the curb it hit the first time where it finally flips over. I thought that when flipped over, it would run out of gas and the engine would shut off, but no. From being so shaken up, the fuel is all filled with air bubbles and the engine is runing in an extremely lean condition. As I ran up to it, one tire was stuck against the curb but the other was in the air and it looked like a pizza cutter it was spining so fast. It must have been stretched out to 10" in diameter. The engine was screaming at such a high pitch and rpm I thought it was going to blow. It was the loudest sound I had ever heard in my life. When I was finally able to shut off the engine by putting my thumb over the air filter, there was the greatest silence I had ever heard in my life. Luckily, it somehow managed not to hit any houses, parked cars, mobile cars, animlas, or people.

And that my friends is why it is important to have failsafe mechanisms.

Re: World's Fastest R/C Car, anyone?
 

If it were me, I'd take a .46 size engine off of one of my r/c airplanes and strap that in with a little centrifugal clutch, and gear it down....just a little....these motors have decent torque and a uber high top end rpm of 20k rev/min. If you put that to a big set of wheels, you'll have one heck of a car. I would also do the steering so that it has a very small range of movement, thus increasing the controlability of the car (you could also set in dual rates on your x-mitter).

Whaddya think? Could it work?
-Bill

Re: World's Fastest R/C Car, anyone?
 

just FYI here are the offical rules of the challenge

http://www.rccaraction.com/rc/news/car_challenge.asp


and here is the set up for the car that has the current record

http://www.rccaraction.com/rc/articles/need_speed.asp


I aslo found this RC fourm with alot of information in their thread

http://www.radiocontrolzone.com/foru...d.php?t=167401


my brain has been running circles around this project since i heard about it

Re: World's Fastest R/C Car, anyone?
 

I think Thunder Tiger already makes a truck with a .70 helicopter engine. It goes fast, but not 112+ fast. Perhaps that's because it is a monster truck and geared for torque.

But an airplane engine is an interesting idea. They rev almost as high as the car engines but come in much larger displacements. It may be difficult adapting a clutch though.

Re: World's Fastest R/C Car, anyone?
 

I would not bother even using a clutch! I would just make the thing direct drive. You would just have to implement some kind of remote kill switch (micro servo?)

If I were to build anything I would definitaly built a car with an engine not a motor!

Batteries are too heavy

Re: World's Fastest R/C Car, anyone?
 

Oooooo, it's about darn time they decided to hold an official competition. :) I've personally been on the r/c scene for the last 5-6 years and have seen some pretty darn crazy creations. The following being two of my toys I've hand built... although the latter has been in the works for 4 years and still isn't done and the former has a little touch up work that needs to be finished such as strengthening the rear suspension and making battery mounts to hang the packs off the side of the chassis to keep the center of gravity down.
http://www.mtsquad.com/phpbb2/viewtopic.php?t=116
http://www.mtsquad.com/phpbb2/viewtopic.php?t=59

Anywho, I can't see a drill motor propelling one of those cars past 111. The brushless motor used in the record holding car would hit RPMs past 60,000 and still have power to spare. Hence why the latest craze on the r/c scene has been brushless motors. Compared to brushed motors they're over twice as powerful, more efficient, and more reliable. However, being a nitro guy myself I always ignore the new electric gadgets. ;) Without a doubt, if you were to build a speed car, you'd need a on-road racing engine. Considering that the newest ones touch 3-4hp and still managed over 35k, I think they'd have enough power. The problem is taking that power and harnessing it in the most efficient of ways. So, and I almost hate saying this, the best drivetrain would be a belted drivetrain. With kevlar belts, it'd just barely be reliable enough to handle that much power. However, I personally think that a 2 wheel r/c vehicle would be the way to go. If you think about it, it's the most aerodynamic, stable (at high speeds), and efficient chassis design to use considering how little rolling resistane there would be. The only problem would be keeping the bike upright during the run while keeping it in a straight line. Perhaps a gyro to control a set of balance weights and some wires hanging off the side to act as training wheels? Either way, that's my two cents on the subject.

Re: World's Fastest R/C Car, anyone?
 

forget piston engines :D
grab yourself a micro turbo prop engine...and connect it to the drive shaft.... search for wren micro turbines and you'll find it.