Kajman

iTrader: (4)

John,you should try GM motors, they are thery cool running.
John, can you tell why is that so, that on carpet chassis tweak shuld be less and on rubber asphalt higher? Why do we use thicker chassis on rubber asphalt?

John Stranahan

iTrader: (27)

The tendency here is to use lighter more flexible chassis for rubber asphalt.

If by tweak you mean flex. You should use less flex on carpet in other words use a stiffer chassi for carpet. This promotes smooth sliding. The lgihter more flexible chassis promotes more grip.

I'll look in to the GM motors. thanks.

Kajman

iTrader: (4)

Thanks John, can I find somewhere explained physics of that process of flex influence on grip? I try to imagine why is it so, but hard to explain...

John Stranahan

iTrader: (27)

It has to do with compliance. They talk about it in Herb Adams Book Chassis Engineering and Carrol Smith "tune to win". Compliance means how well is the tread of the tire conforming to every little bump and valley in the road surface. The better the compliance, the more the tread conforms exactly with a bump, the better the grip (cornering and forward). The next question is how do you get better compliance? You go to softer springs, (lower air pressure in the full size car), more compliant shock tuning (softer), more flex in chassis and arms.

The settings that give good compliance come with a cost. You can get too much traction with an RC car and get traction roll over. The car just rolls over while cornering. You need to go stiffer. You also get sloppy handling with very soft settings. You want the car to steer right now, but because it is soft, the car has to roll and take a good set before it starts behaving well in the corner. Very often an RC driver mistakes instant response for good traction though. You want a balance between the two.

Conrad

iTrader: (3)

Find positive pressure zones on the hood of real cars - [click me]. There is alot of good aerodynamic information on this site and always a favourite of mine for some reading when i'm feeling geeky

Is there an exhaust hole for your duct John? Or is it just forcing the air on to the esc and motor and then flowing out under the body. Even having a rear exhaust that isnt connected to the duct will help remove the heat build up under the shell. It's hard to think of a car with an exuast duct at the bottom of the rear winow tho Dont know how effective an exhaust would be on the rear bumper as it would be in the cars wake rather than having the laminar airflow pull the hot air out from under the shell.

My next suggestion would be to increase the surface area of the motor to keep it cool, the easiest way would be to buy something like [this]. I know the clamp heatsinks arent the best but it would do the job. For something a bit better you could buy/fabricate the motor heatsink setup from a Cat 2000 although this would upset your left to right balance as the heatsink plate sits between the motor mount and the motor but it does transfer the heat from the base of the motor to the heatsinks exceptionally well. [click me]

I made one for my Mardave V12 (cheap basic racer made in the uk, good fun) to help with cooling as the 23t motors get quite hot and it knocked 2/3'c of the motor temp with a closed shell. I did test it with a shell with holes in the front and rear window and it worked even better - 2/3'c again on running with just the heatsinks. [click me]

There was a company a few years ago brought out a water cooled motor heatsink setup, it was from the guy would owns t-tech (makers of the predator buggy) which pumped the heat from the base of the motor through a little radiator and back again to keep it cool. Cant remember the name of the product but i do remember them saying the base of the motor was always the hottest point in brushed and brushless in the tests they performed.

Kajman

iTrader: (4)

Thank you very much John for explanations!

John Stranahan

iTrader: (27)

Kajman-you are welcome.

Conrad-Thanks for the discussion and the links. That's just the type of article I was reading in order to site a cold air intake on the full size Focus. Now it looks from the air flow diagram that I should stay away from the curved section on top of the grille. I should maybe tape the upper slots shut.

I have no exhaust, but there is quite a bit of body that is typically removed at the bottom rear of a ROAR legal TC body. There is a spec that says you can cut no higher, but it it quite high. This body which is factory trimmed has no rear bumper so this area is effectively my exhaust. The air is ducted through a rectangular duct and then into two tubes which spill out over the ESC and motor.

Things that I have coming. A Fantom 3.5 motor with internal fan (this is listed at Stormer but not at Fantom?). The fan will probably do the most good. Tekin RS Pro speed control. The tech claims a 250F thermal temperature cutoff. A fan cooling the solder posts is suggested. Note that I have recommended this on the motor previously (to aim a fan at the solder tabs). You have a highly conductive path right to the coils and on the speed control right to the power transistors.

I have such good luck with the duct in my wide pan which is a lot more direct than the one on the TC that I think the heat sinks may not be needed once I get the airflow that is possible. The pic shows the original duct which cools the speed control heat sink directly with 60 mph air every lap. I put on a duct extension to redirect this air down at the motor tab end of the motor. It ran a minute longer than needed at 105 F. This duct is sited in the same place as the huge radiator duct on the full size Peugeot 905B and 908

Conrad

iTrader: (3)

There are a few other articles on that site about cold air feed intakes, i havent read the first two articles yet but the last two are very good. They are multi part articles and you do need to search the site to find the other parts, there is no direct links which is the only downsides. There are alot of good articles on aerodynamics, undertrays and everything else you can imagine, i usually just stumble on the articles by accident, once i start reading one i keep finding more and more

How's the focus coming anyway, its been a while since i checked your thread about the bike throttle bodies and airbox your were modding up. Top work btw, i considered something similar for my car before and stumbled on your old aol webspace then the focus forum thread. I'll come clean now and admit i am stalking you John j/k but i dont like your style and your work so congrats, you have a fan.

Siting cold air intakes
http://autospeed.com/cms/A_1023/article.html

Ram-air revalations
http://autospeed.com/cms/A_110824/article.html

Elminating negative boost
http://autospeed.com/cms/A_0629/article.html

Negative boost revisited
http://autospeed.com/cms/A_107824/article.html

John Stranahan

iTrader: (27)

Conrad-Thanks for the links and the kudos. First the RC stuff.

I setup a little flow bench. Air dryer aimed at the front of the car. Wind Velocity meter between the rear bumper and the ground on the left side of the car. (my exhaust path). I recorded about 4.9 mph. I closed the top most openings in my grille. No change. I closed a second set there was a reduction. I removed two sets of horizontal cross bars and there was an increase to 5.1 mph. The grille opening are all below the seam of the hood. It appears they are sited well from this small experiment. The Tekin RS pro is installed with a 4.0 for now. Our weather has cooled some so this may turn into a 3.5 powered car after I get some temperatures tomorrow. I drove the car just a little from ground level. It seemed to be strapped. It is not quite so strapped looking when I drive from up high but it it handling well. I have green springs all around now. I moved the lower shock position inward on the A-arm.

The Suzuki's quad throttle body install on the Focus has stalled for the meantime. Two events helped. One is damage from hurricane Ike refocused my efforts on fixing destruction. Two, AOL shortly after decided all of its longtime customers were no longer in need of any Web space. The summarily took off all my Journals, Web stores, and Photos. This killed the topic over at the Focus site as it no longer had any of my photos. Such is life.

What you are looking at is a completed 1 inch thick white ABS intake manifold which we home machined from billet plastic sporting quad Suzuki shortened and modified throttle bodies (From the GXR 1100 motor cycle) pared down to the shortest length possible. Rubber throttle trumpets inside a partially cut away suzuki air box. Work that remains is plastic welding the rest of the air box and installation of a couple sensors in a custom made air chamber at the top of the air box. Copper pipes are for EGR intake air. Fuel injectors are in the head on Fords 2.3 L duratec. This assembly would replace the single throttle body and plastic intake manifold on the Focus ST to keep up part throttle air speed.

brt006

John, i have a couple of questions if you could please help !
Do you run sway bars on your set up at the moment ? Also are you running the itf chassis ? i am getting scrapping on the motor. i am running your set up but seems a little soft. what is the best cure heavier shock oil or spring ?
I am running on a large outdoor track with high speed corners and a bit bumpy in sections and i think is only touching on one main corner. I like the setup and dont want to mess with it too much maybe a little more steering, but the car is fast the way it is and have had lots of great drives, but my chassis is almost rubbed through under the motor mainly. Do you have any suggestions for me to try ? Your help is much appreciated.

John Stranahan

iTrader: (27)

brt006- I add and remove the thickest sway bar front and back depending on track condition. If grip is up, put on the sway bars. If it is low remove them. Chassis wear must be solved by a combination of ride height and roll stiffness. You might need to run swaybars all the time to save the chassis under the motor.



As a side note, Phil tells me he is getting phenomenal traction (traction rolls at will even) on our current asphalt. I am sliding around quite a bit. He is using .049 and .052 inch springs on his T2, which are quite a bit heavier than mine. It will be worth a quick test on my car to similarly equip it. Same tires. Sorex 36. I note that his fiberglass framed car has quite a bit more flex than mine. I do have the ITF top brace coming which, I believe, is more flexible than my top plate which I cut down to a rod almost. It turns out my green springs at .050 are the same as Phils. Must be chassis flex. I will be increasing mine some with the ITF top plate.

Tekin RS pro and LRP X12 4.0 survived a high temperature beating at 99 F. I had only one thermal shutoff at 4 minutes geared 21/93. Will need to drop that pinion back to 20. I have auxiliary cooling air coming from the grill so that the speed control and motor were not over 150F when measured. There is some delay and cooling that occurs, from the remaining 3 fans, as you climb down the stand however. The speed control may have been much hotter at the end of the straight (bad place for a cutoff).

John Stranahan

iTrader: (27)

Increased Torsional Flex ITF

First a little discussion. There is little momentum going to increasing chassis flex for full size cars on pavement with good grip. In fact it is just the opposite. Monocouque stiffness is at a premium. Roll cages haver generous use of shear plates and gussets to stiffen up the car without adding weight.

So what is up with our car. Well there is a property of scaling that can explain it. When we reduce our cars size by a factor of 10 the weight is reduced by the volume reduction of each piece of the car or the linear dimension cubed The weight reduction factor is 10 x 10 x10 or 1000. 1000 times less for a 1/10 scale.

The strength of each piece of the car is only reduced by the cross sectional area reduction of each loaded member. That would be an area reduction by a factor 10 x 10 or 100. We are 100 times weaker.

We are 1000 times lighter but only 100 times weaker. This just does not come up in full scale racing on pavement. This means our chassis can easily be made 100 times stronger than its full scale counterpart. It can easily be too stiff. There are Increased torsional flex (ITF) kits for the TC5 to make the chassis more supple and grip the asphalt.

I have actually measured the torsional stiffness of several cars by mounting them in a vise and them twisting them with a known torque and reading twist on a dial indicater. With several tests completed I have calibrated my hands to a degree. I grab both shock towers and give the car a twist and see and feel how much flex there is. In torsional stiffness order: the twisty-HPI tub chassis (almost rubbery, no tuning helps this car, but it may perform well). TC3 tub chassis, Losi XXXS tub chassis, Losi JRXS front motor chassis, any thick double deck late model carbon fiber chassis including the TC5

I have one of the original TC5s. It has the 2.5 mm chassis chassis and a more complete top deck although it came equipped with the softer arms c-hubs and hubs.

Early on I narrowed the top deck to almost a rod. See the part at the far bottom of the photo. This helped add some flex. I bought this ITF top plate which is an Associated part recently to gain some more flex. I did not. My hand made was the equal.

I tried no top plate. Flex seemed about right, my standard was the X-ray T2 fiberglass chassis car which was very flexible and very hooked up. About Losi XXXS stiffness or slightly less. Front to back flex was awful. I would be very worried about losing the teeth off of that front drive belt in any incident.

Here is a homemade top plate. It controls the front and aft flex that controls belt slack. It pivots side to side at the rear on a CRC center pivot ball and seat. You get plenty of side to side flex but only a modest amount of front to back flex.

Kajman

iTrader: (4)

Thanks John for as always deeply revised problem Have you tried it on track? How much difference?
What ist right and what is wrong with xxx-s flex? I have both xxx-s and tc5r, so both characteristics are interesting to me

trdsupra88

iTrader: (25)

Hey John, I have a mod for the topdeck you may enjoy seeing...I will post pics within a day or two...

John Stranahan

iTrader: (27)

Look forward to pics.

The flex is now similar to the Associated TC3. It is also very similar to the X-ray T2 entry level model with the G10 fiberglass chassis and top plate. That was my target for the moment.

I liked the XXXS chasssis the best of all produced for TC. I liked the sealed drive train, (it needed double belts for stock though) the stiffness was about perfect for rubber tires on asphalt. As is, the car is probably one of the best open mod cars for outdoor asphalt. Losi would have won a lot more races by just keeping and updating this car.

I have not tried the car with the revised top deck yet. I have tried the new Tekin out. I have one unexplained shuttoff to report. It may have been a radio glitch but I think it was a thermal shutdown at the end of the straight. I have turned the amp setting down one notch.
The thing is so small it is obscured by the wiring in the car. If you click the enlarged picture one more time it will get quite large to study more detail like the speed control setup.