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Old 03-11-2009, 09:10 AM   #661
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Hey John, I am starting to do my conversion and just came up with a idea to save some cash when doing it. I am a pan car racer so I am going to use the side shocks from them, not to mention a wide verity of springs also in stock. I am just going to cut the ball cups short so they will fit. Also then I can use regular 4/40 threaded ball studs and not those 2.5m from the RC18...
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Old 03-11-2009, 10:35 AM   #662
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Should work fine if you can get them short enough. I did some of my early front shock installs with them.
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Old 03-11-2009, 08:29 PM   #663
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Here are a couple shots of the HPI R34 GTR. I have a picture of one of the full size race cars above. The big graphics lend themselves well to a one color paint job. There is plenty of additional black trim. So what's the difference between this body and the Sophia after having mounted both.

This body is taller especially at the front. In my experience this concetrates downforce at the front. There is nothing better than a big vertical dam to create vacuum behind it unless you care to mount an undercar diffuser. The front end also clears my Gen X 10 bumper. I was able to replace my chopped bumper with a full size stiff foam bumper from CRC. I think this is essential if you plan to run the graphite bumper underneath. It needs some protection. I only had about 3/16 of foam protecting this graphite on the Sophia body. This is not enough. I find in a recent reading of the roar rules that bare graphite bumpers are not allowed due to the chance of cutting into a marshall. Get a stiff CRC foam bumper to follow the rules and to protect your graphite.

Now at the back the top of the wing is exactly at the top of the body cab, but it is about 3/4 inch to one inch back of the Sophia wing. There is more rear overhang to this body. This is going to suit our outdoor track and 2s LIPO/10.5 powerplant a little better. Some serious speed will be developed on the 240 foot straight. Tacking down that rear end for the sweeper will be quite important.

Is this body better for 4 cell/13.5, probably not. There is a larger cross-sectional area and more drag, Probably more weight. If you run ballast this extra weight is not an issue, you just remove ballast. Don't kid your self, this tall body, tall cab and high wing are going to develop more downforce in the twisty sections than a low body. That is one reason I like the big oval bodies on our long outdoor track. This body is a good replacement for the oval body and is World GT specified.

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CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-hpi-nissan-r43-gtr-resized.jpg   CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-hpi-nissan-r43-gtr-004-resized.jpg  

Last edited by John Stranahan; 03-11-2009 at 09:57 PM.
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Old 03-11-2009, 10:01 PM   #664
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Quote:
Originally Posted by John Stranahan View Post
Here are a couple shots of the HPI R34 GTR. I have a picture of one of the full size race cars above. The big graphics lend themselves well to a one color paint job. There is plenty of additional black trim. So what's the difference between this body and the Sophia after having mounted both.

This body is taller especially at the front. In my experience this concetrates downforce at the front. There is nothing better than a big vertical dam to create vacuum behind it unless you care to mount an undercar diffuser. The front end also clears my Gen X 10 bumper. I was able to replace my chopped bumper with a full size stiff foam bumper from CRC. I think this is essential if you plan to run the graphite bumper underneath. It needs some protection. I only had about 3/16 of foam protecting this graphite on the Sophia body. This is not enough. I find in a recent reading of the roar rules that bare graphite bumpers are not allowed due to the chance of cutting into a marshall. Get a stiff CRC foam bumper to follow the rules and to protect your graphite.

Now at the back the top of the wing is exactly at the top of the body cab, but it is about 3/4 inch to one inch back of the Sophia wing. There is more rear overhang to this body. This is going to suit our outdoor track and 2s LIPO/10.5 powerplant a little better. Some serious speed will be developed on the 240 foot straight. Tacking down that rear end for the sweeper will be quite important.

Is this body better for 4 cell/13.5, probably not. There is a larger cross-sectional area and more drag, Probably more weight. If you run ballast this extra weight is not an issue, you just remove ballast. Don't kid your self, this tall body, tall cab and high wing are going to develop more downforce in the twisty sections than a low body. That is one reason I like the big oval bodies on our long outdoor track. This body is a good replacement for the oval body and is World GT specified.

John
Hey John,

Great work on the shell! When is the maiden voyage?
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Old 03-12-2009, 07:50 AM   #665
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I might run on some concrete this weekend. Our large track is still under construction.
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Old 03-12-2009, 09:22 AM   #666
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I might run on some concrete this weekend. Our large track is still under construction.
john
Wouldn't concrete tear those foam tires apart? Also, I read into your post further and I have a comment to add, and I could be wrong so please feel free to correct me. When you spoke about the front portion of the car; "In my experience this concetrates downforce at the front" and you made the comparison to the Sophia GT body, shoudln't we avoid downforce in the front when we are looking for more grip in the rear so we can propel the car better? I undersand frontal downforce is needed for better steering grip, but from what I am thinking, it looks like it is going to be a game of give and take. More frontal downforce at the cost of the rear grip. I hope I am making a wrong assumption here and please correct me if I am wrong.
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Old 03-12-2009, 10:27 AM   #667
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The frontal downforce is really created in the area of the hood. Behind the air dam. It is well centered over the front wheels. This means that it won't reduce rear grip. It may unbalance the oversteer/understeer properties toward oversteer. To rebalance the oversteer understeer then you need a little more rearward wing or a higher wing position and you need to use purple front tires. What I am going to have is more frontal downforce and more rearward downforce. This helps the car in the infield. On the straight the increased front downforce may be needed toward the end to keep the front end planted with LiPo 10.5. The car will be less slippery in the wind but forward traction, from rear downforce, has a big effect on top speed at our track.

I think there is a misconception about downforce and wedge bodies. The thought is probably that it increases front downforce and rear downforce. My tests in a windtunnel show only ounces of front downforce in front and pounds in the rear for a Peugeot 905B body with spoiler. Rear downforce is easily increased with more spoiler or reduced to ounces with less spoiler. Front downforce is almost impossible to increase without some under car device like a diffuser. One thing is for sure the wedge body has less cross-sectional front area so it can normally attain a higher speed, but not necessarily more downforce than a sedan body.
I would have to check on this but I think Barry Baker has the lap record at our track during the Nitro 1/10 sedan Nationals with a 1/10 sedan body. There are some high skill 1/8 drivers at the Speedline Grand Prix Nationals using the Lola wedge bodies. Fast laps are about as good but not quite. Our track has been described as an infield track by some of these 1/8 racers. There is some magic in the sedan bodies and probably also in Barry Baker.

The foams wear on concrete is similar to the wear on asphalt at equivalent grip levels. If I make both high grip with sugar, the wear is higher on both but still reasonable. I had too much grip on the concrete last time so I will reduce the amount of suger added from 12 to 10 lbs. This will reduce grip probabably to medium and wear to medium as well.

John

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Old 03-12-2009, 01:59 PM   #668
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Quote:
Originally Posted by John Stranahan View Post
The frontal downforce is really created in the area of the hood. Behind the air dam. It is well centered over the front wheels. This means that it won't reduce rear grip. It may unbalance the oversteer/understeer properties toward oversteer. To rebalance the oversteer understeer then you need a little more rearward wing or a higher wing position and you need to use purple front tires. What I am going to have is more frontal downforce and more rearward downforce. This helps the car in the infield. On the straight the increased front downforce may be needed toward the end to keep the front end planted with LiPo 19.5. The car will be less slippery in the wind but forward traction, from rear downforce, has a big effect on top speed at our track.

I think there is a misconception about downforce and wedge bodies. The thought is probably that it increases front downforce and rear downforce. My tests in a windtunnel show only ounces of front downforce in front and pounds in the rear for a Peugeot 905B body with spoiler. Rear downforce is easily increased with more spoiler or reduced to ounces with less spoiler. Front downforce is almost impossible to increase without some under car device like a diffuser. One thing is for sure the wedge body has less cross-sectional front area so it can normally attain a higher speed, but not necessarily more downforce than a sedan body.
I would have to check on this but I think Barry Baker has the lap record at our track during the Nitro 1/10 sedan Nationals with a 1/10 sedan body. There are some high skill 1/8 drivers at the Speedline Grand Prix Nationals using the Lola wedge bodies. Fast laps are about as good but not quite. Our track has been described as an infield track by some of these 1/8 racers. There is some magic in the sedan bodies and probably also in Barry Baker.

The foams wear on concrete is similar to the wear on asphalt at equivalent grip levels. If I make both high grip with sugar, the wear is higher on both but still reasonable. I had too much grip on the concrete last time so I will reduce the amount of suger added from 12 to 10 lbs. This will reduce grip probabably to medium and wear to medium as well.

John
Have you performed the same test with the Protoform Sophia GT and your Skyline body?
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Old 03-12-2009, 02:46 PM   #669
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I have not put these new bodies in the windtunnel and measured downforce with a set of scales.

Some of my comments are based on my gut feeling which is based on many track tests with numerous bodies in both 200mm and 235 mm. I have tested both GT bodies and wedge GTP bodies on the Wide pan. I feel the GT has more downforce, especially in the front. It has less tendency to lift the nose and fly at speed.

I have experience with semi wedge bodies on the 200 mm pan. Nothing flies more often than the semi wedge. My example was an HPI stilletto body which is in a supercar shape. Almost a wedge but not a flat LMP shaped body; well, much like a Sophia. With a 2s LiPo 3.5 I experienced many Spectacular huge embarrasing leaps into the air at high speed. The car just fluttered to the ground or made a 360 degree loop and continued on so there was no danger here. These tests are in the Pantoura thread.

so front downforce goes like this.
Sedan-high
Supercar wedge-low
GTP wedge Peugeot 905B (low downforce version)-low (measured on the windtunnel with scales).
I believe the high downforce 905B version would still measure low in the front, only slightly better from the altered airflow, but would have significant gains in the rear because it is taller in the back. If this shape had good front downforce the 1.5 ton fullsize GTP cars would not have tended to fly. This was a big problem until that front undercar diffuser was well developed at about the Toyota GT1 time period.

Drag goes like this
Sedan-high
supercar-medium
GTP car-low

Now I find the cure for all this flying is a simple front diffuser made out of an HPI plastic wing used upside down on the front end. (Like the Toyota GT1) Who would have thought it so succesful. All my other under car experiments had no effect.
john

Front downforce matters less on a short indoor carpet track. There you may want the most streamlined body. You may have all the front traction that you want and then some. You may be traction rolling if you steer too hard. On indoor asphalt the sedan body might be very competitive, I believe, on 1/10 scale.

We are not in the flying zone with a 10.5 motor but certainly on our new layout good cornering is going to be desired.
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Old 03-12-2009, 05:48 PM   #670
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John I have a question about "too much grip." In theory there should be no such thing. I know in full scale racing they had to take downforce out of the formula cars at Texas Raceway, b/c drivers were getting dizzy pulling 5g lap after lap in the long banked turns. A race was cancelled one year because of this. But in theory more grip always equals more g's, and more g's equal lower lap times. It irks me when the magazines advise taking out grip to improve drive-ability, but perhaps given the driver skill set this is true? Or is there something I'm missing as a non-driver Physicist?

Last edited by SystemTheory; 03-12-2009 at 05:49 PM. Reason: spelling
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Old 03-12-2009, 08:20 PM   #671
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Too much grip
System Theory-Here is the thing. A full size car as well as an RC car has a level of grip that when achieved will make the car do a traction roll. With full size vehicles you don't see this on pavement except maybe with dragsters that have high center of gravity. You do see this on dirt. Somtimes on dirt or sand the traction roll is not the result of a trip (like a hitting a rut or small berm), the tires just dig in smoothly and develop enough grip to roll the car. I have personally seen two full size pickups do this in the sand. There is not much straight sheet metal left. The higher the center of gravity, the more traction there is, the more mechanical grip the car develops, the higher the likelyhood this will happen. Without ground effects it happens at about 3.5 g's of cornering power for full size and RC size. Without ground effects very good race cars are limited to about 1.4 g's. Our full size road cars can get a little bit over 1.0 g's with the right springs and tires. We are far from traction roll. I don't think you will go faster around the track reducing grip except for a case like this.

I have too much rear grip. I don't have adjustments at hand to increase steering grip. The car is pushing. To make the car neutral handling and faster around the track I can reduce rear grip, make the car rotate better in the turn, let the rear drift a little better. The observed effect will be now I can actually steer the car.

Our RC cars have very lightly loaded tires. There is a property of rubber that makes lightly loaded tires more grippy, more efficient at developing g's than heavily loaded tires. If traction is good on asphalt, you can actually corner at 2.8 g's without traction rolling a TC. I have measured this on indoor asphalt. I have traction rolled a similar electric touring car on our sweeper outside on the third day of practice for a big race where rubber was layed down sufficiently to bring traction up to the traction roll level. My cure was to add two thick swaybars. This increased my roll stiffness. Reduced my mechanical traction. Reduced my grip. No more traction roll. So there are cases even on asphalt where you have too much grip. Then you take the car and put foam tires on it and run it on carpet. You have huge grip. You can traction roll much easier than outside. WGT drivers are finding this out for the first time. Now if you were inside the car you would just steer slightly wider when you felt those inside tires coming up off the ground. The same works with the pan car, but you can also take other steps to reduce front grip like using stiffer front springs or gluing up front sidewalls to make the tire stiffer.

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Old 03-12-2009, 08:27 PM   #672
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New post above.

Here are the finished nerf wings. On my car they provide three functions. Axle protection. They carry the body post far outboard. They will carry electronics or ballast to preload the rear for better forward grip when running a LiPo. On my car they straighten out the 3-link suspension's lower links. A CRC design would have to differ some because the rearward bolt hole must be used for the side link at chassis level. It could be made though and incorporate one of the side battery mount graphite plates. This would provide a couple more screw holes.

I like that the wing will be raised some over say a huge flat chassis made the same shape. This will provide roll clearance at the tips. They can also be shimmed or tilted to gain additional clearance. Center of gravity of the car will be low. Polar moment of inertia on the vertical axis will be higher than before. I have moved weight away from the vertical axis. This means the car will be slightly harder to rotate on the vertical axis. Not a problem as if you have driven a pan car you have seen it do a 360 in the blink of an eye on occasion in poor traction. This tendency should be slowed some. The shape remids me of broadhead blades on a hunting arrow. No problem there.


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Old 03-12-2009, 08:39 PM   #673
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John, your description makes sense of the driver's challenge, tradeoffs, and actual physics. I followed up through the sway bar part, where I'll have to think about it taking grip out of the tires. I thought the sway bar takes force off the outside tire that would otherwise go there due to cornering forces, and puts it back on the inside tire, thus improving the cornering power of both tires taken together (i.e., it improves dynamic grip).

You could write for an RC car magazine (maybe you do), and I'm sure your knowledge is appreciated here. Thanks.
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Old 03-12-2009, 09:15 PM   #674
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I thought the sway bar takes force off the outside tire that would otherwise go there due to cornering forces, and puts it back on the inside tire, thus improving the cornering power of both tires taken together (i.e., it improves dynamic grip).

You could write for an RC car magazine (maybe you do), and I'm sure your knowledge is appreciated here. Thanks.
Your description is exactly backward. A sway bar actually loads the outside tire, pushes down on the outside link, and lifts the inside tire. Just take the RC car and roll it severely and you will see this is the case. Tire efficiency is reduced, the car slides more. Handling quickness is improved though. Sloppy rolling is eliminated so you can get on with the corner quicker.

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Old 03-12-2009, 09:39 PM   #675
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Hi John or anyone,
A few parts just arrived today. Axle and diff spacer with small lip. Now the first thing I noticed differently was the diff spacer had a much bigger lip than the one that originally came with my kit. Next I put everything back together as I always do and tighthen up the diff assembly. But this time it appeared it was not tighten up well as slippage was happening on the left wheel and was not as tight as it normally is with the old axle and diff spacer. At this point I tighthen and the threaded part came off the axle? What the heck!!! So I super glued the part back in as it appears that is how it is assembled. I tried again after some hours of letting dry and I still cannot get the diff assembly tight as I once was able to. Any thought or recommendations?





Here is a comparison of the old part and new but it has the same part number and both crc parts.

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