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Old 03-12-2009, 10:23 PM   #676
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Originally Posted by SystemTheory View Post
You could write for an RC car magazine (maybe you do), and I'm sure your knowledge is appreciated here. Thanks.
I have to agree here, John. You have excellent knowledge and even put things in lamens terms where everyone can understand. You really have a unique skill sir. I'd seriously vouche for you to write for reputable magazines like RC Driver for example. Plus your posts are inspiring and make people think about new ideas.

You rule man and I also appreciate your excellent posts.
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Old 03-12-2009, 11:17 PM   #677
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Thanks guys. My writing is on occasion too technical for the mags. It is a good supplement. So we will leave it at that.

Here is the deal on the Gen X 10 axle. Some of these got out with a spacer that is too thin (or narrow). What happens is you tighten your diff nut, it compresses the bellevile washers completely and fails to tighten the diff. What happens next is you tighten the nut a little more. With the washers flat you have made an efficient puller and it pulls the threaded stud out. Bummer. The solution is to increase the thickness of the spacer with a thin axle spacer or two. IRS makes a nice set of brass spacers. These make sure the cone washers are not compressed all the way.

When I pull that shaft out of an axle, I buy a new axle. I have only done this once with an original Pantoura fiberglass axles.

It is hard for the superglue to dry in a deep hole. It is almost like the glue is still in the bottle. Wait a least over night. Better to use some 2 part epoxy that does not rely on air components to harden.

Here is another way to fail. Try spraying accelerator on the glue just before you stab in the axle. You will see the glue turn into a rock just before you get the axle started in. Accelerator is just vinegar. Probably best to apply this just after you stab in the axle and spray glue all over yourself. Then your hand becomes a permanent part of the axle.

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Old 03-13-2009, 12:56 AM   #678
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CRC Wide Pan, Nerf Wings, Electronics install
Here is the install. This has got to be the nicest looking RC car that I have owned. There was plenty of room for the electronics. Nice and low. Far back. The rear preload is 6.6 ounces. This is good for LiPo. I may need some ballast. The right side wing has plenty of room for the Lap timing module from Spektrum.
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CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-nerf-wings-electronics-install-resized.jpg   CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-peugeot-905-b-908-colors-resized-006.jpg  

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Old 03-13-2009, 01:20 AM   #679
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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.
Have you tried the Protoform Nissan P35 which is still available from Corally (at this shop: http://www.pkracing.nl/, item number COR78226, 30 Euro, I think the picture is actually the narrow P-35, but you'll get a 235 mm wide one)?
The front end slopes up a bit more (it sits higher on the body posts), while the rear end is about as high as the 905B.
I can't tell you how it handles because I still need to try it myself.
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Old 03-13-2009, 07:27 AM   #680
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Hey John are those the sts madog nerf wings?

thanks
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Old 03-13-2009, 10:07 AM   #681
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Have you tried the Protoform Nissan P35 which is still available from Corally (at this shop: http://www.pkracing.nl/, item number COR78226, 30 Euro, I think the picture is actually the narrow P-35, but you'll get a 235 mm wide one)?
The front end slopes up a bit more (it sits higher on the body posts), while the rear end is about as high as the 905B.
I can't tell you how it handles because I still need to try it myself.
He did - it's in one of his older threads.

The P35 has a bit more front DF but also a bit more drag (because of its increased frontal area) - if I remember correctly.

Around here, we liked the Peugot best because it was the fastest and we didn't ever really need any more front traction (VERY high traction asphalt - the old SoCalRC) but drag was an issue with 6-cell stock 27t.

But the P35 was really well balanced - a bit less high speed, but a bit more steering.
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Old 03-13-2009, 11:34 AM   #682
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Thanks for the posts guys.

Here is a pic of the Associated Nissan that I ran. I'll defer to Boomer's descriptin of the handling on this body.

S13EVO- No unfortunately those nerf wings are one of a kind prototypes that I made by hand at this point. If you ask for it they will build it unless there are only 3 of us. I saw those STS Madog Nerf Wings listed at CRC but I could not get a photo this morning.
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CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-associated-nissan-prototype-ii-001.jpg  

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Old 03-13-2009, 01:29 PM   #683
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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.
Yes, I had it backwards, the antiroll bar pushes down on the outside tire, and takes weight off the inside tire. According to Herb Adams in Chassis Engineering, there is no net gain in grip, but lets say the front can pull 1.0g in 1:1 scale car and the rear can pull 1.10g, with a proper antiroll setup you can bring both sides up to 1.10g, and this occurs because the camber gain during chassis roll is where you're losing some traction without an antiroll bar. I am not experienced on exactly how to do it myself, but it makes physical sense when described that way. Is it possible that camber gain increases roll steer during a J-turn, and the sway bar improves handling without taking out grip?
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Old 03-13-2009, 01:48 PM   #684
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System Theory-It is certainly recommended to use sway bars front and back when using them. Handling on a road course can be improved. You can lower lap times. I have not seen this data where just adding sway bars improves cornering g's by a huge .1. The springs must be too wimpy. My full size road car is right at 1.0 g. A .04 g increase is very hard fought.

A little further in Herb Adams book he goes through a sway bar calculation where weight transfer and cornering g's are calculated. You can see the drop in g's right there when adding one bar.

Certainly camber changes play a big role in full size cars due to wide flat treads. On our touring cars the tread is more round. Camber changes are less important. Weight transfer and tire loading are extremely important. On our pans the tires are more flat. On the front camber is important but then we are stuck with this horrible strut front suspension.

so when applied to RC what is the typical case. You add a sway bar and you will reduce grip on that end. You add two sway bars to increase roll stiffness and promote smooth sliding on grippy surfaces and at the same time add quickness or responsiveness to the car. You do this in high traction conditions. I stick to my story. RC guys will swear they increase grip with sway bars. What they have increased is responsiveness at the expense of grip.
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Old 03-13-2009, 03:58 PM   #685
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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.

when you glued the axle stud back in the axle you did not get the stud back in far enough..i can see alot of stud that was at one time glued into the axle now exposed..

also it tends to never go back in correctly and won't run true..

if it's a new axle send it back to crc for a free replacement...defective on there end.
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Old 03-13-2009, 06:16 PM   #686
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John I looked at Adams again and I agree with your analysis.

How do you estimate the 2.8g traction, from time through a known corner? A g sensor? Something else?

I ask in part b/c this factor plus the turn geometry sets the back-emf voltage Vbe in the motor model upon exit of a turn, due to coupling through the gear ratio and tire radius. I think gearing has everything to do with the exit velocity at each corner and matching the tire curves to the Dyno through the gearbox, but my model is still under development.
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Old 03-13-2009, 10:09 PM   #687
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System Theory-We measured the radius of a medium turn using a rope to swing the arc of the race line; we put some cans out to mark 1/4 of a full turn and used a stop watch to get the 2.8g. Ac=v^2/r. The turn was traction limited. A 3.5 g tipover result (traction roll) was determined with the weight transfer formula. I calculated at what g was 1/2 the weight transfered. The center of gravity height was determined by balancing the entire car on a tape reinforced section of the body. It was about .75 inch up on a touring car at 6mm ride height.

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Old 03-14-2009, 07:20 PM   #688
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CRC Wide Pan
Here is a photo of the underside of the CRC Wide Pan with my protoype Nerf Wings. Looks good from this angle as well. Final weight is 44.3 ounces. Heavy Items: I have relatively heavy body posts intalled as well as a gold cased battery now. I also have the front diffuser made from an HPI plastic wing. I am happy with the weight.

A couple of things to note. I am still getting used to these GFR body posts. I am convinced only of their beauty body on and off. The lower screws must have blue Loctite or the base unscrews first when removing the body. Note in the rear that the plastic part of the post is one of our standard pan body posts used upside down so the axial screw hole is up. Works great. These are a little more flexible than the GFR plastic. Note the rear body posts end up in a very strong area of the body near the crease with these nerf wings.

I have trimmed my front suspension support plates to suit my 221 mm width. I don't intend to ever go wider on this car. I have tried that. They look less busy this way and still allow length changes.

I have plenty of ride height using the stock side springs in bump (with the 3-link suspension) instead of just in roll. The rear is extremely supple and smooth in roll. More so than stock and more so even than when I use coil over shock springs. I so look forward to a road test on the new surface.

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Old 03-14-2009, 10:58 PM   #689
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Hey John,

I have a question about the Protoform Sophia GT body, seeing as you have one as well. Up until today, I have been using my Protoform Corvette C6-R with raving results. Great on and off power, great on turns, really handles well. However, when I practiced with the Sophia GT, I noticed that I am spinning out on turns, EVEN FLIPPING OVER! Something that rarely happened on my Corvette C6-R, unless I was really pushing the throttle hard on turns. I found it strange that my driving style and setup did not change from the Corvette, yet the car was handling a lot worse. I am confused right now as to what to do. I increased the front camber to -2 degrees, hoping I could have some traction to push through turns, but no avail.

One avenue I am going to pursue is maybe going with stiffer springs in the rear and increase the pre-load until the spring is touching the chassis. But I am afraid that will cause the car to roll too much and even flip over more easily. I am currently using the white springs (that come with the kit).

Can you provide any insight as to what you did with your car when you ran the Sophia GT body? Did you experience the same things I did? I also tried loosening my rear diff for more stability on sharp turns, but nothing. I find it strange that a scale realistic body is outperforming a doorstop body.

Please help, if you can.
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Old 03-14-2009, 11:53 PM   #690
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Harry- I don't have the Corvette C6 in front of me to look at. I have no track time on the Sophia yet. So what I get is this. You have traction roll and the rear is loose on occasion. I suspect that the wing on the corvette was farther back. This does two things. It nails the rear down in the corner. No more looseness. And because the wing is behind the rear axle it unloads the front giving less steering for traction roll.

These are things you can do. You can move the wing back by using HPI wing supports and moving the wing. It is some trouble as both the wing and the body have nubs. You may be able to move the stock wing back farther on the nubs. I am sure you could with new wing supports. You can go at least 1/2 inch back from the centered position. This may be all you need.

If you have too much front traction causing a traction roll, Remove steering throw at the radio (reduce dual rate %). Reduce front traction with stiffer front springs, Glue the sidewalls up to make a stiffer tire. or use a harder front if legal.

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