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Old 05-15-2013, 10:03 PM   #1
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Default Cobra GT Swapping Ends on exit - help

Hey gents
We parking lot race here but it's pretty competitive and I'm having a frustrating set up problem with my Serpent GT car, OS .28 XZ, extreme RC mods pipe.

The car turns in perfectly, fast and tracks straight on the straight away but on corner exit it literally snaps around and spins like it's on ice. I have tried easing on the throttle and it sometimes works but I'm getting beat badly I have to exit so slowly. This car is a rocket if I could just get it under control.

If i drive my Kyosho GT or even GT2 I can hammer the throttle and launch into the straight away with no problem.

Driving the Cobra exactly the same way on the same line it snaps around almost every time.

Here's the strange thing to me. As the Alphas get warmed up it seems to get worse?!?!

My set up is stock using the provided front rear dif oil and gears, ride height and provided shock oil.

In general race car set up theory what can cause this and what set up changes will help the rear end hook up on corner exit?

Thanks!
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Old 05-15-2013, 11:33 PM   #2
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Last edited by MantisWorx; 05-16-2013 at 09:41 PM.
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Old 05-15-2013, 11:51 PM   #3
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Quote:
Originally Posted by OldBourbon View Post
Hey gents
We parking lot race here but it's pretty competitive and I'm having a frustrating set up problem with my Serpent GT car, OS .28 XZ, extreme RC mods pipe.

The car turns in perfectly, fast and tracks straight on the straight away but on corner exit it literally snaps around and spins like it's on ice. I have tried easing on the throttle and it sometimes works but I'm getting beat badly I have to exit so slowly. This car is a rocket if I could just get it under control.

If i drive my Kyosho GT or even GT2 I can hammer the throttle and launch into the straight away with no problem.

Driving the Cobra exactly the same way on the same line it snaps around almost every time.


Here's the strange thing to me. As the Alphas get warmed up it seems to get worse?!?!

My set up is stock using the provided front rear dif oil and gears, ride height and provided shock oil.

In general race car set up theory what can cause this and what set up changes will help the rear end hook up on corner exit?

Thanks!
Run the rear long... Move hub carriers all the way back
Lower the hinge pins for rear arms....too much rear camber with rubber tires is no good make sure tires contact patch is good over whole tread
What is your droop?
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Old 05-16-2013, 09:43 AM   #4
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Sounds like it may be a simple solution. Check your rear droop. You may not have enough and if so your inside rear tire may be making very little contact or not at all with the pavement while cornering, then when you get on throttle most of the rear traction is going to the outside rear tire and the car spins out (swaps ends).
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Old 05-16-2013, 10:25 AM   #5
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+1 on motor and clutch set up.
Also, make sure you have an effective way of deflecting the exhaust away from the car. From the way you're explaining it getting worse, that can be a culprit as well. your left rear tire could be getting a constant dose of oil and fuel.
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Old 05-16-2013, 11:15 AM   #6
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More front droop.
Lower rear roll center.
Softer clutch.
Long wheel base.
Definitely get the exhaust out of the body. I always ran a large exit hole in the body and had a deflector inside to keep the exhaust off the rear tire.
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Old 05-16-2013, 11:27 AM   #7
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Forgot to ask, is it only doing it turning in one direction or either direction?
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Old 05-16-2013, 12:05 PM   #8
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Another option to try is less caster with the 10 degree caster blocks. And a simple setup change is toflatten the front lower hinge pin. Use the lowest block in front and the highest in te rear block of the front hinge pin.
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Old 05-16-2013, 09:08 PM   #9
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Quote:
Originally Posted by OldBourbon View Post
Hey gents
We parking lot race here but it's pretty competitive and I'm having a frustrating set up problem with my Serpent GT car, OS .28 XZ, extreme RC mods pipe.

The car turns in perfectly, fast and tracks straight on the straight away but on corner exit it literally snaps around and spins like it's on ice. I have tried easing on the throttle and it sometimes works but I'm getting beat badly I have to exit so slowly. This car is a rocket if I could just get it under control.

If i drive my Kyosho GT or even GT2 I can hammer the throttle and launch into the straight away with no problem.

Driving the Cobra exactly the same way on the same line it snaps around almost every time.

Here's the strange thing to me. As the Alphas get warmed up it seems to get worse?!?!

My set up is stock using the provided front rear dif oil and gears, ride height and provided shock oil.

In general race car set up theory what can cause this and what set up changes will help the rear end hook up on corner exit?

Thanks!


Quote:
Originally Posted by MantisWorx View Post
Unfortunately that is the tendency of that car but it can be tamed down . First of all the engine you have is a monster and puts down alot of torque and that isnt helping the situation! One thing you can do is go with two carbon clutch shoes/two aluminum and use two lighter clutch springs.
Stand up the rear shocks(outside tower/inside arm and try the purple or red rear springs with 1k weight oil and change your pistons to 2 stage, they increase grip all the way around.
Your tire choice will probably be the most important adjustment. If the tires work worse when they warm up then they are too soft. Usually when the Alphas do not work the SWEEPS will, they rarely ever work great at the same time! Last weekend I raced on a parking lot track with soda prep and the Sweep 45 and 50's worked better.
@Mantis:It's the tendency of the car? Really? I Completely disagree with your whole post' except for the part that the .28 has a lot of power...

@old bourbon: are u using the stock gearing? I will recommend 16/48 in first gear.
Where are u located?
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Old 05-16-2013, 09:24 PM   #10
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Wow! Really appreciate the support.

Droop - well according to the set up directions Serpent says to use the droop screws to set ride height at 10 mm. So I guess that effectively brings the droop to zero?

Exhaust - I learned that the hard way on my K GT car years ago. I now have a decent way of venting the exhaust outside the body w/o restricting the exhaust. I use an oversized piece of heater hose and it works great.

Clutch - Good idea! maybe with the stock clutch and springs the RPMs are spooling up and then kicking in and snapping the car around? I have limited time tonight before racing tomorrow but I'm going to give that a shot.

Tires - I have a set of SWEEPS 50 I believe. I'll put them on and give it a go. I've also got a set of the staggered Ipanemas. I thought about trying them thinking maybe the larger rears might give a bit more contact area?

Camber - I run about 5 - 10 degrees of neg camber front and rear hoping that on cornering the roll will increase the contact patch? Sounds like I should go to zero camber?

Servos - one thing I thought of today at work was maybe my steering servo speed? I forget the model SAVOX but it's the fastest one they make. Do you guys think that since my other lower end cars use either stock servos OR 50 - 60 dollar range servos the speed of the steering servo could be too fast? I might be grasping here but i wonder if the quick steer might cause the rear end to come around?

Rear toe - Everybody disagrees with me BUT I have had great luck running zero rear toe. I understand the theory but to me an on road car suffers from any amount of rear toe. I've always believed that if a 1/8th scale on road car like a 966 uses zero rear toe then the GT should be OK as well. Back to my Kyosho and custom made rear end I've had great success with zero rear toe. Also if the rear end were pushing I might think some rear toe might help? But since it's loose I think any amount of rear toe would add to problem I'm having?

Again - I really appreciate the help. For a parking lot outlaw class I think I do pretty well. When it gets down to the technical aspects of this hobby I know I fall short so I've got thick skin. Let me know if I'm really out to lunch on some of my thinking.
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Old 05-16-2013, 09:30 PM   #11
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Mr Paolo. I'm located in Raleigh, North Carolina. I race down in Fuquay with the guys from ToyTown Hobby Shop.
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Old 05-16-2013, 09:33 PM   #12
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@Jedi - It's breaking loose in either direction.
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Old 05-16-2013, 10:58 PM   #13
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Ride height is 1O in rear but the droop should be measured with the droop Gauges and blocks

You should be setting your ride height with the spring collars on the shocks evenly
With 10mm ride height and 10 mm droop ( measured under the rear upright or hub carrier ). You will get a few mm of chassis up travel

Camber should be around 2 degrees all wheels. This will give you the most contact patch 5-10 in rear and front is way too much
You want to have even tire wear

I run the kit toe blocks and kit roll centers as a start and my cars pretty planted

If you correct this and steering still feels nervous or fast you can try some negative exponential in steering on transmitter

As well as making rear end wider with optional hubs

As for tires. I run sweeps 45 front 40 rear on v4 dish rims but temps tire here is still cool. New York

The split works well. If you have 50 front try 45 rear

Paolo can recommend alpha tire compound for you I'm sure ...


If this all sounds Crazy or your not understanding you need to download xray
Set up book. It explains how to adjust and set suspension etc

Hope this helps
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Old 05-16-2013, 11:17 PM   #14
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Quote:
Originally Posted by OldBourbon View Post
@Jedi - It's breaking loose in either direction.
Just lower the hinge pins for rear arms and make the wheel base longer by moving the rear hubs all the way back
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Old 05-17-2013, 01:02 AM   #15
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Sounds obvious but the first thing to check would be that everything is ok with the rear and/or front transmissions. Since there is no center diff the car would still be moving even if the rear transmission wasn't engaging properly for example. That could be a simple explanation.
In any case, when there is a major handling problem the first thing I would do is check if everything is assembled properly.
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