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Old 03-17-2010, 02:26 AM   #1
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Default High speed oversteer

Hi all,


I'm very very new to this - please be gentle. I have done a quick search but found only rather model specific advise, maybe this would still be pertinent to me but I'm a bit too novice to know at this juncture.

I have a reasonable understanding of 1/1 scale cars - designed, built and raced many of my own. And worked for top end motorsport companies in the past.

I've recently bough an HPI RS4 Pro2. I have two issues I was wondering if any one can help me with?

1. The car never goes straight. I adjust the trim every straight and by the next straight it needs adjusting again.

I bought the car with 12degs castor and buckets of front toe in.

2. Massive high speed oversteer. the slighest of brushes against the steering stick at anything over 20mph leads to the car spinning out. In fact, the trim tab can cause the car to spin at high speed.

To counter the later point I have done the following, all with positive results:
V stiff front end, v soft rear end, lots of ackermann, spooled front diff, 2degs rear toe in.

Any advice greatly received as I was embarrassingly slow at my first race last weekend.

Cheers,
Glen.
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Old 03-17-2010, 02:47 AM   #2
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Some things to check.

1) is the servo horn screwed in tight?
2) Droop Setting equal from Left to Right on the Front and Rear?
3) Shocks the same length?
4) Rebound of the shock shafts the same from L to R on the Front and Rear?
5) Any binding on the suspension?
6) Any bent hinge pins/shock shafts?
7) Bearings good to go? Check inside the rear hubs.
8) Is your Steering Servo in proper working condition?
9) Does your RX glitch?
10) Do the batteries in your TX ahve ample juice?
11) EXPO setting on your radio?

Thats all I can think of for now. Good luck on fixing your issue.
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Old 03-17-2010, 03:12 AM   #3
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Having bought the car S/H (I guess judging by the fact that it's an old car), I would suggest a total stripdown and careful examination of all parts. It is very tricky to start on an old car with unknown history and find what's wrong with it.

That being said, I would look at the tires first. if these are crap or just unsuitable for your track, you're not going to go anywhere fast. Check with the locals at the track and find what tires and inserts you need and take it from there.

Independently, after stripping down the car as suggested above you should become very familiar with every bit and understand what it does and what happens if it's damaged. After reassembly, I would strongly advise to put it on a setup station. It can never be overstated how important this is. The setup station is going to tell you straight away if there's anything wrong and what. You will understand straight away how impotant this is and how much it helps and I am pretty sure you'll find and fix your problems given your tuning experience.

Best of luck and welcome to the hobby. By the way, hope you have a healthy bank balance.
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Old 03-17-2010, 03:38 AM   #4
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Thanks for the replies.


1,8,9 Servo is a prolux S5009, it seems to be fairly smooth. The horn is on tight. All the steering links are on the slowest/torqueist settings and the servo saver is screwed fairly tight (5mm off chassis).

2 0mm droop all round I'm afraid. I will be experimenting with helper springs in the near future.

3 Shocks "appear" to be same length. Haven't checked with a vernier though - will do tonight. I guess you are suggesting the corner weights are out?

4 Not entirely sure what to check there? Can you clarify?

5 No binding

6 No bent pins on first inspection. Will strip and roll on a flat plate to check though.

7 Had the rear hubs apart last night, they seemed good.

10 New alkaline. Worth replacing to check though.

11 Alas, I have a fancy 2.4g Code but it is constantly being sent too and from Schumacher Racing as it is v unreliable. So I have been using a Futaba Attack 27m system without exponential servo control.

Tyres were "donated" to me from a local racer. He watched me suffer with my "wet" tyres (it was a dry day) and gave me his old HPI slicks. He did say that he would never use them - so I guess they aren't great (still leagues better than the wets I had on).

LOL. Still cheaper than my other mistresses! I have a race Mini, BMW 2002 and a 3litre Lotus 7. A weekend racing just one of them is 400/$600..... lets hope this hobby will be 1/10th the cost

Thanks,
Glen.
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Old 03-17-2010, 03:55 AM   #5
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Quote:
Originally Posted by wurlyvalve View Post
Hi all,


I'm very very new to this - please be gentle. I have done a quick search but found only rather model specific advise, maybe this would still be pertinent to me but I'm a bit too novice to know at this juncture.

I have a reasonable understanding of 1/1 scale cars - designed, built and raced many of my own. And worked for top end motorsport companies in the past.

I've recently bough an HPI RS4 Pro2. I have two issues I was wondering if any one can help me with?

1. The car never goes straight. I adjust the trim every straight and by the next straight it needs adjusting again.

I bought the car with 12degs castor and buckets of front toe in.

2. Massive high speed oversteer. the slighest of brushes against the steering stick at anything over 20mph leads to the car spinning out. In fact, the trim tab can cause the car to spin at high speed.

To counter the later point I have done the following, all with positive results:
V stiff front end, v soft rear end, lots of ackermann, spooled front diff, 2degs rear toe in.

Any advice greatly received as I was embarrassingly slow at my first race last weekend.

Cheers,
Glen.
one suggestion i can make is to make the front toe 0 or slightly toe out.
Toe in makes for a very nervous, unpredictable car.
The castor you are running is extreme to counteract the toe in you have. I would reduce this.
Would definately be an idea to strip the chassis and rebuild as per the manual so you start from a base setup.
while stripping and reassembly you might come across issues that are causing, contributing to the current hassle you have.

For reference and your pitbox download the Xray setup manual.
http://www.teamxray.com/teamxray/sho...p?file_id=6143
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Old 03-17-2010, 04:03 AM   #6
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Thankyou, I'd go with that. I haven't tried changing the castor yet so if you suspect that is a cause I'd have to agree! Nothing else has eliminated the o/s.

I prefer toe out too, but I felt (maybe incorrectly) I got less miss-trimming when I had toe in?
I reckon all the balljoints and plastic bits on steering section need to be binned as they are all too sloppy and causing "wandering" on the straight. Can I buy generic ti turnbuckles and ball joint kits? Is ti the answer or plastic better?

Thanks,
Glen.
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Old 03-17-2010, 04:20 AM   #7
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1. new tires <<<--- very important
2. harder springs, .... rear spring too soft and the car will do that.
3. enough shock travel for damping action.
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Old 03-17-2010, 04:59 AM   #8
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It does sound like there is a fundamental problem with the steering. Either the servo, servo saver or steering mechanism is failing to centre properly.

The Prolux servo is, essentially, junk. 8 spent on a Futaba 3003 will give a much better servo.

My other advice would be to strip down and rebuild the car to kit settings. The manual is still available at HPI's website.
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Old 03-17-2010, 05:39 AM   #9
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forgot to mention check the servo saver if it has one.
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