Monday, November 19, 2012

Chatter about chatter

Does your car chatter?

This has been a reoccurring theme lately.  The introduction of the Pit Shimizu and Tamiya "TCS" tires has been a good thing, but it's a lot different from foam tire racing, or even the older style Tamiya tires.

Many of the racers I talk to are concerned about their cars chatter/hopping.  I get a little upset to see it myself.  Typically, a car that chatters in the corners is having some sort of problem.  Pan cars that chatter are worrisome for sure, but consider that we are in a situation which is not typical of pan cars.  These cars now run heavy rubber tires, with a tremendous amount of grip.  They are also narrow.  Now add in a surface like carpet, and you're definitely looking at some hop.  These cars are not smoothly getting into a drift angle like foam tire shod cars do.  Everybody seems to want to cure this immediately since it's so disturbing.

Maybe it's a lot of worry about nothing.

I was thinking back to the 2010 TCS North American Finals.  Danny Hua won the class and the trip to Japan, and I remember quite vividly seeing his car chatter the front end on the left side of the track.  Like a lot of people who see this stuff now, I thought "Wow, his car chatters a lot" with a bit of concern.  At the same time, he had a fast, race winning car.  Could some chatter be the sign that your car is developing enough grip?  It may be.  I remember reading one of the late great Carroll Smith's full size racing books where he explained tire "judder" on full size formula cars.  One thing that stuck with me was not only that it was at one point a big concern to the mechanics and engineers, but when they figured out WHY it was happening , they became less worried.  It also turned out to be an indication that the driver had figured out how to get all the power down, and only the best drivers experienced the judder.

I'm not saying that a chattering car is a good thing, and obviously if the car is going nuts with the chatter, it's a negative.  I just think that maybe some amount of chattering is probably part of the nature of rubber tires, especially on high traction circuits.  To me, if the lap times are there, and the car is getting around the way you want it to, I don't think chattering is huge concern.  If it can be cured I think that is a good thing, but I'm not sure some chatter is 100% bad.

Wednesday, November 14, 2012

Not gone, just underground...

It's been pretty quiet here on the, but it's been busy.  I've been trying to come to grips with a rubber tire setup for a TCS legal F104v2.  So it's been a couple weeks of hiding in the under mountain secret lair/track trying to work it all out.

Anyway, I have been trying a of of things to get my car working consistently from session to session.  I had some times where the car would be very fast, but then be no where near as good if conditions like temperature changed or traction went up or down due to car count.  I also have been getting a lot of good suggestions and tips from friends and acquaintances.  The big thing was to try to boil all this stuff down into something workable.

The big problem with this car being new, and a little unfamiliar, was that I did not have my "go to" adjustments figured out.  Usually I have a few things that are sort of the big adjustments that will send your car in one direction or another and you know you've changed something.  I had a bit of time where I felt like everything was vague and I was flailing a bit.  I was trying to use both what I knew and the concepts I was learning from other people as well, and it was not meshing.  So last weekend I decided to go back to the baseline to try to get my car working.

One thing I was pleased with was using a stiffer side spring.  In the past I had run my Exotek car fairly stiff since it seemed to me the heavier rubber tires needed a stiffer car.  I had recently began to try to make lighter springs work based on what I had seen with some of the on line setup sheets, and when the track was lower traction, it worked well.  As soon as traction came up, it was not easy to drive, and in fact, somewhat unstable.  It was still fast at times.

The problem with stiffer springs is that they can stabilize the car too much.  The link car needs to roll a little to get around the corner, but there has to be a balance to be able to drive the car in a straight line.  This is where the preload comes in.  With the soft springs like Associated black or Tamiya pink/copper. you have to preload the spring a bit in a lot of cases to stabilize the car.  With the softer springs, they really need to be set at just touching or even backed off the pod plate.  This will dictate a lot on how the wraps the corner.  With a really stiff spring, you can be backed of the pod plate so the car will rotate, but when the spring goes into compression, it will keep the car fairly flat.  I think that a lot of the traction roll problems with these cars are generated from the rear of the car versus the front.  This brings me to my next point, dampening.

I'm probably going to sound like a kook here, but I think that really heavy dampening is key.  I had been up to 50,000 wt diff oil in the X1 damper tube, but I was wondering if maybe more could be better.  After talking it over with one of my buddies who was endorsing massive amounts of dampening, I decided to go big.  After some playing around, I settled on 120,000 wt Losi diff oil in the tube.  This made the car much flatter, so much so that it would slide rather than traction roll.  This again goes toward the theory that the much higher unsprung weight of the rubber tires requires the car to be a lot stiffer to control all that mass.

What really got the car working correctly with the higher dampening was a boatload of rear droop.  I am now at 3mm over ride height.  The droop seems to really give the car a lot of forward bite.  I can get on the car pretty much where ever I want to.  Previously, I was having to be a lot more careful with throttle inputs.  Don't get me wrong, I find that smooth throttle input makes for very fast laps with F1 cars, but I feel a ton of confidence with the added bite.

At the same time, a minimal amount of front droop appears to better for me.  I think it helps to keep the weight on the front tires under power to retain the on power steering.  Steering feel is also less "floaty"  and more direct.  I had tried a lot of front droop, but I started migrating back to a minimal front droop setup, and I prefer it.

Another thing I had tried was a very horizontal shock.  Usually this does produce a lot of on power steering at the expense of rear stability in my experience, but I'm not 100% sure about that now.  I actually felt like the car was a little more stable, but more mid corner out.  It still seemed to turn in.  Oddly enough, I also tried some heavy rate springs with the shock in a more angled setting, which I usually run.  The heavy springs also seemed to stabilize the car in certain corners, especially the sweeper.  Returning to the usual Short Black spring set brought the steering back.  I wonder if the stiff shock inhibits the cars ability to roll or at least, articulate the links?  Chassis roll seems to be the key to cornering with the link cars.... At this point, I am running the shock with quite a bit of angle.  That seems to be the best for my track conditions.

I should also add that I was encouraged to run my battery to the rear of the chassis.  I had been running the short pack with the electronics behind it, but I moved the RX and ESC to the sides of the chassis and began to experiment with the battery.  Full back seemed to cause to push in the sweeper, so I moved it forward a small amount at a time.  What seemed to work for me was about 3/16 to 1/4" (4-6mm) off the back of the chassis.  I'm finding it's easy to tune the car a little by moving the battery in small amounts.

So here is the setup sheet....for lower bite try gold side springs and a yellow center shock spring....

Thanks to The Passehls, T Marshall, RedBullFxx and Rocket Ron for the help.....