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.

Not gone, just underground...

It's been pretty quiet here on the F1.blog, 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.....

UF1 Redux

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Latest V2 setup

Latest V2 setup...a little tough to drive but very fast. Need to work on on power/corner exit stability... https://docs.google.com/open?id=0B4jXTVVFFpAoVVFmQnZrSUxfdWs

A caster diaster?

Another of my rambling from my visit to the track yesterday comes from the Exotek adjustable front end. I finally put my Exotek 104 with this front end on the track after working on the F104V2 for quite a while. I have run a front end made of Xpress parts which is functionally similar to the Exotek pieces, but no where near as nice or durable. So I was familiar with what usually works, but I had some ideas on things to try. Lately, with the Pit Shimizu 0571/0571/Tamiya TCS tires, the cars generally will get a little light on the inside rear coming off the corner. This will sound like diff slippage, but if you watch the cars, you cane see they are a bit rolled over. I have also talked with guys who have had this problem completely independent of us and came to the same conclusion, so that is my theory...LOL. I tend to think it is the fact that the tires are heavier, and have very good grip.

I thought that reducing caster would help this problem, as caster tends to cross jack the weight to the opposite side rear tire. I figured the outside rear was just getting way heavy from too much caster. So I set the front end to 3 degrees of caster, as I had been running 4-5 degrees. Three was actually a very good setting for taking a shot in the dark, as the car stayed pretty flat. There was still diffing, but it seemed to be reduced. Now figuring there was more of a good thing to be had I continued to try to reduce caster, but it seemed as I worked my way to 2 degrees, problems popped up. First off, the car did not like to go through the sweeper anymore. It would turn in and then push to the wall. Secondly, it didn't want to launch coming off the corner either. The mid corner push could possibly be solved with more camber or camber gain, but I didn't like the corner exit issues. Again, maybe softening the car down the middle (center shock spring/oil) could help, but the caster is a 2 for one deal on both of those issues. It may be worth investigating if the diff issue is solved, but I am also not 100% convinced a little diffing is so bad. The main problem is when the car starts to get sideways as you pull throttle, usually as the car is still loaded up from the corner. If you let the car settle before you get on it, it's not a huge problem, but to really be on it is not easy.

Going the opposite direction will generally get you going toward a traction roll. Anything much more than 5* caster on carpet is usually asking for trouble. I'm thinking 3-4* is probably the sweet spot for carpet and rubber tire.

That being said, running too much dynamic caster effect in the upper arm is probably also a contributing factor. This is spacing up the rear ball stud on the upper arm so that the caster is reduced on the loaded side - the kingpin stands up as the suspension is loaded. So now you have the loaded side reducing caster - or reducing the weight jack to the inside tire - and the unloaded side has more caster, jacking weight to the outside rear. Diff spin at it's finest!

I noticed that my F104V2 got better as I reduced the dynamic caster as the grip came up. On the fixed arms of the stock V2, this will also reduce static caster as well. I didn't reduce dynamic caster on the Exotek car, but I think this would have been helpful as well. As traction increases, you generally need less of this inclination of the upper arm. Higher grip usually means the front end is not going to wash out mid corner, and it will help reduce tendencies to traction roll as well. For a situation like asphalt, I would probably run about as much dynamic caster as I could get away with. Carpet, not so much on rubber. Foam, oh yes, but for rubber tire too much will be problematic.

Front droop thoughts

I was at the track yesterday, and I had a chance to fool around with my Exotek 104 car. I was trying a lot of front end changes, and one thing that I was noticing was that personally, when I got much past .5 mm front droop, the car got a feeling mid corner that to me was not very precise on a high bite surface. I think it gives the car too much roll, but this may be useful on lower bite or asphalt. The other thing was it felt like it was over rotating. This was as i was approaching 1mm or more of front end droop over the ride height, so a ride height gauge would show 4mm at ride height, and 5mm when the suspension was extended. Once I returned to .5mm I liked the car better.

A shocking reversal........

I have been in contact with a few friends from the West Coast who told me that some of the guys were running a sedan shock on their F104V2 cars with a long shock end and the shock mount set up for the small shock that comes with the car. At first, I had it set up the wrong way, which requires you to space the mount up to clear the upper deck/brace. Here is what the correct way looks like:

I tried it on the track back to back with the "normal" sedan shock set up. It seems to make the car steer more "directly". I'll have to play around with it a little, but if nothing else it did not hurt the setup, lap times were pretty much the same.

A great way to use droop screws or how I realized how dumb I really am

So here is a quick tip on using your droop screws on the front end of your F104 based car. Normally, you are shown a button head screw with a number of washers under to set droop. This is fine and works great, but changing the setting is tedious in that you must remove some parts to access the screws easily. I had been using a button head and had drilled a hole in the top arm so I could quickly adjust up or down. This worked well, but now you are drilling the top arm. Not really the way to go an a Exotek setup..... So it came to me, that I should use a long grub screw driven in from under the arm. This would be obvious if I was a deep thinker, which I guess I am not, LOL. It's plain as day, but I have been doing it the goofy way for months.... Anyway, this is what it looks like:

IIC Vegas F1 A main

RCFIA is awesome

A very well done web site for the RCFIA F1 series in Northern California.... I love the interviews and news bits! http://www.rcfia.com/