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Old 03-08-2006, 07:58 PM   #1
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Default How I threw away 6-months of racing

Heres a quick story to hopefully save others wasting away months of race fees, tires, brushes, etc....

Abut mid summer I started to notice irregularities in the handling of my cars. I was constantly resetting my circles (EPA) and changing dual rates, reseeting steering trim and subtrims. This was a every pack ordeal. IT was driving me nuts and I started to question everything. Well looking back I know where it all begins. It starts by owning so mnay cars-thus reusing models in my radios. This is an issue when you dont reset your d/r (dual rate) and EPA's back to 100%. So I reuse a model, reset subtrim to zero, and then proceed to mechanically make my car go as stright as possible and be as "square" as it can be. Then set my circles to 5' or 5.5' per side. HERES where the problems all began. Imagiine my d/r is set at 60% and my epa's are 75left and 82right and car makes a tidy 5' circle per side. All seems hunky dory right? Well-for reasons that are beyond my skills to type-its the farthest thing from ok. Changes in d/r combined with chnages in steering trim and where your subtrim are at wreaks havoc on your radio. To the point where one change makes one sides circle larger or smaller and can make car pull to one side. So you chnage the subtrim to correct for the drift, but this chnages the size of the circles again, so now it feels like its pushing or way to much steering so you dial in or our d/r and that makes the circles different sizes again. And were not talking an inch here, but sometimes as much as a foot off!!

TO make a long story short, I felt at every club race and worse big race like I was chasing my radio. I would start the race and end races with a different handling car because I made d/r or trim changes before and during races all season long. I even sent my radio in to be thoroughly bench tested and it was just fine!!

So heres the moral of my story and I hope it helps someone!!

Regardless of what preset numbers are in your radio and especially if your going to reuse a model in your radio do this:

Reset steerng trim to zero
reset subtrim to zero
reset d/r to 100 and Only change it in the most dire emergency
reset EPA's to 100 per side

set the size of your turning circles and the equality of your turning circles with EPA only!! This will limit your ability to tune somewhat, but should still allow you room to make steering circles bigger or smaller.

For example on my CRC 3.2 with servo flat-I can have as small a circle as the steering hubs will allow, but I can only have about a 5.75' large circle just using epa's. But that range is enough.

I am not saying that this had any effect on how I qualified in any race, but I am sure it didnt help and it sure made 2005 the worst of my 6 or 7 years of racing form a mental standpoint. I thought i was going crazy every weekend and practice night.

Hope my stupidity helps somone else out!!
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Old 03-08-2006, 08:08 PM   #2
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Its not that bad but your car should always be symetrical. You should have you left and right epa's identical. If yours are not you have one tie rod longer than the other or your center rod between bellcranks is making them not parallel or your tiller arm on the input bellcrank is not 90-90 to your servo arm.

I would hope that no cars on the market have a fundamental error in servo/bellcrank/steering geometry that woud require diffrent L to R end point settings.

On my car I built it and set the epa's so the servo is not stalling or binding the suspension. I look at the epa numbers on my radio and if they are not equal i find and fix the problem. If your epa's are equal you can use Dual Rate and have no ill effects.
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Old 03-08-2006, 08:13 PM   #3
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I am usually satisfied with epa's that are within 5%. Right now on my 12th scale they are within 2%.

Adrian-I am sure your right-if your epa's are exactly the same, you should be able to chnage d/r. I thnk there are combinations that can lead to this not being possible at all times though.
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Old 03-08-2006, 08:25 PM   #4
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Man Ray I hate when my EPA is off more than 1 or 2 digits. It is frustrating thats for sure.
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Old 03-08-2006, 08:58 PM   #5
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I agree set dual rate to 100% (or max) and never touch it.

however my EPA L and EPA R are always the same anyway. if you have your steering links exactly the same lenghts, also your castor and camber settings then EPA L and EPA R should be the same,

the only time i vary the EPA L and R independetly is if the track calls for it. e.g if it has long right sweepers but short sharp left corners. in that case i may turn the EPA R a bit less (for the long right hand sweepers) and/or put the EPA L a bit more.( for the left hand faster corners)
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Old 03-08-2006, 09:14 PM   #6
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So why dont you guys want to change your dual rate?
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Old 03-08-2006, 09:41 PM   #7
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man, i thought i was the only person that this has happend to
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Old 03-08-2006, 09:57 PM   #8
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Lucky for me that I don't touch D/R ,only EPA and abit of Subtrim
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Old 03-09-2006, 02:41 AM   #9
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I didnt see it in your post.. What radio are you using?/ Ive seen funky stuff with the 3pk radios when going from model to model.. ive also seen models completely shut down on some functions.. ie no left or right control...
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Old 03-09-2006, 04:09 AM   #10
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funny, i use a sanwa super exzes, which i think is the stick version of the M8, and had non of the problems mentioned.

my left and right EPAs differ by 15% on my current car, with subtrim set to 10R. using the hudy set up station, i checked steering angles as i changed d/r from 100% to 50% and the car still turned equally left and right throughout the range!
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Old 03-09-2006, 08:00 AM   #11
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JasonC-I know were not alone!! SOmething crazy happens in the brains of these computerized radios when you get the settings out of whack!! Maybe no one will believe me, but I would set the car down and check circles left and right. Lets say they were 5'r, 5'l. Turn off radio and check fiften minutes later..... 5'r, 6'l. Turn of radio and check next day 5'r, 5.5l. Check again in 5 minutes, 5'r, 6'l. and between all these tests-I touched NOTHING!! I checked it at the track, I;d check it at home... NO glitching going on. Just epa's wandering!! IN other words I was driving cars for half a year that would steer different at anytime right to left.

I almost quit racing over it!!
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Old 03-09-2006, 08:12 AM   #12
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Getting your EPA's perfect within 1 or 2 % is almost impossible. This would mean that from center, you would have the place the servo horn STRAIGHT up, which usually doesn't happen because it will be one spline off to the left or to the right, which usually accounts for 5-10% in your EPA. You would also have to have your servo saver assembley/steering rack EXACTLY square and straight. I wouldn't worry about what the numbers say, as long as the car cicles correctly and trims straight.

Making sure you set your EPA's within 1 or 2% could cause more harm than good if it's not what the car needs.

If you set the EPA with your DR at 100, then even if EPA numbers are off left to right, when you adjust the DR, it will still give you even circles.
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Old 03-09-2006, 08:21 AM   #13
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YOu know the heli guys have this rule of 90's (LInk to horns must always be 90 degrees) and they wil keep turning servo horns or trying different servo horns and reattaching till they get it perfect. They also do not believe in any subtrim!! Theyd rather the horn be off just a hair then add subtrim. They do this for reasons of strange interactions among other things. Its not a bad idea.


I always put the servo on as close to vertical as I can, then set subtrim to make my servo horn perfectly perpendicular!! But, I am almost thinking of always using the servo horns that are for multiple brand servos and keep turning the adapetr till I can attach the servo horn perfectly vertical at zero subtrim!! Heres where the problem is!! They dont make these universal servo horns in small 12th scale size and my Losi JRXS doesnt use a servo saver at all!!
IN other words-I allowed for a certain degree of laziness in the mechanical set-up because thats what I thought subtrim, epa and d/r were for!! I dont take any of this lightly anymore.
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Old 03-09-2006, 08:32 AM   #14
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OK, here's something simple.

Rather than stressing and spending hrs getting the horn perpindicular, why not adjust the link bewteen the horn and the bellcrank to get the bellcrank perfectly straight? If the bell crank is sqaure, that's all that "mechanically" matters (although again, EPA will vary each side). Even if you click subtrim in the car, the tires will still only throw to the EPA already set, not further to the side you trimmed to, so the subtrim didn't change anything mechanically, just where the servo centers to.

Think of it this way, if you set everything perfect with no subtrim, as soon as you hit a board and slightly change the toe on the car, all that doesn't mean anything.

I initially set my ST to 0, then set toe using a set-up station, and I know at 0 ST my car is square. BUT, alot of times the track isn't perfectly straight, and your car will drift one way or another on the straights. Then you end up subtrimming a slight bit anyway .
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Old 03-09-2006, 08:39 AM   #15
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do you run a spektrum module? i've heard some cases of crazy radio model settings like trim and epa changing on its own with the use of a spektrum module, sometimes even changing a few clicks while in use...
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