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Old 12-20-2006, 12:07 PM   #1
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Default exponetial/arc settings

I have an Airtronics Mx3 radio which works pretty good.
It has ARC which I guess is the same as exponetial.
I have never messed with these settings, on the advice of an experienced driver. I'm wondering if the majority of drivers use or don't use this feature.

By the way I Race stock electric truck. XXX-t mf2. I'm thinking about this because the track got real dusty the other day, and I felt I could use some traction control coming out of the tight corners.

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Old 12-20-2006, 12:21 PM   #2
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The only time I use Steering Expo is if the car is really just off of center, like really twitchy going down the straight but the car is handleing good in the corners. I was running an 1/18th scale this winter on carpet a slight adjustment on the wheel while going straight would easily put the car on the opposite side of a 3' lane. Put in -25% steering expo on my M8 and the car makes much smaller movements at the begining of the steering travel.
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Old 12-20-2006, 01:55 PM   #3
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Default What about Throttle Expo?

I'm asking about throttle expo.
Thanks.
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Old 12-20-2006, 05:01 PM   #4
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I always use some expo to smooth out a car. Both throttle and steering.

Throttle and brake are set at -30 or so, depending on the motor and available traction. More expo for more motor and/or less traction. I routinely fine tune this. Electric motors usually have a ton of punch right off neutral, so this smooths things out on slick surfaces. Stock motor and gobs of grip could go the other way with the expo for max punch.

Steering is always in the -30 to -40% range for me. I find this a very useful feature. Once I set it, I never mess with it If you watch the amount of steering a the wheels of the car vs. the input at the tx, you will see it becomes close to linear at this -30 to -40% setting for most cars. The way the servo/steering linkage works, it has "expo" that works the "wrong way" built in that makes the steering more sensitive at center vs the extremes. So putting in -30 to -40% makes things pretty close linear or a bit more 'dead' near center.

Most people just get used to driving the car with no expo because they don't understand what it does...... And yes, 1/18th cars can use tons of expo to calm them down. I have 50% or so in my 18t to make it somewhat manageable....

Experiment and see what you like. If you don't like it, put it back to 0. Doesn't cost anything..........
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Old 12-21-2006, 11:01 AM   #5
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Default Makes Sense

I'll have to look into this. It seems like Car Mfg's would have calculated the throw on the linkages and created a linear action.

I wasn't even thinking about Steering expo, but I'm going to mess around a bit.
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Old 12-21-2006, 12:54 PM   #6
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when you are adjusting the expo for throttle, use the adjustments in the esc. Sometimes you can't, but if your esc can, do it that way, it works much better.

As for steering expo, it can help reduce the twitchy feeling, but adding toe in (1/2 deg or less) works better and compromises the handling and response of the car less. Also, try turning your dual rate down and learn to drive using smaller inputs instead, with the wheels turning less, you will carry more corner speed.
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Old 12-21-2006, 01:34 PM   #7
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Amen on the steering D/R adjustment. This is a valuable tool to fine-tuning your car. I am constantly fiddling with it before my run. Lots of times you may feel like you have too little side or forward grip from the rear of the car. Actually it's your over driving the car that is causing the instability coming out of the corners. Dialing down your dual/rate will calm the car down. Usually no more than 5 to 10 % is necessary. I will fiddle around with about 2 to 3 % over the course of an evening.
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Old 12-21-2006, 01:54 PM   #8
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Also as far as expo (short for exponential). I think it was briefly described above, but I think it needs to be clear what it is. It is a function of distance travelled by the steering wheel and not the servo. It in effect tells the servo wether or not to accelerate through its travel and how much.
The term exponential sums it up. As the steering wheel is turned farther the speed that the servo arm rotates accelerates exponentially relative to the distance travelled. In other words if expo is set at 25%, then the servo will increase its speed by 25% for each given distance travelled. The distance is usually a percentage of total potential travel and varies by manufacturer.
Obviously this will make a servo very unpredictable in panic situations. If you are travelling down the straight and come upon a car not moving, you may crank the wheel very far and fast. Your car will probably end up cartwheeling down the straight as a result.
This adjustment is mostly used in large oval track racing. They will turn down the expo to keep from inadvertantly turning the car's wheels too much when changing lines and when running in packs.
Full size race cars will have steering boxes with changeable rates. This is what the D/R does. They will never have a box that has a progressive rate, this would be the same as the expo setting. It would be too unsafe.
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Old 12-22-2006, 06:39 AM   #9
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This is all about personal feel. I run full negative expo on my throttle, and I love it. I feel like I have better control coming out of turns and accelerating, I don't slide as much. Now almost every time someone else drives my car, they feel like it is laggy. One of the faster guys on the track seems like he is either running linear or full positive expo with punch! I drove his car and I couldn't control it because it was too sensitive on the throttle. I run almost full negative expo on my steering too.

This is all about how you prefer to control you car. The way I have my radio set up is right for me. The way the other guys set up their radio is right for them. So set up your radio right for you. There is no right way or wrong way here.
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Old 12-22-2006, 09:12 AM   #10
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I usually go with Negative 20%-30% on the Throttle and Negative 15% on the Steering.... that is if the Tracks conditions stay consistent like in an Indoor Off-Road Track. Outdoors things can change dramatically throughout a race day especially if the Track doesn't get hosed regularly during a race.
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