Saturday, August 15, 2015

RE-Xtreme Drift Bible - Steering Ackerman

With rear drive becoming more popular, You 100% need to know about steering ackerman. So lets take a look at least at what it is and how you can understand it a little better.

With CS cars usually requiring the front wheels to slip a little, the lead wheel did a lot of work and the trailing wheel might be used "almost" as a brake of sorts. Helping to drag the inner line and cause the rear to be pushed outward.

As the RC hobby has evolved, with more angle and radical styles, we are actually moving away from this design to more parallel setups.   

Yokomo sell these knuckles to create MORE ackerman. Have you wondered why there were more than one hole on the knuckle?  Because it's the position of the steering link to the knuckle that controls adjustment of Ackerman angle.

The above refers to MORE Toe Out, but the Toe Setting only occurs during steering lock. And that's where toe and Ackerman must be used together. They are in linked in concept.

In it's simplest form, Ackerman is measured by drawing a line from the from the KINGPIN through the Steering KNUCKLE ball joint and then to the rear axle. Depending on knuckle design, a difference in toe naturally occurs through the range of movement. One wheel will typically get more angle.

Recently there are TRUE and near to TRUE ackerman designs that move back to PARALLEL wheel movement.

Modern Rear Wheel Drive designs are moving towards to this style because the Gyro can control the instability caused by such designs.

So, with the wheels pointing straight there is no difference in toe setting. Ackerman has no effect in a straight line.

So which do I chose.

So when you are DRIFTING, what angle do the front wheels need to be at?

As stated above, CS Car Tune was leading towards toe out on full lock for agility or Toe in for stability, but as rear wheel drive has a little help with steering (by means of a gyro), stability has automatically increased, so we can create a more agile machine and one that is somewhat faster is corner speed, by eliminating toe in or out for stability from front wheel slip / braking.

The increased angles also allowed in modern cars also mean that we can have built in agilty and control through more steering input. So in theory, we should be moving to a more Zero setting or one that results in a zero toe setting at full lock, shouldn't we?  

Now... Zero means that the car's wheels will be exactly parallel when drifting. This fine for those big entries.
But for tight corners. We all know that one wheel has to be on slightly different angle to turn.

Look at the angle of the wheel on the inner line...

I'll just add more ackerman. in CS cars this can help to TURN the car by braking the inside while and kind of inducing a constant load that tries to spin the car. the inner wheel is braking the car slightly. With 4WD, power simply overcomes the loss in speed.

This is usually what happens when a CS chassis is first converted to rear wheel drive only without changing the steering.

In RWD, without any power to overcome the front wheel braking, the car will just spin.

Now this is a very tight corner but it illustrates the point of less ackerman.

Basically toe in during cornering. Depending on the Speed of the circuit a very slight amount of ackerman can increase corner speed.

But also know this. Transition speeds will also increase so prepare for that. As you speed up the front of your chassis ... what happens at the back is equally effected, so be prepared for that too.

Because with both the wheels pointing absolutely parallel, control is much harder like running on a knife edge.

 So in the last few years as the scene has progressed from C-Hub...

 through lower block...

 to Yokomo "Type C" style setups.

And now they give us a crazy amount of adjustment... Why?!?!??!?!?!?!

With these knuckles you can create TRUE, ZERO, MORE or LESS all in the one item.

Adjustable castor, camber, kpi, steering wiper vs steering rack , narrow scrub and wider track and more are changing the way that the Drift scene is heading.  In a way the real drift scene is getting closer.

So it's much more technical allowing for much more flexibility. But that for most means very very complicated.    

 So ... what do we recommend.

I don't dare broach that topic because it depends on the 999999 thousand variations out there.

For my own Rear Wheel Drive. I'm heading towards a near true but slightly more Ackerman setting.
Another way to say that is a slight toe out at lock.
 Less ackerman at lock seems to give a brake effect at speed. Especially noticible on RWD

But that requires a sizable investment in steering parts.

I hope everyone can understand at least what ackerman is in the drift world as opposed to the "race scene" where the car body is virtually in a straight line and opposite to this.

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