We have covered the key elements of the BASIC and ADVANCED alignments for the front in the last two sessions. Links are below if you missed it, or need to review it once again.
BASIC ALIGNMENT - FRONT
https://ameblo.jp/marcus38060/entry-12351833320.html
ADVANCED ALIGNMENT - FRONT
https://ameblo.jp/marcus38060/entry-12351846434.html
Now we are moving into one of the biggest talked about subject in RWD RC Drifting...the ackerman.
WHAT IS ACKERMAN?
Ackerman is the difference in the steering angle from the left to the right tires to make up for the difference in the turning radius, so the tires are able to roll smoothly. When you google, you will find something like this...
WHY ACKERMAN? BALANCING THE PUSH/PULL
Ackerman is what will dictate how your chassis will behave when you are drifting in an angle. In RWD RC Drifting, generally the front tires will either be parallel, or toe out, from neutral to full lock. How you setup the change in ackerman, or progression of ackerman is key to how you want the chassis to behave on the track.
There are many different elements in the "Balance" to keep the chassis sideways in the optimal angle for your style. For making the discussion simple, I would say there are the TWO major elements in maintaining the "Balance".
>Ackerman - Front
>Throttle - Rear
Your throttle is what "pushes" the chassis to be in an angle. The force to "pull" the chassis back to straight is your ackerman. (Rear toe angle also has the effect to straighten up, but will put that aside for now for the discussion of ackerman). If the balance of "push" and "pull" is maintained, you will be able to maintain the angle.
LEADING / TRAILING
Mr Bagi did a 1 hour RWD RC Drift discussion panel on YouTube, which seems to have been taken down. In that video, Mr Bagi showed some extreme ackerman on his DP chassis and had a great discussion on ackerman. One part of the interesting comment was the effect of LEADING and TRAILING tire angle.
The LEADING tire will dictate where the chassis is going with throttle ON.
The TRAILING will dictate the chassis straightening out with throttle OFF.
Therefore in most settings, the ackerman should progressively go toe out towards the end of the steering stroke, and the trailing tire should not stay parallel at the end of the steering stroke, otherwise you have less force to pull the chassis back straight to make the next transition.
WHAT IS THE PERFECT ACKERMAN?
This is where everyone has their opinion and why people talk about ackerman so much. There is no such thing as a "perfect" ackerman that works for everyone and every situation, and it is completely up to what you like and what your style is. Big angles for miles, or lighter angle with more speed, it is totally up to you how you want to run the chassis, and also what track you are running at. I also look at how the chassis straightens out.
The link below is from the Yokomo blog, the final chapter on ackerman for YD-2 setup.
https://ameblo.jp/t-yokomo/entry-12239515532.html
The highlight is the two "examples" of ackerman which I use as a good reference.
More parallel ackerman for larger tracks and having less force or resistance from the front tires.
More ackerman, with trailing tire being more open, for smaller tracks or tracks with tight hairpins.
HOW DO YOU MAKE ADJUSTMENTS?
Making adjustments is not an easy task, and there is no simple way to explain how to make adjustments. As I only own slide rack steering systems, I am not able to provide much tips on how to adjust wiper steering systems, but the basic concept should be the same.
Adjustment tips are based on your chassis having some basic setup already. If you don't, then try going back to the assembly manual and putting everything back to stock to have a good starting baseline.
I would strongly recommend everyone to document or take pictures of the current setup, so in case the changes you make are not what you want, you can always replicate the previous setup. What will happen often is, you try something, doesn't work, and now you can't put it back to the previous setting.
1) Toe adjustment
Toe in or out at neutral steering position is very critical in setting ackerman. Based on front tires having negative camber, slight toe out should be the default neutral setup. Very small changes in the toe angle at neutral, can change the ackerman. Try adjusting by quarter turn on the turnbuckle to toe out or toe in, and see how the ackerman looks and test it for at least 5-10 minutes to see how it feels.
2) Steering link position forward/backward
If the toe adjustment at neutral is not enough, then will need to make adjustments in the steering links to gain or reduce ackerman.
>For more parallel ackerman, move the links forward.
>For less parallel, or more open ackerman, move the link backward.
3) Steering link position left/right width
If the desired ackerman cannot be achieved by turnbuckle or steering link forward/backward adjustment, then you will need to dig deeper into making more significant adjustments. This process may require changing the length of the turnbuckle, so you need to be patient to go through the process several times through trial and error.
>For more parallel ackerman, move the width of the links narrower.
>For less parallel, or more open ackerman, move the width of the links wider.
4) Steering knuckle adjustments
If you still cannot achieve the desired ackerman, then will need to adjust the steering link position on the knuckle. This will not only have effect to ackerman, but also changes the lever ratio relative to the king pin.
>For more parallel ackerman, move the links outward.
>For less parallel, or more open ackerman, move the link inward.
>The closer the link moves to the king pin, the steering will turn quicker or will turn more with same amount of servo movement.
>The farther the link moves from the king pin, the steering will turn slower, or will turn less with the same amount of servo movement.
OTHER CONSIDERATION
I have not seen many people talk about the relationship between ackerman and camber.
When you roll a coin, the coin will roll in the direction that the coin is leaning. This is basically what camber does. So, when the ackerman looks like the trailing tire is open, but trailing has more camber than the leading tire, I believe the tire with more camber will offset some of the ackerman. Based on the front tire alignment, with combination of neutral position camber, the camber will change throughout the steering based on caster and KPI. Leading tire should go from negative camber, to zero, then transition to positive camber, however, the trailing tire should only gain camber, or stay consistent depending on your setting. When setting the ackerman, this is something you may want to look at especially if you have an aggressive setting in caster with slight KPI as the camber gain on the trailing tire should be more significant.
As this session became very long, I will post ackerman from my 3 different chassis with different handling characteristics here:
https://ameblo.jp/marcus38060/entry-12359341125.html
Happy drifting!
March 10, 2018 / Charlotte NC
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