Plotting Cn-Cy and Cn-Ay Graphs.

[apoorv]

thanks sir I will look into this and reply ASAP.

[Tim.Wright]

I agree with Claude and Adam, that the problem is in the static offsets of the tyre curves. However, with no labelling on your plots its impossible to say much more.

Try switching off the horizontal and vertical shifts in the tyre model (by setting their scaling factors to zero) and see if it fixes the problem.

If the tyre has a different (mirrored) construction for the left and right side, you need to first understand which tyre you have the data for (left or right) then in your calculations incorporate a mirroring function which inverts the X and Y axes.

If your tyres are interchangeable left and right and have single specified rotation direction, that means that any static force offsets are going to add together instead of cancelling each other out. In other words the staic offsets in the tyre curves will make the car asymmetric and you just have to live with it.

[apoorv]

Hello everyone,
First of all thanks Claude, Tim, Bill Cobb and Adam for explaining us the differences between both the diagrams and about the assymetry that we got as we didn't adapt the tire coordinate system to chassis coordinate system.
From Fy vs SA graph we can see the forces cancelling out as we mirror about the axes. So in the images attached below we rectified the Assymetry problem and as well as we were able to figure out the problem with Cn-Ay constant steer lines. There was a problem with the yaw rate calculation in the matlab which we rectified as we did a sanity check on our code.
Below I am attaching both Cn-Ay and Cn-Cy graphs. These are the final ones. The green ones are the constant steer lines. I hope these are correct but I still want u to have a look at it and any comments are welcomed.
We are also going to add some other factors such as rollstiffness, camber angles etc.
Once again Thank You
CnCy.jpgCnAy.jpg

[Claude Rouelle]

What about a legend?
What about color that would help the reader to easily identify what the values of CG slip slip angle and what the value of steering angle are?

[apoorv]

Sir,
Here are the images with Legends and markings!


Cn-Ay legend.jpgCn-Cy legend.jpg

[Claude Rouelle]

What is CN positive? Left or right hand corner?

Same question for the sign of the X axis.

How do you define a postive and negative Beta?

What is a positive steering? Turning left or turning right?

Is the steering angle the steering wheel angle or one wheel angle (if so which one?) or the average of the LF and RF steering angle?

Is this a simplified 2 wheel or 4 wheel model?

CN Vs lateral acceleration is a constant speed correct? What is that Speed? Why is that speed not on the graph legend?

CN Vs CY is a constant radius correct? What is this radius?Why is that radius not on the graph legend?

[Claude Rouelle]

What is CN positive? Left or right hand corner? Or less confusing: clockwise or anticlockwise?

[apoorv]

CN clockwise is positive, front wheels steering is +ve for right side. Its not steering wheel angle so no steering ratio and average angle of both wheel. Fy is positive for right side! Beta postive for right side. cn-cy at 16.75m constant radius and cn-ay is at 17m/s constant speed.

[Claude Rouelle]

There is a part of me that will play dumb because your explanations are not precise enough and I am sure other readers have similar questions and the other part that will ask because simply your best definition are not good enough

1. Is this a simplified 2 wheel or 4 wheel model (with weight transfer)? You did not answer that question

2. CN clockwise is positive, OK got it!

3. front wheels steering is +ve for right side. What the heck does that mean? The right side of what compared to what? What is "+" ve? What about the forces sign convention? Is it the same? Please make a sketch!

4. Its not steering wheel angle so no steering ratio and average angle of both wheel. The "and" is confusing! What is it at the end? You could be going into a left hand corner and turning the wheel(s) or the steering wheel to the right because you have oversteer.... Can you simply tell us if its clockwise or counter clockwise from the driver perspective?

5. Fy is positive for right side! Again right side of what compared to what? Pointing towards the right side of the tire, the screen, the corner center?

6. Beta postive for right side. The right side of what? Again a clockwise and counterclockwise definition would be better

7. cn-cy at 16.75m constant radius and cn-ay is at 17m/s constant speed. Got it, thanks but why in the hell didn't you say so!

You think inside your own box. You understand yourself but your explanations for the information for the newcomers are not clear enough. Too much time wasted making sure we speak the same language instead on focusing on the core issue of your questions. If we would be side by side that would be easier but here we are working via a forum posts so we need to have precise definition of our sign convention.

Fix that first and then we will go ahead.

When we will all use the same language we will continue to work but I can tell you already that I see some issues in your graphs. It is about control and stability that are the most powerful and useful part of this graph.


Claude

[apoorv]

1. This is a 4 wheel model with weight transfer (for right hand cornering).
3. Steering angle front wheel is positive for clockwise direction.(It's a right hand cornering ). The lateral forces are positive for the right hand turn.
4. Basically we are referring to a parallel steering here and the delta mentioned is actually front wheel's angles which is +ve for right hand turn.(clockwise with respect to driver).
5. Fy is +ve for right side of the Tire i.e. towards right hand cornering centre Fy is positive.
6. Beta is positive for clockwise direction.
7. By mistake I typed speed as 17m/s but it is actually 27m/s.

PS: All the sign conventions followed are from "Race car vehicle dynamics".

Here is a screenshot of the table that includes all the sign conventions we followed.

RCVD sign conventions.jpg