Adams car question

[peaty]

Hi,

I don't know if there is an Adams car guru around here. I'm new to the software and, to be honest, I don't know very well how it works. I'm having some problems with a front suspension. I'm trying to change camber and toe but I'm not pretty sure where about is that change happening. Some people say it's about the hub, someothers say that it kind of make the upper wishbone shorter...At the moment, everytime I change camber KPI also changes...so I'm assuming that the second option is the one happening!? can anyone shed some light on this!?
Another question regarding Adams cars, would it be better if I change my setup in CAD and then use the new coordinates of the setup as hardpoints!? If I do so, will I get toe and camber I have on CAD directly on Adams? I'm not sure what's the best way to go.

Thanks

[Tim.Wright]

There are 2 ways to change the toe and camber. Parameter variables and adjustable forces.

Parameter variable are in every suspension system and they change the the toe/camber angle in the design position of the car. This is related to the shape of the upright and how it connects to the control arms. It is connected to the DESIGN of the car (specifically the upright) NOT the setup of the car.

When the simulation starts, there will typically be some settling of the springs and bushings and the resulting toe and camber angles will usually be different from those in the design condition because everything has moved a little bit. This is where adjustable forces come in to adjust the angles back to your target values.

The adjustable forces work by changing the length of the toe link and wishbones until you reach the desired static values. This is done in the static equilibrium (i.e. before the simulation starts) and this is equivalent to the way that the static angles are set on the real car. Therefore this is used to modify the SETUP of the suspension and NOT the design of the upright.

I guess in your assy, you are changing the camber angle using adjustable forces and its moving the complete wishbone which therefore also changes the KPI. In the template editor you can change how the camber and toe link adjustments are made because every different type of adjustment will require a different setup in the template.

If the adjustable forces are moving the wishbones in a way which is different to the adjustment method on your car, then you have 2 options:
1. Change the template so the adjustable forces move work in the same way as your suspension adjustment method
2. Model the adjustments in CAD (like you suggested) and copy the new points (but don't forget to update the parameter variables with the new toe and camber values from CAD because now you have changed your design position!)

[peaty]

There are 2 ways to change the toe and camber. Parameter variables and adjustable forces.

Parameter variable are in every suspension system and they change the the toe/camber angle in the design position of the car. This is related to the shape of the upright and how it connects to the control arms. It is connected to the DESIGN of the car (specifically the upright) NOT the setup of the car.

When the simulation starts, there will typically be some settling of the springs and bushings and the resulting toe and camber angles will usually be different from those in the design condition because everything has moved a little bit. This is where adjustable forces come in to adjust the angles back to your target values.

The adjustable forces work by changing the length of the toe link and wishbones until you reach the desired static values. This is done in the static equilibrium (i.e. before the simulation starts) and this is equivalent to the way that the static angles are set on the real car. Therefore this is used to modify the SETUP of the suspension and NOT the design of the upright.

I guess in your assy, you are changing the camber angle using adjustable forces and its moving the complete wishbone which therefore also changes the KPI. In the template editor you can change how the camber and toe link adjustments are made because every different type of adjustment will require a different setup in the template.

If the adjustable forces are moving the wishbones in a way which is different to the adjustment method on your car, then you have 2 options:
1. Change the template so the adjustable forces move work in the same way as your suspension adjustment method
2. Model the adjustments in CAD (like you suggested) and copy the new points (but don't forget to update the parameter variables with the new toe and camber values from CAD because now you have changed your design position!)

Thanks Tim.wright, as I said before, I have learn more today reading your replies that reading some books. So, let's recap to verify that I understood correctly:
1-If I start with the hardpoints of a square setup (0 camber and toe), I'll have to make the changes in the adjustable forces in order to get the desired camber and toe. However I'll have to check in the template how that change is made. I assume I'll have to change the position from where that change happends. I assumed you're talking about "hps_camber_adj_orient", isn't it?. If so, where should that point be located, in the coordinates of the point where I make changes (upper OBJ in my case) in the real car or the same longitudinal and vertical but in the middle of the car? or is it done in a different way?
2-If I start with a given setup (not square), I'll have to update the parameter variable in order to make it match my given setup. right!?
So if 2 is correct, the question is... if afterwards I decide to make a change in my initial setup (I had camber= -1) by changing adjustable forces, my new real setup will be i.e. parameter variable camber (-1) + adjustable forces (-1) = real setup (-2)?

Thanks

[Greg Locock]

One way of cheating is to move the spindle alignment point (if Car uses that), this changes the axis of the wheel bearing relative to the spindle, remember to move the contact patch as well. It's not a good approach on a real design where you have CAD already, but if you are developing the geometry in ADAMS before CAD then it is a good method of only adjusting the thing you are interested in, obviously the 'realistic' methods of setting toe and camber have slight but measurable effects on other things.

[peaty]

One way of cheating is to move the spindle alignment point (if Car uses that), this changes the axis of the wheel bearing relative to the spindle, remember to move the contact patch as well. It's not a good approach on a real design where you have CAD already, but if you are developing the geometry in ADAMS before CAD then it is a good method of only adjusting the thing you are interested in, obviously the 'realistic' methods of setting toe and camber have slight but measurable effects on other things.

Thanks! I didn't consider that possibility!

[Greg Locock]

Actually the Help on the toe and camber setting makes the point more forcefully, it recommends iteratively alternately setting toe and camber if you are using the adjustable forces method.

[peaty]

how do you plot motion ratio and wheel rate in Adams car!? I've been trying to do it but the graph doesn't look correct. I've been doing the following:

motion ratio:
x axis: wheel travel
y axis:wheel_travel /nsl_ride_spring_data_displacement_rear

I'm getting a graph that has a huge peak for x=0 and for the rest of the suspension travel y=0

wheel_rate:
x axis: wheel travel
y axis: spring rate/MR^2

I assume this one is wrong because MR is wrong.

*spring rate: Ks = 4pi^2*fr^2*msm*MR^2

[Greg Locock]

motion ratio is the instantaneous gradient of those two, not one divided by the other. It's a subtle difference.

MR(n)=(wz(n)-wz(n-1))/(sl(n)-sl(n-1))

whereas you are plotting

MR(n)=(wz(n)-wz(0))/(sl(n)-sl(0))

[babias]

Hi, I am also new to the software and I don't understand how to read the results of simulations from the plots. I am talking about the reference frame used for different outputs. For example if I plot the roll angle vs roll center lateral location I don't know which is the positive rotation of the chassis or if the roll center moves towards the inside of the curve or towards the outside.
Thanks in advance.

[Tim.Wright]

The help documentation should give you the sign convention but there are two other sub requests called lateral distance to left & right contact patch which should give you enough info to understand where it's moving.

More importantly to say though, the roll centre lateral position is an absolutely useless parameter to monitor... There's no useful information that you can draw from it which links to the driving dynamics or correlates to any subjective feeling as far as I have seen.

Additionally, you will get a different results depending on how you set things up in Adams. E.g. roll centre lateral position is different between an opposite wheel travel and a roll test, and likewise if you select vehicle or "ISO" reference frames. Then there is the fact that is becomes mathematically undefined when the jacking forces are really low. There are better things to be looking at if you want to understand the roll behaviour.

[babias]

The help documentation should give you the sign convention but there are two other sub requests called lateral distance to left & right contact patch which should give you enough info to understand where it's moving.

More importantly to say though, the roll centre lateral position is an absolutely useless parameter to monitor... There's no useful information that you can draw from it which links to the driving dynamics or correlates to any subjective feeling as far as I have seen.

Additionally, you will get a different results depending on how you set things up in Adams. E.g. roll centre lateral position is different between an opposite wheel travel and a roll test, and likewise if you select vehicle or "ISO" reference frames. Then there is the fact that is becomes mathematically undefined when the jacking forces are really low. There are better things to be looking at if you want to understand the roll behaviour.

Maybe the example of the roll center was not appropriate. The problem is that I don't understand in which reference frame outputs are given by Adams. According to the positive rotation around x (directed backwards) with a positive roll angle I would expect that left wheel travel is in the compression stroke but in the plot is exactly the opposite.
Thank you for your help!

[Tim.Wright]

The sign conventions are a mess in Adams, you need to go to the documentation for each channel you want and get the information there because there are no general rules. Some of the output axes systems aren't even proper right hand axes.

If it's not clear in the documentation sometimes you need to run some simple load cases where you know what the results will be to understand the sign conventions. It will do your head in this software - you should buy an emotional support kitten or something if you are going to be using it for a long time period.

[Greg Locock]

Roll is one of the funny ones, at least in /Chassis, as the body rotations are given in yaw pitch roll order, whereas a normal engineer would expect that if displacements are x y z, the the order would be rx ry rz, ie roll pitch yaw.

Even more hilarious is that our vehicle dynamics toolbox reports front wheel rz as steer not toe, so sometimes I need a -1 and sometimes I don't. On the same car.

To get around the debatable sign of the roll signal almost all of our K&C metrics are reported in terms of spindle rise, which also makes comparison with bump tests easier.

[Greg Locock]

Oh, and on lateral displacement of the roll centre, Saab used to have a theory that it should migrate towards the outer contact patch. It's one of those plots we automatically generate, and automatically ignore. None of the scripts seem to pull it out as a reportable figure. I agree with Tim, the exact point of application of a horizontal force along the line of action of the force on a rigid body makes no difference.

[browney]

It will do your head in this software - you should buy an emotional support kitten or something if you are going to be using it for a long time period.

I am new-ish to ADAMS car its fair to say that I have found it quite tricky, even after having a fair bit of simulation experience.

I was wondering if the above was a common feeling in industry? What do people think is the best resources for help (ie. books, websites, etc.)?