ADAMS Full Vehicle Simulation Error // Static Equilibrium - Straight line 1

[Tanmay_Panchal]

Hello everyone,

So I am working on our first FSAE car and using ADAMS for MBD analysis. So far it has been wonderful progress, the subsystems of front & rear suspensions and steering has been modeled succesfully.

These subsystems work perfectly fine individually (or steering+front suspension) on a 2 post suspension test-rig. But when they are assembled with tires and body in full body assembly I am not able to run even a single sim. I get a static equilibrium failed error even during simplest simulation of straight line with free steering.

I have used the body model of FSAE templates on ADAMS website. So far I have checked communicators, joints and individual subsystems but I am not able to pinpoint the exact cause. The way I have modelled it is that all the element of suspension hook up to the mount part "suspension_to_chassis" and that particular part is hooked upto the body using communicators for mounting.

I have searched a lot for this but am finally posting here being clueless:

1) I understand this error seems most likely that my model is not being assembled properly. How can I pinpoint this problem? (they work fine individually..!!)

2) I am reading the term 'static funneling'. how do I use static funneling? (sorry if it seems stupid). I can only change few stuff under solver menu under settings.

3) Other terms I hear is Debug/Eprint. What are they being referred to?

Hoping for positive replies.

Enclosing a .txt for error message window error.

 

[GregLocock]

First of all check that you can run the default car correctly. Then switch in your subassemblies until it crashes. I suspect you have a problem in your rear suspension, so that's where I'd start.

Yo may need to bump up your static equilibrium maxit in the solver settings. The look in solver settings debugging and play around with those options. It is very frustrating when you can't get the model to build at all, as the clues the solver gives you are misleading and terse. For instance I have a model that usually crashes with all the errors pointing at one lower shock absorber bushing, yet that has nothing to do with the steering bushings where my problem is actually located.



Cheers

Greg Locock


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[Tanmay_Panchal]

Hi Greg,

Thank you for the reply, I was finally able to run the model in open loop and straight line steering events. Closed-loop steering event is still a long way to go.

As it turns out during my last post, it was a simple error of 'hps_path_reference' being too high off the ground. I relocated it to where it should have been and atleast the model runs now.

But I have another problem now, whenever I begin a simulation my front seems to vibrate. I will attach my files and a jpg showing the vibration in post processing. It seems during the start of the sim, my car is somehow 'dropped' from a certain height?
That kind of explains why it changes the damper travel for a time being and dampens slowly.

I am also enclosing all my FSAE files for your reference. If you decide to run it, please only do it with 'locked' steering. It is not running with 'straight' steering because it's an open loop somehow.

If you can point me to some place where I can get to know how does the model fit into driving system that would also tremendously help me.

PS: Really sorry if this seems stupid, I am just a student trying to learn this from internet information.

 

[GregLocock]

Your model is assembled at the defined geometry. Then gravity is switched on and all the compliances come into play so it does indeed drop. One way to get around this is to allow it to settle before running a maneuver, using a static funnel. In your case you appear to have an undamped resonance at 10 Hz, which makes me think wheelhop. Look at the animations carefully and see if you can see anything vibrating, or put a little bit of damping into every compliance. Sorry I'm not going to run your model I use an old customised version of ADAMS.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[Tanmay_Panchal]

Hi Greg,

I can't thank you enough for helping, you are ADAMS genius it seems.

Problem was with the actual damper template, it was a glitch I guess. The template was from ADAMS 15, which wasn't working with the model. I swapped it with the latest one from existing templates and voila, it did the magic. So yes, it was undamped oscillations.

There is only one thing that I am not able to figure out yet. Every-time I run my model in straight line events > maintain > drift (locked steering). My model drifts to the right (video enclosed along with plot of spring travel). If I set steering to straight (machine controlled), my car turns right sharply.

Wierd part is during course events > double lane change, it neither pulls right or drifts left, it goes absolutely straight and then makes the right, left lane change maneuver.

If there was a problem, then driving machine would still turn my model to right sharply. Or in other case, it should drift to left a little but it did not. It worked EXACTLY as expected, am I missing something here for straight line events?

 

[GregLocock]

"straight line events > maintain > drift (locked steering). My model drifts to the right "

Any assymetry in the model will cause this, as you have basically clamped the steering wheel in one position, I think.

This occurs in real life even on an otherwise symmetrical car due to what is loosely termed ply steer in the tires.

" If I set steering to straight (machine controlled), my car turns right sharply.

Wierd part is during course events > double lane change, it neither pulls right or drifts left, it goes absolutely straight and then makes the right, left lane change maneuver."

That makes little sense, look at the .dcf file for the two events and see what the difference in settings is.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?