Rubber/Asphalt contact parameters in MSC Adams 2

[salaheldin]

Hello dear colleagues,

I am trying to simulate a platform with 4 wheels in MSC Adams.
My question is about the contact parameters I need to defines to simulate rubber/asphalt contact between tires and a ground plate.

The parameters required are:
Stiffness, damping, static friction, and dynamic friction.

Can you help me to choose their values?

Thank you.

 

[GregLocock]

210 N/mm,0,.9,.7

should get you started

Cheers

Greg Locock


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[salaheldin]

Thank you Mr. Greg

When I set the damping to 0, the vehicle just fall of the road, I mean as if there's no contact but, when I increased it the model worked as expected.
What does it mean physically that the damping of the contact is zero?

 

[salaheldin]

It would be great if you can suggest me the values of Stiffness, damping, static friction, and dynamic friction for simulating the contact between a walking human and say, asphalt in ADAMS also. Can you guide me in this regard?

Regards,
Mohamed Salaheldin

Mechatronics and Robotics research student.
Egypt-Japan University of Science and Technology.

 

[GregLocock]

If I bounce a wheel and tire off a road it bounces several times. Therefore I conclude the damping is low. Zero damping works perfectly well in my models.

No, I do cars.

Cheers

Greg Locock


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[salaheldin]

Thank you,

Isn't restitution better for simulating a tire that bounces several time? or it can be simulated using both impact or restitution by changing the parameters?
The alternative to simulating the contact using the parameters you provided me, is to use adams/tire. would it make a lot of difference?
And if it does, what resources would you recommend me to learn adams/tire from?
I need some examples, I found resources but, I am not satisfied about the level of knowledge I acquired from them.

Regards,
Mohamed Salaheldin

Mechatronics and Robotics research student.
Egypt-Japan University of Science and Technology.

 

[GregLocock]

I'm wondering if you are trying to replicate the sliding behavior of a tire, in which case you might do better to model it as a damping value rather than friction. For example, in the linear range, a tire with a vertical load of 5000 N on it will generate say 4000 N of sidethrust, at a slip velocity of say 8% of the forward velocity, so you could pretend that it is a damper with a rate of 4000/(.08*fwd velocity) N/mm/s

ADAMS being ADAMS you may need a bit of friction in there just to stabilise the model, but you just have to try it with and without.

I don't actually model a tire like that, I use /Tire. I'm not really aware of any great guides to using /Tire, between Pacejka's book and the manual and help it seems OK to me.

Cheers

Greg Locock


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[salaheldin]

Thank you dear Greg,

I turned to use A/Tire according to your advice.
Now I need 4 wheels for the robotic vehicle I am modeling, the 2 front wheels are different in diameter from the 2 back wheels.
How can I build custom tires using A/Tire?

I used only the available tires and roads in tires.tbl and roads.tbl folders.


Regards,
Mohamed Salaheldin

Mechatronics and Robotics research student.
Egypt-Japan University of Science and Technology.

 

[GregLocock]

which tire exactly are you using?

Cheers

Greg Locock


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[salaheldin]

Thank you for the fast reply,
I used only uat.tir and 2d_flat.rtf, this was during learning about the tie/road tool in Adams. I don't have previous experience with vehicle dynamics but with robots.
You can recommend me a customizable tire based on my described situation: (I need it customizable to use 2 pairs, each of different diameter)

The situation I want to simulate is a robot that transforms into a vehicle, I want to simulate it while going on a straight road to find the critical acceleration at which tipping will happen in the longitudinal direction. In Adams I firstly used torus as a tire, with solid-solid contact and asked here about the contact parameters and you replied me. The front wheels bounce when they touch the road, and the results are not satisfactory.
The 2nd situation is while turning, to determine the critical speed at which the centrifugal force will cause tipping also but in the lateral direction.

Regards,
Mohamed Salaheldin

Mechatronics and Robotics research student.
Egypt-Japan University of Science and Technology.

 

[GregLocock]

I suggest you open uat.tir with a text editor.

Cheers

Greg Locock


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[salaheldin]

Thank you,
I already find a way, I edited Fiala tire and the 2d_flat road to fit my model.
I will edit uat.tir now according to your advice.

How can I decide to use uat.tir or fiala or any model?
and according to my forementioned robotic vehicle case, what is the tire that fits this situation?

Regards,
Mohamed Salaheldin

Mechatronics and Robotics research student.
Egypt-Japan University of Science and Technology.

 

[GregLocock]

I don't know. The company I work for spends a great deal of money measuring thousands of tires every year. From those results we have a data driven tire modelling capability. None the less it is not a reliable way of estimating ultimate grip. So you need to measure the tire characteristics.

Cheers

Greg Locock


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[salaheldin]

I see, thank you.

I started with the Adams/tire module,
I got these ERORRS when I tried to simulate the model after ading tires:

ERROR: Standard exception "There is no solver license!" caught in file L:/source/adamscxx/src/Asol/slv_intr.cxx, line 1618

ERROR: No model has been defined. Check for successful reading of the model before operating on a model.

My concern is about the 1st error, it means what?

Regards,
Mohamed Salaheldin

Mechatronics and Robotics research student.
Egypt-Japan University of Science and Technology.

 

[GregLocock]

It means your copy of adams failed to find a license when it tried to execute your model. Time to talk to your IT people, as the precise cause depends on what type of license you have. If your model runs OK without tires then it may be you don't have the right Tire license, but usually the error message mentions which license it is looking for.

Cheers

Greg Locock


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[salaheldin]

The model worked, I found the linear acceleration at which the tipping happens in the longitudinal direction.

Now, I need to measure the critical turning velocity, this means that I need a road with a turn in ADAMS.
I tried polyline in ADAMS but it says that the road will not appear graphically.

My questions are:
1.Is there a polyline that can be shown even after some modifiv=cation? there are polyline, polyline_1, polyline_3
2.How can I deal with a road that i can't see?

3. What is the standard radius of a curved road if I am going to build a curved road in ADAMS?


Regards,
Mohamed Salaheldin

Mechatronics and Robotics research student.
Egypt-Japan University of Science and Technology.

 

[GregLocock]

No, ADAMS doesn't follow curved roads (generally), it follows the path set by the physics of your steering angles etc.

There is no standard curve, skidpans are often 30 to 60m radius.

Cheers

Greg Locock


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

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[salaheldin]

I see, thank you.

 

[salaheldin]

Mr. Greg, I will use a normal road for my model, which is defined on a circular solid shape (just for visualization).
I am facing a problem in the model I attached (made with ADAMS 2014) it is just a very simple vehicle with 4 wheels. I applied motion (as velocity) of 40d/s on the backward right wheel, and 0d/s on the backward left wheel.
I expected that the model will turn in a circumference of a narrow circle having its center at the left wheel (of velocity zero) but, the model just goes in a wider circle as if there is a motion applied on the left wheel. What is th reason of this?

I attached the .cmd file but changes .cmd to .txt so, please make it .cmd again to open with ADAMS.

Regards,
Mohamed Salaheldin

Mechatronics and Robotics research student.
Egypt-Japan University of Science and Technology.