Altair RISE

A program to recognize and reward our most engaged community members

Nominate Yourself Now!

Contacts for custom vehicle in soft soil vehicle roads

Hi,

I am trying to design a robot for deformable terrain first with rigid elements but later with flexbodies. I am using the vehicle tools extension to test on different terrains (starting with simplest dry sand) however I have the following issues.

When I analayse and run, the robot falls through the roadgraphic and doesn't interact with it. When I try to add contacts between my 'pedal wheels' and the ground, it says my ground object is missing a graphic although it has a road graphic attached to it.

Error: Contact "Contact 0" under "Model" does not have any J Graphics. [General]

With this I have 2 questions:

1. How do I get my robot not to fall through the surface or is this only possible with the vehicle tools example models?

2. Is the carpet model option (where the road just is generated as the car drives to save computation) discontinued for 2023 onwards. I only see it in the tutorial and drop downs for 2022?

Any help much appreciated

Thanks

Gaetan

Community-Pasted-Attachment-1718099889293.png

Find more posts tagged with

English

MotionView/MotionSolve

v2023.0

Accepted answers

GTT Adam

Hi Gaetan,

The Soft Soil Road models in MotionView will only work with an AutoTire entity, and can't detect other solid objects. If you are trying to select it as a graphic using the Road Tools Utility, it will not feature the deformable properties as it is simply a graphic representation.

For this type of robot, which does not feature wheels, you will need to couple it with Altair EDEM to cosimulate the cross-style wheels interacting with the bulk material.

Hope this helps!

Adam Reid

All comments

Orestis_YB

Hello Gaetan,

contact entity if I am not mistaken needs a closed geometry to be used as a graphic. In that case, a road graphic won't work. I suggest that you create a box graphic and connect to ground. In that way you will be able to select it in graphics list. I also see in the first photo that some motion are defined on the cross-wheel bodies. Applying motions to bodies related with contact may lead to several issues. The best practice would be to apply torque. If this in not possible then you could introduce a dummy body to which you can apply the motion and then connect it through a rotational spring-damper to the cross-wheels. Hopes this helps!

Best regards,
Orestes.

GTT Adam

Hi Gaetan,

For this type of robot, which does not feature wheels, you will need to couple it with Altair EDEM to cosimulate the cross-style wheels interacting with the bulk material.

Hope this helps!

Adam Reid

Christopher_Fadanelli

Hello Gaetan,

Going off of Orestes. Contact between a road entity can only be done through AutoTires or links of a tracked vehicle (both in the vehicle tools extension). In addition, for the soft soil roads, there is a special tire file that interacts with the soft soil.

For this project, I highly suggest co simulation with EDEM our DEM tool. There is a dedicated soil library for creating particles.

To co simulate with EDEM please refer to the last section of the Introduction course: https://learn.altair.com/course/view.php?id=496

Best,

Christopher Fadanelli

Gaetan Pans_21058

Hi,

Thank you for the quick and clear answer. I just tried with rigid to rigid bodies to get the robot moving, before attempting the coupling with EDEM however my robot is falling through the ground.

When I add contacts, I get the following run error.

ERROR: Contact graphics undefined for contact force [id=301001]!

I have tried impact and poisson contact model. As well as disabled, dynamic only and static and dynamic only and still the same error.

Also as a pre-follow up question regarding the coupling with EDEM. I will have a hollow box in EDEM holding my soil/sand in which my free body/robot will just drop into and the joints rotating to move forward. Are the contacts between my 'wheels' and the particles calibrated in motion solve or EDEM and would I need to turn on contacts in both or just 1 of them?

Hope this is clear

Thanks

Gaetan

Orestis_YB

Hi,

Thank you for the quick and clear answer. I just tried with rigid to rigid bodies to get the robot moving, before attempting the coupling with EDEM however my robot is falling through the ground.

When I add contacts, I get the following run error.

ERROR: Contact graphics undefined for contact force [id=301001]!

I have tried impact and poisson contact model. As well as disabled, dynamic only and static and dynamic only and still the same error.

Also as a pre-follow up question regarding the coupling with EDEM. I will have a hollow box in EDEM holding my soil/sand in which my free body/robot will just drop into and the joints rotating to move forward. Are the contacts between my 'wheels' and the particles calibrated in motion solve or EDEM and would I need to turn on contacts in both or just 1 of them?

Hope this is clear

Thanks

Gaetan

Hello Gaetan,

I suggest to create a box graphic with the same area as the road you want and add some thickness to it (several times larger than the expected graphic penetration). If you link this graphic to ground body then in contact entities it will be available for selection under contact graphics. I guess the one you are using now is an open geometry and thus it's not available for selection. As for the EDEM part the contacts between the wheel-bodies and the particles will be calculated in EDEM and transferred in MotionSolve. What you need to do is add a DEM system from Geometry tab -> EDEM and select the graphics to be transferred in EDEM. Hope this helps!

Best regards,
Orestes

GTT Adam

Hi,

Thank you for the quick and clear answer. I just tried with rigid to rigid bodies to get the robot moving, before attempting the coupling with EDEM however my robot is falling through the ground.

When I add contacts, I get the following run error.

ERROR: Contact graphics undefined for contact force [id=301001]!

I have tried impact and poisson contact model. As well as disabled, dynamic only and static and dynamic only and still the same error.

Also as a pre-follow up question regarding the coupling with EDEM. I will have a hollow box in EDEM holding my soil/sand in which my free body/robot will just drop into and the joints rotating to move forward. Are the contacts between my 'wheels' and the particles calibrated in motion solve or EDEM and would I need to turn on contacts in both or just 1 of them?

Hope this is clear

Thanks

Gaetan

Hi Gaetan,

The error message points to the contact graphics not being defined. In the Entity Editor, click on Graphics (under J body) and assign the contact graphics.

For more on the coupling of MotionSolve with EDEM, please refer to the following link:

https://2023.help.altair.com/2023.1/hwsolvers/ms/topics/solvers/ms/discrete_element_simulation_motionsolve.htm?zoom_highlight=edem

Hope this helps!

Adam Reid

Gaetan Pans_21058

Hi Gaetan,

The error message points to the contact graphics not being defined. In the Entity Editor, click on Graphics (under J body) and assign the contact graphics.

For more on the coupling of MotionSolve with EDEM, please refer to the following link:

https://2023.help.altair.com/2023.1/hwsolvers/ms/topics/solvers/ms/discrete_element_simulation_motionsolve.htm?zoom_highlight=edem

Hope this helps!

Adam Reid

Hi Adam,

Unless I am missing something, my contact graphic has both an I and J component (see screenshot)

When I export the solver .XML to see the ID it is also present

<Force_Contact

id = "301001"

label = "Contact 0"

full_label = "Model-Contact 0"

num_i_graphics = "1"

i_graphics_id = "90002"

num_j_graphics = "1"

j_graphics_id = "90005"

cnf_type = "Impact"

stiffness = "1000."

exponent = "2.1"

damping = "0.1"

dmax = "0.1"

cff_type = "Coulomb_Off"

enable_analytical = "AUTO"

Thanks

Gaetan