How to modify tire size?

[ychen_441]

Hey colleagues,

Might be a dumb dumb question but it cost me a little bit longer time than I expected.

How to modify the size of a tire?

• When I was trying the demo "demo_VEH_DeformableSoil.py", there was a "Dlobal parameter for the tire", but the operation of changing the value there only led to the starting position of the tire changed.
  • How to change the tire size here? I have noticed that there was a ".obj" file used in the later codes of that demo but the file seems to be more of a mesh generation stuff I guess? Is the tire size fixed by the ".obj" file?
• In another case, when playing HMMVV and citybus demos, I saw their tire type is set by the function "SetTireType()" and details can be found in CPP reference. So I thought this might be a ".json" settings, and I changed the value of tire radius and width in "HMMVV_RigidTire.json" but nothing happened.
  • What about this scenario? Is there a way to change tire size within a vehicle system? (different from the former one using a single wheel)

Forgive me being stupid but I will be grateful if anyone can provide some suggestions.

Thanks, and all best,

Chen

[ychen_441]

Or maybe modifying the parameters in the ".json" file indeed changes tire properties but at the same time, 

visualization is governed by ".obj" file so I can't see any differences?

Chen

[ychen_441]

Updates on this question for who may headache about this:

I have tried to read header files and modify several ".json" files to see if those could help and finally,

the solution was to directly scaling (it's a nasty way for test, if you want to model your vehicle, you should 

design a new one by yourself) the ".obj" file, and the tire size changed which you can obviously see in the picture below!

It is easy to see from the footprint that the width doesn't match well to the new size, so that might be something you need to deal

with ".json" file or others. Also, the stress distribution seems already changed (color difference), the reason of it is still unknown. But, anyway,

questions about tire size are solved now, hope this will help those who have the same confusion about this like me.

Best,

Chen

[ychen_441]

For the two observations mentioned in the last message:

• The footprint seems reasonable when I do the same thing to "tractor_wheel".

• For stress distribution, I think they are generated in the same way as models in demos provided. Methods can be found in SCM paper.

Some further question is that the radius and width defined in ".json" file do not match the dimensions in Blender. For instance, "HMMWV_rim.obj" used in "HMMWV_wheel.json".

The one in ".json" states: radius: 0.268, width: 0.22, while in Blender, the dimension of the wheel rim is (0.285, 0.484, 0.484), indicating radius: 0.242 and width: 0.285, I assume?

Anyone has any idea about this? Again, sorry if this is an obvious and stupid question lol.

Chen

[Radu Serban]

Hi Chen,

 

You may want to read up a bit on the design of Chrono::Vehicle and understand the difference between the subsystem templates (parameterized models) and concrete subsystem models (an instantiation of one of these templates for a particular vehicle).

 

You can start with the description on the Chrono::Vehicle documentation page and look at the Chrono::Vehicle paper.

 

Bottom line is that a concrete HMMWV tire model (whether implemented as a derived class or specified through a JSON file) has the parameter values (including the tire radius) *fixed*.  These parameters must be consistent with each other. Having said that, the OBJ files for the HMMWV are used for visualization only, and so they may have slightly different dimensions than the physical tire model.

 

If you want a tire of a different radius, you must provide a different, alternative HMMWV tire model.  This is exactly what you would do in real life: you replace the tire on your car, you do not change the radius of the tire you already have.

 

--Radu

 

From: projec...@googlegroups.com <projec...@googlegroups.com> On Behalf Of ychen_441
Sent: Thursday, September 5, 2024 9:34 AM
To: ProjectChrono <projec...@googlegroups.com>
Subject: [chrono] Re: How to modify tire size?

 

For the two observations mentioned in the last message:

 

• The footprint seems reasonable when I do the same thing to "tractor_wheel".

• For stress distribution, I think they are generated in the same way as models in demos provided. Methods can be found in SCM paper.

 

Some further question is that the radius and width defined in ".json" file do not match the dimensions in Blender. For instance, "HMMWV_rim.obj" used in "HMMWV_wheel.json".

The one in ".json" states: radius: 0.268, width: 0.22, while in Blender, the dimension of the wheel rim is (0.285, 0.484, 0.484), indicating radius: 0.242 and width: 0.285, I assume?

 

Anyone has any idea about this? Again, sorry if this is an obvious and stupid question lol.

 

Chen

 

On Thursday 5 September 2024 at 13:24:05 UTC+8 ychen_441 wrote:

Updates on this question for who may headache about this:

 

I have tried to read header files and modify several ".json" files to see if those could help and finally,

the solution was to directly scaling (it's a nasty way for test, if you want to model your vehicle, you should 

design a new one by yourself) the ".obj" file, and the tire size changed which you can obviously see in the picture below!

 

 

 

It is easy to see from the footprint that the width doesn't match well to the new size, so that might be something you need to deal

with ".json" file or others. Also, the stress distribution seems already changed (color difference), the reason of it is still unknown. But, anyway,

questions about tire size are solved now, hope this will help those who have the same confusion about this like me.

 

Best,

Chen

 

On Wednesday 4 September 2024 at 16:38:48 UTC+8 ychen_441 wrote:

Or maybe modifying the parameters in the ".json" file indeed changes tire properties but at the same time, 

visualization is governed by ".obj" file so I can't see any differences?

 

Chen

 

On Wednesday 4 September 2024 at 16:13:36 UTC+8 ychen_441 wrote:

Hey colleagues,

 

Might be a dumb dumb question but it cost me a little bit longer time than I expected.

 

How to modify the size of a tire?

• When I was trying the demo "demo_VEH_DeformableSoil.py", there was a "Dlobal parameter for the tire", but the operation of changing the value there only led to the starting position of the tire changed.

• How to change the tire size here? I have noticed that there was a ".obj" file used in the later codes of that demo but the file seems to be more of a mesh generation stuff I guess? Is the tire size fixed by the ".obj" file?

• In another case, when playing HMMVV and citybus demos, I saw their tire type is set by the function "SetTireType()" and details can be found in CPP reference. So I thought this might be a ".json" settings, and I changed the value of tire radius and width in "HMMVV_RigidTire.json" but nothing happened.

• What about this scenario? Is there a way to change tire size within a vehicle system? (different from the former one using a single wheel)

Forgive me being stupid but I will be grateful if anyone can provide some suggestions.

 

Thanks, and all best,

Chen

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[ychen_441]

Hi Radu,

Thanks for your message, I will check the documents again and figure it out!

Bests,

Chen