Differential Terrain Behavior in Vehicle Demo: Articulated Chassis vs. HMMWV

[Leo]

When running the Vehicle Demo, I noticed that when both terrains are set to "terrain/RigidPlane.json", the behavior of vehicles driving off the terrain is different. While the articulated chassis vehicle falls off the terrain when driven off, the HMMWV vehicle continues driving. Is this due to different vehicle properties? Which property does it involve?

[Radu Serban]

Hi Leo,

 

The short answer: that is due to the different tire models used by different vehicle models. 

 

Indeed, so-called “handling tire models” (such as Pacejka, TMeasy, TMsimple, and Fiala) need relatively little information from a terrain system to implement the tire-terrain interaction. Namely, they only query the terrain for the terrain height, normal, and coefficient of friction at a point on the terrain surface below some given (query) point.  On the other hand, rigid tire and FEA-based models interact with the terrain through the underlying Chrono contact system.  For that, both the terrain and tire must carry a collision model.

 

A RigidTerrain patch of type “box” (which is the case for the one specified in data/vehicle/terrain/RigidPlane.json) defines a collision box but also returns meaningful values for terrain height, normal, and coefficient of friction beyond the extent of that collision box (in particular it returns a height of 0 and a normal in the global Z direction everywhere).  As such, a vehicle using rigid tires (such as the ACV) will “fall off the terrain”, but a vehicle model using handling tire models (such as the HMMV where you probably use a TMeasy tire model) will be able to drive beyond the extent of that box.

 

Note that you could modify the HMMWV model to use rigid tires (a JSON file for that is provided in data/vehicle/hmmwv/tire/) and you will see that vehicle also fall off the terrain.

 

--Radu

--
You received this message because you are subscribed to the Google Groups "ProjectChrono" group.
To unsubscribe from this group and stop receiving emails from it, send an email to projectchron...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/d3373930-3fc1-4e88-8a97-75282ed9c989n%40googlegroups.com.