Bushing reaction forces

[Lukas K]

What is the way to get reaction forces from bushing for:

1. ChLinkBushing

2. ChLoadBodyBodyBushingGeneric

When I use Get_react_force() I get only zeroes

[Radu Serban]

Lukas,

 

When using ChLinkBushing, you need to access the various individual ChLinkForce objects, using ChLinkLock::GetForceX(), ChLinkLock::GetForceY(), etc. (see https://api.projectchrono.org/classchrono_1_1_ch_link_lock.html ) and then invoke the GetF() method on each one (see https://api.projectchrono.org/classchrono_1_1_ch_link_force.html).

I realize that this is a bit too convoluted, so I will add a ChLinkBushing functions to directly return the bushing force and torque.

As a side note, ChLinkBushing is implemented as a “free” joint with internal forces on the 6 DOFs, so it is no surprise that Get_react_force() returns all zeros (there are no constraints).

 

For ChLoadBodyBodyBushingGeneric, use ChLoadBodyBody::GetForce() and ChLoadBodyBody::GetTorque() (see https://api.projectchrono.org/classchrono_1_1_ch_load_body_body.html).

 

--Radu

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[Lukas K]

Thanks for guidance and explanations.

I ran demo_MBS_link_bushing.cpp with example 4 which uses ChLinkBushing.

Then I used bushing_link->GetForce_X().GetF() to extract reaction forces but still getting zeroes.

Where I'm making a mistake?

[Radu Serban]

Hi Lukas,

 

Sorry, I gave you the wrong function name (GetF returns the value of the preload in a ChLinkForce, something that is not set for a ChLinkBushing).  The correct function to use is ChLinkForce::GetForce, but that one is cumbersome to use as it takes some arguments (you can access the required values, but that’s not a good API). 

 

So, I added two functions ChLinkBushing::GetForce and ChLinkBushing::GetTorque which directly return the quantities you want.

 

(Note that I cleaned up a bit the ChLinkBushing class and that resulted in a change to the enum used to specicy the type of bushing (Mount or Spherical) – see the updated demo)

To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/c55bd0bf-4831-4ced-b02e-1273add587dan%40googlegroups.com.