[ODE] degrees of freedom in a slider - other joint types

Deak Szabolcs ancient at ludens.elte.hu
Thu Aug 31 12:04:35 MST 2006

Bram Stolk wrote:

>Hi there,
>ODE's slider has one degree of freedom.
>So when considering this image:
>ODE would be the one on the left.
>Is there a way to get an additional degree of freedom, as
>for the slider on the right?
>By the way: the ODE manual erroneously depicts the
>slider on the right, which can confuse the reader.
>  Bram
Not completely on the same note, but I've been wondering if there are 
any plans or at least requests to add more joint types to the ones 
already present in ODE. I don't really think that adding more basic 
joint types and thus features would hamper the usability of ODE, 
although it may present ambiguous situations in choosing the right joint 
I'm trying to use ODE for vehicle dynamics and currently I see two 
methods of doing suspensions: the overly-simplified approach of using 
the specialized Hinge2 joint (which is actually one example of an 
"extra" joint I'm talking about) which is incorrect compared to a real 
suspension in both kinetics and kinematics or model the whole suspension 
with all the arms as separate bodies and connect them by the basic 
joints, which is theoretically correct but a computational overkill 
while most probably introducing severe numerical errors in the process 
of solving the system due to bad mass ratios of the bodies involved. As 
opposed to this, I believe we could use a so-called "distance 
constraint" (a 1d joint) to represent a "massless" link attaching two 
bodies with "ball" joints at its ends (essentially 1 control arm in a 
suspension). This would not be completely "correct" as there is no such 
thing as a massless joint, but the result would probably be much faster 
to compute while hardly any less accurate..

So, I repeat, is there any interest to add more to the joint types in 
ODE or should such attempts remain separate?


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