[ODE] custom universal anchor constraint

[Jaroslav Sinecky]

Hi,

> -----Original Message-----
> From: ode-bounces at q12.org [mailto:ode-bounces at q12.org]On Behalf Of Jason
> Mallios
> Sent: Sunday, April 09, 2006 7:08 PM
> To: ode at q12.org
> Subject: [ODE] custom universal anchor constraint
>
>
> Is it possible to set CFM and ERP values for the anchor alone in
> a universal
> joint?  I have tuned values for the axes but would like to harden the
> constraint that prevents the anchor's position on the two bodies from
> separating.  In other words, I want to constrain the
> translational degree of
> freedom differently than the rotational degrees.

AFAIK it's not possible. Although I believe it should be pretty
straighforward to implement: just setting respective ERP/CFM values for
respective rows in joint constraint equations in universalJointGet2
function.


>
> Would adding a ball joint to the same bodies (in addition to the
> universal)
> be a solution or would ODE optimize this out?

Definitely ODE will not optimize this out, but it would introduce redundant
or "doubled" constrainst which is not very recommended. I'd say maybe better
way would be a ball&socket + 1 AMotor with lo and hi stop eqauls.

>
> Would it be more or less stable and more or less accurate to simply add
> spring / damper forces to the bodies' relative anchor positions when they
> separate since this avoids another entry in the jacobian?
>

I believe if you want a hard joint ie. use very stiff springs, it will
result in lot of jitter.

Hope this helps.
Jaroslav