On Sun, Sep 26, 2010 at 7:47 AM, MightTower
<marcjoeris@uni-koblenz.de> wrote:
Hmm ok now i can control the JointPosition controller, but i cant tell him
that i want to turn around the axis 90 degrees exactly (from the last
position),
the joint angle commands are absolute, if you want relative position commands you'll have to do it yourself (i.e. get current position, send current + relative position).
after 1 command it did turn around and around all the time.
are you talking about oscillatory behavior of the joint? As presented in the tutorial, it's a frictionless system, and actual dynamics are being enforced by the physics engine. You are right that damping (or pid tuning) is necessary to stop the oscillations, ideally you want critical damping for your system.
I tried to wrote my own controller but there the same thing i cant stop it
once it started to turn.
Is it possible to tell the default controller this things or what i have to
do to for this?
In the pendulums tutorials its the same once started they didnt stop. Ok i
can use damping but this dont helps me to turn eg. 90 degrees exactly.
viscous damping will not affect the asymptotic position of your joint. You can easily plot it to see the result (see attached),
rxplot "/test_controller/state/process_value,/test_controller/state/set_point"
The plot is for the single link example with added joint damping of 2 (everything metric units).
If you don't want to deal with the dynamics of the system, alternatively, you can set the pose of the links directly. For that approach, you can write a plugin to call set pose directly. You'll have to do a tiny bit of math to compute the desired global pose of the links.
John
Thanks again.
Marc
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