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ODE Joint, Static friction

asked 2012-11-09 09:34:22 -0500

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Dear All,

In my model I have a horizontally placed slider joint, this gradually moves because apperently numerical error cause it to not be exactly horizontal (angular noise with a magnitude of ~ |1e-4|). Because there is no friction, it drifts towards it's limit. (The bounce at the limit is somewhat unrealistic too, but im not interested in that atm (it adds energy, despite the settings)).

Not an issue since the real robot will also be imperfect. However static friction in the slider joint should stop it from moving, however this settings seems to have no effect! I've noticed in ODE documentation that regular joints (and Gazebo api), that regular joints don't have such atributes (static friction), only the contact joint has this. I'd be great if static friction would work, any way this is possible. Here is the joint code:

<joint name="joint_2" type="prismatic">
    <parent>link_1r</parent>
    <child>puppet</child>
    <pose>0.0000 0.0000 0.00000 0.0000 0.0000 0.0000 </pose>
    <axis>
        <xyz>0 1 0</xyz>
        <limit>
            <lower>-0.1</lower>
            <upper>0.1</upper>
        </limit>
        <dynamics>
            <damping>0.01</damping>
            <friction>0.1</friction>
        </dynamics>
    </axis>
</joint>

I can create some actual contact friction, by recreating bearings and such, but that seems overly complication and prone to error.

Thanks

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answered 2013-01-11 19:15:34 -0500

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This post is a wiki. Anyone with karma >75 is welcome to improve it.

You are correct that we do not currently support joint friction with ODE. I've added this to the gazebo issue tracker as issue #381.

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Asked: 2012-11-09 09:34:22 -0500

Seen: 2,770 times

Last updated: Jan 11 '13