# Joints don't behave as they should.

Hello list,

I have a model with fixed, revolute and prismatic joints. During simulation the all violate the restriction set upon them. The fixed joint does move a bit, and the revolute and prismatic joints also move outside the limits set by the axis tag.

How can I correct that, e.g. how to make a fixed joint really fixed? I cannot find anything in the sdf-format for the joint.

EDIT:

Please see the video unstable_joints.mp4 on my github page for an example of this behavior.

The model is only loaded in gazebo and then the simulation is started. See after about 20 frames. The fixed joint half way the upper leg is temporarily broken, and the seat is moving up and down, which it should not according to the joint description.

Note that after this the behavior is strangely unstable, with I still fail to understand. I start gazebo using roslaunch boot3_gazebo world_boot.launch. and the the model is in boot3_description/urdf. There also is a boot.sdf file you can directly use.

SECOND EDIT:

I removed the invocation of the ros_control plugin from the sdf-file so that it would work directly in gazebo. The strange thing is that the behavior is significant different, it behaves even more wildly, very strange.

Thanks in advance, Sietse

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