how to use "rosparam load" to set specified namespace parameter?

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for example , l creat a node which namespace is robot .Then I try to change some parameters in this node . so l create a xxx.yaml ,and set some parameters' values. And then in the xxx.launch ,I add this line <rosparam command="load " file="$（find xxx）/xxx.yaml"/>, but the parameter doesn't change.

I wonder if there someting should be added in the yaml (ps: I just set values in the yaml ,like "wheel_radius : 0.2" ,and write "using namespace robot " ) ? Or the namespace should be set in some rules ? please help