How to bind a model and a joint with key trigger in MSphysic

[3Dwudi]

Hi!
I tried to bind an object to the specified joint in msphysics by pressing a key, but I tried for a long time and failed. I couldn’t understand it after reading the manual,

I don’t understand how to release one of the models bound on the specified joint!

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key tigger connect Su2014.skp

[3Dwudi]

is there anyone can help me?
my scriptcode is ________________________

onKeyDown {|key, val, char|
bx = simulation.find_body_by_name('bx')
jw = simulation.find_joint_by_name('jw')

jw.connect(bx) #but it's wrong
}