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

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,

and I don’t understand how to release one of the models which is bounded on the specified joint!
20210924084313|446x464

consult!!

my code is there ________________________________

onKeyDown {|key, val, char|

bx = simulation.find_body_by_name(‘box1’)
jj = simulation.find_joint_by_name(‘jla1’)

#jj.disconnect #This method succeeds when the specified joint has a bound object
jj.connect(bx) #Do connect box to joint green But, it`s wrong !

}

if MS Physics is not a must, you can try Fredos Animator for this too, it is probably the faster one for this application.