Question Making a catapult

Hi gyes
I am trying to make a catapult and have some issues i am trying to solve

The catapult more or less works but there is strong jitter(at start of video)
https://clipchamp.com/watch/c2ZUKATaXHe

I am applying a one off angular impulse on the z axis on the 2 dark gray blocks

The two dark gray blocks are connected with fixed joints to the long catapult log and with a ball & socket(x,y restricted) to the main catapult body

When i apply the force the blocks get knocked out of position for a bit which causes the projectile to go in wrong direction.

Is this is a good way to make a catapult using HAVOK? Are there any preferred ways to have more stable behaviour?

Thanks!!

 

I would probably just rotate the arm directly without physics, then at a specific angle you shoot out the projectile with a specific force. (At the angle you hide the non physics rock and instantiate a physics rock at its place)
Or animate the catapult and shoot it out at the correct place, like i've done here:

 

I am using a system similar to besiege, scrap mechanic and things are made out of blocks. I am trying to use physics as much as possible.

EDIT: i dug through the forums and found a solution by setting the inverse inertia of the rotator block X=0, Y=0
thanks to @steveeHavok