Rigid body fixed constraints looks like springs I building simple car animation. I started with one axis with wheels. I have problem with fixed constraint, it behave like some spring, i connect cylinders and cube like on picture. I attached also video what happens :-/ Do you know why something like this occur ?
Picture:


Video:
https://www.youtube.com/watch?v=qTU5fxMvxbk
Try increasing the number of constraint iterations and simulation steps in Properties > Scene > Rigid body world:



10 iterations and 60 steps:



100 iterations and 120 steps: