Hi,I’ve setup a cart system with a character dragging a cart using physics constraints,the constraints itself works well,but when the cart,which is a physic vehicle blueprint,collided with a rock (non physic object),the cart flips around like crazy,how do I solve this? Below I attached a video showing the crazy physics reaction,tried giving the cart a big mass,but it seems that a collision with non physics object wont factor in the mass.
Any idea? Anything would be appreciated 
Have you tried messing around with the cart’s physics settings? Like increasing mass, stuff like that.
Linear and Angular Dampening on the cart may help prevent it from behaving crazy. (Try setting them to 10)
The issue here is that your character is kinematic (infinte mass in essence), and when the cart hits the rock (infinite mass in essence), it cant apply and propagate the resistance through the constraint to the character.
Physics based character can help with this - but is difficult to implement.
The age-old game development question: “What happens when an unstoppable force (your character) meets an immovable object (the rock)?”
The best option is to make the join soft, more like a rubber band than a fixed point constraint. Then break the joint if the forces on the joint are too strong.