Why the robot I imported to unity trembles ……

[patrickyyang]

I import a robot trolley to unity, It trembles in play mode.

the structure of the robot is:

• baselink
  • head
  • left_leg
    • left_back_wheel
    • left_front_wheel
  • right_left
    • rigth_back_wheel
    • rigth_front_wheel

When I remove left_leg and right_leg, the trolley doesn't tremble.
when I add legs back and remove wheels， the trolley trembles a little
when I add all back, the trolley trembles heavily.

So, Why? Is the physics engine not accurate enough?