physics in mmd
what the physics do in mmd?
the physics engine helps simulate movement of objects, like clothes or hair in mmd, it makes the bones movement of the objects automatically to make animations more easily
how the physics works?
the physics engine affects two things : rigid body and joints other things doesn’t have effect on how the physics works, only those two
rigid body
the rigid body is a simple shape used to represent the model mesh to the physics engine
shape
the rigid body can have 3 shapes : sphere, box and capsule
you can change the size and positon with those parameters :
also, you can connect the rigid body to a specific bone
type
three types : bone (static), physics (dynamic) and physics+bone
if you viewing the rigid bodys by type, each type has different color
bone type - the body is static, if it it’s connected to a bone the rigid body will move when the bone moves otherwise it stays in the same place (even when physics is on)
physics type - the body is dynamic and affected by gravity, if it it’s connected to a bone, the bone will follow the the rigid body movement
physics+bone type - the body is dynamic and affected by gravity, if it it’s connected to a bone, the bone will align with the rigid body movement
group
when dynamic rigid body collide with another(static or dynamic) they would react and move accordingly
the group type of rigid body can make them not react to the collision
there are 16 groups, numbered 1 - 16
if you viewing the rigid bodys by groups, each group has different color
to make the rigid body not react on collision, check the number of the other rigid body in the boxes :
example :
physics parameters
those parameters affects the movement of the rigid body they are usually set between 0 - 1
( I tried to explain a bit about the parameters but the explanation might not be very good )
mass - the mass of the body (can be over 1) in a chain of bodys if the lower ones has bigger mass, the chain will move slower
move decay - how fast the movement of the body will dwindle closer to 1, the body movement will be brief closer to 0, the body movement will last longer
rotation decay - same as move decay but for rotation movement (those two parameters are usually the same)
repel - make the body bounce when its collide another body (most of the time it’s 0)
friction - how slippery the body is when the body collide with another : closer to 1, the movement will stop sooner closer to 0, the movement will will take longer to stop
joint
joints are used to connect 2 rigid boys to move together
type
joints can have different types but they are not working in mmd (only mmm) when you change the joint type it also change the model pmx ver from 2 to 2.1
position
you can change the joint position with those parameters : (it’s better to position the joint between the two rigid bodies it will connect)
or you can take position from a bone, select the bone name from the list and click the button
connect to rigid bodys
it's importent to connect the joint to the rigid bodies otherwise the joint is unnecessary ( joints that aren't connected to bodies cause mmd to crash )
to connect to the rigid bodies, select from the list the first body and from the other list the second body
limits
this is the movement limit of the rigid body connected to the joint
move limit - how much rigid body B can move from rigid body A (most of the time it’s all 0)
rotation limit - how much rigid body B can rotate in relation to rigid body A the values is the angle the rigid body B can move in the axis
spring
I'm not sure what it does, but it seems like those parametese restrict the movement












