#physics-joints

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

there are two things you can do to have less clipping in the skirt

1. editing the skirt physics

edit the skirt physics to make them longer and wider

( this tip is for when you make the physics in the skirt plugin, if you already have skirt phyics you might need to change each one or remake them )

in the skirt plugin menu go to :

check those boxes :

when the boxes are checked, the rigid body will gradually change according to the value on the right

and change the values on the right, the first is width the second is height : (you can put different values, what fit your model)

it will look similar to this :

what diffrence it makes?

since the skirt physics are moving the legs sometimes stretching them and causing gaps between them (that’s why the clipping happens)

when you make them longer and wider it keep the shape even when they streched

2. editing the legs physics

sometimes if the legs rigid bodys are too thin they cause clipping, and you need to make them thicker

1. select the legs rigid bodys

2. change the value (change it to something that will cover most of the leg)

you can also make the skirt physics thicker instead

use the third option in the skirt plugin : (the same way like the height and width above)

saving

click in the plugin window on :

then (save as for new file, save for saving in current file) :

choose where you want to save the file and it’s name

loading

to load the information, click on :

then :

and choose the file

you can see the file name on the bottom