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• Let's look at the basic joints in Unity.

• In this example we have fixed joints

• and spring joints.

• This example forms a basic wrecking ball

• that does this.

• Firstly the fixed joint. Fixed joints

• work in a similar way to parenting objects

• in the hierarchy.

• The joint simply locks a game object

• to the point in the world, or to a

• connected rigidbody.

• In this example we simply have placed the

• first capsule in the chain up near

• the ceiling and attached a fixed joint.

• This locks it in place.

• The other parameters of this fixed joint

• are Break Force and Break Torque.

• This is the minimum amount of force required

• to break the joint.

• When the joint is broken the game object

• can once again move freely.

• The other capsules in the chain have

• spring joints. Spring joints work on the

• principle that the game object is trying

• to reach a target position. The target

• position that it's trying to reach is the

• position that it's set to in the scene view

• and any rigid bodies that are attached to it

• will pull it away from this position

• on an invisible spring attached

• to the anchor point.

• If the spring joint has a connected rigidbody

• then the target point that the spring

• is trying to reach is relative to that

• game object rather than to world space.

• So for example, the second capsule here

• is trying to reach capsule 1, and capsule 3

• is trying to reach capsule 2.

• As these move they will no longer be heading

• towards the original positions, rather

• they will be heading towards the anchor

• point of wherever those capsules happen to be.

• The anchor is the pivot point of the joint.

• You should consider it as where the spring is

• attached to the game object.

• This is shown in the scene view by

• an orange dot or box.

• The spring parameter is a measure of how

• strong the spring is. The higher the

• value the tighter or stronger the

• spring becomes. The damper parameter

• is how much the joint will slow down

• under motion. The higher the number, the

• less the spring will overshoot.

• The min and max distances are for setting

• up a sort of dead zone for where the

• spring isn't active. They effectively restrict

• the length of the spring.

• Similar to the fixed joint, the spring

• also has a break force and a break torque,

• which you can set to a certain amount in order

• to find the minimum force required to

• break that joint.

• Finally, Hinge Joints.

• Hinge joints are ideal for things like

• doors and share some properties with

• spring joints. The axis of the hinge

• is the one that it rotates around.

• In this example our physics door

• has the hinge joint attached. The anchor

• is set to 1 in the X axis,

• which moves it from it's center to it's edge.

• Again the joint is represented in

• orange in Unity and you can see a small line

• showing you where the hinge is currently located.

• The axis then allows us to specify

• around which axis the hinge will pivot.

• We've set this to the Y axis so it will

• react like a real hinge with a simple script

• we're applying a force to the door

• when we click on it, which pushes it

• backwards in it's Z axis

• using the shortcut minus transform.forward.

• In the Add Force lesson you may have seen

• that this fires the door straight out of the frame.

• But now that we have a hinge,

• when we apply the force to the door

• it simply pivots around that point.

• and no matter how many times we add force

• to it, it doesn't break.

• In a similar manner to our spring joint

• we can apply spring-like characterises

• by using the Use Spring checkbox

• and using the values underneath the spring settings.

• The other differences between hinge joints

• and spring joints are motors and limits.

• Motors are for introducing a velocity

• to your joint, for example a revolving door.

• The Target Velocity is the velocity the

• joint is trying to rotate at and the

• force is used to try and attain that velocity.

• If Free Spin is checked then the force will

• only be used to try and accelerate

• the joint and not to decelerate it.

• Limits can be used if you wish to constrain

• the motion of your joint, like with the

• normal door. The minimum and maximum

• are the angles between which the joint

• can move. Min and Max Bounce are the amount

• by which the joint will bounce when it reaches

• one of it's limits. And similar to our

• spring joint, yet again we have break

• forces and torques.

• For example, if we add in a reasonably low

• number into the break force property,

• we can break the door off of the hinge

• when adding a force. You should note that

• when doing this the door doesn't fly directly

• backwards but is instead pulled away from it's hinge.

Let's look at the basic joints in Unity.

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# Joints - Unity Official Tutorials

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朱瑛 posted on 2014/05/02
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