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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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B1 UK hinge game object axis break door fixed

Joints - Unity Official Tutorials

  • 101 5
    朱瑛 posted on 2014/05/02
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