Simple Car (HingeJoint / JointMotor / Code Problem)

I read somewhere it is quite easy to build a simple car.

- take a Cube for the body
Make it a Rigid Body


- Take a cylinder for the wheel
Make It a Rigid Body
Attach a hinge from the wheel to the body
Make Mesh collider and cylinder

Copy 4 times and we have a car

This works great. when I give the motor of one of the joints Target Velocity and Force in the UI it even drives!!!

Then I tried it from script but it doesn't work at all.

Does anyone know why?

Below is the code I use. It accepts no input and both Start and FixedUpdate get called. DriveWheels are also set. I checked.

Many thanks for your time.

Code (CSharp):

1. public class PlayerControll : MonoBehaviour {
2.  
3.     public Rigidbody DriveWheelLeft;
4.     public Rigidbody DriveWheelRight;
5.  
6.     private HingeJoint HingeJointLeft;
7.     private HingeJoint HingeJointlRight;
8.  
9.     private JointMotor JointMotorLeft;
10.     private JointMotor JointMotorRight;
11.  
12.     // Use this for initialization
13.     void Start () {
14.         HingeJointLeft = DriveWheelLeft.hingeJoint;
15.         HingeJointlRight = DriveWheelRight.hingeJoint;
16.  
17.         JointMotorLeft = HingeJointLeft.motor;
18.         JointMotorRight = HingeJointlRight.motor;
19.     }
20.    
21.     // Update is called once per frame
22.     void FixedUpdate ()
23.     {
24.         HingeJointLeft.useMotor = true;
25.         HingeJointlRight.useMotor = true;
26.  
27.         JointMotorLeft.freeSpin = false;
28.         JointMotorRight.freeSpin = false;
29.  
30.         JointMotorLeft.force = 100;
31.         JointMotorLeft.targetVelocity = 100;
32.  
33.         JointMotorRight.force = 100;
34.         JointMotorRight.targetVelocity = 100;
35.     }
36. }

 

For some reason JointMotor or HingeJoint.motor does not equal referenz to that specific motor.
You have to do this every FixedUpdate

Code (CSharp):

1. JointMotorLeft = HingeJointLeft.motor;
2. JointMotorLeft.force = 100;
3. JointMotorLeft.targetVelocity= 100;
4. HingeJointLeft.motor = JointMotorLeft;

I don't know why it has to be like that. It seems like the physics in Unity need some work.