Controlling a wheelchair with wheel colliders

Hi,

I have been stuck on trying to create a wheelchair with wheel colliders for a while now. I can get the wheelchair moving and turning but the wheelchair seems to spin very easily without much input, in fact, I am struggling to go in a straight line.

I have watched and read some resources on wheel colliders (mostly for cars) including:

https://www.edy.es/dev/2011/10/the-stabilizer-bars-creating-physically-realistic-stable-vehicles/ https://docs.unity3d.com/Manual/class-WheelCollider.html https://www.youtube.com/watch?v=j6_SMdWeGFI

and many more.

I'm wondering if anyone has done this before and would be grateful for any advice. Please see the code snippets below:

 public class PlayerController : MonoBehaviour
 {
     private float horizontalInput;
     private float verticalInput;
     private float steerAngle;
 
     public WheelCollider BackleftWheelCollider;
     public WheelCollider BackrightWheelCollider;
     public Transform BackleftWheelT;
     public Transform BackrightWheelT;
 
     //public WheelCollider FrontleftWheelCollider;
     //public WheelCollider FrontrightWheelCollider;
     public Transform FrontleftWheelT;
     public Transform FrontrightWheelT;
 
     public float maxSteeringAngle;
     public float motorForce;
     private bool pressureAppliedToLeft = false;
     private bool pressureAppliedToRight = false;
     private new Rigidbody rigidbody;
 
     private void Start()
     {
         rigidbody = GetComponent<Rigidbody>();
         rigidbody.centerOfMass = new Vector3(0, -0.4f, 0);
     }
 
     private void GetInput()
     {
         horizontalInput = Input.GetAxis("Horizontal");
         verticalInput = Input.GetAxis("Vertical");
     }
 
     private void Steer()
     {
         steerAngle = maxSteeringAngle * horizontalInput;
         
         if (horizontalInput > 0)
         {
             pressureAppliedToRight = true;
             pressureAppliedToLeft = false;
         }
 
         else if (horizontalInput < 0)
         {
             pressureAppliedToLeft = true;
             pressureAppliedToRight = false;
         }
 
         else
         {
             pressureAppliedToRight = false;
             pressureAppliedToLeft = false;
         }
 
         //BackleftWheelCollider.steerAngle = steerAngle;
         //BackrightWheelCollider.steerAngle = steerAngle;
 
         //FrontleftWheelCollider.steerAngle = steerAngle;
         //FrontrightWheelCollider.steerAngle = steerAngle;
     }
 
     private void Accelerate()
     {
         if (pressureAppliedToRight)
         {
             BackleftWheelCollider.motorTorque = verticalInput * motorForce;
             BackrightWheelCollider.motorTorque = 0;
 
             //FrontleftWheelCollider.motorTorque = verticalInput * motorForce;
             //FrontrightWheelCollider.motorTorque = 0;
         }
 
         else if (pressureAppliedToLeft)
         {
             BackrightWheelCollider.motorTorque = verticalInput * motorForce;
             BackleftWheelCollider.motorTorque = 0;
 
             //FrontrightWheelCollider.motorTorque = verticalInput * motorForce;
             //FrontleftWheelCollider.motorTorque = 0;
         }
 
         else if (!pressureAppliedToLeft && !pressureAppliedToRight)
         {
             BackleftWheelCollider.motorTorque = verticalInput * motorForce;
             BackrightWheelCollider.motorTorque = verticalInput * motorForce;
 
             //FrontleftWheelCollider.motorTorque = verticalInput * motorForce;
             //FrontrightWheelCollider.motorTorque = verticalInput * motorForce;
         }
 
         //FrontleftWheelCollider.motorTorque = verticalInput * motorForce;
         //FrontrightWheelCollider.motorTorque = verticalInput * motorForce;
     }
     private void UpdateWheelPoses()
     {
         UpdateWheelPose(BackleftWheelCollider, BackleftWheelT);
         UpdateWheelPose(BackrightWheelCollider, BackrightWheelT);
 
         //UpdateWheelPose(FrontleftWheelCollider, FrontleftWheelT);
         //UpdateWheelPose(FrontrightWheelCollider, FrontrightWheelT);
     }
 
     private void UpdateWheelPose(WheelCollider collider, Transform transform)
     {
         Vector3 pos = transform.position;
         Quaternion quat = transform.rotation;
 
         collider.GetWorldPose(out pos, out quat);
 
         transform.position = pos;
         transform.rotation = quat;
 
     }
 
     private void FixedUpdate()
     {
         GetInput();
         Steer();
         Accelerate();
         UpdateWheelPoses();
     }
 }

and anti-roll-bar

 public class AntiRollBar : MonoBehaviour
 {
     public WheelCollider WheelL;
     public WheelCollider WheelR;
     private Rigidbody carRigidBody;
 
     public float AntiRoll = 5000.0f;
 
     // Start is called before the first frame update
     void Start()
     {
         carRigidBody = GetComponent<Rigidbody>();
     }
 
     // Update is called once per frame
     void FixedUpdate()
     {
         WheelHit hit = new WheelHit();
         float travelL = 1.0f;
         float travelR = 1.0f;
 
         bool groundedL = WheelL.GetGroundHit(out hit);
 
         if (groundedL)
         {
             travelL = (-WheelL.transform.InverseTransformPoint(hit.point).y - WheelL.radius) / WheelL.suspensionDistance;
         }
 
         bool groundedR = WheelR.GetGroundHit(out hit);
 
         if (groundedR)
         {
             travelR = (-WheelR.transform.InverseTransformPoint(hit.point).y - WheelR.radius) / WheelR.suspensionDistance;
         }
 
         var antiRollForce = (travelL - travelR) * AntiRoll;
 
         if (groundedL)
         {
             carRigidBody.AddForceAtPosition(WheelL.transform.up * -antiRollForce, WheelL.transform.position);
         }
 
         if (groundedR)
         {
             carRigidBody.AddForceAtPosition(WheelR.transform.up * antiRollForce, WheelR.transform.position);
         }
     }
 }

and Hierarchy: