Custom gravity and Velocity

Hi, I am trying to achieve realistic movements on my object for which I have been writing a custom gravity (with gravity Switched-Off on the RigidBody Component) and velocity script, but my gravity does not act properly. Even if I Switch-On the gravity in the RigidBody Component, My gravity and jump do not work. My gravity(Scripted or from the editor) and Jump seems to work properly when I do not implement Movements. I have also tried reducing Drag below zero and yet my gravity and jump do not work. Here are the Scripts -

Physics.cs -

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. namespace CustomPhysics
5. {
6.      public class PhysicsClass : MonoBehaviour
7.      {
8.          private static PhysicsClass _physicsInstance;
9.          public static PhysicsClass PhysicsInstance
10.          {
11.              get
12.              {
13.                  if (_physicsInstance == null)
14.                  {
15.                      _physicsInstance = GameObject.FindObjectOfType<PhysicsClass>();
16.                  }
17.                  return _physicsInstance;
18.              }
19.          }
20.          //gravity fields
21.          private Vector3 _gravityVector;
22.          private float _jumpAcceleration;
23.          private float accelerationDueToGravity;
24.          //movement fields
25.          private float moveAcceleration;
26.          private float friction;
27.          private Vector3 _moveVector;
28.          private void Awake()
29.          {
30.              moveAcceleration = 5;
31.              friction = 1.5f;
32.              accelerationDueToGravity = 9.8f;
33.          }
34.          public float JumpAcceleration
35.          {
36.              get
37.              {
38.                  _jumpAcceleration = 3;
39.                  return _jumpAcceleration;
40.              }
41.          }
42.          public Vector3 GravityVector
43.          {
44.              get
45.              {
46.                  _gravityVector = Vector3.down * accelerationDueToGravity;
47.                  return _gravityVector;
48.              }
49.          }
50.          public Vector3 MoveVector
51.          {
52.              get
53.              {
54.                  float x = Input.GetAxis("Horizontal");
55.                  float y = Input.GetAxis("Vertical");
56.                  _moveVector = (new Vector3(x, 0, y) * moveAcceleration) / friction;
57.                  return _moveVector;
58.              }
59.          }
60.      }
61. }

GravityAndVelocity.cs-

Code (CSharp):

1.  using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using static CustomPhysics.PhysicsClass;
5. public class GravityAndVelocity: MonoBehaviour
6. {
7.      private Rigidbody RB;
8.      private Transform objectTransform;
9.      private float heightFactor;
10.      private void Start()
11.      {
12.          RB = gameObject.GetComponent<Rigidbody>();
13.          objectTransform = gameObject.GetComponent<Transform>();
14.          heightFactor = 1.75f;
15.      }
16.      private void FixedUpdate()
17.      {
18.          //RB.drag = -100;
19.          if (objectTransform.position.y > 0.1f)
20.          {
21.              gravity();
22.              if (Input.GetKey(KeyCode.Space) && objectTransform.position.y < heightFactor)
23.              {
24.                  RB.velocity = Vector3.up * PhysicsInstance.JumpAcceleration; // * Time.time;
25.              }
26.          }
27.          RB.velocity = (PhysicsInstance.MoveVector);
28.      }
29.      void gravity()
30.      {
31.          RB.AddForce(PhysicsInstance.GravityVector);
32.      }
33. }

So, What i have done wrong? please Kindly, Explain.

 

Answer- when space pressed - downforce += upwardforce;