Unity 2d character controller using 3d physics

using UnityEngine;
using System.Collections;

public class Player : MonoBehaviour {

    // place on cube, add a rigidbody, with Freeze Position Z, and Freeze Rotation X,Y,Z
    // use new physic material with zeroed frictions, and friction combine: minimum.

    public float moveSpeed = 8;
    public float jumpSpeed = 25;
    public float fallSpeed = 64;
    public float maxFallSpeed = 12;
    public float maxUpSpeed = 25;

    Vector3 pos;
    float vm;
    bool onGround;

    // Update is called once per frame
    void FixedUpdate () {

        pos = transform.position;
        float h = Input.GetAxisRaw("Horizontal");
        float v = Input.GetAxisRaw("Vertical");
        bool jump = Input.GetKey(KeyCode.Space);

        if (onGround && jump)
        {
            vm = jumpSpeed;
        }

        Vector3 move = new Vector3( -h*moveSpeed, vm, 0 ) * Time.deltaTime;

        rigidbody.MovePosition( pos + move );

        if (v > 0)
        {
            // jet pack!
            vm += v * Time.deltaTime * 20;
        } else {
            // gravity
            vm -= fallSpeed * Time.deltaTime;
        }

        vm = Mathf.Clamp(vm,-maxFallSpeed,maxUpSpeed);

        rigidbody.velocity = Vector3.zero;
        onGround = false;
    }



    // ---- Collisions ----

    void OnCollisionEnter(Collision c) {

        CheckCollision (c);
    }

    void OnCollisionStay(Collision c)
    {
        CheckCollision(c);
    }

    void CheckCollision (Collision c)
    {
        foreach (var contact in c.contacts)
        {
            Debug.DrawLine(contact.point, contact.point+contact.normal, Color.red);

            // check for floor hit
            if (vm <= 0 && contact.point.y <= collider.bounds.min.y && Vector3.Angle(Vector3.up,contact.normal)<=45)
            {
                onGround = true;
                vm = Mathf.Max(0,vm);
            }

            // check for head hit:
            if (contact.point.y >= collider.bounds.max.y && Vector3.Angle(-Vector3.up,contact.normal)<=45)
            {
                vm = Mathf.Min(0,vm);
            }


        }
    }
}