How to rotate around an object without using unity's built-in functions?

Question

i want to rotate a cube around a 1x1 pipe with arrow keys. (left and right).

The problem is i cannot use built-in functions which sets transform's position and location directly. (Such as transform.lookAt, transform.Rotate or transform.RotateAround). Because I need the vector values of rotation's euler and position for multiple stuff before i modify the value of the transform i want to rotate.

I tried different techniques but no luck so far.

I tried using sin-cos for rotating but could not figure out how to make it work for both rotation and position.

 _timer += Time.deltaTime * _larvaSpeed;
 float x = -Mathf.Cos(_timer) * distanceBetweenCenter;
 float y = Mathf.Sin(_timer) * distanceBetweenCenter;

Here is what i want to achieve. By pressing right or left, move and rotate the object around the pipe.

The result i want. (If i pressed right arrow key a litte bit).

I would appreciate any help. Thank you!

Answer 1

here is the solution using circle mathematics and I strongly recommended not use it, it's just to understand the circular move using circle equation as @FaTaLL ask in the comments

Circle equation... (x1 - x2)^2 + (y1 - y2)^2 = r^2

x1, y1 is the cube position

x2, y2 is the pipe position

r is the distance between cube and pipe;

using UnityEngine;

public class Rotating : MonoBehaviour
{
    public GameObject pipe;
    public float Delta;
    Vector3 nextpos;
    bool compareY;
    bool next;
    int switchx;
    float storeVarAxis;
    float x, y, r;
    private void Start()
    {
        next = true;
        switchx = 1;
        compareY = true;
        x = transform.position.x - pipe.transform.position.x;
        y = transform.position.y - pipe.transform.position.y;
        storeVarAxis = y;
        r = Mathf.Sqrt(x * x + y * y);
    }
    private void Update()
    {
        if (next)
        {
            if (compareY == true)
            {
                y -= Delta * Time.deltaTime;
                if (y <= -storeVarAxis)
                {
                    y = -storeVarAxis;
                    compareY = false;
                    switchx = -1;
                }
            }
            else
            {
                y += Delta * Time.deltaTime;
                if (y >= storeVarAxis)
                {
                    y = storeVarAxis;
                    compareY = true;
                    switchx = 1;
                }
            }
            float v = r * r - y * y;
            x = Mathf.Sqrt(Mathf.Abs(v));
            nextpos = new Vector3(pipe.transform.position.x + x * switchx, pipe.transform.position.y + y, transform.position.z);
            next = false;
        }
        transform.position = Vector3.MoveTowards(transform.position, nextpos, 1f * Time.deltaTime);
        if(Vector3.Distance(transform.position, nextpos) < .05) transform.position = nextpos;
        if (transform.position.x.Equals(nextpos.x) && transform.position.y.Equals(nextpos.y)) next = true;
    }
}

well, the recommended way is using this simple script

using UnityEngine;

public class Rotating : MonoBehaviour
{
    public float speed;
    public GameObject pipe;
    float r, angle;
    Vector3 startpos;
    private void Start()
    {
        r = Mathf.Abs(transform.position.y - pipe.transform.position.y);
        angle = 0;
        transform.position = pipe.transform.position;
        startpos = transform.position;
    }
    void Update()
    {
        angle = angle + speed * Time.deltaTime;
        transform.rotation = Quaternion.EulerAngles(0,0, angle);
        transform.position = startpos + (transform.rotation * new Vector3(r, 0, 0));
    }
}

Answer 2

I think Quaternion * Vector3 is what you are looking for. Luckily the box's rotation in its own local coordinates is the same rotation you need to apply to the box's position.

public float speed; //how fast to rotate
public float radius; //radius of the cylinder
public float angle; //angle around it

void Update()
{

    if (Input.GetKey(KeyCode.LeftArrow))
    {
        angle = angle + speed * Time.deltaTime;
    }

    if (Input.GetKey(KeyCode.RightArrow))
    {
        angle = angle - speed * Time.deltaTime;
    }


    //figure out the rotation (from euler angles i guess??)
    var quat = Quaternion.EulerAngles(new Vector3(0, angle, 0));

    //ok uh what is the box position?? lets just multiply
    var unrotated_position = new Vector3(radius, 0, 0);
    var rotated_position = quat * unrotated_position;

    this.transform.position = rotated_position;

    //oh yea and also rotate the box in its own local coordinates
    this.transform.rotation = quat;
}