团结：绳索秋千3d角色开始跳

Question

I try to create a rope-swinging (penudulum like, around virtual point) mechanic in unity. But on first frame of swing my character suddenly jump far back and down and only then continue moving forward and down pendulum like.

void InitSwing(){
    lineLenght = (transform.position - virtualLinePoint).sqrMagnitude;}

    public void SwingLocomotion()
    {
        Vector3 testPos = transform.position + jMotor.moveDirection *Time.deltaTime;
        float newLenght = (testPos - virtualLinePoint).sqrMagnitude;
        if (newLenght != lineLenght)
        {
            testPos = virtualLinePoint + (testPos - virtualLinePoint).normalized * lineLenght;

        }
        transform.position = testPos;

Answer 1

Could it be due to Time.deltaTime being 0 on the first frame? Therefore the line jMotor.moveDirection *Time.deltaTime would return 0 and testPos would equal transform.position + 0