private GameObject myobject;
public float timeElapsed =0;
public float delay = 3.0f;
float OO = 0.0f;

void Start () {
    myobject = GameObject.Find ("rightarm").gameObject;
}

void Update () {
    timeElapsed += Time.deltaTime;
    Debug.Log (timeElapsed);

    if (timeElapsed >= delay) {
        OO = 30.0f;
        timeElapsed = 0;
        if (myobject.renderer.enabled == false) {
            myobject.renderer.enabled = true;
        }

        myobject.transform.Rotate (OO, 0.0f, 0.0f);
    }
    else
    {
        myobject.transform.Rotate (-OO,0.0f, 0.0f );
    }
}

void Update () {
timeElapsed += Time.deltaTime;
Debug.Log (timeElapsed);

if (timeElapsed >= delay) {
    OO = 30.0f;
    timeElapsed = 0;
    if (myobject.renderer.enabled == false) {
        myobject.renderer.enabled = true;
    }

    myobject.transform.rotation = Quaternion.Euler (OO, 0.0f, 0.0f);
}
else
{
    myobject.transform.rotation = Quaternion.Euler (-OO, 0.0f, 0.0f);
}

// Specify how many degrees you want to rotate from the initial orientation.
public Vector3 amplitude = new Vector3(30, 0, 0);

// Specify how many seconds a complete loop should take.
public float period = 6f;

// Cache initial orientation so we can rotate relative to that pose.
Quaternion _initialOrientation;

// Perform caching on Start.
void Start() {
    _initialOrientation = transform.localRotation;
}

void Update() {
    // Calculate how far along we should be in the wave.
    float phase = Mathf.PI * 2f * Time.time/period;

    // Calculate the angle at this part of the wave.
    Vector3 angle = amplitude * Mathf.Cos(phase);

    // Rotate by angle relative to our initial orientation.
    transform.localRotation = _initialOrientation * Quaternion.Euler(angle);
}