def set_control_user(user_id, prefix='', rconn=None):
    """Set the user who has current control of the telescope and resets chart parameters.
       Return True on success, False on failure"""
    if user_id is None:
        return False
    if rconn is None:
        return False
    try:
        rconn.set(prefix+'view', "100.0")
        rconn.set(prefix+'flip', '')
        rconn.set(prefix+'rot', "0.0")
        result = rconn.set(prefix+'control_user_id', user_id)
    except:
        return False
    if result:
        return True
    return False