giving tradition usercontrol an id rendered html

when i asp:calendar control, give an id:

<asp:calendar runat="server" id="mycal" />

it looks rendered html:

<table id="namemangled_mycal"... />

and i opening component id javascript this:

var cal= document.getelementbyid("<%= mycal.clientid%>")

however, i tradition user control has-a calendar:

<%@ control language="c#" autoeventwireup="true" codefile="weeklyeventscalendar.ascx.cs"
    inherits="weeklyeventscalendar" %>

<div>
    <asp:calendar runat="server" id="innercal" width="100%" ondayrender="rendercell" onvisiblemonthchanged="changemonth" height="480px" />
</div>

and following give an id i supplement page...

<mvs:weeklyeventscalendar id="weeklycal" runat="server" />

that id doesn't arrangement adult anywhere rendered html. i

<div> things </div>

when i want

<div id="namemangled_weeklycal"> things <div>

what am i doing wrong?