Accessing subgrid in CRM 2013 javascript

I'm trying to set the values in a subgrid in 2013 in the onload of a form.

I can't get the subgrid though, I keep getting an error saying 'unable to get property X of undefined or null reference'. I've tried a few different ways of doing this.

Namely:

var subgrid = document.getElementById("Quote");

var subgrid = Xrm.Page.getControl('Quote');

var subgrid = Xrm.Page.ui.controls.get('Quote')

var subgrid = Xrm.Page.getControl(43);

var subgrid = Xrm.Page.ui.controls.get('Quote')._control;

I got the 43 value when I used F12 to get the developer tools and had a look at the code.

This is my code in its entirety:

function LoadQuoteSummaryGrid()
{
	//var subgrid = document.getElementById("Quote");
	//var subgrid = Xrm.Page.getControl('Quote');
	//var subgrid = Xrm.Page.ui.controls.get('Quote')
	//var subgrid = Xrm.Page.getControl(43);
	var grid = Xrm.Page.ui.controls.get('Quote')._control;
	if (grid.get_innerControl() == null) {
		setTimeout(LoadQuoteSummaryGrid, 1000);
		return;
	}
	else if (grid.get_innerControl()._element.innerText.search("Loading") != -1) {
		setTimeout(LoadQuoteSummaryGrid, 1000);
		return;
	}


	//if (grid == null) 
	//{
	//alert("Subgrid is null");
        //The subgrid hasn't loaded, wait 1 second and then try again
        //setTimeout('LoadQuoteSummaryGrid()', 1000);
        //return;
    //} 
	var fetchXml = "<fetch>"+ " <entity name='email'>"+ " <attribute name='from' />"+ " <attribute name='to' />"+ " <attribute name='subject' />"+ " <attribute name='modifiedon' />"+ " <attribute name='activityid' />"+ " <order attribute='modifiedon' descending='true' />"+ " <link-entity name='activityparty' from='activityid' to='activityid' alias='aa'>"+ " <filter type='and'>"+ filter+ " </filter>"+ " </link-entity>"+ " </entity>"+ " </fetch>";
//alert("fetchXml: " + fetchXml);
    //Inject the new fetchXml
    grid.control.setParameter("fetchXml", fetchXml);
    //Force the subgrid to refresh
    grid.control.refresh();
}

I'm leaving in the commented out lines, so you can see what I've tried so far.

Thanks.