Using Odoo v8 local installation

I'm brand new to Odoo and XMLRP. I want to update the quantity on hand of stock using XMLRPC and PHP code, just as if I had clicked the "Apply" button on the "Update Product Quantity" dialog that is reached via, e.g. Warehouse -> Products /<Select Product>/ Inventory tab -> (Quantity on Hand)Update

After much searching, based on the view found by clicking through Settings -> User Interface -> Views -> stock.change.product.qty
as well as the example in the following post:
http://thierry-godin.developpez.com/openerp/openerp-xmlrpc-php-en/
I tried the following PHP:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<?php

set_include_path(get_include_path() . PATH_SEPARATOR . '/home/odootst/xmlrpc/lib/');
require_once( 'xmlrpc.inc' );
require_once( 'xmlrpcs.inc' );
require_once( 'xmlrpc_wrappers.inc' );

$GLOBALS['xmlrpc_internalencoding']='UTF-8';
 
$user = 'admin';
$password = 'acmePass123';
$dbname = 'acme123';
 
$server_url = 'http://192.168.4.2:8069'; 
$conn = new xmlrpc_client($server_url . "/xmlrpc/common");
$conn->setSSLVerifyPeer(0);
 
$c_msg = new xmlrpcmsg('login');
$c_msg->addParam(new xmlrpcval($dbname, "string"));
$c_msg->addParam(new xmlrpcval($user, "string"));
$c_msg->addParam(new xmlrpcval($password, "string"));
$c_response = $conn->send($c_msg);
 
if ($c_response->errno != 0){
    echo  '<p>error : ' . $c_response->faultString() . '</p>';
}
else{
    $uid = $c_response->value()->scalarval();
    
    $values = array ( 
        'product_id'=>new xmlrpcval(8,"int"), 
        'new_quantity'=>new xmlrpcval(7.0, "float"), 
        'location_id'=>new xmlrpcval(12,"int")                         
        ); 
    
    $client = new xmlrpc_client($server_url . "/xmlrpc/object");
    $client->setSSLVerifyPeer(0);
 
    $msg = new xmlrpcmsg('execute'); 
    $msg->addParam(new xmlrpcval($dbname, "string")); 
    $msg->addParam(new xmlrpcval($uid, "int")); 
    $msg->addParam(new xmlrpcval($password, "string")); 
    $msg->addParam(new xmlrpcval("stock.change.product.qty", "string")); 
    $msg->addParam(new xmlrpcval("change_product_qty", "string"));  
    $msg->addParam(new xmlrpcval($values, "struct")); 
    $response = $client->send($msg);
 
    if ($response->faultCode()){
        echo $response->faultString();
    } else {   
      echo '<h2>Update Completed Successfully</h2>';
    }
}
?>

I am able to connect to the system with the above code, but I get an error trying to access the database (full traceback not shown for brevity):

ERROR acme123 openerp.sql_db: bad query:  SELECT "stock_change_product_qty"."write_uid","stock_change_product_qty"."new_quantity","stock_change_product_qty"."id","stock_change_product_qty"."product_id","stock_change_product_qty"."write_date","stock_change_product_qty"."create_date","stock_change_product_qty"."create_uid","stock_change_product_qty"."location_id","stock_change_product_qty"."lot_id" FROM "stock_change_product_qty"
                        WHERE "stock_change_product_qty".id IN ('new_quantity', 'location_id', 'product_id')  ORDER BY "stock_change_product_qty"."id" 
                   
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/openerp/sql_db.py", line 234, in execute
    res = self._obj.execute(query, params)
DataError: invalid input syntax for integer: "new_quantity"
LINE 2: ...          WHERE "stock_change_product_qty".id IN ('new_quant...

The error message itself is clear, but does not give me any idea where to go next. As I am only guessing at the proper calls to make in the code, I clearly have called something incorrectly. I am unsure of the following:

1) What is the correct method to call
2) What is the correct model to specify (I don't know how to find the model that is associated with a method)
3) The correct parameter list for the call

If anyone can even just point me in the right direction, that would be much appreciated. Thanks for any help you can give.