The location of the motor terminals on the polarshield is a bit awkward.  One of them is fine, but the other is directly above the USB socket on the arduino board underneath.  So that’s fine for the PolargraphSDs I make because they use arduino boards with micro-USB connectors.

But for anything else, the pins from the connector will come into the contact with the big USB-B shell on the arduino below, and that’ll short, and that’s not cool.  I always almost always do the following to a Polarshield to get around it:

First snip off the protruding pins and file then down almost flat.  I make extra sure there plenty of solder lining the holes for these ones.

Stick a couple of pieces of electrical tape over the little nubs that are left.

So now it fits flush, that’s good.

I saw this mentioned on Julio Terra’s blog where he mentioned putting a bit of tape over the USB shell to insulate it.  I scratched my head because I always do the above operation for the polarshields I sell as part of vitamin kits.  Except obviously I missed this one!  Tsk! I know, shameful.