Well, the Armor spell doesn't state it requires a voluntary target or that'd be an automatic failure, and other manipulation spells that are more intended to be used on something like a vehicle (Animate, Fix, etc.) do state that the OR must be overcome first, so I'd rule that OR applies against Armor as well. I take it that, by the wording of the spell, whoever wrote the description hadn't considered someone wanting to use Armor (and a few other such spells) on a vehicle or drone.