I’m not sure if anyone else found this frustrating, but I was having no end of problems with my armature. Each time I tried to parent one of the arms to the armature it would fly off into space in a random direction. In the end I figured there must be some compounded errors from an early stage in creating the armature, so I ended up deleting the entire armature and starting over from scratch. After that it finally worked.
Did anyone else get weird errors, or have an idea what went wrong with my first armature?