90 Degree Joint Maths

Hi,

I'm using a type of joint on a model submarine to vector thrust in two
planes that is essentially one 45degree elbow bolted onto another and
wondered if it has a common name/purpose in Robotics so I could research it
further? The idea is that by rotating one X degrees and the other Y degrees
you can vector the thrust in any direction....

Looks a bit like this:
http://www.goratu.co.uk/images/products/products-bedmills.jpg

Cheers,

Michael