Installing a fourth axis on a Hyrel Hydra

https://www.youtube.com/watch?v=_9R6OUMvb-o

All Hydras come with support for 4th, 5th, adn 6th axes.

why ?
what do they do ?

Well, you can print on a moving, tilting, rotating model.

Here's the fourth- and fifth-axis version:

https://www.youtube.com/watch?v=lNURH2fRbY0

very cool - that's got to complicate the slicing !