Animating different parts of one mesh

I am currently trying to animate a robot. Is it correct that objects must be a single mesh for them to work in the ogre engine. If so how do i animate different parts of a single mesh. I have an ik leg with lookat pistons I would like to use.

There is no need to have a single mesh if your application needs multiple-part objects

Skinned animated characters can be single or multi part meshes

See this article for details on using characters made of multiple parts:

Working with animated multiple parts characters

Or if you are not using skinned animation (skeletal), but a hierarchy of nodes, then animate them as you need and export the animation