Radiosity simulations

[Lev]

If it takes that long to render a single frame with a skylight (i assume you are using light tracer for that), try using radiosity instead. It does take longer to calculate a solution, but once you have it, it can be used for all frames, without re-calculating (unless you have animated lights and such). Combined with area shadows, this can give results very close, or even better than with light tracer+skylight, with significantly lower render times.

Another way is decreasing the polycount. If you have more than 50k faces, you are most likely not using rational and optimised models. A few tips on improving that:
1) Use Optimise and Multires modifiers
2) Use simplier geometry with detailed textures and bump maps. A primitive with a right texture would look better than insanely complex geometry with no maps at all.
3) Most likely not all of the geometry is shown in EACH frame - try temporarily hiding the objects that are not shown (This will especially help alot when using global illumination)

As far as i understand, in most cases, the model with the highest detail, (and polycount) is the robot itself. Try removing any unnecessary detail unless you plan on having close-ups on it. You might actually consider having a separate low-detail model of robot for general scenes, and a detailed one for close-ups.