Makeblock is here to solve your robot problems. The t-slot aluminum extrusion is a tried-and-true way of building modular frames, and even simple mechanisms. It works, but it has an Achilles Heel…the nut.
That nut has to be inserted into the slot so that the bolt can torque down on the beam. Some designs include a nut that can be inserted straight through the slot and twisted instead of needing to be slid in from one end (FAZTEK). Others turn the bolt around so that the head of the bolt takes the place of the traditional nut and the nut tightens down from the outside of the bolt (MakerBeam).
A new Kickstarter campaign does away with the nut all together. Instead of using a t-slot, they have a slot with parallel sides and just the right threading to allow you to screw in a nut at any point along the slot.
Makeblock looks like an extremely well integrated system for prototyping cyber-electro-mechanical systems. They have the modular beam system itself, but they also have their own electronics with the correct footprint to fit on the beams and adapters for common things like Lego and servos. Additionally, they have it working in the real world and appear to have the manufacturing muscle to produce a lot of the kits.