[DonRotolo]

#25 chain is more sensitive to proper tensioning. #35 allows teams to be really sloppy and still quite effective.

As to the original question: I like the idea, very similar to our 2007 robot. We used a kitbot frame with a second level of frame at the height of the top of the wheels, primarily to get a flat platform.

Your implementation seems somewhat heavier than necessary. The inner rail doesn't add much strength, it can be 1/16" wall, while the outer rail will take a beating, count on bumpers to stiffen it and lend impact resistance.

You also need to consider cross-rails from outer to inner rail, and again from one inner rail to the other - that way, an impact's force is transmitted to all four elements, not just the one impacted.

If you can mount the gearboxes lower - gotta think about the sprocket wrap - you can end up with a flat (or nearly so) platform over which your manipulator can be built.

Don