[EricH]

Originally Posted by dougwilliams

What are the pros and cons of this 2+2 drivetrain? Why only go two omnis vs 4? I could imagine some scrub reduction, but why not all 4 wheels? And if you are using 4 independent gearboxes, why couple each side with belts/chains? Are they trying to mechanically couple and equalize wheel speed per side?

Let's start with "why not 4 omnis?". Answer: Sideways motion. You are trying to line up to do X, I hit you from the side. Chances are, you're nowhere near lined up now. So by retaining 2 tractions, you get less sideways motion (you're more likely to rotate than slide) and easier realignment. That being said, 4 omnis is a valid drivetrain, IFF you know what you're doing.

Next up, why couple? The Department of Redundancy Department just called, and said they give this design their approving seal of approval. In case of loss of power in one gearbox, you still get power on all 4 wheels, in addition to speed match.

And the last part, er, first part: The rotation center is different. Scrub reduction is a major item, too--4 high-traction wheels in a long configuration, all driven, will bounce 130 lbs of robot around when the robot tries to turn, in most cases. So by using omnis on one end, you get smoother turning, but you also get a very predictable center of rotation...which, as it turns out, can be quite useful in a "precision" game like Recycle Rush.