Well this design certainly caught me by surprise! When I read the thread title I was expecting to see something with four omnis facing one way, and two perpendicular to them, or maybe a hexagonal robot with six omnis forming a kind of "double kiwi" drive.
But I sure wasn't expecting this. Interesting design, and impressive machining (I'd love to see more on the differential), but it leaves me kind of puzzled as to the "why".
Now I really don't want to get too hung up on the "why". I'm quite willing to take, "because it was a cool idea" or "because it sounded like fun to make it" as more than sufficient justification and this design is definitely cool. But there are a few technical aspects that I don't get.
Specifically I'm trying to envision the technical advantages over a standard four-wheel mecanum offered by this design. Certainly it would be more difficult to "high centre" when climbing an obstacle, but there are lighter, simpler ways to achieve that effect. (Just raise the centre wheel a centimetre off the ground, for instance, and only chain it up to one set of wheels, for instance.) I suppose it could offer slightly more forward pushing power than a standard mecanum, if one accepts that increased contact area increases pushing force (a topic of some debate on other threads). My biggest concern, though, is that by having some of the weight on the centre omnis, it will make it difficult to evenly distribute weight to the four mecanums. Mecanums really, really, really need to stay in solid contact with the ground... to the point where independent suspensions are often recommended. (Although it does kind of look like this design might flex about the omni wheel axle...)
Again, don't get me wrong... this is cool, interesting and is obviously making people think about omnidirectional robot design, and that -- in itself -- is justification for making it. I would specifically be interested in seeing a bit more of your differential, that sounds really cool. But I guess I can't figure out what specific technical advantages this drive train design might offer. Can you help me see what I'm missing here?
Thanks,
Jason
EDIT: Aha... the "
six wheel suspension" thread and photo shows what you are going for much more clearly. Now I think the design is even more cool than I did before...
EDIT #2: Now that I see it is meant to help with ramp climbing, I'll link to a
video of our 2007 robot during build... initially it had problems climbing the ramp (0:31 of the video) but after some mods to increase ground clearance and tuning the PID loop for wheel speed (I think it was just a PI loop, actually... each wheel had an encoder on it) we could climb a fairly steep incline with a standard four wheel mecanum drive (1:00 of video).