pic: 6 wheel omni drive

6 wheel drive using mecanum wheels and omni wheels. We built a ball diferential into the sprockets of the omni wheels. Moving forward all six drive. Moving sideways only the mecanum wheels drive. The actual competition drive will use direct drive from the bain bot gear box to the mecanum wheels.

looks cool but, wouldn’t you get pushed around a lot?

Is that #35 chain, #25 will work just as good and save you some weight.

The point of mecanum and omni wheels is to avoid the pushing matches. Will you get pushed? Yes. Will you get into a pushing match? Probably not, if your drivers have enough practice time.

It’s a cool idea. I’m not entirely sure it’s practical, but I’ve seen more impractical ideas for mecanum drive (and even had one of them myself).

Does this design eliminate the ability to strafe? In order for mecanum drivetrains to go sideways, both wheels on each side need to rotate in opposite directions of each other… but it looks like the chain running along the side prevents the wheels from doing this.

Very creative design though, and good job on actually getting it built it so you can play around with it! I like the wheels, too… how did you make them?

EDIT: whoops, somehow missed the text in the first post, nevermind!

He posted drawings of the design before, and said the center wheel was driven on two ball differentials from the outer two. So, it’s rotation would be the sum of the other two’s rotation; in the case of pure strafing, they would have equal magnitudes in opposite directions and result in the center wheel not rotating. However, the ball differential did look difficult to get “tuned” correctly, so we don’t know how well it works in practice.

The answer to your question was posted with the picture.

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?



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 2007robot 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).

Amazing! Nice work. Glad to see bot rise above the doubt some of us had. Any videos planned?

impressive design and manufacturing of that for sure, i am interested in the ball diff. your going to be using for those center wheels. Also, that’s a nice set of custom mecanums. Keep up the good work, i’d personally like to see more teams trying crazy ideas.

Is there any type of suspension for the mecanum wheels?

Very nice design–really unique!! I, too, am looking forward to some video of it driving around.

I see the two round bars that space the left-side and right-side modules, but how does the sheet metal “belly pan” mount to them, since the distance between the two bars will change as the suspension flexes?

Lots of questions. Vidio http://www.youtube.com/watch?v=urFsD0gA1D4
Its not a good vidio but it works.

More pictures and drawings of the ball diferental http://www.team1322.org/ideas.htm

I will be taking pictures of the ball differental soon for our web sit.

The picture with the aluminum plate is for demostration only. A frame would be attached to the two rods and one of the drive halves will be slotted to allow the suspension to work. I have not made the slots yet but will. The whole idea is to allow for ramp use with mecanum wheels and also give alitle more pushing in forward. The final design will have the gear boxes go right into the mecanum wheels. This means if I order everything from bain bots and anndy mark and make the side plates I can throw the whole thing together in no time. The ball differental was easy to make. The wheel took awhile to make but we had all the stuff show in our inventory.

is it really worth the extra weight to drive the center omni wheels, they won’t add much to your pushing force. there is also the added drag of the chain and differential.

We are actualy going for the suspension. Any extra traction would help.

What if we install 4 sets of mecanum wheels and 8 sets of omni wheels on each drive half? Would that give more push power?

I don’t think we would try it but what if?

Yes it will give you marginally more pushing power, but only marginally and not enough to be worth the extra weight and system drag.

Up date to this post:
we used this drive system for our 2010 robot and it did well. in pushing matches it did make a difference, we were able to hold our own. The suspension worked great for the humps of the soccer game.
you can view the completed robot at http://team1322.org/ideas.htm