Mecanum Wheel Setup Help

[DirectXMan12]

Hi,
We have our wheels set up according to the omnidirectional.pdf doc @ firstroboticscanada.org. The configuration that they show seems to be opposite of what you have (i.e. we an O on top). However, we are having problems spinning in circles (namely, we can't spin in circles - we can only skate, not turn). Which is the correct config, and could our config be preventing us from turning?

Best Regards,
Solly (Team 1740 Lead programmer)

[jhersh]

Originally Posted by DirectXMan12

Hi,
We have our wheels set up according to the omnidirectional.pdf doc @ firstroboticscanada.org. The configuration that they show seems to be opposite of what you have (i.e. we an O on top). However, we are having problems spinning in circles (namely, we can't spin in circles - we can only skate, not turn). Which is the correct config, and could our config be preventing us from turning?

You must be misunderstanding the document you found. The behavior you described (can't spin) is exactly the expected behavior from putting the wheel on with an X on the bottom. Rotate your tires and try again.

-Joe

[Ether]

Originally Posted by DirectXMan12

Hi,
We have our wheels set up according to the omnidirectional.pdf doc @ firstroboticscanada.org.

The picture shown on page 8 of that document is INCORRECT, and would cause the behavior you are experiencing.

Originally Posted by DirectXMan12

we are having problems spinning in circles (namely, we can't spin in circles - we can only skate, not turn). Which is the correct config, and could our config be preventing us from turning?

The correct configuration is show here:

http://lib.store.yahoo.net/lib/yhst-...lSpecSheet.pdf

If you have mounted your mecanum wheels so that the rollers form a "diamond" (sometimes called an "O") when viewed from the top, then that is wrong, and it would cause the "no spin" behavior you are observing:

http://www.chiefdelphi.com/forums/showpost.php?p=907174

~

[Ian Mackenzie]

I apologize for any confusion from the presentation I posted - the picture is meant to show the pattern of contact between the wheels and the ground, as if you were looking from above but the top half of each wheel was transparent. I discussed this at length when I actually gave the presentation at the FIRST Conference, but perhaps I should have put more detail in the posted version...

UPDATED: I've edited the presentation to try to clarify the mecanum wheel orientation, and I've uploaded the revised version to both http://www.firstroboticscanada.org/s...irectional.pdf and http://www.chiefdelphi.com/media/papers/1836. (If you try to download the new version and it doesn't have an 'Updated' note on the first page, then it's probably the copy from your browser's cache - try using a different browser to get the updated copy.) Thanks to Ether for letting me know about this!

[mjgard]

So we are trying to figure out which is the correct way to put on the Mecanum wheels. We have done some research and I have attached a link for a research paper on them. This link is the complete opposite from what many of you say and what it shown on the previously attached andymark pdf.

Which is correct and why:

http://www.scipub.org/fulltext/ajas/ajas351831-1835.pdf

or

http://lib.store.yahoo.net/lib/yhst-...lSpecSheet.pdf

[Ether]

Originally Posted by mjgard

So we are trying to figure out which is the correct way to put on the Mecanum wheels. We have done some research and I have attached a link for a research paper on them. This link is the complete opposite from what many of you say and what it shown on the previously attached andymark pdf.

Which is correct and why:

http://www.scipub.org/fulltext/ajas/ajas351831-1835.pdf

or

http://lib.store.yahoo.net/lib/yhst-...lSpecSheet.pdf

Figure 2 and Figure 4 of the first one are incorrect.

The Table and Diagram on the second one are correct.

Explanations are given here:

http://www.chiefdelphi.com/media/papers/download/2826

http://www.chiefdelphi.com/media/papers/download/2722

http://www.chiefdelphi.com/media/papers/download/2739

[jawebste]

Originally Posted by Ether

Figure 2 and Figure 4 of the first one are incorrect.

The Table and Diagram on the second one are correct.

Michael,
I agree with Ether. And Ether you are a great reference for all of us out here. Thanks for posting.
We also found the research confusing and contradicting, but we have had very little problem this year with our first year with Mecanum wheels using the AndyMark diagram. When we numbered and oriented our wheels and the connections to the PWM to match the AndyMark diagram we had no problem getting motion using the Labview Holonmic Drive with Cartesian coordinates. We did have to invert one of the motors, but everything else was great.
This is for Ether, would the Figure 2 be correct if we were looking at it "from the carpet?"
Thanks,
Jean-Ann

[Ether]

Originally Posted by jawebste

This is for Ether, would the Figure 2 be correct if we were looking at it "from the carpet?"
Thanks,
Jean-Ann

Yes and no.

Yes, that is what the rollers should look like "from the carpet", but...

No, the figure must be a "top view" not a "carpet view" because of the way the force vectors are drawn. If the figure were intended to be a "carpet view" then the force vectors would be wrong.

So, if it's a top view then the rollers are shown incorrectly; if it's a carpet-view then the force vectors are drawn incorrectly.

[jawebste]

Originally Posted by Ether

Figure 2 and Figure 4 of the first one are incorrect.

The Table and Diagram on the second one are correct.

Explanations are given here:

http://www.chiefdelphi.com/media/papers/download/2826

http://www.chiefdelphi.com/media/papers/download/2722

http://www.chiefdelphi.com/media/papers/download/2739

Thanks so much! I never showed my students that diagram because though I found that paper as well, I could see the diamond or "o" pattern but the vectors didn't look like I thought they should. Shouldn't the vectors be the same even from the carpet? I am very rusty on this stuff. Last fall when we started research we referred to your posts and info on the charateristics of Mecanum drives, but it doesn't sink in that well for me. Thanks again.

[Ether]

Originally Posted by jawebste

Shouldn't the vectors be the same even from the carpet?

If Figure 2 is a top view, then the vectors are shown correctly but the rollers are not.

If Figure 2 is a carpet view, then the rollers are shown correctly but the vectors are not.


If you have access to a mecanum robot, look at the rollers from the top. Then flip the robot on its side and look at the rollers from the bottom.

The pattern the rollers make is different.