pic: McCannot Wheel

[Ether]

Originally Posted by MrBasse

Couldn't you just put some traction wheels of the same diameter on one side of a robot and your mecanum wheels on the other and drive straight?

Probably not, if you drive all four wheels with the same torque. It's a bit difficult to analyze quantitatively because wheel slipping would be involved, but my guess is the vehicle is likely to veer to the left if the mecs are on the right side (and vice-versa).

[PAR_WIG1350]

What if a set mecanum wheels was built that used 2 axles per roller? Since the roller can't rotate about 2 axes simultaneously, there would be no rotation, but there would still be axial free play. Then you could build a set of wheels that is mostly identical, but which uses only one axle per roller to allow rotation. By comparing the 2 wheel sets in situations where the robot strictly moves forward or backward should tell us if there is significant rotation of the rollers in these cases.

[dtengineering]

Originally Posted by PAR_WIG1350

What if a set mecanum wheels was built that used 2 axles per roller? Since the roller can't rotate about 2 axes simultaneously, there would be no rotation, but there would still be axial free play. Then you could build a set of wheels that is mostly identical, but which uses only one axle per roller to allow rotation. By comparing the 2 wheel sets in situations where the robot strictly moves forward or backward should tell us if there is significant rotation of the rollers in these cases.

I think you're on to something there... depending on the style of wheel it should be possible to non-destructively lock the rotation of the mecanum rollers.

Compare the performance of the robot with locked rollers to that with free-wheeling rollers. If there is a difference in performance, I'd suspect it would be due to the rollers... rolling.

Jason

[Chris is me]

If someone really wanted to find this out, grab your favorite 240 FPS camera (smartphone, gopro, etc), put a sharpie line on the edge of each roller somewhere, and drive. You'll know exactly how much each roller spins. Seems easier than building custom wheels, locking wheels, etc.

[Ether]

Do rollers spin when going forward?

http://vimeo.com/32952134


Is net force (along roller axis) greater than forward force?

http://vimeo.com/33315586

[Chris is me]

Originally Posted by Ether

Do rollers spin when going forward?

http://vimeo.com/32952134


Is net force (along roller axis) greater than forward force?

http://vimeo.com/33315586

While these are helpful videos, in the case of the first video I'm not satisfied with a "test" consisting of someone rolling the wheel along the ground with their hands. They are in complete control of the wheel and could easily induce more axial loading than is present on a robot, etc. It's more likely than not that an on-robot test would yield the same results, I'm sure, but I just wanted to point that out.

I wonder how much of the second video discrepancy is caused by the brief moments in the rotation of the mecanum wheel where the traction wheel loses contact. I'm sure not a lot, but it's something to consider.

[Ether]

Originally Posted by Ether

Is net force (along roller axis) greater than forward force?

http://www.chiefdelphi.com/forums/sh...d.php?t=133309

[lcoreyl]

Originally Posted by Chris is me

While these are helpful videos, in the case of the first video I'm not satisfied with a "test" consisting of someone rolling the wheel along the ground with their hands. They are in complete control of the wheel and could easily induce more axial loading than is present on a robot, etc. It's more likely than not that an on-robot test would yield the same results, I'm sure, but I just wanted to point that out.

I totally agree with you (although maybe not calling the test a "test" ). I don't have access to this stuff currently, but I'm actually surprised someone hasn't done the sharpie marking with a closeup of a robot moving. Anyone with a good mec drivetrain, sharpie, and smartphone/gopro out there??????

Originally Posted by Chris is me

I wonder how much of the second video discrepancy is caused by the brief moments in the rotation of the mecanum wheel where the traction wheel loses contact. I'm sure not a lot, but it's something to consider.

yes, it would be better if the axle of both wheels were actually attached via some structural members, and the traction wheel width was as wide as necessary.
Anyone with some bored underutilized students, a spare mec wheel and extra wide traction wheel of the same radius out there??