2 Mecanums and 2 Omnis


#1

Hello,
My school does not currently have any mecanum wheels, and I was just curious as to if it would be possible to use 2 omni wheels in combination with 2 mecanum wheels in some way to create a drive that can strafe as 4 mecanums do, but have the speed that 4 omnis could. For example, the two omni wheels could be powered for forward and backwards movement, but the mecanums could then be engaged to strafe. Just curious, as I have no way to test this myself.
Thanks


#2

I don’t think there is a practical way to do this.


#3

It could probably be made to work with the mecanum wheels as the center wheels of a 6 wheel base. You would probably wind up with a really wide space to house not only the very fat mecanum, but a chain from back to front to power the omnis.


#4

That sounds pretty plausible. I ask because I have had trouble in the past trying to use 4 omnis with a center omni that is perpendicular to the main wheels for strafing because in attempts to get onto the platform, the wheel would get slightly angled and would essentially become useless. Thanks for the feedback.


#5

You could do an x-drive with all omnis. I don’t believe you can do omnidirectional movement with only 2 mecanums, regardless of where they’re placed.


#6

From what I understand about x-drive, it is difficult to get onto the platform. My goal with the mecanums is to be able to have strafe movement, but also be able to get on the platform easily while also making it difficult to get pushed off of the platform, since this is very difficult to do if the robot has mecanums. However using all mecanums would be pretty slow, so I’m just trying to see if this type of set up could work. Thanks


#7

You could, but only with additional in-line wheels… the mecanum provides the x (strafe) vector, and the in-line provide the y vector.

A two wheel mecanum drive base could tank drive with the option of a perpendicular strafe. It would just have no diagonal strafe potential.


#8

Could you mount four wheels in the corners, with the omniwheels turned like with an x-drive and the mecanum wheels lined up normally? Bad sketch to try to show what I mean:

m----------------------------m
m----------------------------m
m----------------------------m
.--------------------------------
.--------------------------------
.--------------------------------
o------------------------------o
. o--------------------------o
. . o----------------------o


#9

So would that mean 8 wheels? I’m having trouble understanding what you mean and the sketch. I’m on V5, so I would prefer a way that was no more than 4 motors for drive. At the moment I’m thinking 2 motors that would each power 2 omnis with tank drive, then arranging one or two mecanums with one motor that would only be used for strafe.


#10

O-------------O

-------M--------

O-------------O
O is for omni, M for mecanum. Would having one motor power the left side wheels, one for the right side wheels, and one motor for the mecanum in the middle allow for strafing, while also allow for enough friction to prevent being pushed off of the platform and also allow for point turns? I know it is a lot to ask but that is what I am striving for right now, and I would test it myself however I have to wait a little until I can get my hands on some mecanums


#11

Well… you’d have to set it up like an H drive. And that kind of defeats the purpose. Mecanums can strafe because they rotate against each other, and the tilted rollers propel it sideways.

You could get strafing with 2 mecanums on the same side of the drive, I think. Just not omnidirectional movement. And it would take quite a bit of torque.

This is a cool idea. The X drive is meant to simulate the tilted rollers on mecanums, I think, so, in theory, this type of hybrid might just work. #InnovateAward #NewMeta


#12

I understand what you mean by this now. Very interesting. I will look into it and in the coming weeks I should be able to get my hands on some omnis and try this out. Thanks for the help


#13

@Got a Screw Loose Yes I would like to have an H drive in the way that you are talking about, however the way I used to have mine set up, the center wheel would become angled when I tried parking, rendering the wheel useless. With two mecanums, the wheels rotate in the direction of movement, so having them hit the platform on the way up would be no problem. I do like @callen idea though.


#14

It is interesting, a “dragon drive” but with mecanum front wheels.

There might be an issue of a pretty significant difference in speed… The 45 degree omnis move at an equivalent of 1.4 ratio in the direction parallel to the front wheels. The mecanum spend a good deal of motor power in rolling the rollers, which made them move noticeably slower with 393’s. If V5 doesn’t compensate well, the front and rear would be out of sync.


#15

Considering that it would require 4 motors for the drive anyway, it could be tuned in code so that the speed of the front and the back were in sync. Hope I get mecanums soon to test this out. If anyone else decides to test this, please respond on the forum what your experience was like.


#16

Wait, but what does this design offer over just using 4 mecanums with V5? Better turns? If it turns as well as an X-drive, then this would be better over the x-drive for platforming and friction, however 4 mecanums would be functionally the same as this hybrid. Correct me if I’m wrong because I have very limited experience in seeing how mecanums operate


#17

It would turn well (not that a normal 4 omni base turns poorly). The omni end would fit into corners. It may only be novel and fun.


#18

But how do you think it would turn in relation to 4 mecanums? And yes the uniqueness is what makes it so interesting


#19

Definitely different, as the turn center would be toward the front of the bot. Better, maybe? Not dramatically better. I don’t think there was anything wrong about meca turns, the wheels just lost favor in the 393 paradigm due to their inefficiency / slowness (which might be gone with V5) and the amount of robot width they eat up. If you need to run a chain to them to leave space for an intake, its pretty easy for each side to get up to 3.5"


#20

Okay good to know. Thanks for your feedback