How do omni wheels work

[Brandon_L]

We are planning on using omni wheels but we aren't sure how they work.

[Alex Cormier]

Omni wheels work like a powered caster. They rotate when powered like any other wheel and give you flexibility of side movement as well. The rollers are aligned perpendicular to the wheels axis, this allows the wheel to roll on the rollers when a side force is applied.

Originally Posted by AndyMark.biz

These wheels provide propulsion in the forward and reverse direction, while allowing for easy, smooth-rolling sideways motion.

Now, when you use one omni wheel like this: http://andymark.biz/am-0097.html, the rollers do not have a smooth contact to the floor and will shake the robot a little bit. That can be solved for putting two omni wheels together like this http://andymark.biz/am-0432.html.

You can also use omnis to climb over objects like 6" stairs http://www.chiefdelphi.com/media/photos/18050.

[Cyberphil]

What are you looking to do with them? Are you going to try to go in any direction, try to turn better, or some other aspect? Most of the omni wheels that I have seen have allowed the robot to go in any direction. But I have seen quite a few that were used to make the robot turn a lot easier by putting them on the four outside wheels on a 6 wheel drive system. It all depends on what you wish to do with them.



I just posted the image for reference.

[Brandon_L]

How do you get them to move sideways? We're just trying to move sideways.

[Chris is me]

Originally Posted by Brandon_L

How do you get them to move sideways? We're just trying to move sideways.

The sideways wheels on an omni wheel are not powered. They just make sideways friction basically zero.

If you want to use omnis to move sideways, you could mount them in a holonomic configuration like this:

/ \
\ /

[EricH]

Originally Posted by Brandon_L

How do you get them to move sideways? We're just trying to move sideways.

You need to put one (or one set) per side. You want the wheels to form a box around the robot, something like this: |=| To move forwards and backwards, drive the ones on the sides of the robot. To go sideways, run the ones on the front and back sides.

[riptide]

More than you ever wanted to know about omni wheels.

robocup.mi.fu-berlin.de/buch/omnidrive.pdf

[JohnCushion]

The "omni" wheels are indeed just like a castor, but they are more stable with side loads then the shopping cart variety. They allow you to turn about the center of your drive wheels. DO NOT try to power them, because they do not operate well in that manner.

If you are looking to go forward, back, sideways and round and round, look into Mechanum wheels.

Here is an example of them in an industrial application: http://www.youtube.com/watch?v=CjcyHicm3NA

AndyMark sells a 6" and an 8" version as well.

There are some issues with them, such as a certain level of finesse needed in the coding of the robot and each wheel needs individual power in order for them to operate properly. They also do not do well when one of the wheels is lifted off the ground. You may also want to look into using a gyro to maintain a certain orientation of the robot as well.

Hope this all helps and good luck with the rest of build season.

[Vikesrock]

Originally Posted by JohnCushion

DO NOT try to power them, because they do not operate well in that manner.

I'm not really sure what would cause you to say that. The AndyMark omni wheels have a 1.0 coefficient of friction in the radial (forward/back) direction and I know our team and many others have run them under power just fine.

You won't get as much traction out of them as you will out of a traction tread like a roughtop or wedgetop rubber and you may be easier for other robots to push from the side, but you will still have more pushing force with them powered than you would with them unpowered.

[Chris is me]

Originally Posted by JohnCushion

DO NOT try to power them, because they do not operate well in that manner.

I can find you 100 teams that would say otherwise. Powered omni wheels are omnipresent in drivetrains that aren't 6 wheel drop.

[Rick TYler]

Originally Posted by Chris is me

I can find you 100 teams that would say otherwise. Powered omni wheels are omnipresent in drivetrains that aren't 6 wheel drop.

And they aren't exactly unknown in 6WD drop applications, either.

[Akash Rastogi]

You need them in this configuration for holonomic use of omni wheels:

http://andymark.biz/am-0478.html