Truly omnidirectional omniwheels?
 

I've looked at omniwheels a lot lately(brainstorming for next season and all), and I can't help but notice that if you need to move an omniwheel diagonally, it wouldn't work too well. Is this true? It seems to me like potential omnidirectional drivetrains are stopped because omniwheels wouldn't be able to work for their design. Has anyone designed an omniwheel with the edge wheels swiveling so that they can move in any direction? I know that if the little wheels went in the same direction as the overall wheel, it wouldn't work, but that can easily be stopped from happening with a slight design alteration.

So... would it be possible to make an omniwheel like that? It'd probably be expensive, but it would open up a lot of spiffy drive trains. Imagine a hexagon drive train(the result of brainstorming at one in the morning). Or a triangle with two wheels per side. The angles would usually stop it, but with the augmented design of omniwheels, they could be given the ability to work.

I only joined my team this season, and I was one of those, "Come and work on whatever needs to be done" people, so I typically ended up drilling holes in things. Thus, my knowledge of engineering from this season is... limited. Hence, I've come to the ChiefDelphi forums, because from what I've heard, that's where people know stuff. So tell me- is my idea good, or am I just spouting nonsense?

Re: Truly omnidirectional omniwheels?
 

the omniwheels taht i know of are either 90 degrees or on a 45 degree angle and yes if u get pushed at 90 degrees or 45 pending on which wheel you have its easy to get pushed i do not know if there are any omniwheels that swivel though im having trouble picturing how well that would work but thats all i can tell ya

Re: Truly omnidirectional omniwheels?
 

If you move a single omniwheel that way, it might be hard. But when you get them on a robot in a set of three or four, it's relatively simple. Imagine a four-wheeled omni drive set up as a plus sign. Set the wheels along the Y-axis driving one way, and the ones on the X-axis another. The robot should move diagonally (at least as far as I can remember for being up ten minutes >_<)

Re: Truly omnidirectional omniwheels?
 

I've done some omni-wheel research with my VEX kit. It is possible to make an omni-wheel based robot with 3 wheels, 4 wheels, 6 wheels... I guess you could make one with 5, or any other number, but I don't think there are big advantages to doing so.
What Billfred is saying is correct. It takes a little trig to make a 3-sided omni bot work, but it is possible: http://www.cs.cmu.edu/~pprk/

Re: Truly omnidirectional omniwheels?
 

No, I know about kiwi drive and all that. I'm just thinking of certain types of drive trains that would be really fun to build with a better kind of Omniwheel(since my team apparently wants to do holonomic next year and I want to have a more unique drive train than that). There's this design I've been thinking of that would be hexagon shaped, with one wheel at every side parallel to the side(not on the corners) It could be an octagon too, but that would take too many motors. But the omniwheel design is the important part. You know those rollers that are often under teacher desks or projector trays? Just put a smaller version of those into the slots where the sideways wheels usually go. Make a small modification so that it can't rotate enough to make itself go the same way as the larger wheel, and bang, you've got an omniwheel that can move more than just forwards and sideways on its own.

I think it would be great fun to develop. Except for the mill operator. He got mad at me when I mentioned I was thinking up an omniwheel that would take longer to make. Anyone else agree that this kind of omniwheel would be spiffy as anything for oddly shaped drive trains? Even for holonomic drives, I can imagine that the little wheels being about 45 degrees off from their usual range of movement. These little dealies might save some power normally spent moving omniwheels the wrong way.

By the way, does anyone have links to videos of mechanum and holonomic drives, specifically with the wheels showing? I haven't gotten to see either in action, and I'm curious as to their real maneuverability.

Re: Truly omnidirectional omniwheels?
 

This link still works i believe! It shows a prototype of our Kiwi drivetrain sometime before the start of the season back in 2002. We made those omni-wheels ourselves.....but they are very similar to the aluminum style that AndyMark produces today.

http://stuweb.ee.mtu.edu/~alkrajew/FIRST/kiwi.mpg

Re: Truly omnidirectional omniwheels?
 

Maybe a crab aka swerve drive is what you are looking for. 4 independent wheel/motor modules that can each rotate 360 degrees (together or independently, depending on the design). Search around and you'll find some pics.

Re: Truly omnidirectional omniwheels?
 

Sanddrag is right, if you want truly omni directional motion you either have to do crab drive like team HOT has done in the past or do a ball drive(there is a picture of it somewhere on the forums) which functions as a mouse ball does except with motors instead of the roller sensors. Other than that i know of no other way to be truly omni.

Re: Truly omnidirectional omniwheels?
 

I believe the technokats at one point made just for fun a ball drive. It was a robot that had two beach balls as wheels. They had two motors hooked up to each beach ball in a contact method. That way they could get the beach balls to roll in any direction, thus moving the robot. Clever, but probably not exactly what you're looking for. ;)

Re: Truly omnidirectional omniwheels?
 

Actually, the wheels were those garden globes you see from time to time. I believe some sort of grippy coating was applied as well.

(If you search hard enough, you'll also note that their ball drive saw action in 2003. Turns out that a team at one of 45's events had a robot busted beyond repair, so they pressed it into service to let them compete again. It even beat 45's robot in one match.)

Re: Truly omnidirectional omniwheels?
 

If you are doing this, simply pick up some transwheels from Kornylak, http://kornylak.com/wheels/transwheel-4000.html. That's what Team 95 used (4202KU's, since they have two rolls of rollers and thus roll smoothly) for their omnidirection test chassis (that we ended up not using for weight reasons).

Re: Truly omnidirectional omniwheels?
 

A standard omni-wheel, like the AM Trick wheels, should work for what you are trying to do. Keep in mind that when moving, unless going directly in the direction of an omni wheel, the entire wheel is turning (as well as the passive rollers).
Additionally a "holonomic" system can have any amount of wheels. A kilo-drive (kiwi drive) is a 3 wheeled variant, etc. Holonomic just basically equates to a vector-based omnidirectional system. It has a full range of 360 deg motion, and the direction of your force can be changed almost instantaneously (as soon as the motors accelerate). Holonomics suffer in other respects though. They are inefficient in terms of drawing max potential from your motors (often resulting in a low torque and/or speed). The exact loss of potential depends on the amount of wheels in the system. Additionally they require all of your wheels to remain in contact with the floor at all times to work properly. That often means that you are unable to travel up ramps, stairs, etc
A "ball drive" acheives the same functions as a holonomic drive. The motion of the "wheels" is based upon a vector of the forces applied by the two motors on the "wheel" (the "x and y axis motors"). So once again, you suffer an potential loss in how much you can get from your motors. Ball drives do not have the same problems with inclines as a holonomic drive does. Ball drives have a much smaller contact area with the floor, and often are made of a lower traction material (but if you have money/weight I'm sure you can use a higher traction ball), resulting in ball drives being relatively easy to push.
A "mecanum drive" (Jester Drive as dubbed by 357) is another omni-directional variant. This thread has links to explain the exact mechanics of a mechanum drive. Mecanum drives, at least those in FIRST, typically have rollers placed at a 45 deg angle to the wheel. Mechanum once again suffer in losses of the maximum potential of the motors, but they typically have solid traction and can climb inclines with the same ease as a "skid steering" system, if not better.
"Swerve" drives are yet another variant of an omni-directional system. They function by having the drive wheels (typically 4) physically rotate to match the intended direction of travel. Teams 71, 118, 1261, and many others have enjoyed tremendous success with this drive style. The "wasted potential" appears again in the form of the "Steering motors" cannot be used elsewhere on the robot and do not contribute to the power of the drivetrain. These systems typically require a low traction wheel to turn properly, so the traction issue emerges again. Unlike the ball, holonomic, and mechanum systems, a swerve drive cannot instantaneously change direction, it requires time for the wheels to change direction. The biggest problem with this system is often its weight and complexity.
"Crab drives" are a system that has a 2nd set of wheels/drive motors that will move the robot directly side-to-side, in addition to its standard drivetrain. This is also typically fairly complex, and does not offer true omnidirectional motion.
I'm sure that there are omni drive systems I have forgotten, but I have done my best to describe the advantages and dis-advantages of each.

Re: Truly omnidirectional omniwheels?
 

The complete ball drive can be found in this photo with a closeup in this photo. I can't find any threads about it right now and I don't know very much about it, save where to find these images :). You may wish to ask some of the Technokats Alums - Clark Gilbert, Austin Butler, Greg McCoy, and Kyle Gilbert come to mind - about this unique system.

Re: Truly omnidirectional omniwheels?
 

The best thread to read right now is probably this one:
http://www.chiefdelphi.com/forums/sh...t+ball+dr ive , especially the summary on the first page from Andy Baker. I'll look for the video I posted a long time ago and re-uploda it.

Re: Truly omnidirectional omniwheels?
 

Speaking of ball drive, I may have just figured out a way to reinvent the wheel. Think of a stepper motor. Instead of a traditional cylindrical rotor, use a spherical one. Like a golf ball with magnets instead of dimples. Now, use two stators that are 90 degrees apart from each other such that you can rotate the sphere about the x axis and about the y-axis. Voila, compact ball drive.

Now if you'll excuse me, I need to find a patent lawyer.