Truly omnidirectional omniwheels?

[Exotria]

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.

[ajlapp]

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.

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

[sanddrag]

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.

[Simon Strauss]

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.

[Ianworld]

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.

[Billfred]

Originally Posted by Ianworld

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.

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.)

[kaszeta]

Originally Posted by Exotria

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)

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).

[dubious elise]

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.

[Clark Gilbert]

Originally Posted by dubious elise

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.

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.

[sciguy125]

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.

[Cuog]

Not likely gonna need a patent for those hemispherical wheels we were working on them this summer: http://www.chiefdelphi.com/forums/sh...ad.php?t=40770 but take a look at what we came up with its a cool design

[Exotria]

I don't think you guys are understanding my point... I know about the other omnidirectional drives(thanks for the links, however, I like information). My point is a way to make other omnidirectional drive trains by using another design of omniwheel. That... was my intended purpose for the topic, to ask whether another kind of omniwheel could be made that was more... well, omni. I know that all the other drives are successful, but those innovation awards are really appealing, and I think that another omnidirectional drive train could be made with my idea. I've already said it a few times- rotating rollers instead of just the wheels. Basically lets you have the miniwheels have their x axis rotate, with a little modification so that it can't rotate into the same direction as the wheel itself. This would allow there to be traction for the wheel going forward, and allow it to go any other direction without traction. That would allow wheels to face 45 degrees away from each other, , or any other degree, but not oppose each other. That would let there be more drive trains with opposing wheels. Which means more creativity.

[Mr. Freeman]

What about an omni wheel but instead of having a bunch of wheels around the main one, you just have a bunch of ball bearings stuck into it.

I'm not sure if something like this exists yet, I don't see why it shouldn't.

I see a problem with this though. If you were able to push an omni wheel in any direction, then it wouldn't be able to provide any traction when you rotated it with a motor. It would just spin in place.

Now, someone mentioned something about "the wheels on the bottom of teacher's desks."
I assume that you meant something like these:
http://www.photoflex.com/photoflex/p...300/caster.jpg
Those are called "casters", just for future reference.


EDIT: I just saw something about limiting the casters' rotation as so that they don't allow the wheel to spin in place. Ignore the second paragraph in this post.

[Qbranch]

Originally Posted by sciguy125

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.

I've messed around with this idea in order to replicate something I saw in a music video.

A company called Animusic ( www.animusic.com ) makes this sweet midi driven animations... I've always wanted to re-create a scene out of one of the animations... so I'm going for the 3 slightly humanoid looking robots on the "Starship Groove" animation... anyhow back to the story...

The spherical track motor works exactly like a linear track motor except for the fact that the micro-electromagnets are arranged within a sphere made of a non-ferrous material. For my design, this sphere would fit into a matching hemisphere, very slightly larger than the sphere. This, in effect creates a fully functional low-load-bearing ball and socket joint.

OK thats the overview, now heres the problems with it:

There would have to be a processor dedicated to each joint. The design requires at least 3 (4 if it is going to be stable) pulse width modulation channels. It would never be FIRST legal since the victor's update rates are over 26 times too slow for updates. The PWM period would most likely be something like 500ns or so, because of the high instability of intersecting lines of magnetic flux.

The joint itself would have to be encoded for position somehow, perhaps with a hall cell array or something like that. The updates for the servoed position would have to be done every 500ns to keep up with the pulse train, the high update rate is needed to overcome the problems with the intersecting flux lines.

So in a nutshell, here's how it is:
1. Would have to be based on a DSP running around 100MHz for a clock

2. It will eat TONS of current

3. Has to be run at a very very high voltage if you want to get much speed
or load capacity out of it.

4. Will require one UART for positional data input will need 4 channels
of simultaneous high speed PWM, run through a mux chip of some kind
in order to drive the hundreds of micro-electromagnets inside of the
sphere.

5. Will need a super high speed latch chip in order to retrieve data from all
those hall cells.

6. Driver board will have to have a power transistor or mosfet for every
single electromagnet.

7. All parts within about 6 inches of the thing will have to be non ferrous.

8. And oh yeah, the programming will be extremely hard (servoing in 2
dimensions)

Did I lose anyone?

Granted, this is a design which would work for a positional as well as a speed based spherical track motor. But, like I said, my application required positional. It would work for motion purposes as well, though. I'm putting this on my "Things to do before I die" list.

-Q

[Lil' Lavery]

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.