Truly omnidirectional omniwheels?

[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.

[Alex Cormier]

Hey, i remember seeing your team at FLR. Where did you get the inspiration for your omni wheels?

I <3 OMNI wheels!

[Exotria]

Yeah, casters are what I've been talking about. Although with further thought, I've realized that if you have the rotation limited and the caster needs to move that way because the robot is moving in such a way that it wouldn't spin the other way... might have to do something with springs so that the wheels move to default when off the ground. Of course, ball bearings were my first idea, but then I realized the whole 'robot not moving' thing, so I switched my idea into the (heavily modified)casters plan. Probably not traditional casters, though... might want the axis in the center.

And FLR was awesome. Team 229... can't say as I can recall that one, and you have the 1126 site in your profile. Link me to a pic so I can remember. 1126 was awesome, of course. I remember- you guys CRUSHED the opposition. It was so fun to watch! Your shooter was pretty danged great. We(the Duct Tape Bandits) couldn't say we were spiffed to lose, but we had the six hour bus ride home on the AWESOMEST BUS EVER to make us feel better. Seriously, we had a 42 inch widescreen HDTV, strobe lights, lasers, a fog machine, ceiling mirrors, fiber optics, subwoofers, hardwood flooring, sideways leather seating(with tables and cupholders), those things with the electricity where you touch them and all the electricity is attracted to your hand... it was the greatest bus ever. Most definitely my most fun experience in a while.

Also, the inspiration for the omniwheels came when I was bored enough to try to think of an innovative drivetrain, so I was thinking up a hexagon design, until I realized it wouldn't work with omniwheels because the little wheels wouldn't be facing the proper way, and if you moved them so they faced the right way, they wouldn't be facing the right way for moving other directions. So I decided I'd think of a way to make a better omniwheel that would ACTUALLY be omni, instead of just forward and sideways. This was all at one in the morning, of course... took a nap soon as I got home, woke up at 11, didn't feel like doing homework... all that great stuff. You can think up crazy stuff at one in the morning. Best time for innovation.

...yeah. So, with modded casters(methinks they'd need some reinforcements to hold a hundred pounds of metal moving at high speed- I'm thinking some sort of box protection design with stronger sides for holding the wheel so the axel doesn't break under stress), omniwheels can be made to be MUCH more omnidirectional for weird drive trains like the hex drive train I want to do.

...I need some sort of CAD program for my computer so I can draw this. Or I can use one of my dad's programs. He has Python. Would that work for CAD drawings?

(I'm just posting all this stuff here instead of talking with my team because my team probably wouldn't listen to me-not very popular with people because I have problems censoring myself in conversation and am hyperactive)

All right. More opinions on my(hopefully now clarified) idea?

[Alex Cormier]

well, i am no longer on 1126. i stepped up to college this year and am on 229. Clarkson University robotics. The reason why i asked where ya got the inspiration for those wheels, i that i made ones in 04' that looked similar. heres a picture.

also here is a close up of the wheels.


There is more info on www.gosparx.org too

[Exotria]

Erm... I'm afraid I can't see the resemblance between those omniwheels and my idea. They look like regular(multicolored) omniwheels to me... what's making them different from the normal kind?

[Alex Cormier]

Originally Posted by Exotria

Erm... I'm afraid I can't see the resemblance between those omniwheels and my idea. They look like regular(multicolored) omniwheels to me... what's making them different from the normal kind?

i was stating to the ones made on this years robot of yours.

http://robotphotos.org/v/first/finge..._7564.JPG.html

[Exotria]

Ah, yes. Very similar to our design. Great minds think alike. Unfortunately, I didn't know what an omniwheel was before this year. So I wasn't involved in that aspect... which means I don't get to qualify as a great mind. Curses.

And there are pictures of our robot online? Kickin! Those are some danged good pictures too... although it does give the inherent stalker-ish aspect, considering there's a picture of me in there... ah well.

[Exotria]

...I can't visualize omniwheels working perfectly at a 60 degree angle from the direction they're suppose to roll...

[George1902]

Originally Posted by Exotria

...I can't visualize omniwheels working perfectly at a 60 degree angle from the direction they're suppose to roll...

When the robot is moving in the direction of rotation, the wheel rotates and the rollers are stationary on their axes. When the robot is moving perpendicular to the direction of rotation, the rollers rotate and the wheel is stationary on its axis. Any vector in between these produces rotation on both the rollers' axes and the wheel's axis.

[Exotria]

I don't know about your team, but our motors use an autolocking system so that it's harder for us to be pushed. Thus, whenever a motor isn't receiving instructions, it locks itself up, so if certain motors are moving(say, two matching sides in a hex drivetrain design) while others aren't, the wheels wouldn't be rolling to go along with the miniwheels. Omniwheels wouldn't be very omni in that situation. And that's the point of my idea.

[RogerR]

Originally Posted by Exotria

I don't know about your team, but our motors use an autolocking system so that it's harder for us to be pushed. Thus, whenever a motor isn't receiving instructions, it locks itself up, so if certain motors are moving(say, two matching sides in a hex drivetrain design) while others aren't, the wheels wouldn't be rolling to go along with the miniwheels. Omniwheels wouldn't be very omni in that situation. And that's the point of my idea.

the hex drive train that you're talking about would definitely work with traditional omni wheels. you're right about the wheels not being able to free-wheel when the motor is unpowered, but this is a good thing. you want the rollers to only free-wheel in a direction that has another powered wheel opposing it, so that the powered can control motion in that direction. if the rollers swivel, then the drive will be difficult to control, and will have virtually no traction (how much traction does a desk chair get?).

i'm sorry if this doesn't make sense; omni directional drive trains are difficult to explain without delving into vectors trigonometry.

[Alan Anderson]

Originally Posted by Exotria

I don't know about your team, but our motors use an autolocking system so that it's harder for us to be pushed. Thus, whenever a motor isn't receiving instructions, it locks itself up, so if certain motors are moving(say, two matching sides in a hex drivetrain design) while others aren't, the wheels wouldn't be rolling to go along with the miniwheels. Omniwheels wouldn't be very omni in that situation. And that's the point of my idea.

I guess I still don't understand the point. Are you trying to make an omniwheel that rolls freely in every direction? A standard omniwheel does that. Are you trying to make an omniwheel that rolls freely in every direction even when it's prevented from turning around its main axis? That would work exactly against your reason for locking the drive shaft in the first place.