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adj : not directional; being in or involving all directions Let's apply this to radio waves. Sure, with a rotator a directional antenna can signal in a certain direction well, and has the ability to change directions, but can it signal in multiple directions at once? No. As the definition says, the crab/swerve/synchro drive is directional. It cannot move along other axises without first changing the direction of the wheels. True holonomic drives have this instantaneous ability to move in other axises than oriented. Some more reading. A suitable analogy would be if I cold move really fast, say 1/4 the speed of light. I could say I teleported myself. To the average person, they'd believe it, but the educated person knows better. This analogy is suitable because the fast and powerful motors we have allow us to turn the swerve wheels very fast. If we did not have such powerful motors, the limitations would become aparent. Everyone is entitled to their own opinion, I'm just telling you the dictionary and accepted definition. Nobody said yes couldn't mean no. |
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say you have the wheels like so: . . _ . .[_] you only get .5 of possible max power if you are moving directly verticle or horizontal. however, you go diagonally (45 deg. from horizontal) you will get full power. To PatrickRd: Thanks for the offer of help with the omniwheels, however we don't have access to a machine shop and I think the best way to go is to buy our wheels. I found this source (kornylak) that looks perfect, about 5 inch diameter, polyurethane rollers (wooo!), made of aluminum. Only downside is the wheels we would need would total to 516 USD. We can probably do that . . . . if we raise 6large in time to apply for the NASA grant again. pics: The wheels pictured have 3 rollers, you need two wheels back-back to provide for 360 degrees of rotation. Here are schematics: linkies: omniwheel I think that this is the best way to go for long-term durability and for overall funcionality (any rollers we make probably will not be as efficient as these. downside, is again, 64 dollers per wheel. But we will be able to swing it. I asked Kornylak is they would like to sponsor us, so maybe we can swing it for cheaper. Who knows. These are what I'm drawing around as of now. edit: These wheels are also ideal because they are nearly circular, so there will be smooth weight transfer from one roller to another and it will make for a smoother ride than, say, the lexan/disc wheel you pictured above. It is also probably lots easier on the wheel and the gearbox. I'm reading that documentation, its pretty cool. Especially your nod to strongbad: "Eating one battery . . . . Eating Five Batteris" It was so serious up until then, too. I guess you college students just didn't have it in you to stay that way, huh? |
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Main Entry: om·ni·di·rec·tion·al Pronunciation: "äm-ni-d&-'rek-shn&l, -"nI-, -(")dI-, -sh&-n&l Function: adjective Date: 1927 : being in or involving all directions Same as your definition above. So, if you put boxes on both a killough and a swerve drive, both boxes could move in ALL directions without changing the orientation of the box. Since this fits the definitions above, both killough and swerve are omnidirectional. Yes, you can be more technical and argue that swerve can't do them all at once... but like I said before, what is the point? You can't physically be going in two directions at the same time, so why make that a criteria? :yikes: Again, these are my thoughts. I don't however want this turning into a flame war; we should all have the ability to reason and debate without getting angry or start calling each other names. Oh, one more thing. Quote:
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None of the proposed drive systems are omnidirectional because they don't involve the z-axis.
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what would the z axis even be? Logic would say it would involve up and down motion, but common sense would tell you that would never be useful in a drivetrain.
Cory |
the three axis as far as FIRST is concerned are x, y, and theta (the angle)
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:D :p :cool: |
Thanks John,
That's exactly the information I was looking for. indieFan |
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BTW, two of our robot names our "Burninator" and "The Cheat" Some comments on the wheels you found: The design concerns me because a wheel roller is not always in contact with the ground. Usually with this type of wheel there are staggered rollers, such that there always is a roller in contact. So the wheel will be rolling without friction one instant, and then a split second later be scraping against the ground. Please correct me if I'm misinterpreting the design of the wheel. Good luck, I really hope to see more omni-drives around this year :) Seriously, if you run into any roadblocks at all you can't figure out please contact me at prd8@cornell.edu. I'd even make the wheels for your team if I had more time, just to see a four-wheel omni FIRST robot. - Patrick |
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Actually, upon further consideration I will make a deal to any teams out there interesting in constructing an omni-drive. Here's the deal (of course, let me know someone if this breaks a FIRST rule, I will not do this if it does):
That's the deal. The deadline's is Dec. 15. I will send them out at latest the first week of competition (you will have all the dimensions well before to do designs). - Patrick |
Patrick:
you did miss a detail: Those wheels are designed to be put back to back two on an axel,180 degrees apart, so you have six rollers per axle, with either one or two always being in contact, and a nearly circular shap for smoothness. I contacted Kornylak, and they said that the wheels have a .874" hex bore. Is this type of axle readily available? Can I get bearings and standard size gears that will go on this axel? If not I may have to take you up on that offer. I began chassis design the other day (this is all pending on whether this years game will allow for this sort of thing . . ) and I came up with a way to build a solid chassis with four long rectangles of aluminum plate and some angle peices. Light, should be strong, and damaged peices could be easily switched out. as of now, its just a sketch, but tommorow I will calculate sizes and dimensions and whatnot. Maybe I will even begin the gearboxes. Who knows? er, about the omnidirectional debate. This may clarify things. Group A says that killough/similair are the only true FIRST omni because they can move in any x,y direction in an instant. They say that swerve/crab drive is not omnidirectional because the crab modules must turn, so that all a crab module is a quickly reconfigureable chassis, but it can't zoom north and then east with only a few instants in between to do all that accelration stuff, but it can go north, rotate its wheels to the E-W line, thus reconfiguring the chassis, and go east . . . Personally, I think that omniwheel-based systems are cheaper and easier (built like a tank drive, only put the wheels at 90 degrees to each other) to construct, but quality omniwheels are hard to build or obtain. I think that the kornylaks are winners, and I hope that our bot this year reflects that. Essentially, all our robot design is is four wheel drive, one motor per wheel independant of the others, turn the wheels perpendicular to each other, and then put omniwheels on the drive shaft. Same gearboxes. No steering mechanism that uses extra stuff, just standard gearboxes. I just hope it works. But, I'd say the killough platform is as KISS-style as you can go with all these 'omnidirectional' drives described in this thread. |
Kind of like these wheels I spotted at the airport in Zurich, Switzerland :D
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- Patrick |
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