Re: pic: AndyMark Mecanums
 

Have you all seen the vehicles that AIRTRAX is making holonomic?

I was amazed that they figured out how to do holonomic drive for forklifts and scissor lifts.

Just something that caught my interest.

-Q

Re: pic: AndyMark Mecanums
 

With enough weight on the wheels, the TechnoKats' prototype mecanum drive base is very smooth. The installed rollers are sufficiently "squishy" that they don't do a lot of thumping to begin with, and they also wore down a bit to a slightly rounder profile after driving on concrete for a while.

Re: pic: AndyMark Mecanums
 

See these pictures for examples of holonomic and mecanum drive robots. ;)

Re: pic: AndyMark Mecanums
 

Wikipedia actually has a pretty good definition of holonomic as the term applies to robots:
So a robot drivetrain that is truly holonomic as defined above would have three degrees of freedom; i.e., three independently controllable wheels not directed along the same axis. A robot drivetrain with four omniwheels arranged on the corners is actually redundant, but with relatively simple math can be made to function like one that is holonomic. The same statement applies to a robot drivetrain with four mecanum wheels.

Re: pic: AndyMark Mecanums
 

Aka Kiwi drive which is usually categorized with the Holonomic drive Art had above due to their usage of the same type of wheel

Re: pic: AndyMark Mecanums
 

See the explanations above. A "mecanum" drivetrain is set up like a four wheel drive with each wheel independently powered. You cannot have two wheels powered by the same motor/tranny. If you do, you will lose all sideways ability, and you may as well go with four wheel drive. There are three teams that I know about that have used this setup in competition. Note: If you tried to use them in a "standard" omni drive (Art's left-hand pic), you would go nowhere, or possibly spin out or fry a motor or something else equally bad. (Actually, mecanum drive is a subset of omni drive.)

Re: pic: AndyMark Mecanums
 

actually, in a four wheel omni-drive, if you paired the wheels across from each other together and attached them to a motor, you'd be able to translate freely. unfortunately, this'd mean you would be unable to rotate. i believe you could achieve similar results by pairing the the diagonal wheels on a mecanum drive train together.

Re: pic: AndyMark Mecanums
 

Now that I think about it, yes you could, in theory. Again, you could not turn the robot. Also, it might be a bit difficult to link a wheel on the left front corner with the one on the right back corner...

Re: pic: AndyMark Mecanums
 

there are ways, such as elaborate rotating shafts or using tapered gears to angle them the needed degrees then run those together with chain and sprocket with a motor and tranny in the center, would be heavy though.

Re: pic: AndyMark Mecanums
 

When 190 made our mecanum wheel, we originally had our rollers supported by 1/8" aluminum tabs, but we found that lose quickly bent when supporting a 130 pound robot making rapid movements. We switched to 1/8" steel, and while those were much better, we still had the occasional bent tab.

Re: pic: AndyMark Mecanums
 

And mecanums are heavy enough as it is. We can make some pretty light ones if we want to, but they still weigh at least as much as our six-wheel drive. (if you include trannies on both systems)

Re: pic: AndyMark Mecanums
 

Hey Andy,

Is there any chance you could share some general dimensions for these wheels so that those of us who're considering ordering a set can start to work them into our plans? Unless I've missed it elsewhere, it'd be fantastic to know as little as overall diameter and thickness, but if you've got more than that, I'll take it. :)

Re: pic: AndyMark Mecanums
 

1. Mecanum refers to the name of the compnay which the original creator worked for at the time of his invention (or at least to the person whose name is on the patent of the design which is most commonly mimiced by FIRST teams). Bengt Ilon developed this design, if my memory serves me correctly in the mid-1970s.

2. A holonomic platform, most literally is defined as one which has the ability to instantaneously move in any given direction (on a given plane). It does not need to be accomplished with mecanum wheels, and may not necessarily require wheels at all (I'm thinking "bumper boats" right off the top of my head - although not as controllable, these do fit the general terms).

3. There is technically no such thing as a Mecanum drive, although within the FIRST community, a holonomic drive platform using Mecanum-style wheels has become known as a Mecanum drive platform.

I realize this is a few months down the line, but hope it clarifies some things for you -- sorry in advance if any of my "facts" or a bit off, I'm replying to this based solely on memory of research I did almost two years ago. :)


EDIT: His name was not Ilon Mecanum -- Mecanum was the company he worked for. Ooops.

Re: pic: AndyMark Mecanums
 

The guy who invented Mecanum wheels was Bengt Ilon. I have no idea how they got the name Mecanum. They can be also called Ilon wheels.

This is all according to Wikipedia... and as we all know "I SAW IT ON THE INTERNET IT MUST BE TRUE!"

Re: pic: AndyMark Mecanums
 

Ah yes, now I remember. You're right.. I retract my prior statement, and say that the company he worked for was "Mecanum something or other"