Re: pic: 1675's REAL IRI Upgrade
 

Open-field movement is not the reason to pick a mecanum, or just about any, omni-directional drive. The notable advantage is analagous to how these drive systems are used in the real world. The ability to translate in multiple axes without rotating the entire robot. This is particular useful in small, tightly packed spaces.

Think of how you parallel park in a car. Or, perhaps more of a direct analogy, moving from one normal parking space to the one next to it. That's not a very efficient or easy to execute series of actions in a FRC match. Strafing saves maneuvers like that in tight spaces.

Whether or not this is enough of an advantage to avoid the numerous drawbacks of mecanum systems is up to each particular team. I know that I won't support the selection of a mecanum system for teams that I'm associated with if FRC games continue to have a similar field lay-out and style of play. On the other hand, I probably carry a bias since an alliance partners' mecanum drive was a significant factor in ending my senior season in the Galileo semi-finals in 2007.

Sure it would have. "Bumper-locked spins" happen in FRC all the time. The real key to that maneuver was the open space where it was happening allowing for ~270deg of rotation. This type of maneuver is easily possible with a tank drive in a "side-impact" scenario like that. This isn't a perfect example, but it's one that was readily available and show the same principle being executed by a 6WD being defended by an excellent defensive machine who was on their way to Einstein.
http://www.youtube.com/watch?v=Bzpo3vVeGEY#t=3m45s
e; Another example in the same video.
http://www.youtube.com/watch?v=Bzpo3vVeGEY#t=4m48s

Notice how they escape from the spin move at the end, they don't translate directly away. They "spin off" the block, similar to how a tank drive would. Everything in that maneuver could have been executed by a tank drive, and similar situations frequently happen.

Re: pic: 1675's REAL IRI Upgrade
 

deleted

Re: pic: 1675's REAL IRI Upgrade
 

We won Buckeye in 2010 (as alliance captain) using mechanums. During the balance of the season we never felt that we were at any real disadvantage against pusher-bots. In fact, we even successfully stuffed a reasonably-competitive 4WD tank opponent into the goal once. We put a lot of time, effort and $ into the control system to make driving as intuitive as possible however (closed loop on all four wheels, strategic assignment of user I/O, etc.). That, combined with a good driver and a practice bot made us successful, at least at the Regional level which was good enough for us. I don't think we would have been as successful with a traditional drive.

Just another data point...

Re: pic: 1675's REAL IRI Upgrade
 

dunno if this is quite what you wanted Chris, but in this video 1318 litteraly drives circles around the defending robot in green, 3251. Although without any other drive-train details it is difficult to tell what really happened, this is an instance where i would say a mechanum robot definitely out maneuvered at least one non-holonomic defender with ease. Although this video says little about a mechanum driving circles around a defender like 973 (substantially more tenacious than the defenders in the video) I think that it shows the capability of a mechanum drive-train to use the ability to strafe to glide between defenders in a way that would be difficult for a tank drive to do.

http://www.youtube.com/watch?v=lwv9hZgw9r0

Re: pic: 1675's REAL IRI Upgrade
 

What I see in that video is 3251 playing defense solely on 3165 (the team with the white tube) and paying very little attention to 1318. I think it is relevant to note that 3165, with what looks like a mecanum drive, did not come close to getting past the defense of 3251. When 3251 did switch to 1318 at the end of the match, they let 1318 get away when they got ready to deploy.

Re: pic: 1675's REAL IRI Upgrade
 

I'll explain my hatred of mecanums.

I don't hate them. They are a viable solution to a certain set of problems. Personally, I have not seen those problems as being prevalent enough in FRC to expend the resources needed to do mecum wheels. I evaluate this for every single game/challenge/project. If a mecanum wheeled system is the optimal solution to my problem then I will do it. I will also have criteria for why I chose those since I have to justify the expenditure. After the system has performed (usually end of season) I perform an evaluation of how effectively I solved the problem. Sometimes this comes back positively, and sometimes not so much.

The thing that I don't like about mecanums is not the wheels. It is the people that tout them as the Chuck Norris of FRC drive trains. They have downsides, some of them are quite serious (cost, added weight, added complexity, lack of traction, difficulty climbing ramps, requirement of keeping the CoG in mind, requirement of some sort of suspension...) . They also have some very serious benefits that you can't get using any other system. Too many times have I seen the comment that "mecanum wheel r better" espoused by some student. They aren't. But neither is a 6wd or a crab system or a nona-drive. None of them are inherently better than any other solution. Saying that is like saying that a laser cutter is better than an allen wrench. Yeah, if I am cutting out sheet parts (or birch like one of my EWCP friends) then the laser cutter is more effective for that job. But it won't help me if I need to bolt together my parts. My issue with them is that they are often held up as the solution to a problem rather than the solution to the problem at hand.

I've seen teams use the wheels to great benefit. I won't deny that there are benefits to using them. But if you need a hammer you use a hammer and not an oscilloscope.

I know that is probably a wall of text but just take away the next two sentences:
Evaluate how effectively all your options meet your requirements and choose the one that best fits your problem. Don't pick your solution and fit your problem around it.

Re: pic: 1675's REAL IRI Upgrade
 

I agree that this doesn't show an example of mecanum out maneuvering tank drive, but I have to say that the 1318 drivers do the best job of using mecanums that I have seen (in my limitted experince), using the strafing when and where it fits.

Re: pic: 1675's REAL IRI Upgrade
 

This thread has been hijacked. Thank you for your time.

Re: pic: 1675's REAL IRI Upgrade
 

I had no idea 1318 was being defended in that match. They also moved very slowly and aimlessly - not exactly running circles, unless you mean the literal circular path they take?

I honestly don't see why this thread had to turn into an argument. The reason the picture exists is because of two friend teams joking about their disagreement on design choices. They're clearly able to be light hearted about this. Why not us?

Re: pic: 1675's REAL IRI Upgrade
 

You certainly encouraged a non-light hearted debate early on in the thread.

Re: pic: 1675's REAL IRI Upgrade
 

Wow another mecanum debate! :rolleyes:

I have always been skeptical about mecanums but I wasn't solely set against using them until last year 2010 driving at an off-season event and realized how easy it is to push those wheels around the field (robot I was driving was 4wd: two pnuematic, two omni). Ever since realizing how easy it was to push them, I have zero desire to use them* unless there is a game that separates alliances from contacting each other. I could never justify a decision that would leave our robot so helpless under defense.

This year our team built a 6wd plaction robot with the mindset as rookies that we will build a robot that can simply play the game (low row + minibot that averaged a logo and a 1st place minibot at regional level. 12 for 12 deployments and 8 for 8 at STL). We knew we wouldn't be the best in most matches and designed our drivebase to be powerful on the field and pushed around many 6wd/8wd and some swerves too. Not matter how bad your upper assembly turns out, you should always design your drivebase to be one of the strongest on the field.

I have heard a lot of "they can out maneuver" or "strafe around opponents" but whenever I hear that I just want to see someone do it (and bad/stationary defenders don't count). :p

***no octocanums were mentioned in this post***

Re: pic: 1675's REAL IRI Upgrade
 

Why are so many people in this thread concerned about the merits of other teams' robots and feel the need to argue so passionately against mechanum drives? I can see plenty wrong with some of your own robots that I don't see in 1675's, for example. I won't call out case examples.

Fix your own robot's issues first, then maybe you'll have a valid enough stance on something to be allowed to preach to other people. (some of whom are mentors and also former world champion drivers)

+.02,
Agrees with Tom

Re: pic: 1675's REAL IRI Upgrade
 

Show me the mentor who has never built a bad robot and I'll show you either a new mentor, a liar, or Andy Baker. One of the most important things one can do is learn from mistakes and this means that we have to make them. This means you can't discount someone's analysis merely based on the fact that they have screwed up in the past.

Re: pic: 1675's REAL IRI Upgrade
 

the part about them driving a circle around 3251 was mostly a joke. I do think however, that 1318 utilized their mechanum fairly well. although they didnt do smooth lines around defenders, they were able to move through the crowd more effectively than most robots I saw at a regional level.

That is kind of what i was thinking too.

The circles was a joke, the robot did do a lap around a defender. I think that 1318 was able to maneuver better than most of the other robots on the feild, and a large part of that was their drivers ability to use the strafing effectively to move through the congestion, while it obviously says nothing about robot performance at the highest level, mechanums in this case proved to work very well.

Re: pic: 1675's REAL IRI Upgrade
 

That's a little extreme. I mean, sure, we're not talking about the LOLz we got anymore; and, yes, there are already enough threads about Mecanum vs any other drive train, but the conversation has still been somewhat intelligent and hasn't degraded to people just yelling and blindly ignoring everyone else. Actually, this is one of the better threads I've read as far reasonably intelligent posts.

I'm really enjoying this discussion. I have yet to get annoyed by people just posting their opinions without reading what others have posted. Like I just said, this thread isn't really a bad thing... yet.

Thank you for the defense, however, as a member of said team, I'm not seeing this as people pointing fingers at our robot, but the drive train as a whole.

I didn't know that people actually knew that. 2 world championships, just to give him some more cred.