Re: pic: 1675's REAL IRI Upgrade
 

I am an avid believer that using Mecanum wheels (alone, in a purely mecanum drive, and not some sort of octocanum (is that what you kids are calling it now?) drive) is one of the worst decisions a team can make.

How many times have we seen a machine with an awesome manipulator an mecanum wheels get shut down by a team with 6 wheels and roughtop treads...

Agree or Disagree, but the statistics don't lie.

Re: pic: 1675's REAL IRI Upgrade
 

These mecanum arguments never solve anything.

One side talks about how mecanum is suboptimal, and the other side white-knights mecanum until their keyboard breaks. Others bring in good information for the debate, but here's the thing:

There is no debate.

Driver skill matters, but physically there are properties mecanum has and properties traction wheels have. Nothing is going to change this fact.

Teams who want to use mecanum will use mecanum. Teams that don't, won't. I don't think anyone is going to have their opinions on the matter magically changed by arguing back and forth - they need to realize answers for themselves.

Team 1675 used mecanum this year because we believed before seeing the game actually played that the game and our design called for it. We believed that the Zone would be very crowded and that defenders would be willing to risk being right up on the zone, giving you limited room to move around once inside. We believed that having the fine positional control of a well-done macanum system was paramount. After all was said and done I believe we would have been fine with any drive system that could pivot.

Do I think we designed a bad robot just because it had mecanum wheels? No. In the future, I probably wouldn't lobby for using mecanum wheels unless the challenge specifically called for strafing or translation of some sort. However, I would hope that our team looks deeply at the game and our solution to the problems that don't involve movement and make a better guess on how the game will be played before deciding upon a drivetrain.

Re: pic: 1675's REAL IRI Upgrade
 

177 won 2 regionals and Galileo in 2006 by only playing defense because we knew how to win by not playing the game as intended, and somehow everyone else was convinced else we were a good shooter. We intentionally kept the score low and won using the ramping and autonomous bonuses to win.

We actually caused a member of the GDC to lose a bet where he claimed no purely defensive robot would make it to Einstein.

FYI we were the 2 seed in Galileo that year and we rarely scored an offensive point.

OH, and we won Newton and the Championship in 2007 by using defense to distract everyone from the fact we had our partners splitting up the Rack to prevent long chains of tubes to keep the score low so we could win with ramping bonuses.

Re: pic: 1675's REAL IRI Upgrade
 

Oh, you mean the year we COULDN"T use mecanum (Lunacy)?? Yeah...we don't talk about that year. We only played defense because we had to, and while it worked out well at the regional level, did you see how bad we were in Atlanta and IRI?

I can't believe I lost my hair to a defensive robot...:confused: :confused:

Re: pic: 1675's REAL IRI Upgrade
 

Found the video I was looking for. Its not exactly driving circles around the defender, but its certainly a maneuver that would not have been possible without mecanum wheels: http://youtu.be/PDsq1sEVVKs?t=2m28s

Re: pic: 1675's REAL IRI Upgrade
 

I have to disagree on this one. To me, it looked like the defender got distracted by something else and gave up on their push. Had 2761 not stopped in their tracks, 1675 doesn't get a clean release into the scoring zone. A 6WD could have done the same thing (and probably resisted the original push better as well).

Re: pic: 1675's REAL IRI Upgrade
 

After watching the clip about 5 times in a row, I disagree with this statement. 1675's only goal at that point was to get on the other side of the defender and get to the scoring rack. During the two-robot spinning motion, 1675 was on the opposite side and there was really nothing to stop them from translating away from 2761, as shown below -



I think what contributed to this motion was the mecanum wheel rollers being pushed from the side by 2761. The real trick would have been timing the translation correctly.

There's a lot of strong opinions about mecanum drive systems here - which is fine, everyone is entitled to their own opinion. The way I see it now with AndyMark selling mecanum wheels is that this gives teams an opportunity to have an omni-directional drive train with very minimal effort. So you have every team under the sun buying a set and trying them out, even if they aren't necessarily implemented correctly. More often than not, I see teams driving tank style with two sticks, completely ignoring the mecanum's translation capabilities.

So what does this come down to? Mecanum drives are inherently more difficult to control than a standard tank style drive. You can show someone immediately how to operate a tank style drive train and they'll understand it. They won't master it immediately, but I would argue that the amount of time that it takes to 'master' a tank style drive train is less than the time it takes to 'master' a mecanum drive train. No hard evidence to back up that claim either, just something that I've observed.

Most teams don't build second robots and don't have much driver practice time. So when they choose a mecanum drive, they are probably still trying to figure out how to control it out on the field. I think this adds to the perception that mecanum drive systems are a bad choice, when in reality the learning curve is just larger.

I agree that there are inherent disadvantages to using a mecanum drive, and that if your team has the time and resources to build a swerve drive system, then that is the way to go probably. But most teams don't. So they sacrifice some pushing power at the cost of omni-directional maneuverability.

One of our goals this summer has been to get students driving mecanum every week. We will see if it pays off next season - who knows, maybe we will finally be able to produce this fabled mecanum vs. six wheel video.

Re: pic: 1675's REAL IRI Upgrade
 

"Healthy" debate about mecanum aside, I think it's ridiculous that we've gotten to the level of directly insulting 1675's machine and design decisions. They clearly had a pretty good robot this year.

Re: pic: 1675's REAL IRI Upgrade
 

it depends on driver setup.

actually, the drivers got the drivetrain part down very quickly, as the way we set it up was just like the controls in video games like halo work. find a halo junkie and they will have mecanum down in a few minutes.

depends on the person i guess.

Re: pic: 1675's REAL IRI Upgrade
 

Exactly. You can try to automate and control as much functionality as possible on your robot, but when it really comes down to it, it's up to the driver and operator to control the thing. Some teams just have better drivers than others. Better often means that they've had more practice and have had time to get used to how their machine drives and operates.

Anyway, back on topic - 1675's machine is legit.

Re: pic: 1675's REAL IRI Upgrade
 

This is why everyone needs to remember correlation does NOT imply causation, as i said earlier. Too many variables are in play. To name a few: Strategy during the match, driver experience, opposition, the game that year, skill of the robot in question outside of drivetrain, teammates, competition location, driver skill, control setup, speed, etc.

Re: pic: 1675's REAL IRI Upgrade
 

What is it about mecanums that make them so polarizing? The closest analogy I can think of is scissor lifts - they are generally frowned upon for competitive robotics use, but they don't carry nearly as much hatred (or love) as mecanums.
I've yet to see an "I love mecanums they're the best ever" thread; I've seen many "mecanums are the wheels of the devil" threads. Most teams that use them, do so as a bit of a situational compromise - sure, there isn't as much traction or speed as treaded wheels, but there is the gain of lateral maneuverability for minimal mechanical and programming difficulty, compared to swerve/crab drive.

So why the hatred?

Re: pic: 1675's REAL IRI Upgrade
 

It might be the way it was implemented. Teams that dislike mechanum drive may have had bad experiences with them, and rather than risk 400$ and try it again (or use those wheels again), they forsake it forever.

My team on the other hand used mechanum this year and we were very pleased with the result. We were able to weave around defense (atleast when our PWM's were connected). Also, the strafing helped us line up with the pegs.

All in all, teams that have had bad experiences w/ mechanum may forsake it, and teams with better experiences will probably stick with it. Due to the complexity and the relative novelty of mechanum, more teams have had bad experiences with mechanum, or better experiences without mechanum.

Re: pic: 1675's REAL IRI Upgrade
 

This is what I was going to say but you already hit the nail on the head.

Re: pic: 1675's REAL IRI Upgrade
 

I don't understand this debate. What teams choose to incorporate into their robot is their choice and that choice is made under their value system. Yeah sure, 1114 has never used mecanum, but not every team wants to be 1114.