Penalizing mecanum wheeled robots durring alliance selection.

[Chris is me]

Originally Posted by Kevin Sheridan

Yes. We also had new pool noodles that were significantly harder than our old ones. A "downside" is that is also became really hard to play defense with the new bumpers. Our driver could no longer rely on friction pins and had to learn how to stay in front of robots better since it became really easy for other robots to "slide" past the bumpers.

Did you guys try leaving the front and back noodles "squishy" and the side noodles "firm"? Seems like the best of both worlds there; obviously most T-bones don't involve the front of the robot.

[Kevin Sheridan]

Originally Posted by Chris is me

Did you guys try leaving the front and back noodles "squishy" and the side noodles "firm"? Seems like the best of both worlds there; obviously most T-bones don't involve the front of the robot.

We did not have time to test different set ups for front/back and the sides. The bumpers were barely finished before SVR because Colin tested several different fabrics after Waterloo so we had little time to make the new set of bumpers. We also havent had time to revisit bumper testing this offseason because of Chezy Champs.

[c.shu]

So according to the poll as it is right now, ~40% of teams would either move you lower on their list or not pick you at all for having mecanum wheels.

[Sam_Mills]

Originally Posted by T^2

Tank drives such as 254's, 971's, or 1678's can get out of pins precisely due to clever use of bumper shape and material selection. One may even go so far as to say, as others in this thread have done, that the ease-of-use of such drivetrains allows teams to funnel more resources into other aspects of the robot, such as the aforementioned bumpers. Then again, even though I was part of team 1678 for the past two years, I didn't see a single one of our division qualification matches, so what do I know?

I am very aware that some of the best teams in the world are able to get out of friction pins pretty quickly (which is a relative term, meaning the average time to get out of friction pins is anything but quick), this is not what I was addressing. I was addressing the other 2700+ teams that have to decide every year what drive train they want to use. Most of them will not do extensive research, and many will be making their bumpers on practice day. Accounting for this, if for some reason not getting T-boned is their number 1 priority, then tank with traction wheels is undeniably the worst decision they can make.

Tank drives are great and I would probably never willingly field anything else, but relative to other drive trains they are the most susceptible to friction pins. Outlier cases can be misleading, but perhaps my statement was too. Of course the teams that can get out of t-bones the best are some of the highest level teams, but just because something is possible doesn't make it likely.

I will concede however, that I should not have been so rude, and I apologize.

[efoote868]

Originally Posted by c.shu

So according to the unscientific poll as it is right now, ~40% of people represented on CD would either move you lower on their list or not pick you at all for having mecanum wheels.

Fixed it for you.

Going to quote myself to save some effort
[in response to "mecanum wheels have never made it to eEinstein"]

Originally Posted by efoote868

This statement has always irritated me. Mecanum drive trains were extremely rare before AndyMark manufactured them, while swerve drive trains were (relatively) much more popular. The first year I remember AM mecanum wheels was in 2007; before that it took teams significant resources to manufacture them. If I recall correctly, two teams had them in 2005, maybe a half dozen in 2006, maybe a few more in 2007.

2008 didn't lend itself to mecanum drive trains (successful robots were geared 18fps+ with 2 stage transmissions). 2009 mecanum wheels were illegal, 2010 a large segment of the teams automatically ruled them out ("can't traverse the bump!"), similarly with 2012 ("can't balance on the bridge!").

Even now they're still taboo due to all the misinformation floating around.


In my opinion, "never made it to Einstein" has no place in this discussion because it ignores the wheel's history, as well as game designs and strategies. Until there is a year in which a large segment (say 20% or more of teams) in the FRC population uses mecanum wheels, I'm going to give no credit to that statement. After all, 100% of the robots on Einstein in 2009 had hard plastic wheels for their drive train.

In my humble opinion, the game this year did not lend itself to a strictly mecanum drivetrain. The field was wide open, the position of your robot mattered (favoring high traction drives), and quickness and speed mattered (in both short distances and cross field - something that benefits multiple speed transmissions).

If next year's game saw upwards of 30% of teams choosing mecanum drivetrains, and still none of those teams make it to Einstein, there might be something to that statement.


Excluding robots based solely on their style of drivetrain isn't too intelligent; one would do better to look at the complete package as well as how the robot's functionality and performance could fit into a prospective alliance.

[pntbll1313]

Originally Posted by efoote868

If next year's game saw upwards of 30% of teams choosing mecanum drivetrains, and still none of those teams make it to Einstein, there might be something to that statement.

That's a good point. I would be interested in knowing the total number of teams that chose each drivetrain. I don't think a CD poll would ever be a good way of finding this out, as more advanced drive trains would be over represented. (new teams that don't follow CD and used the kit bot would be under represented, where great teams that pick swerve may have 5 members following CD and all select that option in the poll). We would need to look at real scouting data for the answer to that. For example in my division at Champs, Galileo had 10 mecanum bots that I know of based on my scouting. They went 8-2, 8-2, 8-2, 3-7, 6-4, 2-8, 4-6, 6-4, 5-5, and 3-7 in qualifications, for an overall 53-47 record. In Galileo at least, it looks like mecanum drive performed more or less on par with the rest of the field based on that overall record.

Knowing the overall percent of teams that choose each drivetrain, their percentage of making it to champs, and their winning records, would all be pretty interesting information. That probably isn't pertinent to this discussion though as I think you need to judge the robot on individual performance. The difference between a good swerve and bad swerve may be the difference between moving in a match or not, so you obviously can only take these generalizations so far. Assuming you have a functioning drive train I still feel driver practice is the single most important aspect with any drive train.

[c.shu]

Originally Posted by efoote868

Fixed it for you.

Sorry I was not specific enough for your liking. I will try to be much more descriptive next time I make a simple observation so as not to be criticized for the lack of detail.

[AdamHeard]

Originally Posted by efoote868

Fixed it for you.

Going to quote myself to save some effort
[in response to "mecanum wheels have never made it to eEinstein"]



In my humble opinion, the game this year did not lend itself to a strictly mecanum drivetrain. The field was wide open, the position of your robot mattered (favoring high traction drives), and quickness and speed mattered (in both short distances and cross field - something that benefits multiple speed transmissions).

If next year's game saw upwards of 30% of teams choosing mecanum drivetrains, and still none of those teams make it to Einstein, there might be something to that statement.


Excluding robots based solely on their style of drivetrain isn't too intelligent; one would do better to look at the complete package as well as how the robot's functionality and performance could fit into a prospective alliance.

Statistically it doesn't really matter what percentage of teams run a certain drive, it's what percentage of competitive teams are running a certain drive.

I don't really care what n% of teams run, as it's reasonable to state that for whatever reason n% aren't a top team.

However, the decision making process of the proven competitive teams provides much more insight. The top teams, far more than any other, are constantly assessing things for competitiveness. They are also generally the most willing to COMPLETELY contradict historical beliefs (of the public, or their own) because something has value to them.

To me it speaks volumes that more top teams don't run them. I'd wager a fair number of top teams have tested mecanums in private, and chose to not use them. I won't say that we are or aren't a top team, but we tested mecanums (this is the first time it's public knowledge) and were not happy with them versus a fast and well tuned Nwd.

[efoote868]

Originally Posted by AdamHeard

To me it speaks volumes that more top teams don't run them. I'd wager a fair number of top teams have tested mecanums in private, and chose to not use them. I won't say that we are or aren't a top team, but we tested mecanums (this is the first time it's public knowledge) and were not happy with them versus a fast and well tuned Nwd.

Top teams don't run mecanum drives because they don't have to. When they choose to use a holonomic drivetrain, they have the resources and can afford the added complexity of swerve or butterfly - they engineer out the known deficiencies.

To me, the beauty of AM's mecanum wheel is that it makes easy holonomic drivetrains available to low resource teams.

IF we see more field layouts like 2010 (with tight areas to maneuver and precision driving required), I suspect we'll see more teams chose holonomic drivetrains, which will mean more mecanum drives.

[Andrew Schreiber]

Originally Posted by efoote868

To me, the beauty of AM's mecanum wheel is that it makes easy holonomic drivetrains available to low resource teams.

I'm going to disagree with this notion because, as it's written, it's missing a key point.

(Keep reading after it, I do clarify it significantly.)

It makes BAD holonomic drivetrains available to low resource teams.

You know, I can go out and buy a swerve module too? I'd make the exact same statement about a drive with them. Why? Because the hard part about holonomic/omni directional drive systems is they are hard to control. The mechanical aspects of things are hard (yes, even mecanum wheels) but building a reliable, tuned, and intuitive method of controlling them is HARD.

So, let's take team number 4xxx. They are your average semi experienced team. Some resources but not enough to build a second bot. Enough resources to build a solid manipulator and put it on a KOP drive train. Maybe even get a couple hours of driver practice.

Now imagine they put mecanum wheels on that KoP drive (because it's not hard. Costs about as much as adding shifters which is another system this logic CAN apply to). So, I've added some extra work beyond implementing simple skid steer drive. I guess I can use the WPILib's Mecanum implementation. But my robot turns as it strafes because my CG isn't perfect, what do I do? It's either something the driver has to get used to or it's something I have to invest more of my most limited resource (manpower) into fixing. So, now my manipulator has lost an iteration or small tweaks? For what gain?

Most teams don't think of problems this way. But they should.


Mecanum wheels are a solution to a problem. But they aren't as simple as slapping them on and using the WPILib Mecanum Drive class. That's a great way to build a crappy omni directional drivetrain. If you want it to be world class you need to develop and test a reliable and intuitive user interface. And you need to understand how it changes how you can interact with game objects and the field. It needs to be built into your greater strategy. And your driver needs to understand the limitations and benefits of your drive system.


Omni Directional drivetrains ARE inherently difficult. Nothing is ever going to make them easy to do. COTS parts simplify the mechanical issues with them. But the hard part is always going to be the UX.

[efoote868]

I agree that a team needs to build their robot for a strategy. In recent years, the ability to strafe hasn't been high on my priority list.

But if a low resource team were to come to me, and tell me that they must have a holonomic drivetrain for their strategy, and they wanted a recommendation, I would recommend mecanum 9 / 10 times.

In my experience, mecanum drive trains are simple to implement, can be robust with just a gyro for field centric control, and when all else fails you can swap out 4 wheel chair wheels.

I agree though, strategy trumps drivetrain.

[AdamHeard]

Originally Posted by efoote868

But if a low resource team were to come to me, and tell me that they must have a holonomic drivetrain for their strategy, and they wanted a recommendation, I would recommend mecanum 9 / 10 times.

I would tell them their strategy is likely flawed and they don't need holonomic movement.

[Jared]

Originally Posted by AdamHeard

I would tell them their strategy is likely flawed and they don't need holonomic movement.

So true. There has yet to be a game that really requires holonomic drive to win.
(WildStang 2003 may be an exception)

[AdamHeard]

Originally Posted by Jared

So true. There has yet to be a game that really requires holonomic drive to win.
(WildStang 2003 may be an exception)

Well, I'd buy the argument that in some games holonomic makes sense in some ways.

However, for a team with presumably not the same resources as a top team, when you factor resources into strategy, mecanum in my opinion is never the option.

If you're at that level, there are likely other areas of the robot that would have a greater payout for the same resource investment.

[efoote868]

Originally Posted by AdamHeard

I would tell them their strategy is likely flawed and they don't need holonomic movement.

If they wanted to be a lap runner in 2008, or they wanted to quickly clear soccer balls from a zone in 2010, or they wanted to strafe in front of the racks in 2011, or they wanted to strafe sideways to quickly catch a truss shot and release a ball in 2014, or they want to move in an L shaped fashion without changing orientation in 2015 then a holonomic drivetrain might be the correct fit for them.

You cannot know the best implementation to a strategy without knowing the strategy, and you cannot know the strategy without knowing the game rules.