Mecanum vs. Swerve Drive
 

I'm doing some research for an offseason project this year. We have used mecanum wheels in the past to great success, however I want to know if a swerve drive would serve us better.

What are the main differences between mecanum and swerve drive and the pros/cons of each drive systems? Or if there is already a thread that discussed this, can someone link it in a post?

Re: Mecanum vs. Swerve Drive
 

There are dozens of threads and hundreds of posts on this very subject. You can use the built-in forum search feature.

Or Google works too.

Re: Mecanum vs. Swerve Drive
 

Prepare for the worst.

Nearly everyone on CD will tell you that mecanum wheels are completely awful, and have no pushing power.

That being said, there are several benefits to moving to swerve. It is much more efficient in power delivery, and so much more powerful. As a beginning team, mecanum is great for preliminaries. However, as a team that has used them for several years, it may be useful for you to transition into something else. Keep in mind, that swerve is always a work in progress. The best swerve drives are made over several seasons. But don't be afraid to continue with mecanum, if you determine your time should go elsewhere.

Pros to Swerve:
Several alternate control methods
Better power delivery (Speed and no slickness of rollers)

Cons to Swerve:
Not easy to slap onto a robot like mecanum
Requires the use of many motors
Can be unreliable, unless you spend a lot of time getting everything right
Can be expensive (but mecanum can be too)

Pros to Mecanum
Easy to implement
Reliable
Little development

Cons to Mecanum
Rollers
Costly
Can be unbalanced

Re: Mecanum vs. Swerve Drive
 

What "alternate control methods" for swerve do you have in mind that cannot also be used for mecanum?


Mecanum rollers do not have to be slick.

Re: Mecanum vs. Swerve Drive
 

I meant control methods such as "car" steering, crab, swerve, etc.

And I meant the rollers were "slick" simply because they are a roller...

Re: Mecanum vs. Swerve Drive
 

Link to a thread about this very subject. While it's been a few years, feel free to PM me with any questions you have. My team did implement a swerve back in 2011 (My senior year of HS) and I like to think I remember a thing or two from the good ol'e days.

Theoretically, any movement that you can make with a swerve you can make with a mecanum, and vice versa.

Re: Mecanum vs. Swerve Drive
 

Why not build both?! Swervecanum drive!

Serious: We have built Mecanum. We loved the maneuverability we got, and ease of use. Yes, we could get pushed a lot, but the trick to that was to just go sideways around the defender. They are awesome to show off at science night and such, because everyone like a robot that moves like a crab, and you get questions about the wheels, how they work, etc, from people just looking at the bot.

We do have reason to believe that they we one of the reasons we failed to make eliminations at all in 2012, mostly because there is a stigma against them, and, if you are not first round pick, then there is a good chance you will be skipped second round.

Have fun choosing!

Re: Mecanum vs. Swerve Drive
 

I'm not an expert on this (or just about anything, really), and I am going to echo Ether in saying that there are a million other threads about this already. But I just want to say 2 things.

1. People, please don't let this devolve into another thread arguing about whether mecanums are good or bad. Just stay focused on how mecanums compare to swerve. I think everyone can agree that swerve > mecanum, so lets keep this a simple discussion on why that is.

2. To the OP: don't just dive into swerve like nothing thinking that you will have instant success. Know that swerve is very complex and resource intensive, so be cautious. It's good that you want to test out these kinds of things in the offseason, but know your limits. Basically what I am trying to say is: don't underestimate the difficulty of swerve.

Re: Mecanum vs. Swerve Drive
 

We won the Boston Regional in 2011 with Mecanums, and we were playing the DEFENSIVE ROLE!!! If you know how to use them well, and have a full 120lb robot, defense is very possible with mecanums.

Re: Mecanum vs. Swerve Drive
 

while as a drive system alone swerve always wins it is a lot more difficult and resource intensive and hard to program. Ive hated and thought meccanum drives were a bad idea for a while, but i believe that's because ive never seen a team use them to their full potential. Last weekend i got my first real chance to see KnightKrawler 2052 driving (we go to opposite MN regionals typically) and i was very impressed with their driving and how they used their meccanums to their full potential. I believe KnightKrawler has used meccanums for years (i believe one of my friends said almost every year except 09) and have really figured out how to get the most use out of them. Like all drivesystems the key to using it successfully is driver practice. You cant drive a meccanum like a tank drive which i unfortunately see a lot of teams do.

Re: Mecanum vs. Swerve Drive
 

I think this may be some kind of record. We got through 9 entire posts before someone mangled the spelling of mecanum.

Re: Mecanum vs. Swerve Drive
 

I'll stick this here since the video wasn't out for the other threads.

True, but I do sort of revel in being able to 'pick up' mecanum bots and drop them on the other side of the field. You know we love you, Jesters.

We're happy to use swerve to push, but more often we use it to run fast cycles, which can't be intercepted the way mecanums are, and toss in a little jostling of nearby opponents. Swerve basically means the above plus that and that (sorry, STORM) as well as this this, this, and this.

Things like octocanum* can theoretically (Ether?) move similarly, though most people seem to concentrate on strafing. But they can't push or prevent being pushed while doing it, which we do rather constantly. I've never met a mecanum--or octocanum, if I put them in the right situation--that we can't push. Most basic tank drives will go where we want them to, and we can at least slow down and vector most of the crazy ones off course. It's better at two-speeds, you could check with 1717.


In short, swerve gets you from A to B while drastically minimizing the number of people that can...redirect you. That said, it's no cakewalk. It's the best investment we've ever made (we've been making it since summer 2009), but it is an investment.

*Switching traction & mecanum wheels. Lots of threads if you don't know the details.

Re: Mecanum vs. Swerve Drive
 

Have you given any thought to a crab drive? We did one in 2011. It is similar to a swerve except that instead of spinning each wheel individually by a steering module, pairs of two or in some cases all four wheels are spun by one gearbox. The two pairs method makes turning easier.

You could also simplify a swerve in an easy way. Drive all four wheels from one center gearbox with chain, then spin each wheel with individual steering in order to control direction. This method allows the use of two, three, or four motors, or as many as you choose, and then you can more easily impliment a two-speed drive with your swerve.

Side note: In our 2011 crab base, we steered the front wheels in tandem and the back wheels in tandem. Then, we drove the left wheels with one gearbox and the right wheels with another. We used custom shifter boxes to our advantage. So. much. power. I highly recommend using shifters with common gearboxes.

You could also look at one of the more notable swerves this year, Team 1640. They have four individual modules, one for each corner. I believe they use a CIM on a single speed gearbox and a separate steering motor for each corner. I could be wrong, but that is how they explained it to me at Hatboro-Horsham. Seriously, look at them, they made it to Einsteins, and their drive is awesome. And remember, it takes a different mindset in the driver to handle a swerve versus a crab, though from mecanum they are pretty similar.

Re: Mecanum vs. Swerve Drive
 

I'd recommend that you develop your own swerve drive in the off season, mess around with it and interact with other robots to get a feel for what you're dealing with.

In my humble opinion, swerve tends to have many more opportunities for failure than other traditional drives. This can be a good thing if you view failures as learning opportunities, or a bad thing if you want to compete with your robot on the field for every match.

Some of the most successful and inspirational teams use swerve drive successfully every year, but their years of experiential learning cannot be replicated in just one season.

Whatever you do, just don't say we didn't warn you :] .

Re: Mecanum vs. Swerve Drive
 

Thanks for this.

I honestly hadn't thought of that, thanks.

Haha, consider us warned, we don't have any plans on using swerve drive for competitions in the near future but more to get new members interested and for a challenge for other veteran members and it can't hurt to create a showbot using swerve.

We are planning on having our members learn about and how to drive each drive system and for also the drive team to practice for competitions.

Re: Mecanum vs. Swerve Drive
 

I guess it's my turn to be "that guy"...

I'd like to humbly propose that in 90% of cases, omnidirectional drives are unnecessary or even detrimental to the overall robot. Teams like 1640, 148, and 1717 notwithstanding, I often believe that a team would be much smarter to build a more complex manipulator and go with some sort of simple, tested tank drive (even the kit bot on steroids) than build a complex drivetrain and run out of time for a good manipulator.

Yes, swerve and mecanum drives are more maneuverable, and this can have advantages (as attested to on this thread). But that maneuverability requires a fair amount of driver practice to fully utilize. Be honest, how much of the time did the average mecanum robot spend strafing? Any?

Even if you are able to drive this type of drivetrain to its full potential, it takes a lot of time to build and program. The average swerve drive probably has three or more times the number of discrete non-COTS parts as a tank drive, so it would take a lot more time to make. It's not impossible, it's just a large investment of time, time which could be used making a better manipulator. Also, it takes a lot more time to program than you might suspect. Don't take my word for it, ask Adam from 973 or Ether (or just search for their posts about it). This goes for mecanum too, to a lesser degree.

I won't go into the reasons why a swerve or mecanum drive might be better or worse in terms of defense. Other people are better qualified to argue that than me.

Hopefully I haven't discouraged you. No matter what summer project you chose, if you can actually follow through and make it happen, it will be an awesome experience for you and your team. And, if you want to build an omnidirectional drivetrain in the offseason, go for it. The offseason's the right time for this sort of thing, and even if all you've learned that you're never building/programming/driving an omnidirectional drivetrain again, you should call it a success.

Re: Mecanum vs. Swerve Drive
 

One of the guys on our team has machined mecanum brakes which would prevent the rollers from spinning and in effect creating a tank drive. We haven't gotten around to actually testing them yet so I'm not sure if they work.

Re: Mecanum vs. Swerve Drive
 

There are many other threads discussing this matter, the forum search feature will most likely satisfy all your curiosity. Here is the general consensus in a nutshell (with a few modifications).

Mecanums are fine. Don't let anyone tell you otherwise. Mecanums get a bad rep around here for some reason I can't fathom. But Mecanum drive is fine. If a robot on Mecanums fails to perform, it is often because either the rest of the robot didn't live up to the needs for the game, or the team didn't invest enough time into developing the drive system, not because the wheels are cursed. Mecanum does require a fair bit of programming and tuning work to get everything right, but when used properly, they can create a wonderful and incredibly frustrating (for the other teams) drive system. At FLR, one of the lead scoring robots in the field was on Mecanum. They evaded defense like it wasn't there and became the first overall pick in the draft, cut off in the Semi-finals by some very well placed strategic defense. No, you won't be able to push a robot with a strong drive train, but if you're using Mecanum and your strategy is to push, your issues run deeper than the robot.

Swerve is fantastic. It's maneuverable, and it doesn't sacrifice the traction that Mecanum wheels give up. It's a very fancy drive train, allowing for multiple driving styles (see 1640 for a notable example) that allow for versatility in different situations. The issue is, Swerve really is every bit as difficult as its reputation lends to. There are no cutting corners on a good swerve drive; it requires a full development cycle that can span through multiple seasons before being considered ready to put on the field, and even then, without a refinement in design and manufacturing resources (see the Swerve development of 1640 and 1625) it will be heavy and costly. In the long run, the pay-off of Swerve seems to be very good. I haven't seen it through yet, but if you look at the teams who have spent time refining a Swerve drive and continuing to improve upon it... Well, they are generally teams most people are unhappy going up against. Teams like 16 and 1717 have become dominant in FRC, partly because their drive system is just better than all else's. It's a great drive system, and its benefits aren't insignificant, but if you really wan't it to play out well, you need to be ready to invest countless man hours and dollars into the project.

I think that more or less sums it up. It's 1AM, so my head is a little loopy, but this is more or less a general take on Mecanum vs Swerve. Mecanum good, but hard. Swerve better, but really hard. It's a personal team thing if it's worth it or not.

Re: Mecanum vs. Swerve Drive
 

We have used both mecanum and swerve. The mecanum is easier to build provided you pay attention to a few design rules. All 4 wheels need to be in the same plane thus excellent tolerances on the frame design and/or mounting the wheels with shocks/springs of some sort is essential. Keep the mass above each wheel about the same thus symmetrical distribution of robot components (their mass) is critical (don't forget the battery). Finally we had much better performance with encoders on each wheel. If you design the robot keeping these principals in mind the software is pretty simple.

We built mecanum because the students loved to drive it. You will hear many biased opinions about mecanum. But I would have to agree that when playing against bots at the Einstein level the disadvantages are more serious. At the regional level, mecanum is fine and it is fun. A good driver (with some practice) can move around or spin around all but the top tier tank drive setups.

Swerve drive is awesome but quite complicated. It requires more parts, tighter tolerances, more motors etc. Many others in this thread make good points about the complexity. But it is awesome when you get it working! We stopped making swerves when our expert machining mentor became ill and couldn't help with the manufacture.

Either is a worthy off-season effort. Good luck!

Re: Mecanum vs. Swerve Drive
 

Here's a reason why mecanum drives get picked on: It's hard to scout defensive potential well. And mecanum wheels are a proxy for being bad at defense.

At a regional, most of the teams that would make the best defenders are playing offense during the qualifications. And here's why I think that is: Suppose a team can score 25 pts if they go offense, or reduce the opposing alliance's score by 25%. So then they should play defense if and only if 25% of the opponent's expected score is >25 pts. Once you get to eliminations, there will be better opponents, so playing defense will make more sense.

So in figuring out who the best defenders are you end up doing a lot of guesswork. You can try to keep track of pushing matches won or lost but that's about it because so many don't play and defense during quals. So then you're left with pit scouting. Not all mecanum-drive robots are easy to push around, but if you're picking a robot to play defense (or counter-defense) then the scouts have to be sure that the robot you pick won't get pushed around by an average kitbot.

So from this you get teams, like mine, who have used a formula for picking the third robot that looks approximately like this:

1) Eliminate robots likely to be bad at pushing (such as mecanums or omnis)
2) Find max( [average auto pts scored] + [average climb pts scored] )

Mecanums are useful, and using them can improve your robot's performance. However, remember that the teams in eliminations aren't the 24 best teams. They're the top seeds plus whoever those teams think would give their alliance the best chance to win.

Now to the original question, mecanums or swerve: Why not holonomic?

Re: Mecanum vs. Swerve Drive
 

This happened to us this year.
There are teams that have policies of not picking teams with Mechanums no matter how good they have performed that weekend.

Re: Mecanum vs. Swerve Drive
 

Both swerve and mecanum are equally agile when executed well.

Mecanum is easier to execute well and requires fewer resources ($s, mass,...) and less learning or insitutional knowledge to do so. The rollers, however, do compromise traction.

Swerve provides agility without compromising traction, but it is resource intensive. 1640 uses swerve and we are very pleased with the results, but this has come at a considerable investment in learning. We also have to deal with having a finished drive-train rather late in the build season due to long fabrication and assembly times. Control software is also non-trivial. So there is a price to pay for this traction.

It is clear that the investment and cost of swerve has imposed limitations on other systems and capabilities on our robots.

So, like all real design decisions, this one is about what is right for you and your situation. All good designs are good compromises.

More serve info is available at the following link to "swerve central":
http://wiki.team1640.com/index.php?title=Swerve_Central

Re: Mecanum vs. Swerve Drive
 

If for a moment you do not focus on the competition value of complex drive trains, but look at the FIRST mission to inspire students, go for it. Our students learn so much about design and fabrication from the swerve project. It is a complex project and requires a team to develop a design build process. This same process can also serve a team well in all other design build missions. The knowledge gained from going for a swerve project can be huge. Our team recently discussed manufacturing and selling some of the critical parts of our swerve module. Teams would have to make and purchase the rest. There would have to be some interest to make a run. Interest.

Re: Mecanum vs. Swerve Drive
 

Whichever way you decide to go, don't try to reinvent the wheel (pun intended). There are many resources out there - crab/swerve COTS modules, gearboxes built into chassis, programming code shared from others - that make life so much easier for you.

Re: Mecanum vs. Swerve Drive
 

I would assume 1126 can attest to that? I loved being on your alliance at FLR in 2012 but watching you try and drive up onto a bridge was at times quite painful.

Re: Mecanum vs. Swerve Drive
 

Exactly...

In 2012, when 1126 tried Swerve drive out, it was significantly less than stunning. The development cycle was much shorter than it should have been, spanning about the Fall prior to the 2012 season. The prototype, while more or less functional, was definitely not field ready. It would still suffer technical malfunctions and the software control was incomplete. This ended up hurting an otherwise decent robot, making consistent driving a challenge and, of course, those bridges were a hurdle (though that was also a result of the robot being top heavy).

While I presume the mileage may vary for most teams, I would probably target a satisfactory swerve drive at having a 2 year development time:
-Begin development over the summer following a given season
-Span that through the Summer and Fall (though development will probably slow down in the Fall as the team starts to focus on season preparation) -----Don't use it in the coming game
-Resume development in the following Summer
-Enter your prototype Swerve into an off-season event
-Refine based on off-season performance
-Determine if you are satisfied with putting that Swerve drive on the field. If not, repeat for another Summer.

That's just my ball park. Given the complexity of Swerve, I would probably not be comfortable with less than that. Higher resource or more well staffed teams who can iterate their physical design more quickly will probably have their development cycle cut down significant as opposed to a team such as mine who doesn't have significant resources.

Even after that initial development cycle to even get the Swerve on the field, it's important to keep iterating it. Reducing weight, reducing cost, augmenting reliability, simplicity and robustness are important as it allows your Swerve drive to keep a competitive edge. Equally as important as the design of the physical aspect, refinement of programming is just as important, to keep the Swerve drive driving properly.

The only reason I can see not picking Mecanum for a third robot is if the team is trying to push with them. If a team builds a robot on Mecanum wheels and is pushing as part of their strategy, then I really wouldn't want them for a third robot. While most people equate "defense" to "pushing", to assume that pushing is the only way to play defense is a huge error. While yes, pushing is the most obvious way to play defense, a robot on Mecanum wheels with a creative driver and strategy can easily create traffic for any robot. While they won't be a mobile wall, it's still defense. It is more work on the scouting end, but it can be a difference maker. Especially since most teams at regionals who end of being picked as a defensive robot don't really have all-star drive trains.

I've actually wanted to experiment with Holonomic for a while now. I think it's never really involved in these discussions because it's a fairly forgettable drive system. It doesn't really get any exposure because there are few FRC teams with Holonomic drive in the spotlight. I remember 1501 was on Kiwi Drive (the 3-wheel Holonomic variant) in 2010, and I remember seeing one team use it in 2011, but I don't think I've seen one since, though I'm sure there have been some.

I have to disagree with you there. This past season my team used mecanum for the first time. Yes they are very costly but it all panned out in competition. And as far as pushing power, we pushed a robot twice our size and just at Max weight across the field on several occasions

Re: Mecanum vs. Swerve Drive
 

If you're considering swerve, here's some advice. Before you decide to go ahead, figure out some basic stuff about the drive train. Make a simple CAD drawing and figure out where the big stuff is going to go and how the modules will be steered and driven. Make sure you spend time to figure out how the control system will work with the swerve. You need to figure out how the steering feedback will work, and if you are doing independent steering/drive, you need to do some math(see Ether's swerve kinematics whitepaper). Finally, try to find a good machining mentor. It helps a TON to have a machinist help make the modules. If you get an experienced machinist to help out, you will avoid making silly mistakes, and you'll get your modules done faster, cheaper, and with stricter tolerances. But if swerve is something your team is really interested in, it will pay off HUGE! My old team attempted to develop a swerve drive during the build season, and we ended up in 45th place in our regional. We qualified for cmp through the chairman's award, refined our drive train during the extra 5 weeks, and once we had all of our problems solved, we ended up on Einstein that year!

Re: Mecanum vs. Swerve Drive
 

I disagree that programming a mecanum drive takes a significant amount of extra time.

Mecanum pseudo code:
M1 = x + y + z
M2 = x - y - z
M3 = x - y + z
M4 = x + y - z

6WD pseudo code:
M1 = y + x
M2 = y + x
M3 = y - x
M4 = y - x

Mecanum drives are nice and simple, both mechanically and in terms of software. I disagree with claims that in order to drive well, it needs suspension, closed loop control, or other extras.

Re: Mecanum vs. Swerve Drive
 

We used them and loved them as well. I was simply stating the common CD belief that mecanum wheels are awful at defense. We too did the same thing, and held some of the best teams at our regionals to only 2 cycles. We likewise bullied teams pushing them across the field... I personally think mecanum wheels are a great and easy option, provided you build them right.

Re: Mecanum vs. Swerve Drive
 

Isn't this true of almost any drive train (or system in general?),

If you do it right and know the limitations you're working with, you can be successful with nearly any drive train.

That isn't to say success doesn't come easier to certain methods and systems.

Re: Mecanum vs. Swerve Drive
 

There are many adjectives I'd use to describe swerve drive trains, but easy is not one of them.

Re: Mecanum vs. Swerve Drive
 

If I needed omni-directional motion, and I did not have a swerve drive prototyped already, I would probably turn to mecanum--and adopt a strategy that used lots of offense with some "trick" defense. I bet that some of those FCS blockers could have been pretty effective on a mecanum base, for example--but so could have been the FCS, for the same reasons.

However, if I had a swerve drive prototyped that I was "happy" with--that is, that I figured was pretty close to where I'd want it for competition--I would take that over the mecanum.

Of course, I'm assuming here that I actually need omni-directional motion, but that's a discussion for another day, say a couple of days after Kickoff.

Here's what I see as the advantages for each side, just mecanum vs swerve:
Mecanum:
-Potentially lighter
-Easy to turn into 4WD should I decide at the event that I don't need omni motion
-Fewer moving parts, so less likely to break
-Somewhat less control complexity than swerve, on the feedback side mainly

Swerve:
-100% of power goes in the direction I want, no vectoring.
-several ways to set up, each with its own pros/cons (somewhat easy "tuning")
-more possible variants--witness 1625's 6-wheel, the 16/148 3-wheel, and 3928's CIM-in-wheel in addition to more "traditional designs"
-looks cooler

Re: Mecanum vs. Swerve Drive
 

1114 has really good information on drivetrain designs and advantages here.

Re: Mecanum vs. Swerve Drive
 

How often are you picking a third robot with the intention of running an identical strategy to the one they ran in quals? Yes, sometimes it's similar, but there's a lot to be said for flexibility.

The thing is, mecanum isn't only worse than tank drive at pushing. More importantly, it doesn't resist being pushed very much. For a lot of defensive roles (including most of the "creative driving" roles you allude to in your post), if the defender can just be plowed through, the strategy doesn't work.

Here's an example situation. We had two decent choices left for the sixteenth pick at WPI. (The rest had <4 CIM drives, <100% powered wheels, or were not consistent at anything we needed) One was a mecanum drive robot with a full court passer (no scoring) that, while unreliable, could really increase disc throughput for our ground loading partner. The other option was a shifting tank drive with a 10 point hanger and a smart drive team. Yes, we could gamble and pick the unreliable mecanum shooter... but if they jam, what do they do? They can get in the way, but not enough to make much of a real difference in the final score. The ten point hanger could play any kind of defense needed - man to man, line defense, cover-the-disc defense.

Neither of these teams were running the strategy we wanted from them for most of Friday. One was a lot more versatile than the other despite having way less going on simply because they could resist being pushed and push well.

I won't go so far as to say I will never select a robot with mecanum wheels - but it will be despite their presence on the robot, not because of it. I've even seen mecanums play decent defense - it's just that the wheels are no help at all.

(by the way, despite my Mecanum Hater reputation here, I do think 2013 was an *okay* year for mecanum, and teams like 1100, 4134, 3824 played to its strengths)

Re: Mecanum vs. Swerve Drive
 

Or you can use this pseudo code:
M1=y1
M2=y2

Re: Mecanum vs. Swerve Drive
 

Over the years I have only seen a few Mecanum bots that have true omnidirectional movement on the field. They could strafe at best. We love to have our way with them. There have been many times where we had to defend a good scoring Mecanum on our alliance from the opposing alliance defense. I have yet to see a Mecanum on the field have control of chassis orientation and drive direction. I would choose a well developed 6 or 8 wheel tank over Mecanum any day.

Re: Mecanum vs. Swerve Drive
 

How is this not a problem with swerve drives?

Re: Mecanum vs. Swerve Drive
 

The problem is not with the drive train. The problem is with teams that don't properly know how to use it.

Mecanum is a very easy system to implement and use. Code is readily available; we had ours built and programmed within a day when we used it in 2011. This makes it a viable option for low-budget, low-experience teams looking for a quick fix.
In my experience (and this is a broad generalization - I'm not talking about any particular team), teams that use mecanum drive aren't as advanced regarding gameplay strategies. Driving is all about anticipation. Most mecanum-based offensive strategies are all about avoiding defense, not getting into pushing matches.
Mecanum systems aren't as good at pushing because they don't need to be.
Also, if a team does find itself in a pushing contest and is outmatched, it needs to find a way to disengage without pushing back. Mecanums, if used properly, can do this well. Unfortunately, most teams don't utilize this*.

On the other hand, most teams that use swerve drive, and have iterated it to the point of usefulness on the field (I've seen more bad swerves than I have bad mecanums), have a degree of experience and wiliness about them. They're usually well-practiced and well-coached so that they don't get into bad situations in the first place, and if they do, they can get out of them with ease.

*Watching matches, I'm often reminded of the cartoons where Wile E. Coyote is trying to outrun a rocket. He could simply dive to the side and the rocket would fly by, but that never occurs to him.

Re: Mecanum vs. Swerve Drive
 

Yeah, that'd be a matter of "they're easy provided you build them right" (true) vs "building them right is easy" (false).

Chassis orientation is controlled independently of translational direction. e.g, Just push in the defender (because they can't push you), spin around them, and then spin around again until you're lined up the way you want. Like this or this. Or after a brief pin. Or before not being pushed at the unprotected feeder. Or after rocking an FCS blocker.

Taylor - absolutely agree. It's not a theoretical issue, it's a game play one. For instance, there's no way we'd be putting all the swerve work in at this point (nor will we continue to), if it wasn't providing such a huge in-game advantage. Still, I'd think that after 7 years I'd have seen someone riding mecanum that really embraced this. Is coaching and practice really bringing this to (near? video?) zero? I've seen some really excellent drive teams on them, but they just don't seem to weigh this heavily. I know a lot of the biggest benefits for chassis orientation rely on holding traction, but I'd venture others do not. Is the default (or otherwise reasonably doable) code amenable to it?

Re: Mecanum vs. Swerve Drive
 

Err hmm, DC 2013. 383 was a Mecanum bot picked to play 3 point shooter. Exactly the role they played in Quals. I think it worked out pretty well for us :P

Regarding not being picked in 2012 with mecanums – This was a function of their difficulty balancing.

Honestly, this debate can be decided pretty quickly.

Does your strategy dictate that an omni directional drive system is needed?

Does it dictate that you need absolute traction in all directions?

With those two questions you can decide if you need tank, swerve, or mecanum. Remember, strategy needs to be dictated by game play and resources available to your team. If you lack the resources to build a swerve your strategy should not ride on one. If your strategy doesn't ride on it you shouldn't build it ;)

Re: Mecanum vs. Swerve Drive
 

This, in my mind, is a fundamental component in the debate about the effectiveness of mecanum drive in FRC. It's difficult to make a determination about how effective they can be when a significant number of teams that implement them do so very, very poorly.

The conventional wisdom has been that implementing mecanum has become easy. The wheels are available as COTS parts, the code is shared freely, etc. The reality has been, though, that there's a significant performance discrepancy between the few good implementations and the piles and piles of really terrible ones. That suggests that mecanum really isn't that easy to get right and we should probably be putting it into the same category as WCD or swerve -- perhaps still not in terms of effectiveness, but certainly in terms of knowledge required to do it right.

Re: Mecanum vs. Swerve Drive
 

I completely agree. But why? On paper, it should be an easy drive to execute.

Edit: What I'm trying to say, is what's the difference between a good and bad mecanum drive?

Re: Mecanum vs. Swerve Drive
 

Driver Practice.

In my experience, a good mecanum drive tikes time to perfect, not nearly as much time as swerve though. My team used them for the first time in 2013, we ended up having to re balance our wheels and straighten them out and fix programing on several occasions. In the end we did have very very good but un traditional mecanum drive (un traditional on the control end). At our regional we saw some good examples of bad mecanum drives where they were basically tank drive, they could go forward, reverse, and turn but couldn't strafe to save them.

Re: Mecanum vs. Swerve Drive
 

I think it might be an interesting exercise for people to share video of their idea of a good mecanum drive. I suspect most FRC participants have never seen an above-average implementation of mecanum drive in action.

A mecanum drive is, in some ways, a lot like fly-by-wire controls in an aircraft. It requires closed-loop software assistance or it doesn't really work at all.

Re: Mecanum vs. Swerve Drive
 

While I agree, I'd venture this is the case for essentially all DTs. You don't need closed-loop to drive tank any more than you need absolute encoders for mecanum, but there's still a world of difference between the way, say, 11 drives tank and the way xxxx does. Or 25 for the former, to be more colloquial. (I just really like watching 11 this year)


And yes, somebody, please feed me video. ::rtm:: <<pretend it's a monitor

Re: Mecanum vs. Swerve Drive
 

For the sake of sparking discussion and because my programming team did an awesome job, I've found some video of our 2011 robot testing. This was the 'octocanum' drive; it could lower traction wheels when it needed to push its way through defense.

http://www.youtube.com/watch?v=sM8cixsE5fo

http://www.youtube.com/watch?v=Jr-eglZBAHQ

Re: Mecanum vs. Swerve Drive
 

Mecanums can move in exactly the same way as swerve drives, and can do it without having to wait for their wheels to turn. In any holonomic drivetrain, teams can use a gyro throughout the match to keep track of their change in angular position and implement something called field centric drive.

I don't understand why this is a challenge exclusive to mecanum drivetrains, or maybe I'm not understanding your point.

Re: Mecanum vs. Swerve Drive
 

My point is the same as Taylor's. Swerves can and do control chassis orientation simultaneously with translational path. I have to say, it pays off big. There's nothing physical that limits mecanum drivetrains' ability to do the same. (On an open field) The phenomenon is that they just plain don't do it. I'm wondering why.

For instance, Madison's videos are very cool. :) I bet that really worked out for them in Logomotion matches. My question is why, with so many out there, do so few mecanums even attempt to drive this way. Is it the standard control strategy? (Madison mentioned good programming) Is it practice? Is it coaching? (As Taylor said) Do they see less benefit in it for some other reason?

Re: Mecanum vs. Swerve Drive
 

2052. 2052. 2052.

http://www.youtube.com/watch?v=4vlC3EqF_rc

Starting at ~2:30.

I had the pleasure of watching their driver pull moves with their mecanum drive I've never seen any other team do at the MSHSL Championships last weekend.

I can't speak for any of their code or their physical setup, but their driver really knows how to make that mecanum drive sing.

Also, my statement was more along the lines of "swerve is easy if you do it right." I would know how difficult it is when you do it wrong. We did it wrong in 2011 and couldn't move for our first regional.

Re: Mecanum vs. Swerve Drive
 

Why is it necessary to do fancy stuff (turning while traveling in a straight diagonal line, etc) in order to have a "good" mecanum drive? The best year for mecanum was 2011. All a mecanum drive needed to do that year was drive >90% of the time as a tank drive and strafe occasionally if that made it easier to line up to hang a tube.

Our team used a gyro in a proportional control loop to maintain the robot's orientation while it wasn't turning. I concede that I wouldn't want us to run a mecanum drive without that piece of instrumentation, because without it the robot's orientation drifts too much. Regardless, that's still not very difficult to pull off. It's a ways short of PID loops on every motor and field centric control, and it's much simpler than programming a swerve drive.

Re: Mecanum vs. Swerve Drive
 

I think it's less about being fancy and more about ditching the Wile E. Coyote syndrome:

Mecanums, even (especially) those driving in tank, will attract bad situations more than their high-traction counterparts. These situations can often be avoided or disengaged from more easily via mecanum attributes than tank-driving-mecanum attributes. At the same time, they can also set up a lot of plays that don't benefit (and actually exploit) tanks, but they're exceedingly rare. So there's a ton of Coyotes running around who are utilizing all the negatives of their choice and few of the positives.

For what it's worth, swerves could also spend most of the time driving tank and just swerve when "needed". There's nothing wrong with tank drive. But if you're going to make another DT, be it mecanum or swerve, whose physics provides such starkly different competitive advantages disadvantages (vis-a-vis tank), why wouldn't you leverage the advantages?

Re: Mecanum vs. Swerve Drive
 

We posted a video with some footage if you'd like to see. Hopefully this can at least quiet down some of the mecanum haters :cool:
http://www.youtube.com/watch?v=Ogy65hEPIXk

It's a 7 minute video but I'd suggest watching the whole thing as there are some cool moves in the middle and the end.

Re: Mecanum vs. Swerve Drive
 

I agree that it is not about being fancy but about being effective.

Swerve-Drive really introduces a new paradigm to the issue of moving from point A to point B. It requires new thinking. It benefits from new tactics. It is not really an incremental change, but it can feel this way.

It took us some time to catch on to this. We continued to suffer from the Wile E. Coyote syndrome even after the solution was in our hands.

Re: Mecanum vs. Swerve Drive
 

While I've never done a swerve, I actually believe many swerves would benefit from using a tank like "mode". A tank mode is much easier to learn and is much better for long distances. You can still switch to swerve when needed, to take advantage of it's benefits(small adjustments, getting around defense, etc.)

Re: Mecanum vs. Swerve Drive
 

We used to have one. It's driver-dependent (as is everything), but none of our drivers have ever wanted it, 4 having had swerve drive bases. It's not particularly useful given the rest of the controls' freedom, and while the mode itself isn't hard to learn, switching between them is a needless (and rather annoying) thought "jump". There's no inherent cognitive difficulty about driving holonomic long distances, whether opposed to other swerve maneuvers or tank.

Our drive has evolved away from "modes" more and more every year. We've found very little use in that control framework itself when it comes to swerve; not using it is one of the major reasons the drive is so cohesive now. The seamlessness is a major strength of the drivetrain. Our only 2013 mode is a radial spin for aligning the climb; everything else is like playing Call of Duty. Before, drivers would largely ignore all but 1-2 modes (plus an occasional game-specific), and none used tank.

TL;DR: do what your drivers want, but don't be surprised when swerve + modes = no.



pntbll, I moved to your new thread. Cool video!

Re: Mecanum vs. Swerve Drive
 

Drive mode was probably the wrong word. One setup that I've thought of is where one joystick controls direction and speed, the other joystick controls your turn radius, and another button that activates turning around the center of the robot. This is the exact same setup as cheesy drive, except you also have the ability to move in any direction. This allows you to switch between tank and swerve, without switching modes. This is completely theoretical, so I honestly have no idea how well it would work, but the idea is that there must be some way to incorporate the benefits of both drives, without having to switch modes.

Re: Mecanum vs. Swerve Drive
 

Ah. This is roughly what we do, if I understand correctly (though I admit I don't see what it has to do with tank control). One stick controls translation: crab forward, left, back...any of the 360 degrees. The other stick controls chassis orientation, at any of the 360 degrees.* (We used to have a control more along the lines of "turn radius" when it was a snake mode.) I'm not sure what you consider to be "tank" control and its drive benefits in this sense, though. I thought you meant tank control as opposed to arcade--one stick per drive side (forward is FF, back BB, turn left BF, right FB)--but this doesn't sound it. If what you describe as the first stick is "tank", what's swerve, and why is tank easier over long distances than whatever swerve is?


*I don't play COD, but I'm told this is analogous to move & look, for any gamers out there.

Re: Mecanum vs. Swerve Drive
 

The drive style is similar in some ways, but also very different. The drive I'm describing is a combination of your snake and swerve. Imagine a non-field centric drive, where your "swerve" stick controls direction(robot centric) and the other stick controls how big your turn is. I find that tank is really good for long distances because you keep your smallest side going through holes in the defense.

Re: Mecanum vs. Swerve Drive
 

"Tank" has two common (and different) meanings here on CD.

1) An operator interface which uses 2 separate operator inputs (usually the Y axes of 2 joysticks), one of which controls the left wheels and the other controls the right wheels, in a skid-steer manner.

2) A skid-steer drivetrain wherein none of the wheels are steerable, and where the left wheels have a common power source and and are separately controllable from the right wheels which also have a common power source.

Note that a Tank operator interface (definition 1) could be used to control not only a Tank drivetrain but also a mecanum or swerve drivetrain.

Also, a Tank drivetrain (definition 2) can be controlled not only by a Tank operator interface but also by an Arcade operator interface or any other operator interface which does not require strafing.

So it helps to be specific when using the word "tank".

Re: Mecanum vs. Swerve Drive
 

I understand the whole crab movement + cheesy drive turning thing--intriguing--but I don't see how you have chassis orientation. Where would my fingers move to do this? (Note we lead with a corner after disengaging.) ...And sorry this is a "mecanum & swerve" discussion rather an a "mecanum vs swerve" one.


If "tank" just denotes a specific side you're driving with*, and mechanically that side is arbitrary in any holonomic, what does it mean that tank is "much better over long distances"? (Better than what?) And what is it about swerve that you're "switching" to sometimes?


*Ether - yeah, but I get the feeling we're not talking about either of those. Headscratch.