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?
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 :] .
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.
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.
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.
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.
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.
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:
Eliminate robots likely to be bad at pushing (such as mecanums or omnis)
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?