Due to a lack of access to Swerve modules etc, Mecanum is a more accesible drivetrain for teams looking to have omniridectional drive. Since current Swerve modules take 8 motors, would a 8 motor Mecanum have in theory more frontal acceleration and torque? while having slower lateral movement? What are your thoughts on this approach?
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It would have the same effect as adding another set of motors to a 4-wheel mecanum drive of the same dimensions. The friction forces would be the same.
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Keep in mind that while mecanum grants access to omnidirectional drive, the low friction rollers are also more prone to the slightest defense if you’re comparing it to swerve.
Theory is a nice place. I’d like to live there sometime. But in seriousness, yes. Driving forward, theoretically a swerve will have the same speed as a normal drivetrain. I remember that Ether, one of the first to derive the swerve kinematics here on Chief publically and post the information would often argue for people to prove that swerve theoretically wouldn’t be just as good.
But when the rubber meets the road (bum-da-bum-tish)… mecanum have simply never lived up to their promise, and regardless of your implementation will quickly end you up on a lot of people’s do-no-pick lists.
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In my experience pick up lists are made mainly out of actual performance than out of drivetrain type.
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If a mecanum robot it good it ends up being an alliance captain. They tend to be poor 2nd picks because often the 2nd pick robot is being chosen for its defensive qualities. If you think of mecanum as a “poor person’s swerve” then the higher resource teams are going to run swerve rather than mecanum.
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As a team that has run mecanum drives in the past, I can tell you that much of what has been said is true, but with some caveats. First, you are going to get teams that will not pick you regardless of performance because you have a mecanum drive. We had this problem for Deep Space, despite having an excellent robot. Second, adding motors will technically increase your drive’s power, but it does, indeed, depend on the friction between wheels and floor. What that means is, you need to choose the mecanum wheels carefully. The flatter, bigger, and wider the rollers, the more floor contact you get and thus the more traction you have. It will never be the equivalent of a solid wheel, but you can overcome some of the deficiency by good wheel selection. For instance, using 8" mecanums over 6" ones will give you about another 1 1/2" of roller width, which translates into more contact and thus more traction. Finally, gearing them properly is important. Don’t expect blazing speed from them under any circumstances. Turning them faster than they can keep their grip on the floor won’t really help, so don’t waste time on that.
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Team Titanium’s 2017 robot is a good example of mechanism done well. They ran 8 wheels, which I assume helps get more torque to the ground. Additionally they used FTC-Style idler wheels for autonomous odometery.
But all of the above… Yes.
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They ran the same drivetrain in 2019… they got killed by defense.
I watched a couple of their matches and they were driving their mec bot like a 6wd bot in which you lose all the advantages of mecanum but only have the disadvantages.
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Idler wheels became popular in FTC in approximately ~2018-2020, about a year or three after 1986’s 2017 run.
They did it before it was cool 
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We ran Vex Omni wheels for odometry / wheel slip detection in 2009 and were far from the only one.
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Same. Ours were on a strip of lexan to hold them in contact with the ground
And in '17 they made Einstein finals with partners who also had mecanum and all-omni drives .
You can make the claim that “this drivetrain setup is more defendable than that one” but you should really be thinking about if it matters for that years game.
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One step more detailed: Does the benefit of maneuverability outweigh the cost of being more easily defended, in the context of the game, the rest of the robot, and the team’s strategy?
Especially with newer or more inexperienced teams, it is common to shortcut this discussion and simply jump to “nope, don’t use Mecanum”. This is a almost-always valid shortcut. However, it doesn’t justify not having the conversation, or making unilateral statements about how Mecanum should never be used for drivetrains.
That’s true. I didn’t say anything about whether mecanum was a bad design decision; frankly, I wish my team had done it certain years. But I’m just stating what I saw happen at the regional I saw them play at. I also did not state any cause/effect relationship between running mecanum and getting beaten by defense, I only stated a correlation, and I’m not qualified to say that was the cause given my limited experience; part of it was that the other alliance had probably the best defense bot at the competition.
I did not compare the drivetrain to any other drivetrain either. I never made the claim you suggested I made.
If you are going to say something negative but unrelated to my post, please, don’t reply to my post, and instead reply to the thread. But I have a feeling it was targeted at my post, in which case you should have actually read my post and understood that’s not what I meant.
I personally think mechanums totally have a place in FRC
Theoretically, if you are using mecanums you should be able to maneuver around defense instead of trying to push against it, at least I think that’s the whole point behind it anyways. I think mecanums have their place and if your drivers are able to take full advantage what its capable of, I think it can be as much as 80% as what swerve can be.
I would gear the wheels very tall as well so that the robot has a higher top speed and be able to spin the wheels quicker to strafe quickly since you can’t use the extra torque pushing anyways.
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Motor count is not the only factor in acceleration and torque, and in the brushless era it is very easy to argue that it isn’t even the most important factor.
In short, with mecanum wheels you are going to be limited by traction (in any direction) before you are limited by motor power. It is hard to imagine a mecanum application where the extra 4 motors would produce any tangible benefit.
The best way to improve the performance of mecanum wheels is to control slip. This can be done through a number of different approaches, ranging from software / sensor odometry, to incorporating multiple wheels, to suspension systems, etc. This hugely neglected aspect of mecanum drives is IMO the main reason they get a bad rap.
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Made a slight tweak but I agree with all of Chris’s points. With regards to slip, I’ve seen some pretty interesting work in locking the rollers both in FTC and FRC.