Mecanum drive system

My team is looking at a mecanum drive system this year. We still have a few big questions if we are to do it, specifically, what size wheels would be best? Any tips for a team potentially doing one?

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Just, Don’t…

Not seeing the real benefit of any stand alone holonomic drive for this year…

Read this before deciding on mecanum.

Aloha!

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You will find people on this forumn would ban the word mecanum if they could. PM me if you want some actual help.

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While there are valid reasons to be hesitant to use a mecanum drive on a FRC robot, I don’t think the sort of replies seen above are particularly helpful. Mecanum is not nearly so indefensible as the Chief Delphi “ugh mecanum” meme makes it out to be, and there are certainly valid reasons to use a holonomic drive this year (hatch placement does not have that much lateral tolerance…).

That said, mecanum is a surprisingly subtle (not necessarily difficult, but subtle) drive to do well, especially in the lightning-fast modern FRC game where a 4-motor drive will have trouble providing the needed top speed without making it difficult to strafe without browning out the control system.

If you do decide to build a mecanum drive, you’ll want to take scrupulous care to ensure your wheels are evenly-weighted and all in contact with the ground. You will probably also want to look into gyro stabilization.

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Take a hard look at your strategy and make sure omni-directional movement is going to be used fully. Don’t do this because “driving sideways would be nice”.
If you decide to do so make sure you balance weight distribution of your robot with and without game pieces and get plenty of drive practice in. Mecanums don’t rely on pushing they rely on positioning so you want to have a “touch it own it mechanism” to make sure you never get pinned down while trying to grab a game piece. You always want to be flowing around the field in a smart manner. When we ran mecanum for recycle rush one drive practice started by removing the idea of having “the front of the robot” one activity focused heavily on driving to point a, arriving facing the proper direction for picking up a game piece and driving straight to point b rotating our orientation so we were facing the correct way on arrival. Then we worked on navigating obstacles while maintaining good orientations.
Since defense is a hot topic this year the basics are roll out of impacts using the pushing of an opposing robot to redirect your movement. Space yourself from surfaces you can get pinned to. Go through the rules and make sure you understand how to punish bad defensive plays like when you can turn a pushing match into a foul.

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YeAh MaN LeTs BaN mEcAnUmS /s smh

Considering the amount of times I see poor implementations of mecanums compared to good ones (I only need 1 finger for this one), its hard for me, and probably many others, to tell someone that doing so is a good idea, especially if its only for a little side movement to place the Hatch/Cargo. Doing some lateral movement with the game piece instead will be cheaper, easier, and could work better than trying to learn and implement mecanums for the first time during build season, something many people are very keen about not doing when it comes to most other drives.

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We have been using mecanum most years an might again this year. They are fine if you can mount them properly so all 4 wheels touch the ground flush. 8 inch will make you faster but they also pose challenges as they take up much more room. We never had the brown out problem on strafing. It does take a bit for the driver to get used to it as it isn’t natural to think about going sideways. But if you get that down you can get out of dangerous situation with strafing or going diagonally or slipping away. It does pay to have a well practiced driver so it might pay to build a practice skateboard to practice that. This year if we use them then we are going with 6 inch as they run smoother and get the speed from custom gear boxes.

Are you really surprised that you see poor implementations of mecanum when the response to requests for help is “Don’t do it.”?

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Can you be sure theres correlation between the two?

Considering most that ive seen are from teams that do not frequent CD/Reddit/Discord (or at least have a presence), I dont.

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Before my current team, my previous team used Mecanum for many years ( and has used them most years since I left)

I don’t think Mecanum is an always no drive train, that being said I have lowered teams on pick lists because of mecanum and I do know of teams who just won’t pick them. Basically if you are a “good” scoring robot and are in elims I am sending my defender to harrass you. If you are a “bad” scoring robot I am not going to pick you to be on my alliance because your drivetrain will lose most pushing matches. It is unfortunate but that is the bias.

I think others have echoed what I would say about being successful with mecanum and I hope your team does whats best for them.

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Mecanum drives can’t win pushing matches.

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Watch the yellow robot. It’s on mecanum wheels and can in fact win pushing matches. That being said, it is the exception and not the rule. But be careful when you say a definite can’t because there is usually proof against it. Now I personally agree that using a mecanum drive is usually not the best and we have been intentionally not chosen at champs because of having one. And I also don’t see a need for them in this game especially with the slippery surface on the platform.

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When my FTC team that I mentor was deciding on DT we decided that holonomic omnis (4 omnis at a 45° angle) and we didn’t have to worry about weight distribution. I’m not sure if that’s b/c the bot weighs < 20lbs or b/c omni drive doesn’t need weight distribution. Any way, one thing we noticed, a lot of teams drive like its tank, so if you use a holo drive, drive like it’s a holo drive.

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What about the programming a Mecanum drive is difficult?

Meh, I’m not sure of too much really that’s why I do strategy I can put off being wrong until way later in the season.
It just confuses me to see whats normally a very technical and helpful community shut down what is often a very common idea on the grounds of the robot “being pushed” and leaving the discussion there. Where other topics pros and cons would be weighed and a conversation would be had mecanum is always “no you can get pushed”. If it was my first post on a site and the question was “Hey how do I do this well?” and I was told “Don’t do it.” I wouldn’t frequent that site.

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While I agree that many threads are like this and dont do a lot to really say why, there have been a few this year that do at least add info on why it may be bad and/or offer other solutions, like GeeTwo’s post a couple days ago. (maybe people say the same thing cause this question comes up yearly, and the same answer usually applies?)

There are plenty of pros and cons to mecanum. We have used it in the past and have blue banners because of it. You should decide what your overall goals are. Mecanum robots with enough driver practice are great at lining up and are a nightmare to try to get around if they decide to try to defend you by being between you and where you need to be. We used AndyMark 8" HD mecanums that came with side rollers in 2013. Here is a video showing what our Mecanum was capable of. https://www.youtube.com/watch?v=Ogy65hEPIXk (we’re 2052, the short one with the flap)

The first part of this video focuses a little more on our pushing power, and the rest are clips from matches that really show off how we used mecanum to help us score.

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Its really funny when 6 or 8 wheel drives with omnis are so popular and omni wheels are more easily pushed than mecanums. A single pair of Colson wheels won’t turn a robot with omnis into a tank. Its going to be pushed around pretty easily.

There’s plenty of reasons to pick or not pick mecanum wheels but the “pushing around” argument is weak. Most FRC legal wheels are not going to provide nearly enough traction to resist a robot in motion contacting yours.

Pick what you think will work best with your strategy and engineering objectives.

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Nothing is difficult about programming a mecanum. WPIlib has a class. The only difference is that you should have a joystick that also has twist as besides X and Y you have also twist. And if you use the gyro like we do you in lets say autonomous you can kick the robot off path and it still gets there as it “Fixes” its trajectory. You should be able to see our old code on github as its public. Now this years code is going to be slightly different as we are switching to command based and the drive system is still a little open as we are still experimenting with a new one. So right now the Mecanums are a backup.

Fair warning: mecanum wheels are a lot heavier than other choices.