One of the top features my team wanted to implement this year was strafing, for easier autonomous alignment with scoring locations. We lack the budget for swerve, but are considering mecanum instead.
However, we are concerned that the mecanum wheels don’t have enough grip to get up onto the charging station (and/or not slide off at the end). Do you guys think mecanum is feasible this season, is more testing needed, or is it just wishful thinking?
linking this in, there has been a little discussion on this so far.
https://www.chiefdelphi.com/t/are-the-ramps-the-swerve-defeater/421072/21?u=skyehawk
https://www.chiefdelphi.com/t/are-the-ramps-the-swerve-defeater/421072/22?u=skyehawk
This is one of those questions that has two answers. First, it’s likely that mecanum drive will work just fine on the polycarb surface of the Charging Station and you’d be able to power up it well enough that it wouldn’t be a problem. Using mecanum wheels with softer rollers (like the rubber rollers of the Vex versions) will help in this regard. Second, since there will be defense this year, using mecanum drive will be a serious disadvantage to your chances to be picked by an alliance. It’s not so much that mecanums can’t deal with defense if properly powered (though they’re never as good as a tank, WC or swerve drive), but that most teams will dismiss you as an alliance partner almost automatically if you use a mecanum drive. It’s not necessarily fair, but it’s still true in many cases.
If you do choose to be a robot that only place cones and cubes on the Grid and stays within your community, I actually could see mecanum working out. Another team (WCD, Swerve, etc.) could run to the other side to pick up pieces then you could put them on the Grid. Ultimately up to you how you want to play the game though.
What about the viability of mecanum this year? Any ideas how mecanum wheels would fare on the polycarbonate?
Probably best suited for its own thread, so we can get that going if more conversation on that is desired.
In 2012 mecanum was common. With regard to plastic surfaces (key and bridges) they didn’t really have many issues. (Keeping in mind the bridges did have an aluminum lip on the edge to help keep robots on, this is a whole 'nother can of worms with regard to climbing, but that was 2012 specific)
In 2015 (no inter alliance contact) mecanum was common too. The scoring platforms had ramps that were at ~10°
Gotcha. I was going to make another thread but it seemed semi-appropriate to slip this in. I figured with the strong restrictions on defense and mechanical complexity of swerve, mecanum would be an attractive solution (it is to us, but we were worried about it slipping on the plastic). Thanks!
Feel free to make another thread and link ur original post.
You will want to pay attention to the durometer of the rollers on the mecanum wheel some will work better than others and really make sure they are in good shape at comp (have spares and know how /practice swapping quickly)
I remember at least one mecanum team in 2012 act like a stumbling ice skater trying to get up the ramp. It was a struggle.
It was over a decade ago (!) and I may be skewed towards one specific robot (very good shooter that really struggled on the ramps) but I thought mecanums had enough issues that I’d be hesitant to use them this year.
In Rebound Rumble we ran octocanum and had no issue driving up the bridges with either 6" Mecanum or ridiculously geared down traction wheels. The traction wheels stayed put better, of course, but the drive up was fine either way.
I don’t see why any modern swerve with sufficient clearance would have a problem with the charging station, and they can turn the pods to form an X to stay put.
we did ok on the ramps with mecanum in 2012. but I still probably wouldnt this year because you have to go cross field to collect the game pieces, so you need a faster sprint time. our team loves mecanum, like a lot, but even we all agreed immediately that it was a no this year.
We did a test on this earlier today. Just a 4’x4’ ramp at 15 degrees, plywood covered by polycarb. Our old mecanum robot could get up the ramp fine, but had difficulties drifting side to side and turning while on the ramp. Obviously, not a perfect test, but it could indicate issues controlling the robot while trying to get the ramp balanced.
I’m confused here, do you not gear your mecanum drive for high speeds? If not, you are missing out on the main benefit of mecanum over a simpler tank drive, i.e. maneuverability.
*Not to say that mecanum is more maneuverable than tank in practice, but at least in theory that’s the only reason to choose mecanum over a tank drive.
well now were double guessing ourselves so thanks for that 
I think our main concern is the charging station since you get points for it in auto.
it won’t be hard to balance manually during teleop, but during auto a tank would be way easier to balance
Mecanum is quite obviously more maneuverable than tank in practice, unless a tank lined up almost where it needs to be can slide 6" sideways.
Okay, this got split into its own thread, rather than the tangent off the swerve discussion that I’d replied to, so I guess I’ll go all in on an unpopular opinion:
Mecanum isn’t nearly as good as swerve in an objective sense, but it might well be better than a Kitbot/tank/WCD for this game. If you don’t have the money/expertise/experience/confidence to go swerve this season, mecanum could be a great choice.
Yes, you’ll be at 71% torque. Yes, that’ll slow your acceleration and make you more vulnerable to direct-pushing defense. No, neither of those things are desirable. Absolutely not, you should not go all-in on swerve if you haven’t already gotten it under your belt in the off-season.
A well-driven, robust tank drive will beat the pants off of a mediocre swerve this year. You need precision, and a swerve that kind of gets you there is a swerve that doesn’t get you there. If you’re not confident in your drive train options, please strongly consider using the Kitbot. It’s pretty great.
But given the narrow lane of the Community that’s protected from defense and a robot that has to be pretty precise to place cones and cubes, lateral motion looks extremely handy when it comes to scoring. If on a team where swerve isn’t a good option for whatever reason, I’d strongly consider mecanum or maybe H drive. Either one can be programmed as a tank drive for auto if you have to, and gives you that extra lateral maneuverability when you need it.
Personally, as a team that is pretty confident we can pull off swerve this season, it’s a no-brainier. If you’re sure you can do that, do that.
But if you aren’t sure you can do that, don’t ignore mecanum or H just because it has downsides… EVERYTHING has downsides! Add them to your decision matrix and see if they land in the “we’ll probably win more games” spot when all is said and done.
Side note: In the “you only get four CIMs” era we successfully implemented octocanum a couple of times and absolutely loved it, and between anticipated defense and the challenges of the CHARGE STATION, if we didn’t think we could do swerve we’d absolutely do octocanum again, inefficiencies and weight be damned.
In theory, absolutely. In practice, it is highly dependent on how well constructed it is and how well practiced your driver is. A well constructed robot with a well practiced driver will be more maneuverable in the majority of situations, regardless of whether you use tank or mecanum drive. And since it is far easier and faster to build a robust tank drive, they end up with superior maneuverability in practice more often than not.
But it’s NOT far easier to build a robust tank drive.
People talk about mecanum like it’s difficult to build, and that’s just not true. Four identical gear boxes and four wheels, done.
The code for “drives like a tank but can strafe, so it works like a first person shooter” is so easy I can do it (and I’m really terrible at code).
Every time I see “building mecanum is hard,” I can only assume that the person saying so has never done it. It’s about as easy as any FRC-related task gets.
As a team that’s built mecanum a number of times, that’s the basics… but that does not equal a well constructed mecanum robot. A poorly constructed chassis may not have equal engagement with the carpet for each wheel, leading to poor control. An unbalanced robot, with a poor cg, will see more weight on 2 of the wheels than the others, which can also lead to poor control.
Yes, putting the gearboxes, motors, and wheels on is simple. But getting everything working properly together so it drives well isn’t as simple.