I’m rather more positive on mecanum than a lot of people – in 2010 we were undefeated #1 seed with a mecanum drive at Finger Lakes; they don’t have the terrible problems with bumps and ramps that the naysayers always seem to say they do, with the libraries they’re quite easy to program, and kids almost don’t need practice because they control exactly like a first-person shooter (I can’t tell you the number of times I’ve told a kid “it’s like COD or Fallout–one stick turns, the other moves” and watched them maneuver like a champion right out of the gate…
And all that said, looking at this game I can’t imagine why you’d choose mecanum. Except for the exchange your targets are huge, and if you do have to traverse the field (and I’m not convinced that for the most part robots will have to traverse the field) you’ve got bottlenecks you’re going to want to push through.
We’ve very successfully implemented octocanum in the past, and if that’s what my team chooses for this game I’m going to slap my forehead and roll my eyes, hard. If there was ever a game where some kind of tank drive is more than sufficient, this is it.
The decision of mecanum vs anything else comes down to your strategic decisions. If you want to make a maneuverable robot and plan to practice evasive driving, then it wouldn’t be a bad choice, but my team never chooses mecanum due to the fact that our strategies rarely call for such a system, and the (unfortunate) stigma that those drive trains get is also preventative.
Some food for thought may be this: does your climbing strategy account for the possibility of ramp robots? If there are ramp robots in your competition, how well would you be able to accommodate driving up a slope to reach climbing height, or are you going to opt out of your alliance member’s offer and choose a different way to finish the match?
It’s really boils down to strategy (both in-match and in-season scheduling) and your team’s capabilities.
The VersaChassis system is so easy to use and so good that we see little reason to use anything else.
Maneuverability of 6WD vs mecanum isn’t much different. Drivers with practice can hit their spots on the field with a 6WD just fine. Mecanum gives the driver a margin for error since they can strafe to get aligned if they miss, but a well practiced driver doesn’t benefit much from that. At that point, you’re sacrificing traction and power for little benefit.
Mecanums need the right game. We were an alliance captain for 2008 Overdrive due to them. Also ranked 5th to last in 2010 Breakaway and got chosen for an alliance since we showed we could successfully defend against two shooters through agility and speed with a practiced driver. Mecanums aren’t for this year’s game.
I take the philosophy if you are getting caught on a mecanum you are doing it wrong. The drive training I had students do on mecanum was taken from defensive driving courses I took/researched that had an emphasis on avoiding and minimizing hits. I also wanted to do an activity that involved learning how to “riposte” where you get hit on the side of a mecanum and use the momentum from the hit to redirect or roll out and away from a pin (bumpers that are pentagonal or hexagonal really help here). Scoring wise we ran activities that involved re-orienting yourself while traveling in a direction so on arrival of an objective we were ready to perform the required action. But one of the biggest benefits in my mind is that mecanum has is the ability to align a superstructure while moving without adding a turret. Resource wise that means more motors for other tasks which can make a huge difference when a team doesn’t have a large amount of income. From my experience I also generally don’t see teams practice with mecanum in mind cause they never take them seriously.
I dunno in the end I’m stubborn when it comes to considering all options . That and my favorite drive base is butterfly.
Yes, people should have good reasons for what they pick. pfreivald clearly is speaking from a position of experience regarding mecanums. Whether you agree with him or no, you can respect his decision and thought processes and I would not discount picking their team if they were to use mecanums. Unfortunately, in many cases, the teams want to choose mecanum because it is cool, because 1986, or some other prominent team did it and they clearly did not analyze, in detail, the advantages and disadvantages of mecanum beyond “it allows your robot to move sideways”. In such cases, I would want to DNP the team (or put them toward the bottom of the list) because they are likely to have used the same faulty decision making process in developing the rest of the robot.
Having run both mechanum and 6 wheel in competition… Mechanums are much more maneuverable in precise positioning like picking up and dropping off in feeder stations, or aiming for shooting. Unless you are really good, six wheel has an big advantage for defense. Generally team captions and first pick are primarily offense. 2nd pick are generally primarily defense or ramp anchors. If you are not an alliance captain or 1 st pick quality then the disadvantage in defense will hurt you in pickabilty. The power house teams are going to pick based on performance and the robot’s fit in their strategy, not on what type drive you are running.
Then there are teams like ours (or maybe we are the only one), who have never done anything but mecanum (for 8-9 years so far), and just don’t have the time or resources to try something new (for the programmers, builders and drivers). We have never been pushed around much, because our drivers know how to drive mecanum. We successfully dealt with the slick bridges in 2012, and the slick batter in 2016 (we had difficulty because our robot was a little wide to fit easily - oops, but that wasn’t a mecanum issue). We did actually have an issue with the little bump around the secret passage in 2016 because we used large, somewhat fragile wheels to get over the obstacles that year, but we always seem to get picked at an appropriate time given the overall capabilities of our robot, without any obvious disadvantage for being mecanum-driven. Maybe this is because other things bring us down before the analysis gets to our drivetrain, or because the other teams actually see that we know how to work with the characteristics of a mecanum drive. I dunno.
But a couple of things that can’t be ignored are that learning to program and drive mecanum well will most likely take a substantial amount of time (probably more than one season, for most teams), and the robot will be subject to more vibration overall, and definitely when going over bumps - which may cause problems with electrical and mechanical connections. So I’d agree that if there isn’t any advantage for it in the game, there would be no point to switch TO mecanum. But the analysis comes out differently for teams that have already invested the time and work to use mecanum, and would be switching FROM it. I’d urge the “pickers” out there to not sell a robot short JUST because it has mecanum - scout and determine how well the team uses it, whether they actually do get pushed around, etc. before moving them up or down on your list.
Our team has used mecanums for every year except Stronghold (2013 rookies) but we have already decided against them for this season because of how much power they consume. Strafing with mecanums chews up a ton of your battery power, last year we barely had the power to climb at the end of the match and we were fully unable to strafe by the end.
I feel like that is a design issue more the a concept issue. It shouldn’t use up much more power then any other drivetrain. Especially if you compare to a 6 cim 6wd.
This is answered by answering the following question:
What is your strategy?
Look at the trade offs between the 2 drive trains, take into account your teams skill and experiance with each drive train. That should drive your decision, not any opinion here on CD.
Our team switched out our drive train mid-competition at championships last year to avoid getting blacklisted/penalised for having mecanums. I’ve encountered multiple teams that will completely scratch you from their list because of your wheels. As much as I love holonomic drive trains, there are very few games where the advantage they provide is significant enough to outweight defensive drawbacks (e.g. 2015) and I don’t think this year is one of them.
What he means is that Mecanum is most efficient when it’s footprint is absolutely squared (not square but geometrically squared) and all four wheels are in contact with the floor. Which means you expect the centers of each wheel to coincide with a plane.
One way to think of mecanum is that it is a variable “land screw”. Think in terms of a naval screw (boat propeller) but on land. The wheels are subcomponents in a screw system and the floor is the “water” in naval terms or the “air” in aeronautical terms. If one of the wheels is not in contact with the floor it’s as if though you removed one screw from a two screw naval vessel. It’s not going to work as efficient.
He’s right in this regard, you do want to take care that each wheel center is at the corner of a planar rectangle. And all wheels should be as parallel to one another as possible. If it’s not it is still going to work just not as efficiently.
Though, I fundamentally disagree with the idea that mecanum is in any way bad if it’s not perfect.
