I’m less concerned about being pushed by defense this year as I am with trying drive a mecanum robot over the wire conduits on the field this year. I don’t think you could strafe over those bumps on any mecanum wheels under 8".
TANK VS MECANUM VS SWERVE DRIVES.
I am a passive mentor on the (a team…254 deserves equally weighted credit here), that helped pioneer WCD long before I came along (I have since mainly transitioned to a FIRST Field volunteer, with less input than originally toward my team, always wishing to take more of a leadership role, but contribute today in a different manner). I’ll never quit attempting to contribute in the process of design, build, and implementation.
I have seen the team only transition to a mecanum drive 1 time so far since I came along with much better than fair results, as all the rest were a form of WCD. Recycle Rush, which happened to have a lot of the same field elements, low poly ramps to traverse. A FIELD literally cut in half, fast stealing of LIMITED high volume game pcs, pick up and delivery, etc.
So, I looked at game play strategy, looking backwards from Einstein to robot design. Taking into account the built in prejudice against mecanum drives seen here in CD, which does transfer to alliance picks right or wrong, added those 4 very low easy to traverse beautiful smooth transition profiles this year of those 4 cable runs to and from the scale and switches. Pics of the field with them taped down to the carpet of the Manchester reveal field are posted here in CD already…I urge everyone to study then closely as they appear to be a lot less of an issue in my mind today than yesterday morning during the reveal.
ADDED IN Knowing our 1 step out to mecanum dealing with almost identical profile same type material ramps, minus that bothersome seam tape at the top of each platform ramp(s)…(Thank you Frank and Company on the GDC in advance for eliminating that top seam tape and all that no doubt ensuing nasty retaping and maint. work is now gone!) And, understanding our history, that we played in Sub division playoffs for the first time I have been with the team, since my 2011 join date, using a non WCD mecanum chassis.
I won’t rewrite my book on my imaginary robot, as it is posted elsewhere here in a “Switch or Scale” thread…Swerve drive with soft aired pnumatic tires thank you. I want to strafe and steal cubes fast, avoid robot to robot contact, but be able to push and not be pushed if necessary…and I anticpate huge choke points and a zone strategy, that will often go haywire due to opposition, both planned and unplanned.
But, you (and your team), must decide simply based on your specific game play strategy. If you do, then the rest (along with a ton of hard work), will take care of itself.
I learned here on CD a few years back (from a number of very wise very repeatedly succesful few participants). To parse the game and rules first, then look backwards. “What 3 robots will win Einstein, then decide which of those 3 robot designs you wish to build.”
“Then, AND ONLY THEN…design & build that bot well and fast, practice, practice, practice…then cheescake all those willing you play with, to get there.”
My imaginary robots on kickoff plus day 1 have worked tremendously well ever since…practical application in real life on a team perspective, not so well.
Mastering the dark tunnel of turning theory into reality is THE REALLY HARD PART.
“One step back, two steps forward.” TY FIRST Founder and Inventor Dean Kamen.
THERE are just more than 2 types of drive choices. There was once long ago a point in time where WCD type tank drive did not even exist. WILL you be the one to invent a new type this year? 4 wheels or 6…8 you say? A mix of wheel materials and types on the same robot? Only your imagination at this point and a ton of convincing others, a bit of but, not too much prototyping please! There is a time that prototyping stops, attempted convincing must end, acceptance of design type, and production must begin…so that practice begins sooner rather than later. AND a bagged working bot (and possibly a very fine tuned duplicate), is ready come that unbagging at the first event and you hit the field running.
That being cued up for your first practice match is critical. It is usually the difference between a great season and disappointment.
Good “Power Up” Luck teams in FIRST FRC 2018 season! HAMMER THE BOSS…wherever, and whatever he or she is!
“CHUTE DOOR?” is now Chute Ram? Lol Who will be the first to post that question on the Q & A and take a trip back in time?
After some time today, we decided to go with tank because of its superior defensive ability. As pointed out, the switches and scales are big so precise movement is not all too important and the pros outway the cons of tank drive.
I would say that, for most teams, the question is: How many of our systems do we want to go into uncharted territory with? Furthermore, I would say that a tank drive will never be the wrong decision for an FRC robot. Could there be better options? That’s up for debate, but a tank drive is Ole’ Reliable. Tank drive is home.
If you have never done a mecanum drive before, either in a previous season or the offseason, then maybe building a tank drive you know how to build (the kitbot even comes with instructions!) frees up your time to develop the other mechanisms for your robot. On the other hand, if you’re experienced with the drive and like what you get with it, then go ahead and do what your team is comfortable with. So, it it worth it for your team to develop a new drivetrain in season, or would your manipulator/programmers/something else benefit more from that time?
Do keep in mind that there are lots of teams that are frequently in picking positions at events, that will factor in your mecanum wheels negatively when making picklists. More practically, one of the major elements of scoring requires you to drive on a slanted, slippery plastic surface. These are facts.
I would never do a mecanum drive on any FRC robot in any year (Recycle Rush doesn’t count), because tank drive just works. You can do tank drive, and then spend more time doing something else. Chances are you have another tank drive robot already, so theoretically, your drivers could start practicing now. Some teams will be successful with mecanums, and others will not. The same can be said for tank drive. The bottom line is you need a dependable drivetrain, so if you know you can make a tank drive that works, just do it and move on.
As someone who tends to like holonomic drive trains, I agree with this sentence SO HARD.
It is so weird to see people study EVERYTHING else on the robot so precisely and come up with some amazing new innovations, but then have the vast majority (not everyone thankfully) think that there is no need to do anything but 6wd.
I always treat a drivetrain like it has stat bars from a video game. 6wd is equivalent to default settings. I for some reason never want to play with default settings. So much so that I actively resist 6wd because people pick it without reasons.
I want people to have reasons for what they pick!
As a scouting mentor, I am generally helping my students build an alliance to execute and/or withstand defense and mecanum does not make itself particularly helpful for executing such an objective. Mecanum drives are easily pushed around during precise movement (such as placing/acquiring game pieces) and traversing narrow parts of the field, which are major requirements of both Power Up and Steamworks.
While mecanum provides small gains in maneuverability, with enough practice, a tank drive is not much less effective at mobility but is SO MUCH better under aggressive defense. I don’t want to pick a robot with such a blatant Achilles’ heel.
The exception is if I’m a 6/7/8 alliance captain with tough odds in quarterfinals. Then, I’d be much more willing to take on risk with the chance of getting lucky and pulling off the upset. But I would advise against aiming to be someone’s desperate high-variance pick.
The location of the null zones creates choke points which are the ideal places to play robot to robot defense. In previous years taking time to play defense usually took away from some offensive potential. If your alliance has control of the scale or your alliance partners are in the process of taking it back, playing man defense is a valuable use of your time.
Do you think a 2+2 drivetrain similar to what 971 used last year will work?
There’s more to drive train choices than how much on-field advantage it has in any given game over a simple 6wd. And there’s more to teams that consistently win regionals saying on CD that they will not select a mecanum for eliminations. It’s cool if your team wants to do mecanum for reasons, like, it’s fun and looks cool. Just don’t be surprised and disappointed when the alliance captains pick someone who is ranked lower than you.
Playing man defense does nothing to stop your opponent scoring if they are in control of the switch/scale. Only adding cubes will stop that, if you play defense when the opponents are in control, you put yourself at a 2-3 Advantage in scoring ability
These are fine points.
The crux is that unless you have built a omni drive of any sorts then the severity of the flaws or gains you mention have no value to them. Just like prototypes of everything else you need to actually see both sides of the story to be able collect data. You can blame a lot of flaws on both systems to design, code, driver, etc. and not the actual drivetrain concept itself.
Most people assume you get thrown around the field like a puck on ice. Which is not true. Yes you lose pushing matches in the long run. But how many head on head pushing matches have you seen in FIRST? (ones that had a win/lose purpose to them) You can still play defense and you can still fight back against someone playing defense on you. An onmi bot that t-bones a 6wd in open field will “pin” them. a 6wd that t-bones an omni in open field just has the omni drive away. Those t-bones hits are the most common thing to happen in FIRST.
You mention “small gains” in maneuverability. If built with the same level of detail people build 6wd, again, Not True. The difference in agility is huge. You have a whole extra axis of travel to work with.
At the end of the day, both drivetrains are INCREDIBLY valid choices. Its just up to the team to get the most value out of them.
If the opponent has control and your alliances rate of scoring cubes is less than or equal to your opponents, then you will never catch up and need to find another way to win. Either you forfeit the scale and try to make it up elsewhere or you play defense in hopes that your alliance can tip the scale.
im just curious to know much of a penalty most teams associate with a mecanum drive, even one that is more effective than other teams with tank drive robots
Gear down to speed up.
Really… in FRC speed isn’t about peak velocity, but rather how long it takes you to go from being stopped at one position to being stopped at another position.
You need to be traveling a fairly long distance before you’re able to reach and sustain your peak velocity. Up until that point having greater acceleration is more important than having a higher peak velocity.
Play around with some of the drivetrain simulations available in the white papers here on CD and you’ll hopefully find an optimal gear ratio to match your wheel diameter. You may also find a low geared robot to be more maneuverable… fast is good, but perhaps quick is better!
Jason
We know the word on Mecanum from reading these threads, personally they don’t enter into a decision of who we like or don’t as much to partner with. On our team the Mecanum discussion happens then we move on each year to else.
Not that we won’t ever use it but there has to be a solid reason too. I have seen good Mecanum so I know it can be good.
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.
People were saying the exact same.things last year and I saw tons of mecanum bots that were way more effective at putting gears on than our wcd.
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.
By the way, this is another longstanding myth about mecanum wheels (Myth being mecanum wheels don’t work well on ramps)
From past team experience, ramps haven’t bothered mecanum wheels:
2006 - 868 used mecanum wheels to climb up the diamond plate ramps (which were very steep, around 30 degrees if I recall correctly)
2010 - 868 used mecanum wheels to traverse the carpeted bumps (which were also very steep, around 45 degrees if I recall correctly)
2012 - 868 used mecanum wheels to climb and balance on the polycarb? teeter totters.
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.