Our team is considering several options for this game, but one that is being advocated is a strategy and design of using a mecanum drivetrain in combination with a low goal scoring dumper that would require getting to the fender and dumping two cargo at a time into the low HUB
Our situation is:
we have gone from a fairly high achieving team to a lower resource team this year due to turnover in students and mentor capability
we have had success with mecanum in 2019 (playoffs at worlds) but also felt the pain of heavy defense at higher levels…uncertain how that would play out in this game
we are trying to keep our design and build simple yet still be capable of competing at a high level. Building a shooter with and indexer and floor intake is perhaps beyond our capability this year. Our goals for Autonomous are pretty basic as well. (1 ball and taxi)
as we compete in Ontario, the season is uncertain…we are signed up for two regionals, we may not be permitted to travel to provincials if qualified and worlds is not an option, so competition this year doesn’t go very far anyway…competition level will not be as high as typical years
So what are the thoughts on this strategy/design? I think it is either genius or a disaster in the making. Not sure if defender would come after this robot as it would be an easy target or would they just leave us alone and defend a more high scoring upper HUB shooter?
In my limited experience, I have yet to see a Mecanum drivetrain that would have performed worse with a standard WCD.
I don’t see any reason this year, the lower hub is a circle, there is no “lining up” like 2019, and for the low goal you just make a beeline for the hub.
This is my opinion though, and obviously it seems like you are more experienced.
Based on your self evaluation I think you would be better served with using the kitbot chassis in standard configuration, and going with the low goal, and the low or mid rung in the hangar. Build quickly and get as much driving practice as possible!
It seems that this post in the other thread about mecanum drive may be very applicable to your team’s situation.
With the situation the way it is in Ontario now and for the foreseeable future, it might make sense for your team to focus on having fun and learning something during this competition season. There is no guarantee that you will be able to meet in the off-season to do the learning that many people will tell you to do before using something new in the competition season.
If you do happen to choose to go with mecanum drive for the fun/education aspect and if you can afford it, I would suggest making your bot a hot rod by installing 2 motors on each gearbox. A dumper mechanism should not require much power so you can dedicate all 8 of the 40A ports on the old PDP to the drivetrain. That will change the game with regard to playing defense and having defense played on you. And it would be fun
I have a sense that this year’s game will have defense similar to 2014, where there is little to no line between offense and defense. Mecanum drives often get bullied under defense, being pushed easily. The reason teams go for omnidirectional drives are the agility it gives them, so if you were to go with one you’d need to practice getting around defense instead of through. A well driven tank drive can get around almost as well as a swerve drive and push through defense at a comparable level. So if you are going for competitiveness, I would go for the Kitbot like others have suggested and practice like heck. If this is going to be a more educational year, go for the mecanums and learn as much as you can with them.
A smart alliance plays defense against the bot that would cause the greatest loss in points for their alliance. As an example, say you have a bot with an offensive rating of 10 and one with 8 when undefended. When defended, 10 becomes a 8 but the 8 becomes a 6. By this logic, you want to defend the original 8 because the overall alliance offensive rating is lower in that configuration (10 + 6 = 16) over the other one (9 + 8 = 17). It can seem counterintuitive to leave the best bot undefended, but you have to consider the entire alliance. Karthik talks to this point in his Effective FIRST Strategies presentation. Here’s a clip of him answering an audience question about this. IMO a mecanum drive is historically worse under defense and therefore more likely to be defended.
One important consideration for meccanums this year is some of the small lips in the field. I would doubt that they would handle well going up the floor protector by the hangar zone or over the cable protector in the middle of the field.
We had few problems bottoming out with 6 inch mecanum last year. We were in the center a lot, and the only time we had any issues were when we hit the crossbeams such that all 4 wheels were crossing the bars at once. If we did that wrong, the robot chassis bottomed out on the pole (we used the Kitbot chassis and our bumpers hung too low).
This year’s protector is lower and ramped a bit. I am relatively certain this would not be an issue.
Workable mecanum is pretty niche, and I don’t see anything this year that screams mecanum. Asking for information - what made you think that mecanum would be specifically useful this year?
I’ll be a little more optimistic than some in here, in that the corrals create some protection not unlike the dividers at the airship in 2017. And, obviously, you have some past history with this style of drivetrain.
Two big questions:
How much of the old knowledge and reference material do you have? Looking at old code and implementations of it on robots is always beneficial.
Do you have your 2022-intent mecanum wheels in-hand, right now?
If those aren’t “quite a bit” and “yes”, I’d use the drive base kit in bone stock form. But if they are, I don’t think it’s a crime to explore it.
One positive I see for mecanum this year is that over the past few years, lining up a climb has been difficult. Last year in particular, I saw many climbs missed because the skid steer was difficult to maneuver the way the climber needs.
Thanks to everyone for all of the great feedback so far.
This was my first post of CD and it has been helpful.
To answer some of the questions asked:
we have good code references and resources from previous years. We also have material on hand
our thoughts on WHY mecanum are as follows:
/ better ability to line up and manuover for climb…we think that area is going to be tight and chaotic
/ better ability to chase down cargo. we struggled in 2020 positioning our intake accurately to pick up power cells with tank drive, especially when they were up against a wall or other obstacle which we see as THE major challenge in this game
/ we like the idea of scoring low, being able to stay facing the HUB and picking up returned cargo as they roll out the low HUB returns, then scoring them again
Based on some more thinking and the responses on here, I think I am now leaning towards a tank drive option…thinking that the risks of mecanum do not outweigh the potential rewards.
I have to agree with others. If you don’t feel you have limited resources enough to not shoot the high goal, then it seems unwise to spend additional resources on mecanum drive.
Additionally mecanum will handicap your ability to play defense. Especially as a low shooter, you will likely be unable to keep up in scoring with high shooters at a certain point (depending how good you are that could be districts or worlds). SO, if you proceed down this mecanum path, how will you play defense? It is not impossible, you just have to have a good plan and choose the right robot to perform the plan on. If there is a hub shooting robot you can stay between them and the hub, they are able to push you, but you work to stay between them and the hub, ruining there game. If you choose the robot that can shoot from anywhere, there is likely little you can do other than steal balls (which may work out to be a valid strategy).
For 1, I agree it will get crowded , esp. during eliminations. However, there is more difficulty in finding the right spot left to right due to visibility than due to maneuverability. If you want to go sideways for the climb, putting a trolley on your hook so you can get out of the way sounds like a good plan, after you get all the basics working.
For 2, this is a big contributor to the popularity of horizontal floor pickups that span essentially the entire robot width. Using vectored (mecanum) wheels at the ends or having a funnel behind will bring cargo to center.
For 3, watch out for G302. In any case, how do you expect to know which of the four lower exits the cargo will use?
