Swerve vs Wheeled Tank

[Pault]

I have to very strongly recommend against swerve if you aren't confident in your ability to build a tank drive. There are going to be years (like this year) where swerve just isn't a practical option for everybody that isn't team 16.* There are also going to be other years where swerve would technically work, but doesn't fit your strategy well and so you would be better off putting the resources elsewhere. But as long as the kitbot is a tank drive, FIRST is never going to design a game where you need an omni-directional drivetrain to be competitive.

* I think there were a couple of other robots that ran swerve. I'm not sure if any of them saw much success with it, though.

[ClockworkGold]

The offseason is a great time to test all of those seemingly crazy ideas you had during build season. I believe that the best thing you can make during the offseason is a tank drive for multiple reasons. One being that it is likely going to be your next drivetrain going on a competition field. Having a spare drivetrain allows you practice weeks 1-2 of build season, while having a spare for drivers practice. Want to build something else? You now have a somewhat realistic robot for mounting things. In the past few days, we have repaired our spare drivetrain so we can practice driving with our favorite style of drivetrain. This will lead us to making a manipulator, it being an arm, elevator, or whatever we want that fits. Use this project to catapult yourselves into a better position.

[JesseK]

There are a lot of concerns about swerve design.

What if the OP chooses to purchase COTS swerve modules from AM or 221 Robotics? Given the very long runway until the next season, do the opinions change?

[Andrew Schreiber]

Originally Posted by JesseK

There are a lot of concerns about swerve design.

What if the OP chooses to purchase COTS swerve modules from AM or 221 Robotics? Given the very long runway until the next season, do the opinions change?

My opinion of "it'd be better, competitively, to really nail a 6wd and drive the heck outta it" doesn't.

That being said, some folks aren't about maximizing competitiveness and are about doing something cool.

So, it's priorities - there's very few times in which a swerve is going to offset the cost (weight, money, complexity) from a competitive perspective but there's plenty of times in which it brings other benefits to your program as a whole.

[jeremylee]

Originally Posted by Andrew Schreiber

That being said, some folks aren't about maximizing competitiveness and are about doing something cool.

Some WCD additions that accomplish both:
2 speed (auto shift)
Current limiting
Path planning with encoders and gyro (Math and PID fun)
Vision assisted aiming
PTO
Octocanum

[Jonny_Jee]

1114 made a great Ppt. discussing different types of drivetrain designs.It might be worth a gander.

http://www.simbotics.org/files/pdf/drivetraindesign.pdf

[Jonny_Jee]

1114 has a great Ppt. discussing different styles of drive train designs. might be worth a gander.
http://www.simbotics.org/files/pdf/drivetraindesign.pdf

[Tom Bottiglieri]

Figure out how to make a wheeled tank drive robot as reliable as possible inside of your team's resources then move on to the next design challenge.

[EricH]

Originally Posted by carpedav000

Developing a motor-in-wheel swerve would be the most educational (IMO)

You weren't on 3928 in 2012, were you? Sounds like something they'd say.

(For anybody not familar with that reference, they were rookies that year, though they did have an experienced mentor whose robots in high school had a habit of using unusual--and preferably swerve--drivetrains... and built a motor-in-wheel swerve. Yep, a motor-in-wheel swerve as rookies.)

[pwnageNick]

As one of the biggest proponents of swerve out there, I would highly suggest you lock down a super sound tank drive before going near swerve.

Having a lot of resources in your shop isn't the biggest factor, but rather how many people you have to make all the parts you need, how much machining experience they have, and how much time you're willing to spend come build season on assembly and programming.

Our team locked down an incredibly solid 8WD that we were extremely happy with before we ever started with our swerve drives. It takes time, and in the end it can be one of the most effective drive systems, but you have to take steps towards it as others have said.

[carpedav000]

If you want tank and swerve maneuverability, I would look at a 624-style butterfly drive.

[Munchskull]

Having seen the resources required for good swerve I would recommend against it unless you have access to cnc. That said 2471 does have some amazing modules that were all manual machined.

My suggestion is if you really want swerve work towards that, master the machining over the summer and as time permits make modulesure till you have at least 3. Then give your programming team lots of time to play with them.

While doing this work on making a couple of tank drive designs, my personal favorites are WCD and ECD. Figure out how to master tank drive and you will always have an elegant drive train at you disposal.

[Clem1640]

We are a team that uses swerve as our default drive-train (all of our robots from 2010 through 2015 were swerve drive) and we love swerve drive.

That said, it's not suitable for all situations (we are not using swerve for Stronghold), whereas wheeled tank drive is. If you want a drive-train that you know you can use next year, focus on wheeled tank drive.

It also takes a lot of time and effort to get swerve working up to its full potential. This took us three years.

I would strongly recommend mastering wheeled tank drive before plunging into swerve. Swerve can be an awesome drive-train if it is executed well, but the advantage over tank is very game dependent. Poorly-executed swerve can be a disaster.

[Kevin Ray]

Originally Posted by asid61

I have always figured that if I didn't need to support the outside, I won't. WCD lets me use lightweight 2x1 aluminum tube is basically a box shape, whereas if I had to add a plate on the outside for support I would have to spend space and extra pounds while mounting it via spacers and bolts- not to mention the added machining time. Plus with WCD I can run chain-in-tube and save even more space. There's nothing wrong with a dead axle or outside support drivetrain, but I feel like WCD just offers more benefits than risks. I've never had issues with either drive when made properly.

To address the fact of chains-in-tube never failing, I'd ask 1477 Texas torque about their chain-in-tube issue. I seem to remember that they had issues; in the Alamo Regional between quarters and semi's they replaced themselves with a back-up 5754. As a result, At Utah they ended up spending all Thursday moving their chain OUTSIDE the aluminum tube. They did an amazingly quick change over and ended up being very competitive. I could have been misinformed, but I seem to remember that being the case.

Back to the OP's original topic though, we had a skilled CNC machine shop sponsor during Lunacy and attempted the swerve steering. All of the components were perfect, the problem was the chain management. The chains were of poor quality and kept stretching. The sprockets were not cut to the proper specs (Thanks to 118 mentors for pointing that out to us or we'd never have known). Between these two issues we wasted an entire regional making adjustments. In the end we did a complete drive train swap out to skid steer on Thursday of the following regional and made it to the division finals at the worlds.

So...with that being said, I would most definitely recommend staying with 8 wheel drop center skid steer. Yes, for teaching purposes, you'd have much more to learn with swerve steering, but you may end up with the unintended lessons of the less than optimal drive train difficulties associated with the swerve steer if you don't build it correctly.

We have tried almost all of the drive trains at one time or another for the same reasons you state- for educational purposes. We wanted to teach, and learn the positive attributes of the specific drive system and potentially perfect it so that it would be in our repertoire. In the end, however, we realized that WE (not necessarily all teams) were not sufficiently capable of picking and choosing which of the drive systems we would prefer to use that particular season. We stick to tank tread, skid steer, and mecanum drives.