Drive Train Choices

[Akash Rastogi]

Originally Posted by bardd

The major disadvantage is it's way more complex than 4/6WD, and you can't use the KOP to build it (not enough wheels, you need special c-channels since the KOP ones only have one lowered hole)

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This is not entirely true. An 8wd is easy to chain together even with the kit setup. You'll obviously need the additional hardware and parts. It is very easy to modify the kit chassis with little blocks of tubing bolted on with 3/8" bolt holes milled into them. Select your drop, select your wheel spacing, mill the blocks, bolt them on and you're good to go. You can also drill/mill new holes right into the kit frame, like 2495 did in 2012, but using blocks allows more room for error. I'm sure plenty of teams do this, but 2495's are the only pictures I can refer you to:

http://i.imgur.com/32N82ta.jpg
http://i.imgur.com/Xey74Gy.jpg
http://i.imgur.com/rUbLYc9.jpg

Is there something specific you find to be complex about 8wd? Perhaps I can explain it better if you have a question.

Other than added stability, 8wd allows for the ability to cross obstacles on the field without needing huge wheels. See the top 2012 robots as examples and 2010 robots. I would highly suggest prototyping 8wd and figuring out the best amount of drop to use, wheel spacing to use, and even which wheels work best.

Originally Posted by tuXguy15

I think its safe to say that my team has just about mastered 4 - 6 Wheel Drive.

When your drivetrain itself has single-handedly won a regional, you have permission to say you've mastered it.

Nobody has "mastered" any sort of drivetrain. Prime example: Team 254, who has their drivetrain down to a science, and have been iterating new and better versions of it for almost a decade, still has not "mastered" the 6wd. Their's is very good, if not one of the best I've seen, but they are always iterating and improving it year after year.

tl;dr: Build a 4/6/8 wd that outperforms 254, and then you can say you've mastered it and move on.

[BrendanB]

Originally Posted by Andrew Lawrence

When your drivetrain itself has single-handedly won a regional, you have permission to say you've mastered it.

Nobody has "mastered" any sort of drivetrain. Prime example: Team 254, who has their drivetrain down to a science, and have been iterating new and better versions of it for almost a decade, still has not "mastered" the 6wd. Their's is very good, if not one of the best I've seen, but they are always iterating and improving it year after year.

tl;dr: Build a 4/6/8 wd that outperforms 254, and then you can say you've mastered it and move on.

I believe what he means by "master" is that they have reached a comfort zone and would like to try something new. This is where we fall into. We have used three 6wd robots over our competition seasons and would like to try something else we could potentially use if the game challenge and our strategy would be better served with omini directional movement. We are still going to iterate custom 6-8+wd this fall using new build techniques and maybe try belts/gear or WCD style depending on what the team views as top criteria for what we want to get out of our drivebase.

As for what you should make, it really comes down to what you want to get out of it, and how much do you want to invest in the project. Mecanums are a quick and inexpensive way to play around with multi-directional drive. They do have their drawbacks in competition but all you need is the wheels and two years worth of KOP components to get yourself rolling. Swerve/octocanum/butterfly will take a considerable amount of time, design, machining, and will be more expensive to make depending on what you have lying around your shop.

Right now it seems like you have a very broad idea of what kind of a project you want to do based on your only criteria being "any kind but the standard FIRST KOP wheels". A lot of teams do this by saying, "We want to make a West Coast Drive (or swerve) because all the good robots use them" without setting priorities of what is more important for their team. Pick what most matters to your team in terms of (weight, maneuverability, reliability, simplicity, size, ease of maintenance, manufacturing time, looks, special features, # of parts, ability to climb obstacles, etc.)

[bardd]

Originally Posted by Akash Rastogi

This is not entirely true. An 8wd is easy to chain together even with the kit setup. You'll obviously need the additional hardware and parts. It is very easy to modify the kit chassis with little blocks of tubing bolted on with 3/8" bolt holes milled into them. Select your drop, select your wheel spacing, mill the blocks, bolt them on and you're good to go. You can also drill/mill new holes right into the kit frame, like 2495 did in 2012, but using blocks allows more room for error.

I'm assuming not owning a mill. I don't know how common they are in the USA, but I know many people there I talked with don't have such equipment, and in Israel only 3-4 teams have them (that I know of, but knowing the teams in Israel I highly doubt a team I didn't ask has one). If you have a mill, than yes, the job's easier.

What I meant by it being more complex is not being hard to design as much as 4/6WD being very easy. I mean, if you have the drive base parts, you can build a drive base without even having to think about it, and I'm not talking only building the KOP by instructions: we've been using KOP parts for our custom drives every year since we started, excluding 2010 and 2013. None of these drives were ever CADed, or even pre-thought of ("let's put plaction wheels, I heard they're better" was usually the most discussion about it before actually building). Only one of these drives ever failed, and even that was because we got the wheels super-late and didn't have time to place them properly.
With dropped 8WD, you obviously can't do that. Not saying it's a good practice to do that, and I really don't like the concept of doing that (the reason we didn't do that this year), but the fact it can be done shows how much easier it is to get a 4/6WD than 8.

[magnets]

If you are looking to get a more competitive drivetrain over the summer, I would recommend improving a six/eight wheel drive. If you are looking to have fun building a cool looking robot, you could try swerve/mecanum. In the past 4 years, there have been almost no good robots with swerve drive.

To develop a good swerve you need multiple seasons/off seasons of development, people who are skilled with CAD software, lots of money, and lots of CNC and machining equipment. Look at team 148, one of the most competitive teams. They have only done swerve once, and that was in 08, when their robot didn't have any other manipulator/features, it literally just drove in circles! After 08, they stated that swerve is almost never beneficial to have.

As for meccanum, I personally have a strong dislike for these horrible wheels. Many good teams automatically cross off teams with meccanum wheels from their pick list, just because they know they will be inferior to a 6wd.

If you are interested in making your 6wd more competitive, figure out how to make it lighter, cheaper, simpler, and more reliable. Make it a two speed (if you haven't already) and play around with different gear ratios to see which works best. You could also try to implement a more advanced method of control such as a gyro that helps your robot drive in a perfectly straight line, or something like team 254's cheesy drive. There is currently no team in FRC with a perfect 6wd, although the cheesy poofs are getting pretty close.

[Jay O'Donnell]

Originally Posted by magnets

In the past 4 years, there have been almost no good robots with swerve drive.

What about 16 in 2012? And 1717 all of the last 4 years? Those are only two off the top of my head and I know there are others.

[bardd]

Originally Posted by Jay Money 1058

What about 16 in 2012? And 1717 all of the last 4 years? Those are only two off the top of my head and I know there are others.

He did say "almost"... There are good examples of swerve out there, they're just very uncommon. 1640 is the only team that I know of to use swerve in the past 3 years other than those you mentioned.

[Brandon_L]

Originally Posted by bardd

I'm assuming not owning a mill. I don't know how common they are in the USA, but I know many people there I talked with don't have such equipment, and in Israel only 3-4 teams have them (that I know of, but knowing the teams in Israel I highly doubt a team I didn't ask has one). If you have a mill, than yes, the job's easier.

What I meant by it being more complex is not being hard to design as much as 4/6WD being very easy. I mean, if you have the drive base parts, you can build a drive base without even having to think about it, and I'm not talking only building the KOP by instructions: we've been using KOP parts for our custom drives every year since we started, excluding 2010 and 2013. None of these drives were ever CADed, or even pre-thought of ("let's put plaction wheels, I heard they're better" was usually the most discussion about it before actually building). Only one of these drives ever failed, and even that was because we got the wheels super-late and didn't have time to place them properly.
With dropped 8WD, you obviously can't do that. Not saying it's a good practice to do that, and I really don't like the concept of doing that (the reason we didn't do that this year), but the fact it can be done shows how much easier it is to get a 4/6WD than 8.

We did not use a mill, nor do we own one. Just carefully measured and drill pressed. Not really an exact science and could be done better but we never had an issue with it.

As for more complex, its not at all. If anything maybe even easier because you can just plop the gearbox/motors dead center in your bot. you just double sprocket the two inner wheels as you would a center wheel on a 6wd.

without even having to think about it

wheres the fun in that? The only thought that went into ours was wheel spacing, because we wanted to make sure we could clear the bump with no issues (beaching ourselves on it, breaking chains, ect) which we just did some simple geometric drawings in CAD for, not even a full 3d model. If it werent for that, you can pretty much just evenly space them.

[Andrew Schreiber]

Originally Posted by Jay Money 1058

What about 16 in 2012? And 1717 all of the last 4 years? Those are only two off the top of my head and I know there are others.

2008 - 16, 148 (World Champs)
2009 - 111 (World Champs)
2010 - 1717
2012 - 16 (World Champs), 1717, 973
2013 - 1717, 1640

16 has been swerving for years and have iterated the crap out of it, same with 1640, 1717, and 111. 973 built several in the off season before running it in season. Of interesting note are the teams that swerved and never went back to it:

1114 - 2004
67 - 2004, 2005
1503 - 2007
469 - 2007, 2008


Of particular interest, the Beatty Curse. They haven't won a World Championship since they started swerve drive. (This is a complete joke)

[magnets]

Originally Posted by Andrew Schreiber

2008 - 16, 148 (World Champs)
2009 - 111 (World Champs)
2010 - 1717
2012 - 16 (World Champs), 1717, 973
2013 - 1717, 1640

16 has been swerving for years and have iterated the crap out of it, same with 1640, 1717, and 111. 973 built several in the off season before running it in season. Of interesting note are the teams that swerved and never went back to it:

1114 - 2004
67 - 2004, 2005
1503 - 2007
469 - 2007, 2008


Of particular interest, the Beatty Curse. They haven't won a World Championship since they started swerve drive. (This is a complete joke)

If you notice, all of the good teams with swerve have been at it for years. (111 has had swerve since at least 03, 1640's had swerve since 09, 1717's had swerve for 4 years, and 16's had swerve for as long as I can remember) The reason 16 was so great in 2012 was not because they had swerve. They were great because of their ability to quickly collect balls, and accurately score them. These teams' success is not caused by their swerve drives, but the swerve drives happen because these teams are so good at building robots.


The only exception to this is 148, who successfully implemented swerve in one season. However, JVN has said that he "wouldn't recommend" swerve, and that there are close to no situations where swerve is as beneficial as people say it is.

My point is not that swerve drive ruins robots, but that swerve is VERY easy to do wrong, and if the original poster was interested in making their robot as competitive as possible, they should work on their 6wd.

[Akash Rastogi]

Originally Posted by tuXguy15

Hey guys by drive train i mean different wheels like mecanum wheels, swerve wheels, etc. Any kind but the standard FIRST KOP wheels

There are omni wheels (90 degree rollers) and there are mecanum (45 degree rollers) but there are no specific wheels a swerve needs.

The AM Hi-Grip wheels in the kit are great, and they are making improvements to them for 2014 to prevent failures that some teams saw this year. You can try out AM Plaction wheels which are pretty sweet and affordable. VEXPro also offers a variety of wheels to try. Then there's Colson wheels which 11 and many others use, but they require a hub that can be purchased at WCProducts.net

PM me if you want some specific suggestions for your team in particular.

[thefro526]

Originally Posted by Akash Rastogi

This is not entirely true. An 8wd is easy to chain together even with the kit setup. You'll obviously need the additional hardware and parts. It is very easy to modify the kit chassis with little blocks of tubing bolted on with 3/8" bolt holes milled into them. Select your drop, select your wheel spacing, mill the blocks, bolt them on and you're good to go. You can also drill/mill new holes right into the kit frame, like 2495 did in 2012, but using blocks allows more room for error. I'm sure plenty of teams do this, but 2495's are the only pictures I can refer you to:

For what it's worth, there's an even easier way to go about this than the method that Akash described, and that's to use standard COTS pillow blocks and drill the C-Base to match (if need be). Assuming the blocks are bolted to the frame, you can then shim them up or down with washers/shims/etc to tweak the drop or move them around for different configurations.

Or, if you've got an extra C-Base rail or two sitting around, you could cut it into a series of 3-4" long segments and use those as your 'axle' blocks. To be honest, if you're one of those teams that doesn't use the C-Base or has an extra one laying around, I'd suggest modifying it with axle blocks and trying different drive configurations to get a better first hand understanding of the pros and cons of each type.

Regardless of what you decide to pursue, I'd suggest emphasizing reliability over all else until you're confident that you can build a 'zero-failure' drive train. I've seen way too many teams chase performance at the expense of reliability and it's a really disheartening moment when an awesome drive train fails in the middle of a match - and it's usually the 'most important' match of the day...

For example, the 341's drive this year is probably the best drive train I have ever had a hand in over 8 seasons of FRC. It is by no means the lightest, or the fastest, or the coolest, but it's bullet proof. Over the course of 60+ matches on season and hours of off-season use, we've never had a single failure - and have not needed to do any maintenance work other than swapping wheels when they've worn too much.

[Akash Rastogi]

Originally Posted by thefro526

standard COTS pillow blocks

I like these ones from Mcmaster http://www.mcmaster.com/#8600N5, but I'm sure you can find a supplier in/closer to Israel for these.

[DampRobot]

If you want to build something you'll use in the season, build a WCD. If you want a cool drivetrain that you shouldn't use for the season, build a mecanum drive.

For a myriad of reasons, WCDs are great drives for the season. Their maintainability and reliability are second to none, they drive very well, and are easy to machine compared with other "top notch" drives like butterfly or swerve. They're also very easy to learn to drive, especially with a drive system like cheesy drive, yet have a very high upper end in terms of performance. Butterfly, swerve, and to a large degree mecanum are comparatively hard to learn to drive in a short amount of time. Plus, building a drive very similar to the Poofs or the Greybots does have some innate cool factor.

Mecanum is very cool though. Non FRC people love omnidirectional motion, and the ways those wheels spin can look very cool too. It's a also less difficult to build than, say, swerve, although probably harder than a WCD. Buy some AM components and design a chassis to hold it all together, and you're most of the way there. However, I would not encourage you to use them in the season. While their lack of skills on defense is probably overrated by most people, they have other disadvantages too. It's a quite heavy system and usually forces you to have a higher CG by necessitating bigger wheels. Also, it's basically never driven to its full potential in a match. Unless drivers get a ton of practice beforehand, they never are able to take full advantage of its strafing abilities.

Don't build a swerve. Unless you are really really on top of your game, the project will be a failure, most likely because it will never get off the ground. Even of it does, lots of things can doom a swerve drive, most prominently poor control. Designing a swerve drive is a great challenge on the other hand. I've done it, and it's very rewarding.

Good luck this offseason! Your work now will definitely pay off come 2014.

[BJC]

Originally Posted by Koko Ed

Our operator is obsessed with creating a version of your 2013 drive train for our team (we used Mechanums last year. It was good for qualifications but cost us in the elims. We got put out by strong defense @ FLR and I beleive it cost us from being considered as a viable pick at the championships in spite of performing well. People just don't like Mecanums).

I'm glad that we could serve as inspiration. That's really what this program is all about.

In my own experience Mecanums are definetly looked at as inferior and will drop a robot on the pick list if not straight off of it. Especially when looking for a second pick, alliances are generally looking for robots that can play defense if needed. This combined with the general stigma against Mechanums makes them a mark against you in the scouting department even if your robot is quite good.

Good luck on all your future drivetrain endeavors! (and I'd love to hear thoughts if your team ends up designing/building a WASPdrive.)
Regards, Bryan