Drive Train Choices
 

Our team wants to experiment with different drive trains and was wondering which would be the best to play with. What are the advantages and disadvantages of them?

Re: Drive Train Choices
 

What does your team have experience with? What are your manufacturing resources? Where do you have/lack experience (CAD, programming, machining, sensors, etc.)? Are you looking to work on systems you are inexperienced in or perfect ones that you already have a bit of experience with? Are you looking to work mainly with the kit frame and just improving upon it, or going after a custom construction?

An example of how these questions matter: a team with significant sheet metal sponsors and access to water jet cutting and a sheet metal break will likely design something differently from a team with mills, lathes, and experience using box tube aluminum. Heck, 1714 makes the majority of their robot out of lexan because they have a big sponsor that specializes in acrylics and other plastics!

My team is currently looking into octocanum. All the maneuverability of mecanum plus the traction of tank without the time and price of swerve

Re: Drive Train Choices
 

I highly reccomend perfecting your 6wd before you look any further into special drivetrains. A good 6wd will carry your team for many years. Once you have a solid drive, you can expand from there, based on what your team wants.

While mecanum, swerve, octocanum, and nona(and many others) are known to provide extra "manuverability", I personally find that this manuverability is often not used correctly, and better performance will usually come from more driver practice instead. I think it would be more worthwhile your time to look into a drivetrain that uses less resources or improve your current drivetrain(reduce resources too).

One promising drivetrain is butterfly. Butterfly can be built using very little resources. In addition, it offers performance increases over typical 6wds like getting out of t bones, straighter tracking for auton, and being unturnable(also butterfly can be built to have two different speeds).

There are many additions you can do to a 6wd too. We personally have added motors, used wider wheels, reduced resources to build our 6wd(primarily using new COTs parts), and reduced weight. Other notable additions that we are testing during the offseason are belts and drop down omnis/ball casters to get out of tbones.

Re: Drive Train Choices
 

I believe the best advice I ever read on drive trains was a quote in a paper by team 33 that said ~"the best drive train in robotics is the one that gets you to the spot on the field where you want to be as quickly and as reliable as possible."

The Simbots have a terrific resource on the different drive train types including a general weighted table. http://www.simbotics.org/resources/m...rain-selection

The only addition to the ones mentioned on that page would be the octo./butterfly drive which had been mentioned earlier in the thread.
For butterfly I would start looking here http://www.teamneutrino.org/seasons/...bot/butterfly/ on team Neutrino's page.

This site has terrific pictures/caddings on the different drive types. http://www.frc-designs.com/drives.html

Re: Drive Train Choices
 

I think you are talking about this thread Post #24. Our best two seasons are arguably 2011 and 2013. In both of these seasons we used a chassis that we prototyped in the offseason. The 2011 one was had articulating back wheels and the 2013 one was just a normal 8wd. The benefit from the articulating wheels was marginal in hindsight but the fact that we already had a drivetrain solution we knew would work was invaluable in terms of speeding up the design and build process.

Attempting to follow the 2011 and 2013 success trends we are prototyping the second iteration of our 2013 drivetrain this summer/fall. I only recommend that once you pick a drive type you stick with it over the course of a couple seasons and refine it each offseason. It's pretty hard to go wrong with this tactic no matter what you choose.

Regards, Bryan

Re: Drive Train Choices
 

I (and many of the other people here) could probably fill multiple encyclopedia-sized tomes with the advantages and disadvantages of different drive trains and configurations of drive trains. There's an entire world of custom drive trains that opens up the moment you step outside of the appealing and excellently designed kitbot-shaped box.

I'll reiterate for a moment what KrazyCarl said-- before you even start thinking about what kind of custom drive train you're going to build, consider very carefully your resources-- what kind of budget does this have? How much time is your team willing to spend developing it? What kind of sponsors do you have? What are the lead times on parts from those sponsors (we have a waterjetting sponsor that needs us to give them CAD files at least three weeks before they manufacture, which limits their use during build season)?

Once you've answered all those questions, then brainstorming is a good idea-- if it's just for the joy of designing something out of the box, then you might very well consider octocanum or swerve drive or any of the other myriad of cool custom drive trains out there-- if you're developing it for competition, your goals are probably quite different. If you're developing specifically for competition, in fact, you'll probably want to stick to making a 6WD that you can manufacture and start driving super fast, in addition to being as flexible as at all possible. There has never been a year where you couldn't complete the game challenge with a well-designed 6WD (at least in recent memory).

In terms of awesome projects for drive trains, a lot of great ones have already been mentioned-- an octocanum is a very cool project (in fact that's what my team has been working on). Butterfly is, as mentioned, a nice, relatively simple project (considering that 3928 has so kindly used a good deal of COTS parts and posted many pictures). This late, I wouldn't suggest developing swerve-- you might be able to pull it off, but there's a lot of mechanical and programming complexity there.

Another suggestion would be to CAD all of the above drive trains-- it's good practice and you'll learn a lot about your program of choice. And CAD has that nice thing about being free. If you do that, then you can look at all your designs and pick out the one that makes most sense/ you'd like to build the most.

Re: Drive Train Choices
 

We just want to try something new so we have some experience during off season instead of fulling around with it during build. I think its safe to say that my team has just about mastered 4 - 6 Wheel Drive. We want to try new stuff to see if we like it and want to use it in a future year instead of the same 4 - 6 drive every year. We just don't know which one to pick to start with.

Re: Drive Train Choices
 

IMO there's still a ton of development your team can do within 4-6-8 wheel drives.

Once you've iterated through those, the only one I'd suggest next would be butterfly or octocanum. But, I'd say continue on the route of further refining your drives. Try belts in a 6 or 8wd, try custom gearboxes, try new wheels, etc...

Re: Drive Train Choices
 

"Which drivetrain should we prototype in the off-season?" is a whole different question than "what are the advantages of each drivetrain?"

If all you're looking for is a simple answer to the former question, I'd recommend mecanum for a few reasons. One is that it can be mastered in a season. Two is that if all else fails, swap out regular wheels and you'll have a drive that you're familiar with. Three is that it will make a good demo bot all by itself, since most people aren't familiar with mecanum wheels.

Hope this helps.

Re: Drive Train Choices
 

I'll echo what everyone else has said about making sure your 6wd is perfect. It's important to have a strong "default" drive system. However, I don't think you came here to read a couple of posts that are not helping you make a decision like you wanted! However, you could still experiment by designing or iterating your own gearbox (or other improvements to a standard Tank system)! My team is currently examining this possibility because we recently acquired new machining resources and it would be a cool project and a valuable resource to have in our pocket.

Hm... Well, Mecanum drive is a good one to prototype during the off-season. It's a challenging exercise for your programming and mechanical subteams (which is a reward of itself). It also opens the door for Octocanum drive in the future (which I've wanted to look into for a while). The wheels and gearboxes are going to be kinda costly but other than that it can be mounted to a standard C-Channel chassis, which is nice if you don't want to mess with a special setup system.

I've wanted to check out Butterfly drive for a bit as well (if you were unaware, Butterfly drive is Octocanum but which omni wheels instead of Mecanum wheels, it has the added maneuverability without the strafing and cost of the wheels). It's a fancy system that will also challenge your mechanical and electrical teams, as the development of a good, reliable wheel-switching system could be a bit of work. This is also a fairly new drive system, so there is a lot of experimentation that can go into it because not much has been done with it already. The machining of the modules might require resources beyond the standard team's availability though, so research into a design is required beforehand.

If you don't want to venture too far away from your Tank drive systems, Drop Center 8 Wheel Drive has been becoming increasingly popular. I'm not sure what the strict advantages are to it over 6wd, but there are some teams now (some of whom are very high-leveled) who are swearing by it now, so there must be something that makes it so desiring.

It all depends on what kind of drive train you want to have up your sleeve. If your team really just has an itch to play around with a drive train, then present a couple ideas to the team and see what sticks! You might find one that really interests all the people on your team. Just remember to consider cost, machining requirements, needed man-power, general complexity, and the support the FRC community can provide in the endeavor!

Looking forward to see what you guys come up with! Feel free to share if you make something cool!

Re: Drive Train Choices
 

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 Mechanums).

Re: Drive Train Choices
 

Building a test bot with mecanums can be a valuable learning experience.

Put it up against your 6wd kitbot, and you'll see quite quickly why most teams refuse to use them. You lose every time in a pushing match, if you've got mecanums, and they're a tank.

IMO, the only "omnidirectional" drivetrain worth building for a competition bot is a swerve. The problem, is that the mechanical and coding complexity of swerve drives tends to make them unreliable, AND it makes building one eat a significant portion of your build season.

During my 9 competition seasons with 1075, we built:

2003: Steered track unit, unpowered trailing wheels. A bit like a snowmobile in reverse, steering the track. Allowed turning at full speed to reach the top of the ramp first.

2004: 14" bike tired 4wd, the trailing wheels articulated vertically with the arm, so that hanging from the bar was primarily a "lift the wheels, rather than the bot" motion.

2005: Didnt compete

2006: 2+2 Coaxial Swerve, All 4 wheels driven from same gearbox, using 1 turn pots for position feedback. I couldn't tell you how many pots we snapped with this robot. It was awful. For the offseason, we built the first iteration of our belted drives.

2007: Belted drives (motors inside the belts driving a shaft running the length of the unit, through the guts of a supershifter, a bevel gear, then chain to the drive cog). I believe we competed with the 3rd iteration of this drive. 4th iteration in the offseason. We kept having problems with belt breakage, many of the iterations added deflection (sometimes variable) to the bottom surface of the track.

2008: 5th iteration of the belted drives. Partway through the offseason, we switched to a more standard 6wd drop center, and walked away with BE7.

2009: 2+2 Swerve again, only this time, with encoders, and independent motors for each wheel. MUCH better than 2006.

2010: 2+2 Double Sided Swerve. Essentially the same design as 2009, only with an extra set of wheels on top, in case we flipped going over the bumps.

2011: Another iteration of the 2+2 Swerve.

2012: Another iteration of the 2+2 swerve.

Then I left 1075 to go work with 4343.

2013: 1075 built a 4wd, front two omni drive, and 4343 built the kitbot drive.

Each year 1075 did the swerve? The drivetrain ate up so much of their season, that they were scrambling to get the end effectors working properly.

Working with 4343 in 2013 using the kitbot drive? That made life SO much easier.

Re: Drive Train Choices
 

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

Re: Drive Train Choices
 

As a big fan of tank drives, I'd suggest you try the 8WD, with the two middle wheels lowered. I only know one team that does it, 2630 from Israel, but I'm sure it's a common design, I just never looked into existing designs (since I know people on 2630 that does it so when I have a question I just ask them).
The great advantage of this design is that you have a very small wheel base, even smaller than dropped-wheel 6WD, and since you have two lowered wheels, it only rocks when you have high-speed collisions. 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).
2630's drive in 2010, first time they did it. It's kinda hard to see but if you look closely you'll notice the external wheels are a bit higher than the lower wheels.

Did you ever do a west coast drive? If not, you can try that too. It too is harder to make than the standard drive, but it clears up a lot of space inside the chassis, which makes component placement much easier, and in some cases allows for better game mechanisms.

Side note: most of 2630's 8WDs were west coast drives, if not all.

EDIT: Sorry, I didn't see the "different wheels" post. I'm keeping the post though, for anyone else who might be interested in trying something new and looks at this thread.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.)

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

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.

Re: Drive Train Choices
 

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)

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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.

Re: Drive Train Choices
 

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

Re: Drive Train Choices
 

I strongly disagree. The easiest drive to learn in a short amount of time is some form of field-centric omnidirectional drive. Just point your joystick in the direction you want your robot to go, and it goes.

Re: Drive Train Choices
 

I think Damp was assuming that the team was somewhat new, and therefore not quite at the point where they could program good field-centric drive code.

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Even with a field-centric drive, I have witnessed many first-time drivers struggle to grasp omnidirectional driving in the time they can easily grasp simple arcade drive. It's the mind set of properly using the drive train by translating in multiple axes rather than always rotating to change direction that most seem to struggle with. Re-orienting the robot to change direction is intuitive since that's how most things we are used to work (humans, cars, etc.). Keeping the robot facing a constant heading while changing direction is counter-intuitive for most, while it may seem easy for others.

Re: Drive Train Choices
 

Exactly.

I've never driven an omidirectional robot, but have talked to and observed many of their drivers. The best ones (1640, 1717, etc.) all highly prioritize driver practice, and through this extra work can bring out the advantages associated with the extra maneuverability. However, the worst ones just drive their mecanum or kiwi drive as if it was a glorified tank drive with huge wheels and rollers.

I have driven both Cheesy Drive (arcade) and regular tank, and can say that even Cheesy was more difficult to learn than tank. With tank, pretty much any old kid can walk up to the driver station and start driving, while with Cheesy drive, you have to take a few moments to figure it all out. There just appears to be something extremely intuitive about one joystick controlling one side of the drivetrain. However, I will admit that Cheesy Drive and other non-tank driver setups have higher ceilings than tank. Drivers (with practice) can do things with those systems that are amazing.

But just like in drive trains, to take advantage of fancy driver setups, you need experienced and practiced drivers.

Re: Drive Train Choices
 

Exactly. I know for a fact that 1640 has their drivers practice on a robot from the first day of build season, to the last day of their competition season.

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Even with a skid-steer vehicle (6WD for example) it is straightforward to program a driver interface wherein the vehicle will turn in an arc so as to go in the direction of the joystick angle with a speed proportional to the joystick radius. For example: http://www.chiefdelphi.com/media/papers/2438

With an omnidirectional drive (like mecanum or omni or swerve), it can be programmed to immediately go in the direction of the joystick angle while simultaneously rotating to align itself with the direction of travel. Or, with the push of a button, instead go in the direction of the joystick angle without aligning.

Re: Drive Train Choices
 

I'm not aware of any powerhouse team that doesn't prioritize driver practice, which is to say I doubt the "extra" work the best omni-directional teams do is really "extra" at all.

What I witnessed in 2010 was that once field-centric drive was demonstrated (this robot doesn't know it has a "front" side), people with no driving experience had the robot moving around the room much faster than I witnessed others with driving experience during 2008, all without accidentally banging into desks, chairs, or freshmen.


From what I've seen and what I've read on CD, there are many teams that have poor experiences with holonomic drive trains because they don't use field-centric drives; field-centric makes a world of difference.

I actually had that in the back of my mind when I was posting about field-centric, but I was trying to be concise :o

Re: Drive Train Choices
 

I've built and driven a few omni-directional drives in my day and have never put field centric code on them. Rarely had major problems driving them. However, many students have had problems. A lot of it will come down to the driver.

I guess I need to sit down and make a vex kiwi drive and put field centric drive on it.

Re: Drive Train Choices
 

I dunno about you guys, but several of our Vex robots ran non-field-centric slide drives and at least one of the drivers was able to master it fairly quickly and drive it well without too much practice.

The hardest part for me about omnidirectional test chassies is usually that I can't figure out which side is the front, because it's just a chassis :)

Re: Drive Train Choices
 

That's when you mount a VEX flag on the chassis and call it the front ;)

Re: Drive Train Choices
 

As a team that likes swerve and has done swerve for the past four years, I would strongly recommend building your base competencies with 6wd first. 6wd is pretty darned good. Master this first. After you've got 6wd nailed, expand to other options.

We use off-season (summer-fall) projects to experiment with new concepts, both drive-train and in other areas. This allows us to build institutional knowledge outside the frantic pace of build season.

Re: Drive Train Choices
 

This, here, is the crux of good FRC drive development. The time for crazy ambition and reach-goals is the offseason, when you have neither strict time constraints nor immediate demand for success.

As a rule for drive, I promote the following: During build season, you should never consider a drive system which you have any doubt about your ability to execute. Any sufficiently complicated drive system should not even be on the table for build-season unless you have successfully executed it within the working memory of the team. The best way to build up your catalog of usable drive designs is thus to devote time in the off-season to experimentation with new designs.

Keep in mind that it is human nature to be overly-optimistic (often to silly extents), and that you must make a conscious effort to place your judgment of what you are able to do significantly below your initial feeling. This holds true for all design goals, but is especially pertinent for drive. For a drive, reliability trumps every single other concern, no exception. If your robot is unable to move, you are not able to play the game.

Re: Drive Train Choices
 

Rules compliance. Sadly this is overlooked nearly as often as reliability. I would say those are the two criteria that every single drive train in FRC should meet. The kit bot meets both if done according to directions, so there is truly very little reason for a drive train that is not reliable and rules compliant.

Re: Drive Train Choices
 

What oblarg said about reliability is very true. Unless you are one of those teams who has really mastered swerve (111, 1640, 1717) you won't see any benefits. Swerve is just so hard to do right. You don't get drive practice time until the season is almost over, and unless your swerve modules are 100% perfect in every way possible, you'll have one fail at competition, and you'll drive in circles for a match! For 95% of teams, the kitbot drive setup (or at least a simple 4/6wd) is the way to go.