Best Drivetrain
 

I am posting this because a rookie team in Davis was having a hard time deciding and creating a drivetrain for their robot. There have been many different types of drivetrains used in FIRST. So in order to help all the rookie teams for nex year, what drivetrain has been the most dominant from the 2005 season and on?

-rc

ps Pictures please

Re: Best Drivetrain
 

I would say the KOP transmission with 2 CIM motors per side, driving six wheels via chains. More robots use this than all other layouts put together. My observation. YMMV. Offer not valid in Michigan.

Re: Best Drivetrain
 

6 wheel drive with either lowered center wheels (~1/8") or omnis on the corners. This has without a doubt been the most successful drivetrain in the past and is very simple to build. As long as you can build a 4 wheel drive you can fairly easily add 2 more wheels. If you really want to improve it, add traction wheels such as ifi and a 2 speed transmission. An even better addition is directly driving the center wheels off the transmission shaft so that even if all of the chains break the robot will still be powered. This requires a little bit more work though and most likely precise machining capabilities.

Re: Best Drivetrain
 

Specifically, it requires a longer output shaft than any standard transmission will give you.

Usually it's just as much weight to do the bearing blocks for a direct drive setup as it is to do an AM hub with AM flat sprockets with extra chains. Since it's more difficult to do the former, most teams stick with the default method.

Re: Best Drivetrain
 

If they are rookies, BUILD A SIMPLE DRIVETRAIN. Overly complicated systems have killed rookies and vets alike. Our best best years came from simple 6 wheel "rockers" that were very quick and easy to fix. Your programmers will also thank you.

Re: Best Drivetrain
 

My old FRC team has never built a really great robot (sad, but true), but their chain-driven, 6WD chassis with the KOP gearbox has been bulletproof all four of the last seasons. The concerns about breaking #35 chain (in my experience) are exaggerated -- if you don't do anything weird or stupid, they simply won't break before the motors stall out. When you start getting into more exotic choices, stuff starts breaking. It might be worth it if you have a sophisticated robot and build process, but I think most teams would be well-advised to go with a proven drive-train and spend their brain cells on building better game mechanisms.

Re: Best Drivetrain
 

Direct drive does require modifiying all but the andymark super shifters. Although getting a longer shaft machined is really not that difficult. My preference for direct drive is that even if all chains somehow snap, the robot will still perform just as well since the center wheels are always in contact with the ground. This also makes it slightly more reassuring to use #25 chain since no matter how many chains break the robot will still run. #25 chain saves a ton of weight over #35 and it also only uses 4 chains versus at least 6 in a normal 6 wheel drivetrain. The only thing to remember with #25 and really even #35 chain is to have a way to easily tension the chain. If you can keep the chain tensioned and lined up properly then you will never break a #25 chain.

Re: Best Drivetrain
 

2007 Super-Rookies - 2056 Patriotics

6wd built on a kit-frame. Winners of Waterloo, GTR, and IRI that year.

http://www.oppatriotics.com/pic_0139.html

I wish there was a simple way to convince every rookie team to go this route and have their drivebase complete by 2nd week of build.

Actually, there are times when I wish I could convince veteran teams to do this too =).

Re: Best Drivetrain
 

Sorry, guys, but you are ALL wrong.

The correct answer is: we don't know.

The game hasn't been released yet. Maneuverability might be key, power might be key. We don't know. We won't know until January.

That said: Rookies should NOT attempt a swerve or holonomic. Even veterans have trouble with those sometimes.

4WD or 6WD skid steer, Kit frame, would be my best advice. Those are really versatile, especially the 6WD drop center. Kit trannies would be recommended, but I'd have to see the game before committing to anything. Exactly what setup depends on the game. Chain drive, due to ease of use. Because this is a rookie team, tensioner of a block of delrin under or over the chain mounted so the chain digs into it a little. While it is possible to get away with not using a tensioner, that's something that only a veteran team or a team with decent CAD/manufacturing ability should attempt.

Re: Best Drivetrain
 

FIRST Champions:
2005:
330- 6WD, higher traction center wheel (possibly dropped)
67- Swerve
503- 2WD w/ omnis (correct me if I'm wrong)

2006:
296- 2WD w/ casters
217- 6WD, lowered center wheel
522- Treads

2007:
190- 6WD, lowered center
987- 6WD, lowered center
177- 6WD, lowered center

2008:
1114- 6WD, lowered center wheel
217- 6WD, lowered center wheel
148- Swerve drive


correct me if any are incorrect

Re: Best Drivetrain
 

Dropped is definite. (It's also variable drop, if you play with it--the center wheel was pneumatic.)

Re: Best Drivetrain
 

The most dominant drivetrains have a few common attributes:

1) The drivers are comfortable with the robot. This usually means it's a drivetrain they can build early in build season (or can build a spare of for practice easily enough).

2) Reliability. Robots that throw chains and don't turn don't fare that well. That applies for the long haul, too--1251, a dominant force in the regular season last year, had to sit out the elimination rounds at Mission Mayhem because they kept having troubles.

3) Quickness at the task at hand. The drivetrains that can get a given job done fastest tend to do better. That doesn't always mean raw speed--71 shuffled its way to a world title in 2002 going awful slow while ensuring that all three of the goals that season would get to their zone.

In my experience, this usually entails some flavor of 6WD. Some teams have reached a level of sophistication where they can go with more advanced drivetrains (see also: 148's coaxial swerve this season), but most of us are still where 6WD is the way to go for most cases.

Re: Best Drivetrain
 

What Billfred said.

Also, a couple questions so I can clarify my answer for you:

1. How advanced of machining do they have access to?
2. Do they want to rely on the kit?
3. How fast do you want to move? (fast, slow, push anything, etc)
4. Are you looking for a lightweight system, or something that's an absolute beast?

Re: Best Drivetrain
 

My $0.02:
For a rookie stick with a #35 chain drive. Its far more forgiving than #25. The weight savings isn't worth the tolerance hassles or the effort to get sprockets that aren't from the KOP.

If the point of asking the question is to save labor so the rookies can focus on other mechanisms then the kitbot is the best way to go. It works and is solidly reliable and doesn't take long to build freeing your team to focus on make other parts for the robot, isn't that why we got the kitbot in 2005?

Re: Best Drivetrain
 

ARGH! I hate to be a bit aggravated in my response, but NO NO NO! If you don't have a rookie team start experimenting now with a newer system, how will they ever get to it?! Why are we discouraging innovation and trying new things?! Isn't that counter to EVERYTHING FIRST is about?!

Besides, #25 chain is more than strong enough, provided it's done correctly! Here's what I mean by correctly, so I'll have a post to link people to every time this nonsense comes up: It needs to have the sprockets perfectly co-planar. The chain needs to be properly tensioned (not too tight, not too loose). That's ALL! I've used #25 for 4 years now and NEVER had a failure, and that's for both arms AND drivetrains!

Another point: We all have NO idea what the Kitbot is going to be, NONE of us do! It hasn't been built yet, so we don't know what kind of chains, if any, will be on it. Let's please save from making generalizations about a system that hasn't been delivered yet.


I apologize for the outburst, but I HATE the myth that #25 is "too weak" or "too hard" for FIRST use. So please, OP, whatever you build, save yourself the 5ish pounds, and use #25!

Re: Best Drivetrain
 

If you want the easiest drive system to build do what we did;

have the boxes output be gear, have the wheel shaft have a gear, have the gear on the box directly attach to the shaft that said wheel is on... one box 2 CIMs per side, two drive wheels per side, have your front be skids (literally no work what so ever)... very simple tank drive...

Re: Best Drivetrain
 

(insert standard inspiring and changing the culture retort here)

For the first season, I find nothing wrong with going the safe route. Get going in the right direction, and you can start optimizing in the off-season once you know what the heck you're doing. (Show of hands, how many people didn't know what they were doing until they were through their first season?)

From experiences, teams don't always have the means of making everything perfectly coplanar. Tensioning with the kit frame isn't always a cakewalk, either.

To each their own--I've seen teams do great things with #25, but I think our capabilities are better suited to #35. I'll agree to disagree.

Re: Best Drivetrain
 

Well, let's not discourage innovation; rookies should go for no less than a full swerve drive. :rolleyes:

It's a fact, #25 is weaker and less forgiving in tolerances than #35; not attacking #25, It's just fact. A lot of teams have the experience, resources and ability to work with #25, but, not many rookies do.

I have seen plenty of issues with rookie/newer team's drivetrains with #35 chain. I support what Peter said; let a team get a decent drive going in all other aspects before they start trying out #25.

Re: Best Drivetrain
 

Craig, I presume by your answer that you are offering to teach this ROOKIE team all the ins and outs of chain usage, particularly #25 vs. #35. Especially, how to use #25 so that it does not break or come unseated, as it likes to do when run improperly.

Look, we're dealing with a rookie team here. This is why we are advocating a "failsafe" approach. If this were a veteran team, we'd go to a "riskier" solution.

Re: Best Drivetrain
 

Yeah, I am offering to teach this ROOKIE team how to properly use this system. It's only as simple as using CAD to design your chain runs, and CAD is supplied free to all teams (in any flavor you want, too...). I agree that it's safer for you to avoid giving advice that may result in a bit of failure, but at the same time, if you don't start reaching for the sky early, it takes longer to get there.

There's a HUGE reason I always advocate #25: acceleration. A lighter mass to get moving will accelerate faster, so the weight loss from a moving part results in a HUGE acceleration increase.

So here's an offer: if anyone has ANY questions about how to change over a system from the heavier #35 chain to the lighter #25, please feel free to ask me.

Re: Best Drivetrain
 

Actually, Craig, you're almost close enough to mentor them in person. Davis to the Bay Area is only a couple hours or so, as I recall. Unless you're going elsewhere for school, of course.

I know of a team that stopped using #25 because it kept failing. They spent more time fixing the chain on their old robot that they were using for a practice robot than practicing. Sprockets weren't aligned right. That team now only uses #25 for very light-duty applications where they can check the alignment and #35 for heavier duty, like drive. Team "tradition", if you will. They have also been able to make weight with a minimum of speed holes each year. With a newer team, you can get the #25 usage ingrained faster than for some old teams that have been around for a while.

Note, I'm not saying that they don't use #25 because it is weak, I'm saying that they use #35 because they had problems in the past with #25. Meanwhile, you haven't had a problem in 4 years with #25.

I don't quite follow the acceleration; after all you're moving about 150 lbs (battery, bumpers, robot) any way you look at it. You're just moving that weight out of the drive into the rest of the robot. Rotationally, yes, but then you have to translate that into the rest of the robot.

And for the "reaching for the sky early": true. There is also the element of keeping them from discouragement when they reach and fall short the first few times. This is why we have mentors.

Re: Best Drivetrain
 

2008:
Most beautiful drivetrains: 254/968, 1251, and 1538 from what I saw. They all proved to be very functional also.

Holy Cows, 1251 and 254/968 build the most beautiful machines year after year.

As for the debate on chain size, a lot of teams commented about ours after observing our robot this year.
We've had issues with #25 chain before and debates on whether #35 chain was too much at times.
We went with a bike chain which is stronger than #25, looks like #35, but with a weight nearly that of a #25 chain. We used them for our electric vehicles and never had to swap them out for any reason this year due to stretching or skipping issues.

Re: Best Drivetrain
 

As far as reliability issues goes, this coming from the bot that probably had more chains than anybody bu 118 (they crazy:ahh: ). We had 7 chains on the drivetrain this year all #25, 3 of those chains were really long, 1 going all the way around the bot to steer our wheels. And the one chain not in the drivetrain was what cocked back our shooter, and if you've seen the amount of surgical tubing on that guy, thats alot of stress.

We've been through 4 competitions, not a single chain related issue, you just gotta keep it aligned and tensioned, which i realize takes some work, but i think the weight savings is definetely worth the work to align it properly

Re: Best Drivetrain
 

hmmmm...it took us till our 3rd year to get our chassis designed in CAD....there is a bit of a learning curve! And we're probably a year or two away from being comfortable enough with our design/fabrication abilities to try something other than #35 chain, and then it might be belts instead of #25 chain :)

Re: Best Drivetrain
 

This was our teams 3rd year and my 4th year involved in FIRST and we implemented #25 chain for the first time and will never be going back to #35. We had a 6 wheel drive with the center wheels directly driven. The outer wheels were tensioned by sliding the axle in a shaft cut into the frame plates and then tightening the screws that hold the axles, a very simple system. We never broke a single chain and in fact never had a single problem with our drivetrain through one regional and championship.

Re: Best Drivetrain
 

While this may be good advice a good chunk of the time I feel as it may be a little bit of blanket statement. Although I'm sure you had no mal intent.

I have seen very capable rookie teams that would be able to handle making a swerve or holonomic and I've seen many many many veterans who would not be able to pull one off.

Judge your teams capabilities...if a task looks daunting, it probably is...if you think your team may be able to pull it off, go for it. FIRST isn't about winning, its about learning. Go for the design that will knock peoples socks off...who cares if you dont get 2 weeks to drive it around before competition. Thats just my honest opinion.

Re: Best Drivetrain
 

Down here in Greenville we like 6WD too!

It took a very strange game and very strange robot design to make us go with a Coaxial Swerve. I sincerely doubt we would go that route again, and I would never recommend that route for anyone else (who I like).

Long live the Wrangler-Drive, hopefully coming back for 2009.

Re: Best Drivetrain
 

Few things I am observing.
1) Chain use: To put this matter to rest: run your stress analysis numbers! You need to calculate the tension on each chain (both sides of the sprocket). Then use your fancy Machinery's Handbook (Every team should have a copy. Awesome resource ;)) and calculate the stress in the chain and compare that to the breaking strength of the chain. Remember to include a factor of safety!

2)For Rookies:
For flat game (no climbing) the simplest and most efficient drive train that you can build is two powered wheels that are center aligned (or slightly off center depending on how you want for turning characteristics) with "skid wheels" such as hard plastic caster wheels that don't turn. I've seen more rookies (and veterans) be competitive with this than any other because its simple and effective.

For a climbing game the simplest and most efficient drive train for a rookie would be the six wheel drive platform. It allows you to climb and still have good maneuverability.

3)For veterans:
Build what you can afford. Build what you feel best matches the game. Don't build until you have done your research. If you have resources to build a crab/swerve go for it. If you need to climb something and can afford the treads build a tank. Every type of drive has its pro's and con's so you need to weigh your options and do your research.

4)
Don't get closed off to one type of design whether you've built it or not. The good teams become good because they take a risk and try; they learn from their risks. Many teams have had success at things you may have failed with. Use it as a learning opportunity and to add another design into you book of tricks. Every year everyone comes out of the season saying what they could have done this or that better. Well don't forget it, and do it better ;).

Re: Best Drivetrain
 

The 'standard' six wheel drive configuration does seem like the most reliable drivetrain I've seen, and it can be implemented easily too. A dead axle system with a kit-style frame layout works great! Three chains per side; transmission to back wheel, transmission to middle wheel, middle wheel to front wheel. Give each one a tensioner, and you're done. This is the most common way I've seen it done, and I haven't seen one suffer a catastrophic failure yet.

As for the 25/35 debate, I'm all for 35, mostly for the reason that it's easy to obtain and keep working. <almost> No precision necessary. I also don't mind having the extra weight in the drivetrain; if you design the rest of your robot properly then you can afford the heavy chains.


And for the record, team 125 wins the best drivetrain award for 2008. 34 comes in a close second.

Re: Best Drivetrain
 

While I agree with Brandon on most topics, this is one we don't see eye to eye on.

In my experience a fully functioning, simple robot is much more effective and reliable than a figurative time bomb on wheels. Remember that reliability is a part of your scope, as is function. If this doesn't click, think about what you look for in a car. There's a reason Honda and Toyota have risen to the top of the proverbial food chain.

The enemies of scope are time and cost. (FIRST has a third enemy: experience. But that is for a different discussion!)

Broken robots = stressful = no fun = less inspiration

Re: Best Drivetrain
 

This was our platform in 2005 -- probably the most interesting year in 1294's history. The robot performed perfectly, all the time -- except when the team forgot to plug in PWM cables, or unplugged the compressor and didn't turn it back on, or when the drive team, which changed practically from match to match, didn't know what to do with the robot. It was a perfect storm of a simple, reliable robot that didn't LOOK reliable due to poor teamwork. A sobering lesson (and not my fault -- really).

Re: Best Drivetrain
 

CAD isn't going to make the average rookie team have an entirely straight frame, properly aligned sprockets and axles, proper chain tensioning, or the general machining precision necessary to have a fully reliable #25 chain drive. While everything may work fine in the computer, it doesn't always translate to the real robot.
#35 chain is plenty reliable and competitive for any team, not just rookies. While #25 has its advantages, I'd suggest rookies spend their resources and times developing other aspects of the drive and whole robot rather than worrying about #25 chain just yet. Spend more of those resources on better wheels, transmissions, electronics, or manipulators (or about anything else). Get done with your drive a little bit quicker with the supplied #35 and let your programmers have more time.

The best thing for a rookie to do is come up with a reliable, fully-functioning, usable drive with enough time for their programmers and other sub-systems to have access to the bot to do what work they need to do. That way they can spend more time programming, testing, de-bugging, and integrating the systems, as well as the all important training of the drivers.

Re: Best Drivetrain
 

As a rookie team, here's my suggestion.

Build a drivetrain that:
1> is within your machining capabilities. (If you don't have any machining capabilities, then the kitbot is your friend)
2> is within your mechanical capabilities (If, by the beginning of next build season, you do not know the mechanics of a swerve drive ... don't build one). Mechanical drivetrain failures are the downfall of many young (and some veteran) teams.
3> is within your budget (many drive systems require you to purchace parts ... make sure you've bugeted for them)
4> is within your programming capabilities (Holonomic and vector controlled drive systems require programming expertise ... If, by the beginning of the build season you do not have the programming expertise needed ... don't build one of these drive systems)
5> is easily and intuitively driveable by your drive team.


If you do these things, then whatever drive system you choose will be right for your team

Re: Best Drivetrain
 

No one said the robot had to be broken...just because it is more complex, or took more time to develop doesn't mean it is going to break.

I dont know tom, i guess we'll have to agree to disagree here...it seems to me that learning some more complex engineering substance is just as valuable as any other part of FIRST.

Re: Best Drivetrain
 

I have to back Tom on this one, mostly because I think he just has another take on the same issue. Teams sometimes need to make a decision about where they aim to provide the most inspiration to kids - in the workshop through innovation, or at the competitions through empowerment when they see their creation. Sure a complex design is an amazing feat to accomplish and everyone can take pride in it, but how much fun is it if you don't finish it or you don't get a chance to utilize it because your focus was on making it happen at all. If you can finish your design early you get to show kids another very important aspect of engineering - testing and training. If you took any talented driver and told them they would be driving a Wildstang robot for the first time at a competition right after the coders finish testing, they would flip out. Not everyone can take a positive message out of a complex design if they don't pull it off in time or they don't get to use it to its fullest. I don't want to come off saying that winning is the inspirational experience, but sometimes competing needs to take a little more precedence over designing and learning how to tackle a complex project like any robot within the constraints of the competition is something teams ought to consider too. So there is nothing wrong with attempting a complex design, because there is no reason it shouldn't succeed, but teams ought not lose sight of their final goal: to have a competitive, fully operational robot completed within six weeks (without forgetting about their drivers or coders!)

Re: Best Drivetrain
 

This was probably one of the biggest lessons I took away from this year. Over the course of my FIRST career, my designs have ranged from the super-simple to the super-complex, and everywhere in between. This year was by far the best robot I've ever worked on, and it was also probably one of the simplest. Coincidence? I think not. Everything was simple and reliable, and it worked every time (barring a mishap with a wire and the terminal block). After 4+ years of constantly having to fix things at every event, I had two stress-free competitions, both of which were greatly successful.

The takeaway from all of this: especially for drivetrains, most teams will benefit from something simple and reliable. The less experience and assistance you have, the more critical this becomes! The last thing you want is to spend your whole competition season getting the robot to move. A 6WD chain drive may not always be the perfect drivetrain for every competition, but it's easy, simple, and reliable, and it will always be serviceable and successful for any game. (Until we get that water game, or Dave punishes us by banning all wheels.... :rolleyes: )

An addendum on the #25 versus #35 question: I consider myself to be a pretty experienced designer, but I will ALWAYS use #35 for drivetrains. It doesn't matter how well you can CAD a drive base, if your fabrication tolerances are not tight enough, you WILL have problems with #25. I will take the reliability and forgiveness of #35 over the weight savings any day. I've seen too many #25 systems fail due to misalignment to do it any other way.

Re: Best Drivetrain
 

Chris/Tom

I agree with you guys, but I think your missing my point. I am not saying to go out and build some ridiculous design...but as a rookie team I feel it is good to set a precedent that you are going to do your best to make a robot that is to your ability every year. Some teams simply cannot machine an entire drivetrain, that is understood...but if a team has the means to make a part of their drivetrain, a little complicated, or innovative, why not?

I think it is important to balance the idea of "being competitive" with learning science and technology too.

I guess what I fear is a team saying, well yeah we could do that, but why don't we just buy this and call it done...

Re: Best Drivetrain
 

I have to chime in here as well.

1) There's no rookie team in Davis, maybe they were referring to a rookie team that attended the Davis Regional.

2) Not to stiffle creativity and the thrill to innovate, but for a rookie team or 2nd year team - I highly suggest a robust 6WD setup with kit transmissions (if supplied).

Pic... http://www.travisusd.k12.ca.us/vande...n/DSC05175.JPG

Last year was probably our most reliable drive system (yes - even with banebots). Kit transmissions, chained to a center-traction wheel (kit wheels), the center wheel chained to the front and back wheels. Tensioned with UMHW off-center cams. The whole drive system was put together using nothing more than a cordless drill and a band saw (neglecting the welded frame which could be replaced by a kit frame).

THE MOST IMPORTANT THING FOR A ROOKIE TEAM IS TO GET THEIR DRIVE SYSTEM WORKING BY THE END OF THE THIRD WEEK. Our team was very competitive last year, simple because of it's dependablity and driver practice. Our drive team had over a week of practice before ship.

3) Use innovative ideas to develop a cool manipulator or strategy. There's absolutely nothing more troubling than to have your robot unable to drive.

I think back to the days of 2000, 2001, 2002 when there was no simple drive system that came in the kit. You had some cordless drill motors, transmissions, and skyway wheels that you had to make work. That took our team the bulk of the 6 weeks.

Re: Best Drivetrain
 

We had a 3WD drivetrain with crab drive.

Re: Best Drivetrain
 

I don't think anyone is doing that. I just think the drive base aspect of FIRST robots has gotten to a point where it is more economical to "drag and drop" components. Design considerations for "learning" can be made in other areas of the robot.

You have when to hold your cards and when to fold your cards. Take the ace that FIRST has given us and build the kit chassis or a simple 6wd setup with COTS. The time you save will allow you to invest more into your functional designs, which are usually the things that make or break a robot design.

Re: Best Drivetrain
 

We used a six wheel drive based off the KOP and it worked great and never failed during a real match. It was easy to build and easy to service (not that we ever really had to). I would recommend any rookie team try a six wheel drive with the KOP Wheels and Transmissions just because of the reliably aspect. My favorite feature I integrated into the drive this year was using bolts as axles and pvc spacers to keep everything in place. It made dropping a wheel out take all of 2 seconds and we saved at least a pound or two by not using collars.

Re: Best Drivetrain
 

The Following is Fact:
The purpose of the drive train is to get the manipulator in position to score as many points as possible in the minimum amount of time.

That’s all you need to know. The best drive train is the one that accomplishes this task the best. Period.

It doesn't mater how many wheels, chains, motors, or gears you use. If 2WD will get the job done, use 2WD and use the time/money/resources saved to work on the manipulator.


The Following is my Opinion:

Historically, 6WD with the center wheel lowered has been the fastest system.

If you need to climb a ramp, 6WD is necessary to prevent bottoming-out.

But if the playing field is flat, why bother with 6WD at all? I mean, two of the wheels aren't even touching the ground. So why bother? If the playing field is flat, save yourself some weight and only use 4WD with the wheel axels spaced 12" apart and casters on the front.

Some will argue that swerve, mechanum, omni, and tank treads offer advantages over 6/4WD. But when you consider how many teams consistently win regionals and championships without these systems it becomes hard to see what the real benefit is.

As for the 25 vs 35 argument...

2006 Our team used #25 in 2006 with the kit frame and it was a COLLOSAL disaster. We couldn't keep the chains in line, or tensioned and they kept falling off. :(

2007 Deciding we would never use tensioners or #25 chains again ;) we switched to #35 with movable axels for tensioning. This dive train was very robust, but also very heavy.

2008 Deciding that maybe we had been too rough on #25 we switched back, implementing the same movable-axel tensioning system we used in 2007. Worked great. Much lighter and we never lost a chain.

So it really comes down to tensioning. #25 needs to be really tight, so you need a good tensioning system. #35 can be much looser. Some teams like 766 and 330 have gotten away without using any tensioners.

Re: Best Drivetrain
 

What about defensive robots? ;)

Re: Best Drivetrain
 

Two Words:
Normal Force.

If you want to build a robot capable of pushing, you want every ounce of weight sitting on top of the highest traction drive wheels you can find. If you have weight sitting on non-driven wheels (like casters) you are reducing the amount of normal force available.

In some games or for some strategies pushing is not an important consideration. In these cases a 6WD may not be important.

Brief Aside:
In my opinion drivetrain design is very formulaic. "If you want to do X then you need to do Y." It is all about the functionality requirements your team has, and the design trade-offs you are willing to make (these trade-offs may involve things like weight & team resources, or things like pushing power & top speed.)

I should write a paper on this sort of thing.

-John

Re: Best Drivetrain
 

You can win playing defense. But you can't win without playing offense.

Defensive robots depend on offensive robots to win. Building a robot that can't score, or even one that isn't designed with scoring as the primary strategy, is risky.

Re: Best Drivetrain
 

Yeah, I noticed that. I would suspect that the team in question would be a 2nd-year team now.

Brandon, we don't know anything about the team, other than approximate age. So I called conservatively. If I knew for sure that they had that extra capability, I'd go a little more risky. Some rookies will have the capability and desire to go beyond the 6WD. Most won't.

Re: Best Drivetrain
 

233 has used #25 drive chain for 10 year with minimal problems.
This year we used #25 drive chain with no tensioners and have had no problems.
The bot still has the same chains since the mid february assembly date.
mike d

Re: Best Drivetrain
 

Hey just wondering, how does two wheel rear wheel drive with two non-powered omni wheels up front work? I know in VEX that seems to be the best.

I know this year team 303 used #25 chains (which we did not have problems with) with Mecanum wheels which I really did not like that much.

Re: Best Drivetrain
 

Pink also has some of the best engineering support in FIRST.

#25 chain is strong enough, as long as you understand all the forces and requirements that will be put on it. A rookie team may not have such understanding ... thus the safety margin that #35 chain provides may be wise.

Re: Best Drivetrain
 

Could someone from team 233 please post up some pictures of your drivetrain. I have always loved it whenever I get a chance to see it up close but I didn't get a chance to look at it at Championships

Re: Best Drivetrain
 

Ah, the 2WD caster system (without the casters). A word of advice--while it works fine, you want the traction wheels under the CG as much as possible. (Or rather, the CG over the traction wheels.) Not too much, but if you have the traction wheels in the rear, you want your CG aft of center. This allows for better control.

Bear in mind that 2WD can be pretty squirrely. You might want a 6WD with a dropped center--it turns kind of like a 2WD, but has extra wheels that will assist in traction.

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On our FTC bot this year the CG was a little bit forwards of the rear wheels so it worked well. My guess is if we did an FRC bot next year we would go with a six wheel drive system using omni wheels on outside with traction wheels in the center. Just on another note whats the best kind of omnidirectional drive in the real world and not just looking a pros and cons of the designs of each.

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little hint, i would advise never to do a 2wd setup with the wheels centered in the bot and 4 casters at the corners, why? because if you get tipped forward or backward at all you have no power going to the ground, reason #2 you have almost no resistance to turning so without some nifty programming and maybe a gyro it will be a pain to control.

If you do a 2wd put the driven wheels at one end of the robot, that makes it so if you tip you have twice the chance of having power to the ground than a 4 caster setup, this also uses the inertia of the robot to provide resistance to turning and results in a much more controllable setup.

I also suggest Omni wheels above casters, as when casters spin around they put unpredictable "whoop de doo's" into you motion.

Also you can power omni wheels to provide additional forward traction rather than wasting weight on dead wheels.

An example of a 4wd 2 grippy 2 omni is our 2006 robot, search for any videos of IRI 2006 and our bots the fridge with the orange bumpers(which by the way is sick)

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OK, that might work. Don't go with a "rocker" system if you do, though. That's too much maneuverability.

Actually, I just remembered. 494 did this a few years ago...
Corner omnis. The idea is a 4WD with the traction wheels on, say, left front and right rear. The other slots are omnis. Apparently it works pretty well.

Omnidirectional drive is the holonomic/mecanum/crab/swerve drives. The best type depends on the game.

Mecanum: 4WD with specialized programming and each wheel independently powered. Oh, and mecanum wheels.
Omni: 3-6 omni wheels arranged so that you can slide. It's a little trickier than mecanum.
Crab/swerve: each wheel turns. 3-4 wheels.

Re: Best Drivetrain
 

Actually Pink has no mechanical engineers.

Re: Best Drivetrain
 

I think both of you miss understood me but its my fault since I am not quite down with this 2WD, 6WD... etc... lingo. :)

The best setup I think of for a FRC bot is a 6 wheel tank style bot using omni wheels as casters on the outside wheels and traction wheels in the center. I would also make it so all wheels would be touching the ground.

Also I understand what omnidirectional is and the different types of it but I was asking what seems to work best in different situations.

Re: Best Drivetrain
 

Here's one option that hasn't been said yet: 4 wheel drive, with omni wheels on opposite corners. This worked really well for my team last year, and was easy to maintain. Having the omnis on the corners increases turning ability but not to the extent that your robot turns too fast. It also works well for climbing ramps and such.

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but we gots a good left hook
mike d

Re: Best Drivetrain
 

i've seen you guys practically do chinups on the overpass, noones doubting your bots, your bots are the only things that could make me "okay" with the color pink :D

Re: Best Drivetrain
 

Team 303 did use #25 chain on our robot and we had only one problem: when a gusset came loose during practice and got caught in the chain. I can assert that our chains were not perfectly aligned, so I am not sure how precise #25 needs to be to be reliable.

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I know this year we direct drove the centered wheels of the AM supershifter3's
it DEFINITELY had its advantages when rogue robots would decide that our chains needed a tearin'

Re: Best Drivetrain
 

Lol, sorry "that FRC team I was on" is 303. Really, I did not know that we broke a #25, that happen in Atlanta?

Re: Best Drivetrain
 

Here's a quick interpretation with the setup you described:

2WD--Center wheels are the only powered ones.
4WD--Center and one end are powered.
6WD--All wheels are powered.

Now, I want to warn you, that setup can be easy to turn. There are ways to fight that, however.

A similar setup is the "rocker" setup. If you see the Kitbot frame, one hole right in the middle is lower than the rest. The "rocker" or "drop center" lowers the middle wheel slightly to give the same maneuverability as a coplanar with omnis on the corners, but it's harder to turn because all six wheels are traction wheels.

What works best in different situations depends on the game. Some teams are able to make mecanum or swerve work year after year. Others stick with skid steer (the standard 2WD, 4WD, 6WD, tank tread). Others switch between the two depending on the game challenge. I really can't answer that question before January.

Re: Best Drivetrain
 

Team 612 has found the easiest drivetrain to build and use is the 6 wheel drive train (along with everyone else in the thread). I'll save time and not explain the benefits of this drivetrain as our fellow FIRSTer's have clearly explained this in previous posts.

One suggestion for building your 6 wheel drive train is the use of Belts and Pulleys rather than chains. They save lots of weight and are just as strong if not stronger than chains. Belt and pulley suppliers (ex. Gates) will provide you with the correct spacings for your belts and pulleys to ensure the perfect tensioning, this can help you if you CAD your robot. Along with that belts don't stretch (slightly if anything) but not as much as chains do. Before 2007 my team used chains and had numerous problems. Once we switched to belts in 2007 we have been hooked.

Here is a picture of our belt setup, if you have any other questions please feel free to PM me. http://www.chantillyrobotics.com/photo_gallery/main.php?g2_view=core.DownloadItem&g2_itemId=6177& g2_serialNumber=2

Re: Best Drivetrain
 

I do like that setup but I alway did not like the idea of letting the robot rock since it seems unstable to me but it is probably fine. Also depending on which way the robot is traveling and weight distribution it could really mess things up. I looked at a nice 6wd setup by team 25 at the NJ regional and in Atlanta. That seemed to drive very nicely. I am guessing how much you drop the center wheels can also make a big difference in driving since I heard from one of my fellow 303 team members that a 6wd drive they tried last year jerked around a lot since they did not drop the center wheels enough.

By the way what was team 1114 using on there drive train? Looked like a 6wd all traction wheel setup.

Re: Best Drivetrain
 

Lil' Lavery says they used 6WD drop center traction. Take a look at his list: 217 (x2), the entire championship alliance (2007), 1114 (2008), 330 (2005).

You don't have to have a lot of drop. The best results come between 1/8 and 3/8. Weight distribution will affect handling; put the weight to one end so it doesn't rock as much. 25 uses coplanar 6 traction; they force their turns.

How much you drop the center wheel will affect handling, but not quite that much.

One thing: Like I say, drop center doesn't mean you will rock automatically. Find 330's matches from 2005-2008, any match. They don't really rock noticeably. Every single one of those robots has 6WD drop center. And only two have ever tipped completely: 2005 went over endwise once, and it was pulled over, and 2006 went down leaving the ramp once or twice. 2007 and 2008 almost went over sideways once each. It isn't all that much rock. A low CG will help keep the robot upright.

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During our 2 years of experience with 6 wheel drive, we have found that 1/8 " was a bit to little of a drop, and 3/16" was about right. When we went with 1/8" in 2007, we couldn't turn the robot very well in high gear. This year, we went with 3/16 " and it worked quite well. There are probably many threads on that topic somewhere though.

On a side note, it would be interesting to take this year's bot and try out a couple of different drop distances because it only involves cutting 4 more plates and spot welding them together to change the height of the center wheel on last year's bot. Hmm.

Re: Best Drivetrain
 

Then I am truely in awe.

Their arm design and drivetrains are always exceptional.

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Doing this would require exact spacing on the drive axles, which means the drive train (including chain runs) is done in CAD. I only learned CAD last August, but was able to CAD most everything on our '08 bot in Solidworks. The one thing I didn't have time for was wiring and chains. Could anyone direct me to a short tutorial on how to properly make the chain and mate it in Solidworks?

Re: Best Drivetrain
 

The drop of your center wheel should be dependent upon how rigid your frame is. We build a very rigid frame every year (welded box beam inner frame with drive "pods" bolted on each side). Last year we did 3/16" drop and it was a little too much for us, this year we went for an 1/8" drop, and guess what, it was still a little too much for our liking.

As you can see in this video: http://www.youtube.com/watch?v=OBTPLcIByU4 we have no problems turning, even with only 1/8" drop in the center wheel

Re: Best Drivetrain
 

Just wanted to highlight the points that reinforce what I was getting at. Drive is not a system you have to spend all season on anymore. If its your teams first year you're better off driving with what you are given in the kit, and spending the effort on coming up with a way to score points. I love the kitbot for this reason.

Also I agree 25 is strong enough for a drive, but that wasn't the point I was making. I have used both #25 (2004) and #35 (2003, 2005, 2006, 2007, 2008) successfully with only minimal maintenance. As a design mentor I tell the students every year why we use 35, because its more forgiving of tolerances.

Re: Best Drivetrain
 

Yeah sure, I'll upload some tonight when I get home, might be kinda late though.

Re: Best Drivetrain
 

You also need to take tread wear/how frequently you change tread into account when setting the drop.

Re: Best Drivetrain
 

Last year we used wedgetop...we changed tread at every competition...this year we used nitrile, we never changed tread, and we never had a problem turning.

But yes, tread wear should also be factored in.

Re: Best Drivetrain
 

I would say, for creative drivetrains that work well enough. Build ours!!! Linkage drive is not that hard to do and it gives you all the fun of omni / swerve drive!!

And its reliable (only broke once, and it was a dumb mistake on our part)

But thats just a creative solution, not by any means the most popular choice, but if your like us, we like to think outside the realm of 6WD!

go creativity!!!!:D

Re: Best Drivetrain
 

If 330's tread wears too far, they change their wheel.

That's one other thing. There are these devices that McMaster sells called pneumatic casters. Take the wheel out and it's pretty high traction. You'll need your own hub, but that isn't too hard.

Re: Best Drivetrain
 

One solution that hasn't been mentioned yet is using six wheel drive without the drop wheel and a reduced friction wheel on the outsides. We used this setup this past year and it worked out quite well (that combined with inset corner wheels) after some practice. For the "scrub wheels" we used IFI's with worn out rough top flipped over so the backing was contacting the floor. I found this to be ultimately superior to omni wheels for two reasons. The first is that if you are tipped forward or back they offer more traction that an omni wheel does. The second is while turning it adds just enough scrub to slow the turning down to a reasonable speed (reducing the "squirrellyness"). It does however reduce your overall pushing force per wheel due to your weight force being divided over 6 wheels vs. 4 and also due to the lower friction on the corner wheels. That said, we deemed that trade-off acceptable for the maneuverability and over power loss of the system.

Re: Best Drivetrain
 

No corrections to be made, but I WOULD like to point out that taking the fact that there are more 6WD drive, etc. teams on this list as proof that it is a better way to drive and that there is no benefit to more exotic types is somewhat suspect logic and silly generalization.

The reason I say this is that lets say that in the data for 2005, there are what, 800 or 900 robots? Sure, hypothetically. But lets say there were 30 robots with crab drive built that season. Well, in that case, one could say that swerve drive is over-represented, and that obviously, building a swerve drive will afford you a better chance of doing well and getting in the finals, because while only 30 teams had swerve drives, one of them made it (1/30 odds) while then there were probably around 200 robots with 6WD, only two of them made it (1/100 odds.) I'm not saying this data doesn't have ANY merit, but come on guys, lets be responsible in our generalizations. In order to use this kind of analysis, you'd want to make it more statistically valid by either opening it up to all the regional and championship division winners of a particular year.

I've designed three drive trains in my tenure in FIRST, 1 4WD tank with omni (6-motor), 1 crab drive (4 pods, 2x2 chained together), and this year's 6WD with AM Supershifters. I have also given a presentation on drivetrains with Bill Beatty.

But what I would recommend to ANY team is that you shouldn't say "OH THIS DRIVETRAIN IS THE BEST 6WD 4EVAR" and be done with it. You really need to take some time and think about your design requirements--what you want the robot to be able to do, and then build a drivetrain to those capabilities.

The other thing you need to consider very closely (and this is echoed in the ANSI#25 vs. ANSI#35 debate) is your manufacturing and designing capability.

If you are a team that works in a garage with a hacksaw and a couple power drills, you are simply not going to be able to build a lot of really exotic drive systems without outside help. The reason is that many of these systems require tight tolerances (if you want to build your own gear reductions effectively) and if you are off by even a minuscule fraction, you can bind the whole thing up. If you have the capability to do this kind of stuff and build exotic systems, I actually very much encourage you to do so as long as you feel it is in line with what you want to do with your robot.

In terms of DESIGNING capability, if your team has lots of experience building drivetrains, have at it, do what you want. If you are a rookie team, I might encourage taking it easy for perhaps the first year and going with a simpler drivetrain and focusing on manipulator design and also programming. You can do a lot of amazing feats programming even a simple skid-steer robot. But once you have been in the community for a season, even a single regional, you will start to see all the stuff that has been done and is being done--you'll be more familiar with the "state of the art" and be that much more experienced, and ready to go for the next year. Then build something you think will be neat like a swerve or a linkage drive (woo Winnovation!) in the off-season, make sure it works like a charm, and then implement it on your season robot. This way, if you don't get it to work in the off-season, you can still just build the robot with the kit-drive or something else that you KNOW will work. I encourage this methodology for veteran teams too! Plus, you can have a second, better iteration of the design for the season with all of the bugs corrected.

Finally, whatever drivetrain you build or choose to build, learn it inside and out. Learn EVERYTHING about it, how it feels when you drive it, etc. Build SENSORS into the design. Try to do some modeling (mathematical, or build a little replica out of wood, or even a little Vex robot) so that you know how it can move and you can think about how you will control it.

Autonomous driving is only going to get more important guys, lets not kid ourselves.

So I guess, I can sum up my comments as follows:
1.) There is not necessarily a BEST year-after-year drivetrain.
2.) Decide on your drivetrain including your robot goals, manufacturing capabilities, and design experience as parts of the equation.
3.) It is awesome to be innovative and unique (I LOVE INNOVATIVE AND UNIQUE) but please do it in a safe fashion so that what hits the field isn't a janky prototype but a second-iteration. This will help your team, all other teams, the spectators, etc.
4.) If you're a rookie, you need to take a GOOD LONG LOOK at your capabilities, and it may be wiser to take it slow and learn the ropes, and build something phenomenal in the next season.
5.) Whatever you do, think about the design carefully and take controls into the deepest consideration.

Re: Best Drivetrain
 

Personally I like a 4 wheel tank drive. With two cims motors going in too a gear box with direct drive shafts. This may not be the best but it is my personal favorite.

Matthew Simpson
Team 75 Driver

Re: Best Drivetrain
 

What is the advantage of a direct drive?

Re: Best Drivetrain
 

If your chains break, the wheel that you have direct driven still has power. And at least for us, it means one less chain to tension and design for. With that in mind, if you are going to go with direct drive and then run chains to the rest of the wheels you want power to in the drivetrain, drive the one that will be transmitting the most power to the floor, and/or will yield simpler chain paths, and/or will be the one you want to still be connected to your drive motors if your chains fail.

Re: Best Drivetrain
 

One wheel is guaranteed to work.

The problem is that the wheel sends its load straight to the gearbox. It's also a little trickier to do. It can be done, but it takes a little doing. I think 254 has done it in the past. You might want to talk to them a bit.

Re: Best Drivetrain
 

I know they have been doing it at least every year since 2004. I don't know about before then though.

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The impact loading on the gear teeth isn't reduced by a final chain reduction or spread out across a chain wrap around the sprocket. Theoretically you can fracture gear teeth easier with this type of loading.

I've never run the calcs for a drive train to what the loading for this is, but I have seen it some of the other gearboxes we've built that don't have a clutch or other slip mechanism in them.

Re: Best Drivetrain
 

125 did it this year too.

We extended the center wheel shaft into the gearbox where it was coupled via gears to the rest of the cluster. It worked out really well, although it was a bit tricky to pull off.

Re: Best Drivetrain
 

if your using chain drive and something hasen't yet broke, something soon will..

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Not if you designed, built, and maintained it properly.

Re: Best Drivetrain
 

I was not trying to suggest that any drive-train was superior, I was just supplying facts. Notice how I didn't even post any conclusion, just raw data. Some may have drawn erroneous conclusions from this, and I apologize for that, but that was not my intention. It would be silly to judge this data without full numbers on the amount of teams, teams with each drive, and other data. But, sadly, most of that data either doesn't exist, or would be next to impossible to compile, and to make any assumptions about it could and would lead to equally erroneous conclusions. It would be plain stupid to ignore the manipulators, software, electrical reliability, drivers, strategy, and alliance formations of each of the champions as well.

Take it with a grain of salt. It isn't showing the relative superiority of any drive method, rather showing the drives that a handful of successful teams have selected and done well with, for whatever reason, since 2005. Strong teams with strong engineering principles selected these drive-trains for various reasons, that's all I'm saying.

Re: Best Drivetrain
 

We also used direct drive this year for the first time, going to a pair of half-tracks centered along the sides for added stability in tight high-speed turns. Also, we wanted to try something different using our success in past years with tank treads.

I agree with Peter, though--a chain to the drive shaft does offer that protection from impact loads, especially with the higher-speed gearbox that we went to after our first regional. Those stresses may have transferred to the tread belts and may have been the cause of a couple stress fractures. We were fortunate that we never lost one during a match--they were found during pre-match checks.

Re: Best Drivetrain
 

After a few days of watching TBA and reading some of these posts, I'll make perhaps the only valid & incontravertible sweeping generalisation for FRC:

The best drive train is the one that works every match.

This includes all of the subsystems such as electrical wiring, pneumatics (if you shift or have linkages), voltage of the battery at the start of the match, and the control system the drivers use. These concepts should be drilled into rookie teams just as much as any other drive train concept. They are just as important since (well, without voodoo magic) the robot can't move without them.

Re: Best Drivetrain
 

I guess I just wanted to make sure that nobody was making those erroneous conclusions ;) . I didn't mean to imply that you were in particular, my apologies.

On another note, and somewhat drivetrain related, does anyone have experience with using the Gates synchronous belting that has been supplied with the kit on a drivetrain?

Re: Best Drivetrain
 

See the post by Shan of 612 earlier in this thread.

Re: Best Drivetrain
 

I like direct drive myself! Mainly because our linkage wouldn't work without it (generally... I suppose I could find a way.. but direct drive is the easiest way). That and because we don't have precison tools, tension is harder to maintain (it can be done, but is done much better with pecison)

We used all direct drive this year (4 omnis), those banebot transmissions have a nice long output shaft for that!!:D

Re: Best Drivetrain
 

Team 418, Purple haze has been using #25 chain for 5+ years and never had any failure in the chain itself. we have very limited machining and fabrication capabilities, limiting to a manual lathe, chop saw, band saw, and drill press. it really is not difficult to construct a functioning drive train with those tools and a large Tsquare. not only that but since before 2007 they had 3/4" plywood bases with aluminum pillow blocks (made form box alum wit ha band saw and drill press) and bearings from mcmaster.
honestly there is little trouble from #25 chain besides tension, and there are plenty of easy solutions to tensioning the stuff, that require little more than a idler sprocket or delrin or something like that, and you probably wont need to tension that chain more than once, unless you go to multiple regionals and nationals and i double that many rookies are doing ALL of that. in other words #25 is perfectly sufficient for the purposes of a FIRST rookie team, and allows that extra 5 lbs to go towards something else more deserving

Re: Best Drivetrain
 

Often the key to meeting proper tolerances is not the equipment, but rather the people using it. If you have experienced people using basic manual tools, they will produce good results. If you're involving high school students with minimal experience in your build process, sometimes those tolerances don't end up quite as tight as you would like. I'd rather just use #35, and then not have to worry about it.

Re: Best Drivetrain
 

I saw this, especially the sentence i've bolded out, and had to comment. 6WD isn't a hard or expensive thing to build. I was a rookie this year but if you ask me, I believe it should be built before the kickoff. just have a vote on the second or third day wether you want to change it or keep it after you see what the game will be like. This year, we didnt do that. Our lead mentor insisted on what Eric said, and we ended up finishing our drivetrain on the second week (we've ordered sprockets on the end of week one). So here its a bit differen because after you order something here it takes it a week and a half to come.
So that was my 0.02$ :)

Re: Best Drivetrain
 

You are not allowed to build your competition robot before the build period starts, which is the kickoff. Anything you build before that date is not legal for competition.

Re: Best Drivetrain
 

To add to what Rick said: There were possibly rumored cases of this happening in the 2004 season. Size constant, build now, we'll do the manipulator later.

The result: Instead of 36" x 30", you now have to fit in a 38" x 28" box. If you try that and say that on here, there is a risk that the GDC will decide to change the sizing on you.

The size has changed AT LEAST three times that I know of. Something small, 36" x 36", 36" x 30", and now 38" x 28".

Re: Best Drivetrain
 

Oh cmon. The Robonauts are using the same compex mechanism for three years now (correct me if i'm wrong). I'm sure the didnt build the whole thing from scratch this year. And even if the did i know of a lot other teams doing that..

Anyway, I do thank you for the comment, I personally didnt know that and Its good to know. Its probably best not to educate the rookie teams to bend the rules..

Re: Best Drivetrain
 

[quote=zivo123;744793]Oh cmon. The Robonauts are using the same compex mechanism for three years now (correct me if i'm wrong). I'm sure the didnt build the whole thing from scratch this year. And even if the did i know of a lot other teams doing that..

I would be interested in the list of all those other teams that you know about
mike d