Best Drivetrain

[R.C.]

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

[Rick TYler]

what drivetrain has been the most dominant from the 2005 season and on?

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.

[sdcantrell56]

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.

[JesseK]

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.

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.

[hipsterjr]

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.

[Rick TYler]

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.

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.

[sdcantrell56]

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.

[Mr. Lim]

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

2007 Super-Rookies - 2056 Patriotics (http://www.thebluealliance.net/tbatv/team.php?team=2056&year=2007)

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 =).

[EricH]

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.

[Lil' Lavery]

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

[EricH]

FIRST Champions:
2005:
330- 6WD, higher traction center wheel (possibly dropped)
Dropped is definite. (It's also variable drop, if you play with it--the center wheel was pneumatic.)

[Billfred]

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.

[CraigHickman]

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?

[Peter Matteson]

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?

[CraigHickman]

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?

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!

[XXShadowXX]

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...

[Billfred]

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?!(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?)

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! 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.

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!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.

[AdamHeard]

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!

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.

[EricH]

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.

[CraigHickman]

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.

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.

[EricH]

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.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.

[waialua359]

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.

[Aren_Hill]

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

[MrForbes]

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...).

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 :)

[sdcantrell56]

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.

[Brandon Holley]

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



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.

[JVN]

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.

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.

[Pat Roche]

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 ;).

[s_forbes]

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.

[Tom Bottiglieri]

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.
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

[Rick TYler]

For flat game (no climbing) the simplest and most efficient drive train that you can build is two powered wheels that are center aligned with "skid wheels" such as hard plastic caster wheels that don't turn.

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).

[Lil' Lavery]

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.

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.

[Daniel_LaFleur]

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

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

[Brandon Holley]

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

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.

[Chris Marra]

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.
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!)

[Jeff Waegelin]

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

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.

[Brandon Holley]

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!)

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...

[Doug G]

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/vanden/clubs/robotics/Sitefor07-08/pics/06-07/BuildSeason/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.

[K-Diddy]

We had a 3WD drivetrain with crab drive.

[Tom Bottiglieri]

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...
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.

[thefro526]

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.

[=Martin=Taylor=]

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.

[Lil' Lavery]

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.

What about defensive robots? ;)

[JVN]

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.


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

[=Martin=Taylor=]

What about defensive robots? ;)

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.

[EricH]

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

[Triple B]

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

[Lowfategg]

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.

[Daniel_LaFleur]

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

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.

[sdcantrell56]

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

[EricH]

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. 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.

[Lowfategg]

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.

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.

[Aren_Hill]

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.

Two Words:
Normal Force.
-John


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)

[EricH]

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.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.

[Cory]

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

Actually Pink has no mechanical engineers.

[Lowfategg]

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.

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.

[BBnum3]

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.

[Triple B]

but we gots a good left hook
mike d

[Aren_Hill]

but we gots a good left hook
mike d

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

[DMetalKong]

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 the FRC team I was on used #25 chains (which we did not have problems with) with Mecanum wheels which I really did not like that much.

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.

[Uberbots]

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.

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'

[Lowfategg]

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.

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

[EricH]

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.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.

[deshirider430]

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

[Lowfategg]

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.


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.

[EricH]

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 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.

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

[AustinSchuh]

The best results come between 1/8 and 3/8.

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.

[Daniel_LaFleur]

Actually Pink has no mechanical engineers.

Then I am truely in awe.

Their arm design and drivetrains are always exceptional.

[JesseK]

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

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?

[Brandon Holley]

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.


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

[Peter Matteson]

#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.


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.

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.


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.

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.

[ducttapedude]

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

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

[Peter Matteson]

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

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

[Brandon Holley]

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

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.

[T3_1565]

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

[EricH]

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

[Pat Roche]

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.

[Nikhil Bajaj]

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

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.

[chessking132]

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

[R.C.]

What is the advantage of a direct drive?

[AustinSchuh]

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.

[EricH]

What is the advantage of a direct drive?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.

[AustinSchuh]

I think 254 has done it in the past.

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

[Peter Matteson]

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.

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.

[Brandon Holley]

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.

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.

[XXShadowXX]

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

[MrForbes]

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

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

[Lil' Lavery]

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 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.

[M. Mellott]

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.

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.

[JesseK]

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.

[Nikhil Bajaj]

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.

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?

[Lil' Lavery]

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?

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

[T3_1565]

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

[roboticWanderor]

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.
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

[Jeff Waegelin]

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

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.

[zivo123]

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.

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$ :)

[Rick TYler]

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.

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.

<R27> Prior to the Kick-off: Before the formal start of the Robot Build Season, teams are
encouraged to think as much as they please about their ROBOTS. They may develop
prototypes, create proof-of-concept models, and conduct design exercises. Teams may
gather all the raw stock materials and COTS COMPONENTS they want. But absolutely no
fabrication or assembly of any elements intended for the final ROBOT is permitted prior to
the Kick-off presentation
<R28> During the Build Season: During the period between the Kick-off and ROBOT shipment
deadline, teams are to design and fabricate all the COMPONENTS and MECHANISMS
required to complete their ROBOT.

[EricH]

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".

[zivo123]

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.

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..

[Triple B]

[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

[EricH]

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.They have used the same basic drive and arm strategy for a while now.

But I am sure they do NOT use the same mechanism from year to year! We were all surprised when they unveiled the V6 in 2007. They improved it the next year.

Oh, by the way, if you're going to accuse 118 of this, then you also need to go after the following:
--254/968 (drive)
--60 (drive)
--25 (drive)
--330 (most of the robot, 2005, 2007-2008)
--16 (drive)
--233 (arm and drive)

You see my point? A lot of teams build on old designs. They don't necessarily use the same parts (which is also prohibited--no build pre-kickoff, and no re-using mechanisms from old robots). So I'm guessing that they just say, "Does this work for the game? If not, how do we change it?" and then re-engineer to optimize for the new game. They build in 6 weeks just like every other team.

[AdamHeard]

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..

That is quite an accusation, and I am sure they did build the whole thing from scratch after the kickoff date.

[T3_1565]

once you build a drivetrain, it becomes very easy to build again from scratch, so although it may seem prebuilt (because they finish so fast) its not, its just they have all the resources set up to build something, all bugs were worked out on the other system, and all upgrades were prototyped.

I know for a fact it took us 3 weeks to build our Linkage drive during build season, and I know we could put another one together (given we have metal to do so) in about 4 days. Once you have a plan, things come together very easily.

[Brandon Holley]

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..

wrong answer my friend...

Your first assumption that is completely wrong is that they have been using the same mechanism each year. Look at their DT last year and this year....they are not the same, although they may accomplish the same result (swerve/crab drive that totally rocks)


What else have you heard about other teams?

I guarantee they build the entire thing in their given timeframe.

You cannot make allegations with no support against other teams on this forum, its not fair to them, or to anyone else that cruises chiefdelphi because then someone has to take the time to explain to you how wrong you are about this.

There is no rule in FIRST about tweaking an old design and using it again in a year, this is the advantage experience brings.

[Lil' Lavery]

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..

The robonauts have been using a swerve drive since 2005. Each of their robots have had turreted manipulators seated on top of it during those 4 years. The similarities end quickly after that. They have constantly evolved, just unveiling their "V6" last year, and updating it again this year (no DeWalt this time). They have made massive updates and advancements to their electronics each year, and their manipulators have varied greatly as the games vary.
Just because a team uses similar designs each year, doesn't mean they cheat. It means they have found a system that they find works for most games, and ways to implement it year after year successfully. And just because its complex doesn't mean it's cheating either. 118 has a history of technical proficiency, some of the best mentors, and very smart and dedicated students. I'd suggest you do a little more research before making such bold claims.

[zivo123]

Wow i didnt meen this to come off like this..
First of all, i am truely sorry i've accused 118 for bending the rules. It was based on nothing and it was a false accusation.

The other teams i was reffering too are mostely from Israel, where this rule is not beeing checked at all and when i think about it, its probably for a good reason:
Because there are a lot of things that we have to order from the states and are not available here. Usually it takes there things about a week and a half to arrive and the cost us about three times of the original price because of the delivery and custom payments. As you can see i was reffering to the order of parts, thats at least what i've meant.

So im sorry for my previos posts and if i've affended anyone...

[EricH]

I would like to make one note: While you can't actually build anything for the competition robot before Kickoff, you can order parts and test designs pre-season. Then it's a lot easier to do them in the season, because you already have some idea of what's going on.

[JimWright949]

Another good source of parts are previous years robots. 949 in it's seven year history has only kept three and a half robots complete, the rest have been taken a part and reused in other years robots. You can't use the machined aluminum but the bearings, wheels, and sprockets are all in good condition. You do have to remember the cost of the parts from year to year to report it on the parts list.

-Jim

[EricH]

Another good source of parts are previous years robots. 949 in it's seven year history has only kept three and a half robots complete, the rest have been taken a part and reused in other years robots. You can't use the machined aluminum but the bearings, wheels, and sprockets are all in good condition. You do have to remember the cost of the parts from year to year to report it on the parts list.

-Jim
Yep, that is legal, provided that they're not assembled into the mechanism that they were in on the old robot. Also provided that they aren't custom when removed.

[zivo123]

I wish weve had three and a half robots to keep alive. every year we are forced by budget issues to take out all of the parts you mentioned from the previous robot..

[Richard Wallace]

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".I really hope someone from GDC is reading this. IMHO, we are overdue for a new robot footprint. I'd like to see it get smaller, maybe 35" x 25" or something similar.

A smaller footprint would encourage lighter robots. It might also encourage finesse (read: manueverability and control), rather than raw traction, as a distinguishing feature of FIRST's most capable machines.

-------------

I agree the best drivetrain is the one that gets your robot in position for a scoring attempt, or to stop an opponent's scoring attempt, or to support your ally's scoring attempt, and right quick. Which type that is will always depend on game design.

931's last five drivetrains were:

2004 -- custom 4WD with four independent motors, two 9" pneumatics, two 9" custom dual omniwheels. Not finished early enough to perfect control, but reasonably effective.

2005 -- 6WD with #35 chain and 4" Colson wheels, powered by two kit transmissions (thanks, Paul -- those were incredibly tough and easy to use). We unfortunately put a great drivetrain on a questionable chassis, made from 8020 with poorly reinforced corner joints.

2006 -- custom holonomic. We built our own ominwheels and gearboxes, and a custom chassis made from aluminum channel with gusset plates and lots of 1/4-20 clinch nuts. A work of art that won a design award at IRI, but not particularly effective for keeping our ball shooter on target.

2007 -- 6WD with kit gearboxes on a kitbot chassis, #35 chain to the kitwheels on the center and #25 chain to the AM aluminum omniwheels on the corners. Very reliable and manueverable, resulting in a good offensive robot when the defense was light. We were easy to turn when defended heavily.

2008 -- custom live axle 8WD with #35 chain to the four center wheels, and #25 chain to the 1/8" raised corner wheels. AM Supershifters with one CIM per side. Very controllable, resulting a consistent 4 line hybrid mode and good speed during teleo.

Our custom drivetrains in '04, '06, and '08 were all fun to build and we learned a lot. But my overall takeaway is this: if it looks feasible to use a 6WD kitbot chassis next year, I'll be pushing the team to do that.

931 won regional Chairman's Awards in both of the years that we used 6WD with kit gearboxes. :) Coincidence? Or does spending less time fiddling with custom drivetrains allow us more time for other aspects of our program?

[Rick TYler]

I really hope someone from GDC is reading this. IMHO, we are overdue for a new robot footprint. I'd like to see it get smaller, maybe 35" x 25" or something similar.

I thought the weight/height rules last year were a good start. How about leaving the footprint the same and reducing maximum weight by 25%? That would generate some creative engineering, and force some serious priority-setting.

FRC robots have been pretty much the same since I've been with the program. I think it's time to start making some steam rise up from overactive brains.

[IbleedPink233]

I think that the width requirement was intentional - just barely small enough to get through doors with the bumpers on. The GDC is trying to give us problems to solve wherever we go with the robot. One of the disadvantages I see to going to a smaller footprint is the impressiveness factor. One of the most common comments that I get is "I didn't realize the robots you kids make were so big." Bigger is not always better, but it is often good for showing off, one of the best ways to promote FIRST.

[EricH]

I think that the width requirement was intentional - just barely small enough to get through doors with the bumpers on. I understand that you are mostly correct. Back in the day, the teams with 36" by 36" robots had a hard time fitting through standard doors, as I understand it. So they changed it. They changed it again, before bumpers didn't count against weight or size.

[The Lucas]

I would like to make one note: While you can't actually build anything for the competition robot before Kickoff, you can order parts and test designs pre-season. Then it's a lot easier to do them in the season, because you already have some idea of what's going on.

If you build a preseason prototype drive and decide it fits the game, it can become your practice bot. When the season starts, give it to your auton programmers and let them tune their code while the mechanical teams are building the competition robot. If you build similar drive trains every year keep your old robot together because it can also be used for this.

[roboticWanderor]

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.

heh, one thing we do pride ourselves in is that our robot is practically completely designed and built by students on our team. and i assure you, if we can lay out a great chassis with a t-square, anyone else can, at least with little bit of care and thought, anyone can learn to draw a line strait or drill a hole right, thats what mentors and teachers are there for. what i am saying is that #25 chain is as simple and easy to use and work with as 35. also, sprocket spacing is a lot easier (each link is 1/4 inch long, making spacing a snap)!

[AdamHeard]

heh, one thing we do pride ourselves in is that our robot is practically completely designed and built by students on our team. and i assure you, if we can lay out a great chassis with a t-square, anyone else can, at least with little bit of care and thought, anyone can learn to draw a line strait or drill a hole right, thats what mentors and teachers are there for. what i am saying is that #25 chain is as simple and easy to use and work with as 35. also, sprocket spacing is a lot easier (each link is 1/4 inch long, making spacing a snap)!

#35 chain has much more room for spacing and alignment error as it larger and stronger.

For a team already struggling with a drive, get it done with #35, and then maybe work on #25 in later iterations.

#25 isn't a magical thing to be afraid of, but definitely requires decent tolerances.

[waialua359]

I believe one of the factors of not changing the footprint in recent years is due to cost. If the footprint were to change, lets say to double the size, that would mean a larger kit frame, longer chain, etc. which may cost FIRST or some other vendor more to create. It may also not be feasible for the playing field size to have 6 robots on at the same time.
I truly believe one of the big issues with the 2008 game is that the field was too small to have 6 robots fighting traffic trying to achieve the game challenge.
Also, if the footprint changed by just a few inches, why even do it?

[EricH]

Also, if the footprint changed by just a few inches, why even do it?For the same reason that they changed it in 2005. Prevent teams from pre-building drives.

[waialua359]

For the same reason that they changed it in 2005. Prevent teams from pre-building drives.

I think you can essentially create the "same/similar" type drivetrain even if the dimensions change by a few inches.

[Cory]

For the same reason that they changed it in 2005. Prevent teams from pre-building drives.

Who says that's why they did it then?

[EricH]

Who says that's why they did it then?Something I heard back then. I'm not sure on accuracy. Maybe they did it just to give an extra challenge.

[Cory]

Something I heard back then. I'm not sure on accuracy. Maybe they did it just to give an extra challenge.

I just don't remember any discussion about such a situation, back then.

[David Guzman]

This year we (1251) decided to try something new for us. An 8 wheel drive, it worked great for us, lots of traction when being hit/pushed side ways and it could also turn on dime. The key was how far apart the wheels were width wise and having the front two wheels 1/8 higher.

As far as chain goes we love 25 chain. We have used it in 07 and 08 w/o major problems, in both arms and drive train. Last year we were having issues at our last competition because our robot had such a beat up. and the sprockets on the wheels started to get bent and throw the chain off. The important thing to use 25 chain successfully is the alignment of the sprockets. This year (2008) we used live axles and 25 chain and we never lost one. The chains that were put on the robot back in February are the same ones that are on there now.

[T3_1565]

One of the disadvantages I see to going to a smaller footprint is the impressiveness factor. One of the most common comments that I get is "I didn't realize the robots you kids make were so big." Bigger is not always better, but it is often good for showing off, one of the best ways to promote FIRST.

Agreed! This is one of the best ways for us, as a team, to get interest. Something that is big, flashy, makes noise and looks dangerous (even if it isn't) always seems to draw attention from us high school students (and I'm not sure why...:P)

[Brandon Holley]

Agreed! This is one of the best ways for us, as a team, to get interest. Something that is big, flashy, makes noise and looks dangerous (even if it isn't) always seems to draw attention from us high school students (and I'm not sure why...:P)

Do you really think a 2 inch change is going to be so noticeable that people are not going to be impressed by the size of your robot?

[T3_1565]

Do you really think a 2 inch change is going to be so noticeable that people are not going to be impressed by the size of your robot?

I dont see the point in reducing it by only two inches! every other change has been at least 6 inches (if I'm not mistaken).

And I find a 6 inch change to be huge! our 2007 bot is 6 inches smaller than our 2008 bot, and its surprising to here students comment on how much bigger our 2008 bot is, and how "wimpy" (there words not mine) the 2007 bot is lol.

[EricH]

I dont see the point in reducing it by only two inches! every other change has been at least 6 inches (if I'm not mistaken).The last one was 2" in each direction. You could tell the difference.

[Brandon Holley]

The last one was 2" in each direction. You could tell the difference.

Yes you can tell the robot is a little longer, and little skinnier but saying that takes away from the overall impressiveness is just plain not true.

[Tom Bottiglieri]

Yes you can tell the robot is a little longer, and little skinnier but saying that takes away from the overall impressiveness is just plain not true.
Why do people go to Monster Truck shows? :p

[Cory]

Why do people go to Monster Truck shows?

To see stuff getting ran over/crushed.

[T3_1565]

To see stuff getting ran over/crushed.
by giant trucks!

[Triple B]

thats what im talkin bout!
mike d

[usbcd36]

I understand that you are mostly correct. Back in the day, the teams with 36" by 36" robots had a hard time fitting through standard doors, as I understand it. So they changed it. They changed it again, before bumpers didn't count against weight or size.

I agree that it was done to make it easy for robots to get through doorways. We blew up the trackball inside our robotics room this year, then realized that the ball was 40" in diameter, but the doorway was only 36" wide. Not a big problem, since the trackball deforms with enough force, but if it had been the robot instead of the trackball, I would've cried.

[mrs. p]

but we gots a good left hook
mike d


i saw that fight

[RobJ]

i saw that fight

Cory has to go in for surgery next week.

[vivek16]

One recommendation for any type of drive train: make sure you can accomodate for unforseen problems in the future regarding weight. Try to make it as light as possible. Budget out your weight strictly.

We had to remove a wheel from our omniwheel drivetrain. This is why we were fishtailing so badly during the MN regional.

-Vivek

[sgreco]

From my experiences I would recommend that most teams build 6 wheel skid steers with slightly dropped centers.

On another note, swerve has the most capability because it has full power in all directions and can instantly change direction.
My advice would be to try to develope a swerve drive in the offseason and if you aren't comfortable with the swerve drive by the build season then go with six wheel skid and finish developing your swerve drive for the next year.

[Lil' Lavery]

On another note, swerve has the most capability because it has full power in all directions and can instantly change direction.
My advice would be to try to develope a swerve drive in the offseason and if you aren't comfortable with the swerve drive by the build season then go with six wheel skid and finish developing your swerve drive for the next year.

Swerve cannot "instantly change directions", it has to allow for the wheels to be re-oriented. Holonomic and Mecanum systems are as close as any FIRST team has come to instantly changing directions, but even they still have to overcome momentum and interia.
Additionally, while you retain essentially full power from your drive motors, you don't apply any of the power from your steering motor into your drive (in any swerve system yet implemented in FIRST), so it never really has "full power". However, it still can apply equal force to a scrub steered (4WD, 6WD, etc) system, something that holonomic and mecanum systems cannot do (assuming the same motor configurations).
Swerve has a great deal of capabilities and potential, and allows you a lot of strategic options. Some methods, however, do reduce (or eliminate) certain functionalities while enhancing others. 118 and 148, for example, could not rotate their robot's frames. 148 had no reason to, though, and 118 overcame it by placing their manipulator on a turret. Both were able to save weight and increase power by centralizing their drive motors though. It is also the most resource intensive drive system.

[R.C.]

What about the crab and tank drive trannies?

[EricH]

What about the crab and tank drive trannies?What about them? What do you want to know? We can answer, but you'll need to be a little more specific than that.

[R.C.]

For starters how to build one. The pros and cons. Also the weight comparison and some pics of the best ones

[EricH]

I think the team to look at (or teams) are 118, 16, and 148. Those three raise the bar/push the limit every time they do a crab/swerve. 111 as well. (Two championships and a finalist on crab/swerve, plus regional wins/finalists, isn't bad.) Weight comparison--can be heavy compared to tank drive.

Now, how to build...Coaxial? Crab? Swerve? (There is a difference between crab and swerve.)

Pros: maneuverability and power and speed in one package to a greater extent than skid/mecanum/omni drive

Cons: may take time to turn, may require a turret, heavier, more complex.

If you're going to do one, start prototyping now.

[Jetweb]

For starters how to build one. The pros and cons. Also the weight comparison and some pics of the best ones

In addition to the teams who have already been posted, I would add 1625. There swerve drive was up there with the best of them and they published a lot of info about it on this site that a simple search should find.

[hillale]

Cons: may take time to turn, may require a turret, heavier, more complex.

If you're going to do one, start prototyping now.

Turning is definitely something to look into, either programming a way for the wheels to turn a certain direction when told to go to a specific point (if doing a coaxial, they may take the longer way around). As far as the turret goes, we powered the front/back wheels separately and were able to tank drive sideways at the start of the season to reorient (slow/painful). However during/after our 2nd regional we developed "drift" buttons. Pressing one of these buttons would cut power to either the front or rear gear box, allowing the robot, while moving sideways, arc in orientation. Once our drivers figured out how to best optimize these buttons, reorientation was much easier and a whole lot less painful (we still used tank steer, but not nearly as much).

In addition to the teams who have already been posted, I would add 1625. There swerve drive was up there with the best of them and they published a lot of info about it on this site that a simple search should find.

Thank you for the recognition. Our team is very proud of our third iteration swerve drive, which handled 3 regionals and champs without any throwing of chains or any mishaps at all, actually. Being able to drive a swerve is something else, but the control system this year takes a lot of practice.

[Kellen Hill]

Yeah, just ask my brother, Aren Hill, if you have any questions about our swerve or just swerves in general. He has done our drive train the past 2 years and made our swerve a beautiful thing to watch. If you want to know how good our swerve was, you can take a look at his signature which has a quote from JVN.

[R.C.]

Are the banebot gearboxes any good? In 07 the teeth kept chipping and it locked up 6 times in 2 regionals and the championships. Also any personal experiences?

[AdamHeard]

Are the banebot gearboxes any good? In 07 the teeth kept chipping and it locked up 6 times in 2 regionals and the championships. Also any personal experiences?

I don't have the most experience with them, but I am very familiar with the AndyMark line of gearboxes. No matter what good experiences people have had with the 56mm banebots, I've heard far too many horror stories for me to ever consider using them. The AM gearboxes are a far superior option in most situations.

[Smaug]

Drive train: simplicity is key. keep your center of gravity low.we have used the same chassis for three years and it will except about anything you through at it. the past couple of years we have use a 4 wheel drive because it is simple and so versital.

also our programmer and figured out how to get crab to rotate so we dont need a turret.

[vivek16]

I have actually been thinking about that. Couldn't you lock the wheels of a crab in a 4wd orientation and (if you have each side independently driven) just turn like a 4wd bot?

Has anyone attempted this?

-Vivek

[Lil' Lavery]

I have actually been thinking about that. Couldn't you lock the wheels of a crab in a 4wd orientation and (if you have each side independently driven) just turn like a 4wd bot?

Has anyone attempted this?

-Vivek

Yes, teams have done this before. Look at 111's swerve drive for a great example.

Swerves have a great deal of flexibility in how they perform and how they are built. Each configuration will result in different strengths and weaknesses.

[thefro526]

I have actually been thinking about that. Couldn't you lock the wheels of a crab in a 4wd orientation and (if you have each side independently driven) just turn like a 4wd bot?

Has anyone attempted this?

-Vivek

You can do pretty much anything you can imagine with a swerve. Just if you have a coaxial like 148 or 118 where there's only one central gearbox providing power to all of the wheels you can't turn like a tank. With some tricky Programming and the ability to steer either side independently then you could turn in theory but it wouldn't be easy. My suggestion would be, if you have a vex kit you could prototype a bunch of swerve drives and try different motor configurations and control systems.

[Pat Roche]

You can do pretty much anything you can imagine with a swerve. Just if you have a coaxial like 148 or 118 where there's only one central gearbox providing power to all of the wheels you can't turn like a tank. With some tricky Programming and the ability to steer either side independently then you could turn in theory but it wouldn't be easy.

That's not necessarily true. The reason 148 or 118 can't turn like a tank is because it has on central gearbox powering the entire drivetrain (not the rotation but the wheels). Coax crab can still be accomplished using two (or more depending on your preference) independent gearboxes that control the wheel nodes independently. If you only have one gearbox then regardless of programming you won't be able to turn like a tank.

[AdamHeard]

That's not necessarily true. The reason 148 or 118 can't turn like a tank is because it has on central gearbox powering the entire drivetrain (not the rotation but the wheels). Coax crab can still be accomplished using two (or more depending on your preference) independent gearboxes that control the wheel nodes independently. If you only have one gearbox then regardless of programming you won't be able to turn like a tank.

If the wheels are steered separately in pairs, one pair can be turned 180 and steering in place is possible.

[Pat Roche]

Right, exactly. You also don't necessarily need to limit them to 180 degrees of rotation (I understand the argument of why you would I'm playing devil's advocate). You could use a coaxial style setup (shaft inside of shaft) and run two sides of the robot independent of each other. In that case you are still doing a 'crab drive' as we have coined the term. The difference being the two sides are independent of each other rather than being run all off the same rotator and power transmission.

[thefro526]

With some tricky Programming and the ability to steer either side independently then you could turn in theory but it wouldn't be easy.

lol that's what I said earlier, but it's still only spinning in place.

[Andrew141WOBOT]

It really depends on the game... our 2008 bot drove like a car. 2 Cims, direct drive, to each rear wheel, with an electrical differential. The front wheels drove used the acrynom principal, so when the bot was turning left, the Left front wheel turned more than the right. It was really strong this year, but it probably won't for any other game.

[Rick TYler]

The front wheels drove used the acrynom principal

Ackerman principle, not acronym principal. :]

[Aren_Hill]

I have actually been thinking about that. Couldn't you lock the wheels of a crab in a 4wd orientation and (if you have each side independently driven) just turn like a 4wd bot?

Has anyone attempted this?

-Vivek

We did, We had one gen2 driving the front two wheels and one on the back two. So if we wanted to "tank drive" we just pointed the wheels sideways and drove around like a wide bot (wider=less effort to turn). This setup also enabled us to create "drift" buttons, We had 2 buttons on the joystick base and each one cut power to the respective transmission. So when we were going sideways we could kill a gearbox and the other one would drag its end around. This enabled us to effectively reorient on the fly, which greatly decreased our lap time.

[R.C.]

I was wondering, what if you leave omni's in the front and put one dewalt to each of the remaining wheels. Direct drive or chain drive???

[Aren_Hill]

I was wondering, what if you leave omni's in the front and put one dewalt to each of the remaining wheels. Direct drive or chain drive???

I'm guessing your talking 6wd? If so this would create a very robust drive if done correctly, yet i suggest you mechanically link the driven wheels on each side so if one set is off the ground all the power still is driving the wheel touching the ground. I believe RUSH 27 has used a similiar setup before, at least in '06.

[R.C.]

So youre saying to power each wheel but link them by using chain and would this style of drivesystem be more effecient than the standard gearbox on each side thing

[EricH]

So youre saying to power each wheel but link them by using chain and would this style of drivesystem be more effecient than the standard gearbox on each side thingI'm not sure about efficiency, but you don't have to worry as much about putting, say, 2 CIMs into one DeWalt. On the other hand, you just added 2 DeWalts to your robot, which adds weight. (Assuming a 6WD.) You may gain efficiency (fewer gears in interface) or lose it (chain slop, twice the gears for the same amount of power). You have a fully redundant drive system, though; theoretically, any one motor can power the entire side even if the other motor's gearbox explodes all over the field.

[R.C.]

It still wouldn't be as much weight as a supershifter and i remember that rush got up to 18 to 20 feet per second with drive system and Erich, you are right about the slight chance of losing efficiency

[AmoryG]

Now I've done searches, but I've never seen any team attempting a "ball drive" drive train. It might be under a different name, but it's simply a drive train that uses spheres for wheels. I've tried to think of a few ways of doing this, but because I have no examples to follow I can't say any of my ideas would work.

With spheres you could rotate the ball in different directions without having to rotate the thing that holds the ball inplace. The ball wouldnt have to be a complete sphere.

Has anyone tried to do this successfully?

[EricH]

Now I've done searches, but I've never seen any team attempting a "ball drive" drive train. It might be under a different name, but it's simply a drive train that uses spheres for wheels. I've tried to think of a few ways of doing this, but because I have no examples to follow I can't say any of my ideas would work.

With spheres you could rotate the ball in different directions without having to rotate the thing that holds the ball inplace. The ball wouldnt have to be a complete sphere.

Has anyone tried to do this successfully?Team 45 prototyped such a design a few years ago. I'll see if I can find it.

[edit] Tom beat me to it.

[Tom Bottiglieri]

Team 45's ball drive
http://www.chiefdelphi.com/media/photos/15197

[AmoryG]

That's a really neat drivetrain. It's interesting because this is much different from all of my ideas I've had so far. I turned my thoughts away from doing it like this because I always imagined the ball would slip around or would be too smooth to control. It's nice to see an effective way to use balls instead of wheels.

But are there any designs which are effective using only balls and no wheels? That's what I'm going for.

[EricH]

That's a really neat drivetrain. It's interesting because this is much different from all of my ideas I've had so far. I turned my thoughts away from doing it like this because I always imagined the ball would slip around or would be too smooth to control. It's nice to see an effective way to use balls instead of wheels.

But are there any designs which are effective using only balls and no wheels? That's what I'm going for.Not that I know of, however, it could be done given enough motors. I think the reason is, not enough decent motors. You need 2 per wheel, and that means 8 motors. Yeah, we have that many. No, they aren't all what we'd want for that. We'd need 4 CIMs, 2 FPs, and 2 globes. Not enough decent motors left to put much on top of the drive, unless pneumatics are used for an arm. (Banebots, window, and maybe van door are left.)

[AmoryG]

Actually pretty much all of my designs require 5 or less motors. One for each ball and one to change the direction all of the balls spin.

My newest design requires as few as 2 motors, but it would be extremely impractical with only 2. It would require 3 or 5 to work well. I'm sorry I can't really describe it, but I'm only willing to explain once I get the design done in solidworks.

Another thing I need to work out is how I can hold the balls in place so they're held loose enough to rotate freely, but it would be impossible for them to come out of it's casing without taking it apart.

[EricH]

Actually pretty much all of my designs require 5 or less motors. One for each ball and one to change the direction all of the balls spin.I think that's what we call a crab drive.:p

I think the main reason that ball drives aren't more popular is that there are swerve, crab, omni, and mecanum drives to choose from, some of which are simpler and some of which are more complex to plan and easier to build.

[AmoryG]

I think that's what we call a crab drive.:p

I think the main reason that ball drives aren't more popular is that there are swerve, crab, omni, and mecanum drives to choose from, some of which are simpler and some of which are more complex to plan and easier to build.

Actually, yea, it is pretty much crab drive... but it still would like pretty:cool:

But my latest design is far different from what I originally intended to do. My first designs involved using a sort of gear like wheel above the ball which would be attached to the motor. The gear would run along the top of the ball and on the poles there would be a turning mechanism where you could stop moving the ball and turn in another direction. The wheel above would rest on a turning device which would be controlled by controlled by the 5th motor.

Now I received criticism from my mentors that it would be too difficult to land on the exact tooth to have it turn. It would also be a slow job if it were possible since you would need to slow the motor down so it COULD stop when it needs to.

So instead of teeth the wheel on top of the ball would have bumps on it and on the sphere it would have sorts of crators. The bumbs would fit into it and because it would fit loosely inside you can stop at anytime and turn when you need to.

But yet again I'm rethinking the design. The whole point of what I'm designing is to make a drive train that is extremely menuverable and controllable which at the same time obtain a fast speed. Rolling it from the top like a normal gear doesn't sound like it could reach the highest speeds and having to stop the robot to move again everytime would make it even slower.

That's what I'm trying to solve and I think my latest idea might be an improvement compared to my original ones.

[Lil' Lavery]

Not that I know of, however, it could be done given enough motors. I think the reason is, not enough decent motors. You need 2 per wheel, and that means 8 motors. Yeah, we have that many. No, they aren't all what we'd want for that. We'd need 4 CIMs, 2 FPs, and 2 globes. Not enough decent motors left to put much on top of the drive, unless pneumatics are used for an arm. (Banebots, window, and maybe van door are left.)

This comment got me thinking...
There's already been an idea posted to implement a ball drive in a similar fashion to a crab, but there are boundless other motor possibilities.
Once I have some free time I might try and run some vector calculations and see what I can come up with. Even toying around with the idea in my head I can think of a couple relatively simple ways to control the drive with 4 (or fewer) motors, in a very similar fashion to a holonomic system. The question then becomes to you gain any advantages over a holonomic system, and that's where I'd need to run a few calculations to see if this configuration could allow for any new types of movement (my suspicion is no), or more efficient movements in any direction.

[T3_1565]

I doubt you will find any advantage, besides the cool factor!

I think it would be neat to make a holo-ball drive!

(Thats also what I was thinking reading the other posts before you Larvey)

[EricH]

This comment got me thinking...
There's already been an idea posted to implement a ball drive in a similar fashion to a crab, but there are boundless other motor possibilities.
Once I have some free time I might try and run some vector calculations and see what I can come up with. Even toying around with the idea in my head I can think of a couple relatively simple ways to control the drive with 4 (or fewer) motors, in a very similar fashion to a holonomic system. The question then becomes to you gain any advantages over a holonomic system, and that's where I'd need to run a few calculations to see if this configuration could allow for any new types of movement (my suspicion is no), or more efficient movements in any direction.Great... I guess I now know how to find engineers/engineers-in-training. As in, give them a challenge.

I've done a little thinking and it could be pretty fun to try a coaxial crab on top of the balls. Then again, why not just put it on the floor?

[Colin]

I think 45 beat you to the punch on that.

http://www.firstroboticscanada.org/site/files/active/1/335_large.jpg

[EricH]

That's the drive type we've been discussing today...

[AmoryG]

Well, with a ball drive system it would be kind of like having crab drive. I imagine it to be slightly better than crab drive. I know this can't be proven until an effective ball drive robot is made (only balls are used to drive the robot), but I suspect that since rolling a ball in any direction seems kind of more "natural" for a ball to do while rotating wheels around to drive in another direction doesn't seem so much so it sounds to me it's possible ball drive could potential perform better than crab drive. Like I said I can't prove this, but it's worth putting it to the test in my opinion. You can't stop trying to look for other ways to do things, or that really defeats the whole purpose of inovation.

[T3_1565]

you might have a little more manuverability with balls but I can see less pushing power as a sarcafice. I still think it would be mega cool to do. You would have to think of the balls material very careful and find the best balance of grip and slip lol.

[Richard Wallace]

Has anyone here taken apart a Dyson ball vacuum cleaner (http://www.dyson.com/usa/dysonball.asp)? I wonder if the innards of that ball drive could be retrofitted with an FRC kit motor?

[cooker52]

Looking at it, I'd love to. Taking it apart and using it in FIRST, that might be difficult. Using the concept on a robot, very probable. Thinking about it, you could have the whole setup like a normal wheel, and then make the platform yaw left and right to turn the bot. This could get you down to two casters on the back of the robot for stability, and then you would have a pretty cool robot to show off.

Traction may be an issue, though...

[AmoryG]

you might have a little more manuverability with balls but I can see less pushing power as a sarcafice. I still think it would be mega cool to do. You would have to think of the balls material very careful and find the best balance of grip and slip lol.

Well, like I said before I'm trying to create a fairly simple design and as far as I can tell there would be no sacrafice of power. And the ball surface would be similar to bicycle tires.

[sgreco]

Now I've done searches, but I've never seen any team attempting a "ball drive" drive train. It might be under a different name, but it's simply a drive train that uses spheres for wheels. I've tried to think of a few ways of doing this, but because I have no examples to follow I can't say any of my ideas would work.

With spheres you could rotate the ball in different directions without having to rotate the thing that holds the ball inplace. The ball wouldnt have to be a complete sphere.

Has anyone tried to do this successfully?

I don't know if anyone has done this successfully, but I have never seen it done successfully. Most teams that are looking for motion like that would do a swerve drive or use mecanum wheels.

[Madison]

Now I've done searches, but I've never seen any team attempting a "ball drive" drive train. It might be under a different name, but it's simply a drive train that uses spheres for wheels. I've tried to think of a few ways of doing this, but because I have no examples to follow I can't say any of my ideas would work.

With spheres you could rotate the ball in different directions without having to rotate the thing that holds the ball inplace. The ball wouldnt have to be a complete sphere.

Has anyone tried to do this successfully?

This isn't quite what you're describing, but take a look at this thread - http://www.chiefdelphi.com/forums/showthread.php?t=40770&highlight=hemisphere - for an interesting drive idea that's similar.

[AmoryG]

Well, my the fact that swerve drive and mecanum wheels have already been used in quite a few robots before hand makes it clear that one of the reasons so few have tried to create a ball drive robot is that it just hasn't been proven effective. As I said before it's impossible to know until a good example of it has been made. By a good example I mean a ball drive robot that ONLY uses balls and doesn't use any wheels to help it move.

M.krass, that's an interesting idea. I'll take a better look at it later.