Best Drivetrain
 

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

-rc

ps Pictures please

Re: Best Drivetrain
 

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

Re: Best Drivetrain
 

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

Re: Best Drivetrain
 

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

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

Re: Best Drivetrain
 

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

Re: Best Drivetrain
 

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

Re: Best Drivetrain
 

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

Re: Best Drivetrain
 

2007 Super-Rookies - 2056 Patriotics

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

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

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

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

Re: Best Drivetrain
 

Sorry, guys, but you are ALL wrong.

The correct answer is: we don't know.

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

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

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

Re: Best Drivetrain
 

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

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

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

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


correct me if any are incorrect

Re: Best Drivetrain
 

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

Re: Best Drivetrain
 

The most dominant drivetrains have a few common attributes:

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

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

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

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

Re: Best Drivetrain
 

What Billfred said.

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

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

Re: Best Drivetrain
 

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

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

Re: Best Drivetrain
 

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

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

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


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