Re: Best Drivetrain
 

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

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

Re: Best Drivetrain
 

(insert standard inspiring and changing the culture retort here)

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

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

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

Re: Best Drivetrain
 

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

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

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

Re: Best Drivetrain
 

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

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

Re: Best Drivetrain
 

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

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

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

Re: Best Drivetrain
 

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

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

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

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

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

Re: Best Drivetrain
 

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

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

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

Re: Best Drivetrain
 

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

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

Re: Best Drivetrain
 

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

Re: Best Drivetrain
 

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

Re: Best Drivetrain
 

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

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

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

Re: Best Drivetrain
 

Down here in Greenville we like 6WD too!

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

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

Re: Best Drivetrain
 

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

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

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

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

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

Re: Best Drivetrain
 

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

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


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

Re: Best Drivetrain
 

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

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

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

Broken robots = stressful = no fun = less inspiration