Best Drivetrain

[Uberbots]

Originally Posted by JesseK

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]

Originally Posted by DMetalKong

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]

Originally Posted by Lowfategg

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]

Originally Posted by EricH

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]

Originally Posted by Lowfategg

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]

Originally Posted by EricH

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]

Originally Posted by Cory

Actually Pink has no mechanical engineers.

Then I am truely in awe.

Their arm design and drivetrains are always exceptional.

[JesseK]

Originally Posted by 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

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]

Originally Posted by AustinSchuh

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]

Originally Posted by Lil' Lavery

#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.

Originally Posted by Jeff Waegelin

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.

Originally Posted by Doug G

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]

Originally Posted by 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

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

[Peter Matteson]

Originally Posted by Brandon Holley

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]

Originally Posted by Peter Matteson

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!!!!