What Drivetrain?
 

So I made a thread like this last year and I'm once again curious what drive train did your team use for Ultimate Ascent. Here is a link to the old thread I'm curious how the two compare. http://www.chiefdelphi.com/forums/sh...vetrain+ poll

Re: What Drivetrain?
 

So, officially, my team used a 4 wheel tank but that was result of the products of the new robot dimensions and a wide orientation yielded a small enough track length for a 4WD.

- Sunny G.

Re: What Drivetrain?
 

I love how you added Mecanum as the only choice in italics

Re: What Drivetrain?
 

Actually, the italics denote the choice you voted for. For example, on my screen, '4-wheel tank' is italicized, as it was the choice I selected.

Re: What Drivetrain?
 

Guess I learn something new everyday.

Re: What Drivetrain?
 

Personally, I LOVE 6 wheel tank and think it can work for a lot of games.A lot of systems like swerve, west coast, ect are robot specific and strategy specific, while I think tank is easy to build, fix, and operate.

:)

Re: What Drivetrain?
 

Erm, west coast drives are a form (in my opinion the best form) of tank drive.

Re: What Drivetrain?
 

It would be interesting to compare the pit scouting data from CMP and IRI, FiM and MAR, or any other sets of tournaments or regions to see how different regions or events compare in drive train usage. I'm familiar with the CMP division pit-scouting and am anticipating something similar for IRI, but is there a giant Google Docs spreadsheet of pit scouting?

Re: What Drivetrain?
 

I agree, wholeheartedly! WCD is a great drive-train choice, but it is tank, executed well.

Re: What Drivetrain?
 

But I am a Swerve-Drive guy at heart. Yes, it is expensive (time, machining, weight, $s,...) and it is exceedingly difficult to execute well (and very easy to execute poorly). But well-executed Swerve-Drive is hard to beat as an FRC drive-train (this judgment is, of course, game dependent).

Swerve combines true 2-d drive capabilities with excellent traction. Since direction of travel is independent of chassis orientation, it does not telegraph intent like tank does. Its ability to vector drive force in any desired direction makes it formidable in defense as well as offence.

But this comes with a high price tag, which includes extensive and continuous driver training. This never stops for us.

Re: What Drivetrain?
 

Could someone please explain "butterfly" or "nonadrive"?

Re: What Drivetrain?
 

A butterfly drive is a drive train with four omnis in the corners and then a pair of deployable traction wheels to allow you to drive staiter and not being pushed, while also giving you a quick and nimble drive train with the omni wheels. Most these ive seen drive the two sets of wheels at different speeds resulting in a "shifting" drive train. ALthough some teams (148 maybe?) run all the wheels at the same speed allowing them to have omnis down on one side and traction on the other changing where the robot rotates. Here is some info on 3928's butterfly drive http://www.teamneutrino.org/seasons/...bot/butterfly/

A nonadrive is a butterfly drive but with a center set of omni wheels positioned perpendicular to the other wheels allowing for the whole drive train to strafe from side to side. Heres a video of 148s 2010 nonadrive you can see the drive train specifically at 1:10 and 1:33 http://www.youtube.com/watch?v=_hTyXQUgYLE

Re: What Drivetrain?
 

TIL

Re: What Drivetrain?
 

About them being the best, what do you qualify as WCD. They aren't the best for every team though. If I mainly used sheet I wouldn't be cantilevering wheels.

Re: What Drivetrain?
 

We used a 6WD West Coast Drive this year for several reasons:

Note: we have a square robot (27.5" x 27.5")

1. The field had no raised obstacles, so no need for mechanisms like in 2010 or 2012 to traverse the field.

2. It gives you the widest wheelbase/track possible for the size. (I suppose wheelbase is debatable because of the dropped center.)

3. Our drive base is very simple and easy to fix, just a piece of extrusion, bearing blocks, chain, and wheels. (Don't trust hex bearings.)

4. It gave us more room for electronics and other mechanisms because of how little space the entire drive system takes up.

5. The drive base is very maneuverable, the added ability to shift allows us to go around or under the pyramid quickly, in addition to being able to push through defenders.

I am sure there are other reasons, these are just the ones I can remember off of the top of my head.

Re: What Drivetrain?
 

The "standard" definition of a WCD is a 6WD drop-center, cantilevered wheels, live-axle, center directly driven off of the gearbox (usually a 2-speed gearbox), outside wheels chain-driven off the center axle.

I don't necessarily agree that WCD is the best of the tank drives, partly because it does take some precision to make and thus might be rather difficult for some teams, but it is up there if a team can build it properly.

Re: What Drivetrain?
 

What if your team switched drive trains through the season...

No, it didn't end well.

Re: What Drivetrain?
 

Last year, our team changed drivetrains at Championships. Try to avoid that.

Re: What Drivetrain?
 

Actually... Switching drivetrains is something you could get away with, IF you've planned correctly. For example, if you've got the extra hole(s) drilled already, it'd be relatively simple to go from 8WD to 6WD, or vice versa, or 4WD to 6WD, or 4WD to mecanum (with a pair of transmissions added). Planning correctly means that you built the robot to be able to switch--though it does not necessarily mean modularity.

330 did that back in 2005--the competition robot had an extra set of transmission slots so we could swap to mecanum from 6WD if we thought it was a good idea. The testbed--a Kitbot--ran mecanum. We didn't have the weight that year to switch. To this day, 330 has yet to run mecanum on a competition robot.

Re: What Drivetrain?
 

When you say extrusion, did you use something other than the normal 2X1 tubing?

Also whats up hex bearings?

Re: What Drivetrain?
 

The one year we did mecanum (logomotion) we machined our frame with holes to easily be able to add dropped center wheels if the mecanum didn't work. We were happy with it's performance because the ease of strafing to hang tubes and that games rules limiting defense.

This year we made major drivetrain changes at our second regional and we were inspected and driving by 2:00 on Thursday. It can be done if you plan properly and practice the change, a second robot is invaluable for this.

Re: What Drivetrain?
 

Not sure if this is what he was getting at, but I'll give it a shot. There have been a couple of issues with hex bearings this year. One of the main ones was simply supply. For a long period of time this season, hex bearings were completely sold out wherever you looked. There were also problems with the hex itself, which was often oversized or undersized.

1/2" hex bearings are sold out at VexPro and West Coast Products (although their store is down for maintenance). They used to be sold out at AndyMark, although it looks like they're back in stock with an order limit of 10.

Re: What Drivetrain?
 

Yes, we use 1/8" 1 x 2 aluminum extrusion.

The hex bearings are a problem because they shouldn't exist, at least not for 4 dollars. It seems that the vex pro ones are just normal bearings broached to fit a 1/2" hex shaft. The problem with this is that the added force on the corners of the shaft crack the inner race and render the bearing useless. This happened to use every couple hours of driving in practice, and a 2 times in competition. If you use hex parts, do it with round bearings if at all possible. (you can machine down a 1/2" hex shape on 5/8th shaft)

Re: What Drivetrain?
 

Has anyone else had this problem with hex bearings?

I'm curious because I know they're other teams that run WCD's with hex bearings and to my knowledge they don't have any problems.

How exactly were your bearings configured on your WCD? What was your bearing block setup like? How close together were your bearings? Did you do anything very different from the stereotypical WCD in your drivetrain?

-Adrian

Re: What Drivetrain?
 

There was a lot of discussion about their issues this build season.

Here is an example of one thread:

http://www.chiefdelphi.com/forums/sh...d.php?t=111513

Re: What Drivetrain?
 

Interesting. We have a lot of time on both our practice bots, and 4 events on comp. All on 1/2" hex bearings from AM; no failure or issue whatsoever.

Re: What Drivetrain?
 

I've never seen a hex bearing that came "out of the tube" with significant runout issues or race damage. We've bough bearings from AM, WCP and VP. That said, poor (read: >~.008 too tight) press fits, mishandling, or excessive loads can damage the bearings. Especially damaging is when you press on the inner race while pushing the outer race into a too tight press fit.

I've never seen using 1/2" hex broached bearings per se as a problem, but there are a couple of hypothetical workarounds. First, you could turn down the 1/2" hex to 1/2" round to fit in a bearing (this would only really work if the round bit was at the ends, so it wouldn't work right for a traditional WCD). Also, you can press a 1/2" hex broached 1/2" ID 3/4" OD brass bushing into the inside of a 3/4" ID ball bearing. We've done somthing similar with 3/8" hex in a 1/2" bearing. A little excessive, but it would let you use 1/2" hex unmodified in a bearing that didn't have the inner race broached. Others have mentioned fine foxes as well.

To answer the origional question, we did 4WD skid stear. It was solid but not excellent.

Re: What Drivetrain?
 

I can only talk for the VEXpro bearings. I forgot to mention that the entire first batch we got was nowhere near concentric, the second batch was still not great but we didn't have the time to wait for more. The Andymark/WCP might not have the problem of cracking, but the VEXpro ones sure did. Next year we will definitely be using round bearings.

Re: What Drivetrain?
 

We use Six wheel drop center.

Re: What Drivetrain?
 

3539 used a 6w WCD this year. The past two years, we used 8 wheel standard tank drive, but this year we tried WCD to open up the inside of our frame for our ground intake and we were EXTREMELY happy with the results. Our drivetrain was easy to build, easy to maintain, rugged, light, and extremely nimble. We had a 1/8" drop on the center wheel, direct driven from our gearboxes. Custom 6" aluminum wheels with roughtop tread. We were geared for about 13 fps, so we were able to drive around most other robots on the field. We were very satisfied with the WCD style and will likely be visiting it in the future.

Here's a little video of our robot driving around at Troy. It was fun to watch this thing go :)
http://www.youtube.com/watch?v=gnDLFystS1Y

Re: What Drivetrain?
 

To the people selecting "other", could you explain? Thanks!
~

Re: What Drivetrain?
 

Our robot: http://www.chiefdelphi.com/forums/sh...=3397+Serenity

It runs two wheels in the front, a floating omni-wheel in the back. It does not really fit into any of the categories that were provided, I believe it is called a "kiwi" drive, which is not on the list.

If you want reason as to why we went with this design, all of the details are in the thread linked to earlier.

Re: What Drivetrain?
 

A kiwi drive has 3 omni wheels all driven offset at 120 degree angles from each other the only team i know of that did one this year was 1425 but im sure there are others i havent seen. you can kind of see the drive in this video http://www.youtube.com/watch?v=jWGYa...ature=youtu.be

Re: What Drivetrain?
 

"Other" = no drivetrain.

Re: What Drivetrain?
 

We called our a "stingray" drive, due to the shape of the frame. I was just told by someone that it was kiwi, thanks for clearing that up.

Re: What Drivetrain?
 

The inverse kinematics for Kiwi are very simple and are shown here on one page.

Re: What Drivetrain?
 

Yes. We destroyed probably a half dozen bearings in a non-loaded low speed application. We ended up not using that particular mechanism on the robot. However, the incidents of failure left us with a very low opinion of the current generation of hex-bearings.

Our application was single shaft non-cantilevered (supported by bearings at both ends). The bearings blew out sideways after the races cracked.

Re: What Drivetrain?
 

That's amazing... I've never seen anything like it. We used hex bearings, and even Vex Pro hex bearings, on very high axial load, high torque and cantilevered shafts without any problems. Perhaps there was a bad set?

Re: What Drivetrain?
 

Interesting. Were these were vexpro bearings?

Re: What Drivetrain?
 

The VexPro hex bearings are complete garbage. All the other parts from vex pro are well made, and designed with attention to detail, but the hex bearings are awful. We have an older robot for demonstrations that has a transmission that uses a hex bearing (not on a cantilevered shaft). For 6 years and thousands of cycles in competition and at demonstrations, the original hex bearing worked. Then, we took apart the mechanism for cleaning, and we decided to try out the vex pro hex bearing. After 3 cycles of the arm, the bearing failed completely.

Re: What Drivetrain?
 

Same as us. Bad bearings, don't do that. :mad: