paper: 1625 Swerve Through the Ages

Thread created automatically to discuss a document in CD-Media.

1625 Swerve Through the Ages
by: Dillon Carey

A brief paper covering why we used swerves, and what we have learned.

I started working on this paper at the end of the 2010 season, and recently remembered to finish it. Sorry about the delay.

swerve doc.doc (9.24 MB)

With all the discussion going on about omni-directional drivetrains, I remembered that I had never finished this paper.

Thanks Dillon! This helps allot on deciding what to prototype during the fall, not swerve. I personally think swerve is the best, but our team doesn’t have (resource wise) what it takes to build a swerve.

But a few questions,

On the 6wheel swerve was the middle wheel dropped?
How much time did it take to make the swerve (design and all)?
What resources do you recommend having to make a swerve (besides $$$)?

Wow Dillon, this is great! Always great to see awesome student-designed swerves. Our team is 3 iterative-years behind you guys (we started independently steered swerve in 2010), and it’s great to see how you guys have done it. Definitely agree with a lot of those lessons.

How’s your durability been, especially on the mini modules?

Yes, the middle wheel was dropped on the 6 wheel. It was adjustable via placing different sized spacers between the thrust bearing on top of the module and the frame. I believe we ended up with somewhere around 1/8 of an inch drop.

I started designing the first mini-module probably a month or so after the end of the 2009 season (basically once the burnout had worn off). overall I believe I designed 4 mini modules, and at least 3 drivetrains (I made 4 and 6 wheeled versions). If you include the system we used during the 2010 season, I spent the majority of the summer, start of the school year, and 6 week build season working on this. As far as a hour count goes, I really don’t have a clue.

As you can tell by the way the mini-modules are constructed, we relied heavily on our sponsor’s waterjet in creating them. However, I believe it wouldn’t be terribly difficult to create a similar module using CNC, or even manual, tooling. Programming was a very difficult step for us, it took upwards of a week to finally get a glitch worked out that wouldn’t allow the modules to spin all of the way around, so I would recommend having a competent programming mentor.

The durability had a few flaws to begin with, but I believe we worked them all out by the end of the 2010 season. On the first mini-module we used banebots wheels, which did not stand up to the abuse when we placed a robots worth of weight on them and spun them on the carpet. The second module we tried using bushings in. This didn’t work, and created concentricity and drag issues. The module we used during the season ran into one major flaw. We tried running a needle bearing on the upper shaft, which was hard anodized aluminum. Right as the elimination matches of our second regional began, the wear on the aluminum became enough to throw the drive sprockets out of alignment, causing the chain to come off if we hit any large bump. The final thing that was a slight problem during 2010 was the bottom flanges of the module. I had to extend them out quite a ways to enable the robot to go over the bump, and because of this they could be bent. This was never a big issue.

I saw a teaser of the 6wd swerve a while ago, its nice to see how it really works, the 45 degree swerve module is crazy, i would love to see it work.

Thank you so much for posting this. I hope other teams will follow your lead.

I would love to hear/see more discussion of your 2007 season. I feel this is important as it would be a frank discussion over FYSS (First Year Swerve Syndrome). Most teams that would like to emulate your success (you guys are great role models) should also understand the difficulty that first year is likely to bring.

The great thing about that teaser – it doesn’t appear that the 45-degree module has any ‘magic’ behind it other than specific sheet metal work. Even though there are issues with angled tread like they have, it’s a very creative approach to reducing the number of moving parts imo. I too would love to see a working concept.

Ok so how did this effect you chain run? Did you have to adjust the sprocket every time you put another spacer in? And since you only had 4wheels on the ground at a time were the front 2 wheels and the back 2 wheels in sync? and how did that work?

(sorry for all the questions, this is really interesting)

Dillion,
your modules are amazing (a lot smaller than what my team used this year). We used a “hybrid” swerve system. We had four modules, the front and rear wheels were turned as sets using window motors. The front modules were populated with omni wheels, and the rear ones had traction wheels. This was to allow us to drive it like a tank robot, as we had very little time actually practicing with the robot in swerve mode. This resulted in a robot that was easy to drive, but yet had some curious turning/ strafing abilities.

I would like to ask you how you guys set up your controls (aka, which buttons did what). We had difficulties coming up with controls that were intuitive enough to be driven without thinking about what buttons to push (this is for “true swerve”, without the omni wheels). If we can fix this problem in the offseason, I hope to convince the team that it is worth pursuing swerve drive this year (game allowing of course).

Thanks.

In 2007 we ended up having < 5min or so of actual drive time before competition, obviously not optimal for your first time with swerve. The auxiliary ended up not being too competitive so we ended up playing defense and being fairly good at it. What most people don’t know about st. louis regional in 2007 was that most of the time I didn’t know which way was forward due too our robot being completely symmetrical on 2 axes.

We threw the steering chain a few times due to some sloppy manufacturing and alignment stuff.

It was also a 3speed dewalt setup, which playing defense we stayed in low gear the majority of the time which was 3.5fps free speed…which happened to be just fast enough to stay between the opponent and the rack.

So I think we did decently well with it for the first time ever doing swerve in competition.

First of all, don’t worry about asking questions.

When we added spacers to adjust the module height, we also flipped spacers around to adjust the sprocket height. Even if it was slightly out of alignment it wasn’t a big deal, because of how long of a chain run it was.

All of the wheels were always pointing the same direction. There was one loop of chain that went around the entire robot.

We had 2 joysticks, which functioned just like a normal 2 joystick skid steer system. when you pulled the right trigger, it switched to single joystick swerve control. We added one other mode before champs, we called it 469 mode. we designed it specifically in case we had to play defense on 469. when you hit the top button on the right joystick, the modules turned 90 degrees and locked there. Then when you moved the joystick left or right, it strafed left and right. I ended up using only our “469 mode” and normal 6 wheel drive all the way through champs and IRI, barely touching the true swerve mode.

(This is where the idea for the 2011 lobster drive started)

2011 lobster? I would like to hear this

This is lobster drive.

It is common to refer to this as “crab drive”, to differentiate it from swerves with other steering designs… some of which have also been dubbed with various names (but few as widely accepted and understood).

**

I know that the different names refer to different styles, I just have never known whivh name refers to which orientation. On 1625 we usually just call them all swerves, then add some detail about the steering setup. Slightly less effective communication, but overall easier to understand in my opinion.

Can someone tell us more about these 45 degree modules? I’m confused how they would be oriented relative to the ground and robot, and how they would be arraigned into a full swerve drive. What advantages might these give over traditional 90 degree modules?

Thanks!

We’ve actually hunted down some 20deg or something bevel gears since then, but the goal of that module was to decrease the number of parts by removing the horizontal axle. It would still be oriented with the support bearing straight up top, but with the wheel running on an angle in relation to the floor.

Not on the top of the list if we do another swerve, but a fun idea to toy with nonetheless

I’d like to pitch making a swerve drive to my team because all we ever did was the traditional 4 wheel/4 motor drive (and mecanum this year). We really like the mecanum but we lost all of our districts in Michigan this year (especially Niles) due to us getting pushed around. On to my main question, I heard that crab/swerve drives can weigh a lot, how much does your swerve weigh?

Not to sound like a broken record, but if you want to make a swerve drive during the season, you should make one in the off-season first. Every team that I know of who has done swerve has either done one in the offseason first, and been very glad that they tried a swerve then first, or wished they had made one in the offseason before they made one during the season. Swerves are hard to build and program.