Re: Team 2471 swerve drives
 

Thanks, as I said earlier, I wasn't able to fully understand your programming papers. So I was hoping you could tell me if our current programming is similar to what you guys call ocelot drive.

Re: Team 2471 swerve drives
 

How much pushing power does this have? I have always liked this idea but it never seems practical if you are going up against any mildly strong defensive team. I feel like you could be smelling those motors after a small pushing battle.

Re: Team 2471 swerve drives
 

Theoretically, swerve is just as strong as a matching tank drivetrain with the same wheels and gearbox ratios. However, from what I have heard the big problem with independent swerves is that when you get into a pushing match two wheels tend to come slightly off the ground, causing you to lose 50% of your power.

Re: Team 2471 swerve drives
 

The small motors are just used for rotation, so there's not a ton of risk of burning them out in a pushing match.

Pushing performance is tied to how the CIMs are geared. At 17 FPS like these modules, probably not as pushy as a shifting drive or at a lower speed. CG is also a factor as ideally it should be low enough that tipping off of a wheel or two isn't as easy in a pushing match.

Best of luck on getting the code on this up to 1717's standards. The vast majority of swerves never get there, but with time in the off season to prepare it's totally possible. I love the mechanical design, especially the gearbox made from a single piece of extrusion.

Re: Team 2471 swerve drives
 

This robot's "pushing power" will be minimal,(although I estimate it is about 100 lbs) but what I don't think many people understand about swerves is that it is the best drive train for getting around defense.

When many tall geared offensive robots try to get around a defensive one, they dodge left or right early. To do this they must slow down a little. Then the slower D-bot (defensive robot) begins to move in that direction. The D-bot is not fast enough to get directly in the way of the O-bot, (offensive robot) but it can run into the side of the O-bot. In most situations this costs the O-bot a few seconds because the friction between their bumpers is high enough that it is difficult to get unstuck.

Now if an S-bot (swerve bot) has an defender in the way, it can head full speed directly at the D-bot without giving away which direction it is planning to go. Then, with just a few feet left between, the S-bot can dodge on way or the other without slowing down, their is no D-bot that I know of that would be able to accelerate fast enough to get in the S-bot's way.

Now, lets say that S-bot wants to play defense. They still will never have to get in a pushing match. Because S-bot is most likely as fast as any robot it will face, S-bot just predicts where O-bot wants to go then just sits in the way. In our programming, every time you let up off the joy sticks, the wheels make an X formation. So to push S-bot when it is not moving would require that O-bot have more traction than S-bot and Have so much torque that It can Break loose S-bots wheels.

So in conclusion, we will not be able to push other robots but they won't be able to push us either, and we will be able to change direction almost instantly while moving at high speed.

PS. sorry for the long post, but I just find it strange that many people think a swerve robot would be easy to push.

Re: Team 2471 swerve drives
 

Thanks, I did almost all of the mechanical design summer after 2012, so it's nice to finally see it in person.
On a side note, as light as the gearbox is right now, another change I am considering for the season is the wall thickness. As it stands, it has .25" wall, and I think the welded frame of the robot would fall apart before the box would see a dent. I'm thinking of .1875" or .125". I know that that .1875" would be strong enough, (I've personally jumped up and down on a piece) but the rest of the robot frame is always made from CNC'd .125".

This is a factor that I had considered but I frequently forget about. Thankfully the CoG of this robot is approximately 5" off the ground. It's one if the lowest robots my team has built. I also think a low CoG improves the driving performance, much like a car's handling is affected by its CoG.

Re: Team 2471 swerve drives
 

These swerve modules are really neat. I like how you have pocketed out plate on the wheel holder.

I'd keep the bottom plate at 0.25". The top plate could probably be 0.1875", or maybe eve 0.125", but the bottom plate has to handle the load from your thrust bearing. To save weight you could cut away some of the bottom plate that goes around the CIM motor. In the first picture you could probably remove quite a bit of material from the side. You could get creative with the shape of the plates. The only sides that need to be flat are the ones that you are welding to, so you could do something that isn't a square. Also, it's probably worth making the swerve modules stronger than they need to be. We also make our robot's frame out of 0.125" thick aluminum, but we've dented it before. If the swerve modules get dented, it's not good.

Re: Team 2471 swerve drives
 

Thanks, Those pocketed side plates are personally my favorite part. That is part of why I am reluctant to change them to add more strength to side load.

Good suggestions. Although, I think your concern about the bottom plate may be unwarranted. Our first test box had .1875" wall, and to prove a point I set the box on the ground. Then I put one foot on the plastic collar that ends up supporting the robot (we aren't using a thrust bearing). I proceeded to jump up and down on that foot. There was no visible deflection in the box. I wouldn't describe myself as a big guy, but I weigh about 145 lbs. So I'm pretty confident that the bottom plate could handle being .1875" thick. I like your idea of making some parts thinner than others though.

Re: Team 2471 swerve drives
 

There are easy ways to get around this. Putting drop down casters on one side of the 6wd causes the defensive bot to spin the offender instead of t-boning it.

The second you telegraph your moves the defensive robot can react. I doubt this delay is long enough where the defensive robot will actually have a hard time blocking you. Furthermore, good defensive robots are going to predict and trap, effectively neutralizing this advantage. Furthermore...

what makes you think if that you can predict your opponents moves they cannot do the same on you.

In conclusion, I'm not saying that swerve is a bad drivetrain. There are clear advantages like precise movement and not telegraphing moves. However, I personally find that a 6wd can accomplish your same goals with good drivers, lots of practice, and a few small additions.

Re: Team 2471 swerve drives
 

Interesting idea, I've never seen it before in competition, but it sound cool none the less.

Your right, as soon as S-bot begins moving in one way or the other, D-bot can begin reacting to that. My point was that S-bot is already going 14-17 fps and S-bot is going zero. A six wheel drive O-bot could also be going that fast but they slow down when they turn.

My other point was that S-bot does not give away which direction in intends to head based on the robot orientation. Where as O-bot must turn before it can start to head in one direction or the other this.

Originally, I was just trying to make the point that in general, it is harder for any given D-bot to form a pushing match against a swerve robot than a 6wd bot.

Re: Team 2471 swerve drives
 

Most FRC Drivers, especially at the regional/district level seem woefully unprepared. 2471 is not one of those teams. Sure, they are likely to see a little harder defense in elims and at champs, but so will any drive base/drive team...

Re: Team 2471 swerve drives
 

If the drive teams you see are unprepared then a 6wd should be able to get by them just as easily as a swerve.

Re: Team 2471 swerve drives
 

The point I was making, is that you can do this with any drive style, it really comes down to skill and experience.

Re: Team 2471 swerve drives
 

Sorry, I misunderstood. I thought you were rebuking rather than agreeing with me.

Re: Team 2471 swerve drives
 

4 wheel independently steered swerve allows several moves that are not possible with a non omni-directional drive. First a simple side slip. When approaching a defender just as they are about to hit side slip and go on your way. A improved version is the role out maneuver. Same as a slip except as the side slip begins add a chassis roll to it. Its all most impossible to get into a "well driven swerve". Our 2013 driver was very good at this. Look how far he took us. The defender does have more of a chance in a tight restricted area. Walls can be death and field structures. This year the pyramid sides formed a restricted zone. We could go under the pyramid and many times performed the roll out in this zone or went under the pyramid and on our way. Swerve only provides a competitive advantage if the driver is well trained and skilled enough to use the additional degrees of freedom provided by swerve. Alignment in the game is a big advantage to swerve. This year alignment to the feeder station and alignment for shooting were greatly simplified by swerve. So even if you manage to build a swerve system and mechanically get it right your only about half way there. The driver interface and driver training are just as hard. We recognized this and have been working very hard training our rookie drivers for 2014.