Chief Delphi - Question about wheel preferences

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Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- General Forum (http://www.chiefdelphi.com/forums/forumdisplay.php?f=16)

- - Question about wheel preferences (http://www.chiefdelphi.com/forums/showthread.php?t=97938)

Andrew Lawrence

23-10-2011 17:28

Re: Question about wheel preferences

I see mecanums as an assist rather than a straight on defense. While it would be tough to use a bot with mecanum wheels to push aside a 6WD robot with treads, the maneuverability of mecanum wheels allow them to play defense in a more indirect sort of way. For example, there was a team at Cal Games yesterday who had a mecum drive, and used their mecanum advantage to heard tubes to their alliance, and to keep them away from their opponents. They executed a very good starvation tactic, and left the other team tubeless. We did a similar tactic at Cal Games, but we had a 6WD.

If you want to play defense, and can play indirectly without any opponents getting in the way, then mecanum is the way to go. If opponents pushing is a problem, then you may want to go with a stronger drive train.

IndySam

23-10-2011 18:23

Re: Question about wheel preferences

Quote:

Originally Posted by Marc S. (Post 1082250)

The reason i say it needs more practice is because, its omni-directional. While it probably doesn't require as much practice as a swerve drive it still has the complexity of one. A 6wd yes does need a lot of practice to make perfect but it is very easy for a new driver to control. I personaly have never driven a mecanum robot so my expirence comes from swerve drives.

Yes they don't need chains or sprockets, but they are still larger and very heavy. The larger diameter the wheel, the more force you need to excelerate regardless. Add weight and the required force goes up even further.

Yes maybe claiming that someone could push a mecanum with a finger was a exaggerated. Frankly I might just be spoiled by robots that can't be pushed at all.

I'm not trying to say whether they are better or not or when they should be used, I'm just tiered of the assumptions and rumors that are tossed around.

You say they need more practice but you have never driven one. You say they are very heavy but totally discount the weight and extra complexity you need for six wheel drive.

I just want everyone to know that when you state facts you better be sure of them.

IndySam

23-10-2011 18:26

Re: Question about wheel preferences

Quote:

Originally Posted by BJC (Post 1082255)

I have to say that I see way too many teams using mecanum drives that are opperating them like a tank drive. Mecanum drives can be effective if they are utilized properly. This requires practice. I know that 2337 does extensive driver training which utilizes a very different mindset then driving a standard tank. They practice stuff like using the opponent's inertia to assist them and peeling off of defenders; a lot of things that are nearly impossible for a tank to do because they REQUIRE the ability to move sideways. So I would say that they require a similar amount of practice for the driver to become proficent (you can never have enough practice) but an entirely different mindset. This is what most teams don't do and a part of the reason why mecanum wheels have a bad name.

Practice is practice, the statement was that they require more practice than six wheel is what I questioned, not if a team should use them. You just validate my point.

BJC	23-10-2011 18:45

Re: Question about wheel preferences

Quote:

Originally Posted by IndySam (Post 1082263)

Practice is practice, the statement was that they require more practice than six wheel is what I questioned, not if a team should use them. You just validate my point.

That's good because I was agreeing with you. Just pointing out that a different mindset is required when driving mecanum then a tank and that using a tank mentality when driving a mecanum drive makes for a poor combination and is generally ineffective.

IndySam

23-10-2011 18:48

Re: Question about wheel preferences

Quote:

Originally Posted by BJC (Post 1082267)

Man I hate it when people agree with me :)

Alan Anderson

23-10-2011 19:40

Re: Question about wheel preferences

Quote:

Originally Posted by Marc S. (Post 1082243)

3. Can be easily pushed(with 1 finger).

A lot of people have called "foul" on this point. I'll provide a teeny bit of support for it instead.

If you install the mecanum wheels backwards, you'll end up with a drivebase that can be spun with just a little bit of force applied at a corner. At the same time, it won't want to turn under its own power very well at all. So if you can push a mecanum drivebase easily with one finger, it has been put together wrong and just needs to be fixed.

Ian Curtis

23-10-2011 21:04

Re: Question about wheel preferences

Quote:

Originally Posted by IndySam (Post 1082263)

Practice is practice, the statement was that they require more practice than six wheel is what I questioned, not if a team should use them. You just validate my point.

IMHO, they require more practice because people aren't use to driving things that can slide sideways whenever they feel like it. People are good at picking up something they are use to... in the vast majority of cases the largely unconstrained motion of a mecanum drive is fairly foreign. A car or a tractor isn't quite skid-steer, but it is much closer to skid than mecanum. (Though FPS video games probably help somewhat in reversing this trend)

Think of it like all of the conventions in the machinery we operate every day. The gas pedal is always on the right, the clutch is always on the left, and the brake is in the middle/left on an automatic. There was a time when this wasn't the case, and if you ever get a chance to drive very old cars you will frequently find yourself with a very angry gearbox. (And driving a Model T is one heck of an experience if you can convince someone to teach you!)

Up through WWII, the French had backwards throttles on their airplanes to the rest of the Allies. If you import these planes back into the States you are required to flip the throttle the "right" way!

That said, I think they definitely have there place. If 190 had more time to refine their 2005 mecanum drive set-it-and-forget-it robot I think they would've been a top competitor.

Quote:

Originally Posted by BJC

I know that 2337 does extensive driver training which utilizes a very different mindset then driving a standard tank. They practice stuff like using the opponent's inertia to assist them and peeling off of defenders; a lot of things that are nearly impossible for a tank to do because they REQUIRE the ability to move sideways. So I would say that they require a similar amount of practice for the driver to become proficent (you can never have enough practice) but an entirely different mindset. This is what most teams don't do and a part of the reason why mecanum wheels have a bad name.

Huh, that's pretty neat. I'd love to see an informational piece about what top teams do to train their drive teams.

Chris is me

23-10-2011 21:15

Re: Question about wheel preferences

Quote:

Originally Posted by IndySam (Post 1082247)

1. Lots of practice needed to be a good driver. Totally not true. They need no more practice than a tank drive.

About that... I'm a pretty competent tank drive driver, but it took me quite awhile to get the hang of your (awesome, btw) robot at IRI. Which drive system does it have again? :)

IndySam

23-10-2011 21:23

Re: Question about wheel preferences

Quote:

Originally Posted by Chris is me (Post 1082287)

About that... I'm a pretty competent tank drive driver, but it took me quite awhile to get the hang of your (awesome, btw) robot at IRI. Which drive system does it have again? :)

Ah but you were perfect the first time you drove a robot! Remember driving towards yourself, how did that go? :)

akoscielski3

23-10-2011 21:36

Re: Question about wheel preferences

p.s. : Check ur e-mail i can help u a little with them.

but for being a rookie team i don't think you should use them quite yet...

Chris is me

23-10-2011 21:36

Re: Question about wheel preferences

Quote:

Originally Posted by IndySam (Post 1082288)

Ah but you were perfect the first time you drove a robot! Remember driving towards yourself, how did that go? :)

It's gotta be a mental block thing, but I can do that reasonably well with a tank drive, but the second you tell me to strafe facing myself, I lose every bit of intuition I have.

AustinSchuh

23-10-2011 21:39

Re: Question about wheel preferences

Quote:

Originally Posted by BeltSanderRocks (Post 1082253)

Also, a mecanum robot can do VERY well against another mecanum robot in defense. This occured in Finals 1-1 at CalGames, where our driver pushed 1323 quite a large distance. Ill try to find a video and come back with it.

I would be very suspicious of that, and only believe it if 1323 backed you up. The same drivetrain that 1323 used pushed 469 at Worlds with ease, and 469 has an 8wd pneumatic wheel robot...

Andrew Lawrence

23-10-2011 21:48

Re: Question about wheel preferences

Quote:

Originally Posted by akoscielski3 (Post 1082289)

but for being a rookie team i don't think you should use them quite yet...

Agreed. If you want to experiment with mecanum wheels, you should try them in the offseason. Especially if you are a rookie team. I would suggest making a small drivable base with 4 mecanum wheels, and a simple electronics board. From there, you can practice as much as you want throughout the off season. You can also experiment with different types of weights and attachments, and see how you go from there.

One thing on my team: We almost never try something new that could radically change the robot in the build season. ALWAYS in the offseason.

R.C.	23-10-2011 22:10

Re: Question about wheel preferences

Quote:

Originally Posted by BeltSanderRocks (Post 1082253)

Im gonna have to disagree with this, it is very possible for a mecanum robot to play defense. Defense is a broad term and does not always have to include pushing another robot, it could mean simply harrassing the other team by getting in the way, pushing tubes around, distracting a defender, etc.

Also, a mecanum robot can do VERY well against another mecanum robot in defense. This occured in Finals 1-1 at CalGames, where our driver pushed 1323 quite a large distance. Ill try to find a video and come back with it.

I actually have the webcast on my computer and remember the match quite well. We backed up into you guys and then went forward to grab another tube. The other instance was when we were getting pushed against 254. I don't remember/see getting pushed during the comp by mecanums.

During the entire event, we were able to push teams with ease. One of the matches we pushed our alliance partner 10ft or so on accident.

-RC

Cory	23-10-2011 22:42

Re: Question about wheel preferences

Quote:

Originally Posted by Marc S. (Post 1082250)

Yes maybe claiming that someone could push a mecanum with a finger was a exaggerated. Frankly I might just be spoiled by robots that can't be pushed at all.

Everyone knows Truck Town is the only team that can't be pushed ;)

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