Question about wheel preferences
 

My mentors have no interest in mechanum wheels, and i love them. How efficient are they or arent they. I just want outside information about different preferencs on wheels. :confused:

Re: Question about wheel preferences
 

When you say "efficient" what do you mean by that?

Re: Question about wheel preferences
 

I just mean like what are the good and bad about these wheels. And what wheels could make up for the bad things about the wheels. if that makes sense

Re: Question about wheel preferences
 

Not to discourage you from asking, but you might want to try the forum search feature. There have been many many discussions about this. You might be delighted to discover how much you could learn. It's worth the effort.

Re: Question about wheel preferences
 

alright thanks.

Re: Question about wheel preferences
 

This will get you a lot of hits:

1) Go to the forums advanced search page.

2) Set the options as shown here.

Re: Question about wheel preferences
 

I'll say two things real quick, then you can go search the topic as much as you'd like:

1. If you like Macanum because they allow superior manuverability to get around defence, then do NOT use them. They are not superior in this regard and are actually MORE suceptable to defence because they can be pushed around so easily. There was a thread on CD a while ago asking for proof of a mecanum driving "circles" around a tank drive. Although there were many videos of the tanks driving circles around mecanums there was not a single video of the opposite.

2. If you like mecanums because they allow you to more quickly allign to field elements this is slightly more valid. However, the lack of traction is still probably an overpowering reason not to use them. Building a simple tank and practicing with it will yield much better results then a mecanum. (Another point: you need lots of practice to be a good mecanum driver.)

Happy searching, Bryan

Re: Question about wheel preferences
 

Just a few pros and cons

Pros:
1. Omni-directional movement.
2. Relatively easy to build.

Cons:
1. Usually requires larger heavier wheels(than 6wd's) .
2. Harder to use 2-speed transmission(meaning more load on motors and slower top speeds).
3. Can be easily pushed(with 1 finger).
4. Requires a lot of practice to make effective.
5. Only works for offense.

Re: Question about wheel preferences
 

I'm not a fan of mecanum wheels but I gotta call this one out. Where is your source for this?

Re: Question about wheel preferences
 

I don't think so.

1 finger will not push a 150-lb mecanum drive. Or a 150-lb 4wd. MAYBE a 150-lb omni-drive (with only omni wheels) in the sideways direction can be pushed with one finger.

It's more accurate to say that mecanums have lower pushing resistance and lower pushing power than X drive (where X is some other specific drive type).

Also, I've seen mecanums play effective defense. Effective defense is just as much getting in the way as it is ram and shove someone else around.

Re: Question about wheel preferences
 

It all depends on the game. We used mecanum last year because of the maneuverability and lack of defense in the scoring zone and were quite happy with them. They also aided in easy pick up of tubes. Having said that, the only way we would use them again is if the game had similar rules. The odds are probably 80% we won't use them again.



But common guys lets not over generalize on their faults.

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

2. Heavy - wheels are heavier yes but you only need 4 and no chains or sprockets are required so this is also a straw dog.

3. Push with a finger - now your just making things up.

Re: Question about wheel preferences
 

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.

Re: Question about wheel preferences
 

I'd love to see your mythical perfectly stationary robot...

Re: Question about wheel preferences
 

Mecanums aren't larger in diameter than most wheels. They're larger in the axial direction. (Now, if you use 4" wheels, you might think that mecanums are larger, but most teams use 6-8" wheels.)

Re: Question about wheel preferences
 

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.

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.

Re: Question about wheel preferences
 

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.

Re: Question about wheel preferences
 

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.

Re: Question about wheel preferences
 

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.

Re: Question about wheel preferences
 

Man I hate it when people agree with me :)

Re: Question about wheel preferences
 

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.

Re: Question about wheel preferences
 

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.


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

Re: Question about wheel preferences
 

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? :)

Re: Question about wheel preferences
 

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

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...

Re: Question about wheel preferences
 

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.

Re: Question about wheel preferences
 

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...

Re: Question about wheel preferences
 

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.

Re: Question about wheel preferences
 

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

Re: Question about wheel preferences
 

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

Re: Question about wheel preferences
 

Especially the 2003 one, before the ruling.

Re: Question about wheel preferences
 

Gosh was that a good looking robot. They did so much research on what tread to use. I was going through one of 68's cabinets last year and found about a half dozen tread samples (12+ treads each)...

Re: Question about wheel preferences
 

My bad then, our driver said he was doing the pushing so I believed him

Re: Question about wheel preferences
 

Based on your team number and assumed rookie status as an overall team, I would strongly suggest staying away from mecanums for your first year of competition. There is only ~2 months to kickoff, which I don't believe is enough time to purchase, build, code, and practice with the drivebase.

My suggestion would be to build a 6wd as soon as you get the kit of parts, and start driving it. You should be able to source everything you need directly from the KOP with a few additions. A well built kitbot can out perform ~50%+ of what teams put on the field each year.

Go watch the "Kitbot on Steriods" video that team 1114 was nice enough to film and post for everyones use. If you find you would like to improve upon the KOP chassis setup, review the gearing and consider using treaded wheels, IFI/VexPro and AndyMark have lots of options available.

As a rookie, build a simple robot that you know how to maintain and fix, and really focus on your superstructure/manipulators that interact with the field and game element.

I am personally tired of the mecanum vs. 6wd debate; each have there uses, tradeoff, and advantages. This opinion is not based on my preference of traction drives vs. omni-directional drives. It is based on the resources, cost, and training that I believe are required to produce a solid rookie robot.

Re: Question about wheel preferences
 

Why would being a rookie team prevent them from using mecanum drive? In our experience (2011) we found the mecanum drive to be easier to install, more robust, and with less mechanical problems than a traditional chain-driven 2WD, 4WD, or 6WD*. Plus, canned code for mecanum can easily be found. We simply plugged in some sourced code and went at it.

With an hour or two of practice, our rookie drivers performed admirably at the CAGE Match, comparable to our "professional" regional drive team this past season.

Given, mecanum wheels are not cheap, but if any team has the resources and initiative, I say go for it.

*Of course this comes with the type of implementation. We put the wheels directly on AndyMark nanotubes, and put the kitbot chassis on top of that assembly. Aside from having to keep an eye on the axle bolts that hold the wheels in place+, we had no issues at all, we didn't have to fool with chain runs, and our drive system was in a small, compact, constrained space.

+ checking them every 3-4 matches to make sure they were tight

Re: Question about wheel preferences
 

Didn't Truck have Mecanums this year?

So does this mean the Mecanum are un-moveable in the right situation?

-Clinton-

Re: Question about wheel preferences
 

Only TruckTown

Re: Question about wheel preferences
 

You can make the case for your mecanum drive being more reliable than your previous 2/4/6wd's, but not the general case that mecanums are more reliable than 6wds.

Edit: Fixed, thanks Taylor! Also TIL what FTFY actually means!

Re: Question about wheel preferences
 

FTFY.

And that's exactly what I was doing. In our experience, we found that to be true. I did not intend to make that a global statement. As with everything, your results may vary.

Re: Question about wheel preferences
 

Quoted this for emphasis. Many, many teams would benefit immensely from taking the standard kit bot and tweaking it slightly. You don't even need a 2-Speed if you do it right. Just gear conservatively (~11fps or so) with some traction wheels and odds are that you'll out perform most machines at your event - especially if you always move.

Re: Question about wheel preferences
 

I'd gear a bit lower than 11 FPS for games without open fields. 8-10 FPS is better where control is desired for inexperienced teams and drivers (including my own)

Re: Question about wheel preferences
 

Better to be too fast than too slow and you can always slow it down in code, whereas speeding it up is a bit more of a mechanical affair. (Yes, I know, you're not using the motors in the most efficient manner, this is assuming you're not over gearing and only dialing back your speed 15-20%.)

Also, FWIW, our guys handled our 12-13FPS drive in high gear without many hiccups Chris. Maybe you should work on your driver training skills there bud. :P (We're still BFF's right?)

Re: Question about wheel preferences
 

I'm just reminiscing about the lack of precise control we had when making verrry small adjustments at the rack. You guys had a better robot so you didn't have as many small adjustments to make as we did, but we have a super long arm which makes lining up a bit of a challenge.

For the full field, we love the extra speed, but at the rack we need some work. Maybe we can adjust our controls appropriately.

Re: Question about wheel preferences
 

The point shifts with the amount of friction in the drive, but past 10 fps with 4 CIMs in drive as a single speed is a risky proposition. Many teams have achieved success with it, but it requires more skill to drive. Slowing down in code is a complete nonsolution and provides no more benefit than the driver just deflecting the joystick less. It doesn't add any resolution.

The lack of precision due to the higher speed is one downside, and the ability to push real well without tripping breakers becomes marginal.

In my opinion, the single most beneficial thing a rookie team can to to reach competitive success is to build a 6wd kop frame with supershifters.

Shifting completely eliminates the tradeoff of being able to push hard enough, and drive fast enough.

Re: Question about wheel preferences
 

Any time we've experimented with slowing the drive down in code we've used scaling functions and never had issues, always felt like it drove the same, just slower. Actually helped our drivers utilize mid-range speed much better, for what it's worth.

Re: Question about wheel preferences
 

Team 957 used a modified 2wd kitbot frame. The "center" 2 wheels (standard kitbot wheels, not high-traction wheels) were driven directly, and the 4 corners were low-friction idlers (Lunacy wheels).

We were geared for a ridiculous speed -- I recall it being close to 20 fps theoretical, although I don't know what speed we actually reached. We had 4 CIMs on the drivetrain, using CIMple boxes. We had encoders mounted to the CIMple boxes.

Using feedback from the encoders, we electronically stabilized steering in our "high speed" mode (reducing the tendency to overshoot during corners), without limiting control authority.

We also had a "low speed" mode which directly controlled wheel speed (we used proportional controllers, not caring about steady-state error or derivative control). I believe we ended up scaling the joysticks to +- 2 fps -- this mode was intended to be for hanging the tubes, picking up tubes, and deploying our minibot. In practice, it was extremely precise and accurate (the closed-loop control more than replaced the resolution lost by gearing higher).

It's definitely possible to replace a shifting gearbox with closed-loop electronic control and high gearing in terms of control. However, I suspect that it would not have been traction-limited had we used "grippier" wheels, so this is not a suitable replacement if pushing power is important.

Re: Question about wheel preferences
 

We had a similar problem, but we needed more control at the minibot deployment stage. We implemented a "slow button", which reduced the joystick input by 1/2 before sending it to the motors when the driver clicked the trigger. This gave us full speed in open court and control at the tower. Just an idea, hope it helps!

Also, as far as the OP's question, we had mecanum wheels last season and did not have very much practice time for the drivers due to a variety of obstacles and our drive team did not have two many problems. We ended up using the joysticks, but considered using a ps3 controller. This might be a good idea for teams considering mecanum drive because of mecanum drive's similarity to some fps controls. We did not push other robots in the opposite direction, but we did bring some robots to a full stop when we attempted to. Not as good, but slowed our opposition down in addition to the tube herding that we implemented. Of course, results with any drivetrain vary based off of how the robot is built and the robot's purpose, so drivetrain should be a case-by-case decision.

Re: Question about wheel preferences
 

Our team has used mecanum for the last few years with increasing success. I will say that we got pushed around more than we would have liked when we got involved in a defensive battle with a tank drive bot.

However, we were pleased with our maneuverability and speed (15 fps). The big fix from previous years was avoiding chains and going direct drive to save weight and avoid complications. If it hadn't been such an offensive game in general, we may not have been as pleased though.

Re: Question about wheel preferences
 

HMMM! Situation-ally, No one pushes Truck!

Re: Question about wheel preferences
 

As rookies, Team 3489 used 4WD on nanotubes and 6 inch performance wheels with a custom overmolded urethane tread. The tread had a subtle tread pattern and was crowned to aid in turning. We produced molds on a 3D printer, and molded them with a 50 durometer low-viscosity urethane. The process entails a few secrets to improve adhesion to the wheel, but I'll share if anyone's interested.

As expected, the traction was good, turning fair. The trick to not getting pushed was the implementation of jack stands (think F1/Indy race cars). 4 air cylinders deployed conveyor belt pads to the carpet, lifting the 'bot about 1/8". Testing during build here was positive. Competition was a struggle as we had zero time to practice, and the defensive strategy didn't seem popular this year. For the fall SCRIW scrimmage, we changed out 2 urethane wheels for omnis, figuring that the manueverability would be better (much) and the jack stands would prevent our being pushed. As an [url="http://www.youtube.com/watch?v=Sd7vXl6h2JM"]earlier poster said, sometimes defense is just getting in the way. Video of us defending 1902 "Exploding Bacon" at SCRIW can be found below (hopefully). 1902 uses a 6WD drop center with conveyor tread. You can't see in the vid, but 1902 throws a tread, we have yet to lose one.

http://www.youtube.com/watch?v=Sd7vXl6h2JM