Mecanum vs The Barrier
 

My team is strongly considering Mecaum this year. However, we are a little concerned about the 4 inch high steel barrier. We did some tests and our 8 inch mecanum bot can go over the barrier without too much problem. However, we are a little concerned about if the mecanum wheels will get worn out over time. The wheels are delicate and ramming into the 4inch high steel barrier can't be the best thing. We might go for 10inch heavy duty mecanum wheels but would either set of wheels get worn out considerably?

Re: Mecanum vs The Barrier
 

To put it delicately: Those wheels are gonna be broken in 2 by match 3.

Mecanums have no traction, and worse, are very fragile. Most teams will be going full speed to get over those ramps, and if you do that with mecanums, then they'll get broken before they become useful. Not to mention, it'll be hard to get any traction on the bridges.

If you do use mecanums, then be careful, use them the grippiest way possible, and double check your choice.

Re: Mecanum vs The Barrier
 

Don't do that if you want the wheels to last..

The barrier can be overcome with enough momentum but your wheels and frame are taking a hit every time.

Re: Mecanum vs The Barrier
 

Keep in mind, the barrier has a 1/4"(1/2"round) fillet on both edges, this will reduce wear.


SuperNerd256, pneumatic wheels will go flat, and the mecanum rollers are replaceable.

Re: Mecanum vs The Barrier
 

Unless you put "skis" about a centimeter off the ground.

Re: Mecanum vs The Barrier
 

We used mechs. in 2010, never again. They were destroyed because of the 2010 bumps, I can't immagine what the barrier will do to them.

Re: Mecanum vs The Barrier
 

Counterpoint: We used mechanums in 2010 and they were not destroyed by the bumps.

Re: Mecanum vs The Barrier
 

Ours actually held up fairly nicely in 2010 through two regionals, and we were back and forth on the bumps a lot.

The center rail this year is a bit more severe, particularly you're trying repeated high-speed traverses. I'd definitely be concerned about bending the roller supports out of shape. Traction could also be a significant concern, particularly on the bridges when they're tipping.

Re: Mecanum vs The Barrier
 

One more thing about Mechanum wheels vs. the field.

The key is not carpet, which is plastic, and will turn your Mechanum wheel robot into a "spin my noisy wheels" robot. In addition, if you do have any intention on balancing, Mechanum wheels may have a problem with that as well.

I suggest that you and your team thinks a little more about it, runs some tests (if possible) about mechanum wheels on the field, and carries spare 8 inch wheels to competition, so if your wheels break/are ineffective, you will be able to switch them out.

Re: Mecanum vs The Barrier
 

Team 1310 used 8" mecanums in 2010, and used them to go over the bump.

I won't claim that the forces are the same as going over this year's barrier but at least I can share some real experiences.

The wheels lasted through 2 regionals. We had to replace 2-3 broken rollers I believe, but broken rollers didn't cost us any matches IMO. You can lose one roller, and it doesn't impact you that much during a match. The bigger problem is that the driveshafts eventually bent a bit. They never failed completely, and in fact we never did replace them, because it was so difficult to get the wheels off the bent shafts.

We had to hit the bump pretty fast in order to carry enough momentum to get over the bump, so they took a pretty good beating.

However, 1310 employed a very very simple suspension that probably save both the wheels and driveshafts from a lot of damage. Some would argue that you should have a suspension when doing mecanum regardless, to ensure all 4 wheels are touching the ground as much as possible.

If I were to consider mecanum for this year with the intention of going over the barrier, I doubt I would do it unless I also put serious resources into a suspension system.

A few practice / build season video from 1310 in 2010:
http://www.youtube.com/watch?v=PneD_...0&feature=plcp

Re: Mecanum vs The Barrier
 

maybe the uber-heavy 10" steel plated mecanums... those would hold up...

http://www.andymark.com/product-p/am-0298.htm

keep in mind they are HEAVY....

Re: Mecanum vs The Barrier
 

Do you have any concrete evidence to support that claim?

Re: Mecanum vs The Barrier
 

My team is prototyping a variation on a mecanum system that should reduce the impact on our wheels. Each mecanum wheel will be paired with a traction wheel positioned ahead of the mecanum and raised so that it doesn't contact the ground while driving normally. When the robot drives over the barrier, the traction wheel will contact the barrier first and lift the front of the robot, putting the mecanum wheels in a more advantageous position to drive over the barrier. I'll probably post a picture or a detailed drawing once our design is more finalized.

We used mecanums last year and in a 2010 summer project, and have never encountered the problems usually associated with them. They have excellent traction on a variety of surfaces, and while a mecanum bot wouldn't win a pushing contest against an 8-wheel roughtop-treaded gear-shifting defensive beast, we have pushed tank drives around with no problems. Our newest set of wheels, from AndyMark's current line of mecanums, have survived use on multiple robots, and they will survive through this year's competition. As long as you design your drive system so that the barrier impact point is not at the very front of the wheel, so more of the force is directed into pushing the bot over the barrier than into deforming the wheel, you should have no problems.

Re: Mecanum vs The Barrier
 

Just imagine what the bump will look like following a regional.

Re: Mecanum vs The Barrier
 

After reading all the posts so far, it seems that more people believe the mecanum wheels will be able to handle it. Would it be wise to put in the money (and weight) to buy the 10 inch heavy duty wheels over the 8 inch wheels?

Re: Mecanum vs The Barrier
 

Depends on the rest of your robot. If you need a low center of gravity, or to be close to the ground to pick up balls I would stick with 8"(My team has the 8" and I am unable convince our students not to use them). but if your have other factors that would need a ten get them.

Re: Mecanum vs The Barrier
 

That's 52 pounds of wheels!!!!!

Re: Mecanum vs The Barrier
 

Any concerns with the Mecanum wheels getting over the bridges? Is there going to be enough traction to climb the bridge enough to get on it and over it so you can cross or balance it?

Re: Mecanum vs The Barrier
 

We have used the same mecanums without replacing any rollers for two years now. They have been over the Breakaway bumps and driven on asphalt during many fairs and celebrations and they are still working as good as ever.

Re: Mecanum vs The Barrier
 

Those go over the $400 individual part price limit.

Re: Mecanum vs The Barrier
 

Interesting how the wheels are mounted in the video.

Re: Mecanum vs The Barrier
 

I'm curious whether [R17] applies to a set of 4 mecanum wheels. They are available for $180 each, which would be legal under [R14]. However, a single mecanum wheel isn't very useful by itself, so [R17] might make them illegal.

Re: Mecanum vs The Barrier
 

buy them individually.

we had no problems with mechanum in 2010, just with everything else falling apart... the bumps were hard on it. depending on your strategy, there may be no need to cross the bump. however, the bridges will be fairly slippery.

i've been toying with the idea of having a pair of powered kop wheels that could be pushed down when needed, and lifted off the ground when not. I figure that they would overcome the mechanum's lack of traction, while still allowing strafing when not in use.

Re: Mecanum vs The Barrier
 

Ha ha! Impressive that you noticed.

Re: Mecanum vs The Barrier
 

Yeah, there should be no problem with buying a set of 4 since they are individual parts. It would be no different than buying something in bulk to save money. Even if you consider two wheels a set (Left and Right), you are still at $360.

I think the real concern is weight. With the SIMs you have invested a huge amount of your weight allowance on your drive train. Still tempting :)

Re: Mecanum vs The Barrier
 

Our robot in 2010 not only could get over the bump at high speeds with rough mecanums, but also seemed to have better traction than the high traction wheels. We were able to win against any other robot in a pushing contest unless they had the same wheels. I also noticed other teams with rough mecanum wheels outpushing most robots. Things can shake loose if you don't use locking nuts and lock-tight, but that was not a problem for us.

Re: Mecanum vs The Barrier
 

no they don't. you are buying 4 wheels.

all AM 4 wheel mecanum sets are over $400... and people have been using the sets legally for years under the same $400 rule...

Re: Mecanum vs The Barrier
 

Not.

Re: Mecanum vs The Barrier
 

oops... memory fails me.

I wonder why I remember them costing more...

Re: Mecanum vs The Barrier
 

barrier for the win :)

Re: Mecanum vs The Barrier
 

If you're absolutely set on using mec wheels, but are worried about the wheels not holding up under the repeated stress of climbing, i definitely recommend making your own. in 2010 we made our own and the process was repetitive and a little bit tedious but fairly simple, and if you do them the same way we made ours, they'll be very sturdy. another bonus is that you can cast the rubber for the rollers in your own team color and have the hubs galvanized to look pretty also. if you want something to reference, you can look at my team's wheels on our website (http://www.roboteknix.com/gallery/?&...71623918928449) or even look further in the past: in 2006, with the game Aim High, team 357 made their own mecanum wheels that they dubbed "Jester Wheels".

Just food for thought if you have a little time and patience on your hands.

Re: Mecanum vs The Barrier
 

video proof of Mecs driving up and balancing on this year's bridge.

Re: Mecanum vs The Barrier
 

Getting off it is a problem with our 2011 bot, though, because it's so top- and front-heavy (it almost tips over each time we drive off).

Re: Mecanum vs The Barrier
 

so you were the ones that made those (saw the pic on wikipedia)... very nice!

if you have CNC access or at least a very skilled machinist, I guess you can make those... not for the faint of heart I'd say.

Re: Mecanum vs The Barrier
 

If you'd like to play around with the numbers, there's a small 16-bit mec roller design app (sorry, won't run on 64-bit Windows) at this page. Click on the "2011-09-30a mecanum roller design calculator " download link.

You enter desired wheel radius, roller center radius, and number of rollers, and you get the information shown in the attached screenshot, plus an XY data file of the required roller profile. It's easy to iterate to try different solutions. The solutions are for a "bumpless" mec: the wheel circumference is circular with no gaps.