Mecanum vs The Barrier

[Unglued]

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.

[Joe Schornak]

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.

Originally Posted by SuperNerd256

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.

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.

[Chickenonastick]

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

[Charmander]

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?

[mesamb1]

Originally Posted by Charmander

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?

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.

[mayde]

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.

[Andrew Schuetze]

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

[Djur]

Originally Posted by Andrew Schuetze

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

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).

[ratdude747]

Originally Posted by mayde

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.

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.

[Ether]

Originally Posted by mayde

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

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.