Re: Mecanum on the bridge?!
 

So basically if you practice and engineer them well they work. In my past experience I love these wheels they make chasing balls very easy. But once again you need practice time to make them work. And a quick thinking driver.

Re: Mecanum on the bridge?!
 

I'm not sure what you are trying to say. From what I understand, the polycarb that will be in use on the field is on the bridge as we have in the video. HDPE is what the key is made from and looks to be about 0.25" thick and horizontal. I would expect the key to be less troublesome than the bridge, but I have been wrong before :yikes:

Re: Mecanum on the bridge?!
 

We've also done some testing with a mecanum DRIVE TRAIN (Keep this in mind, there was no extra weight on the robot than the necessary electronics, the frame, and the wheels)

We were able to climb over the bump WITHOUT the assistance of any sort of wedge while using 8" Mecanum wheels. In order to satisfy my curiousity, I also rammed the bump at full speed and was able to climb over with no trouble. The only time that we had a problem was when you WEREN'T quick enough and the robot bottomed out. (Which was rather simple to stop from happening entirely) Wedges were added later and did make it easier to climb over. We used some sort of bent metal bar that our mentor picked up a local hardware store.

We also tested two bridge materials one of which was mildly representative of a legitimate bridge and the other was a plywood mockup. The "mildly representative" bridge was essentially a folding table at a 45 degree angle and we were able to climb it AS LONG AS we had some speed before we attempted to climb. We were able to get to the top of the table in ~3.5 seconds (depending on the driver). On the plywood bridge, we were able to climb in no time at all. We also were able to balance rather easily as we were able to spin on the spot and better focus our mass.

Keep in mind that these tests may not be at all representative of a 120 pound robot.

Re: Mecanum on the bridge?!
 

FIRST Team 1296 used mecanum last year and it worked well. We finished 2nd to 148 (by a single point in one match) during qual rounds in Dallas and did well Saturday afternoon. Our drive train ran perfectly all season - it still is. I think 148 has used something they called octocanum in the past (mecanum plus 4 high traction wheels). All to say that it CAN be done and done very well. It took a very good bot and good drivers to attempt to slow us down last year. We simply slide a little to one side or the other and push by on their corner. A 6-wheel drive bot will push around mecanum if they are pushing parallel to the long axis of the 6-wheel bot but that does not happen very often. Most of the time we had a little fun teasing 6-wheelers, spinning them around and faking them out.

The clues to making mecanum work are precise mechanical alignment and using encoders on all 4 wheels with good software. So its only a good choice for teams that can implement and support these prerequisites.

Winning robots have ultra-reliable drive trains that aid in implementing their game strategy. Given that platform - it is clever, reliable mechanisms on top of the robot that put you in the top 8. For example we had a quick, reliable arm and claw last year on top of a drive train we never touched after week 2 of the build season.

HTH

Re: Mecanum on the bridge?!
 

148 actually uses something called Nonadrive, 4 traction, 4 omni wheels, and one drop down omni for lateral movement. They did not use the drop down omni last year, to my knowledge.

I'm sorry if I sounded like I was saying that there are only a few good mecanum teams. If you look at my post, you'll see that I used the word "Personally", meaning that those are some of the teams I've seen UP CLOSE that use mecanum wheels effectively. I've never seen your team compete, therefore I can't pass judgement.

Re: Mecanum on the bridge?!
 

The "nonadrive" is an evolution and you are correct, they discarded the center wheel in 2011. One of their mentors told me their drivers were rarely using the center wheel so they removed it. Earlier versions (from previous years) used mecanum wheels instead of omni wheels. They didn't see a huge benefit and wanted to reserve more power so they switched away from mecanum.

No need to apologize but mentors should be positive (in my humble opinion) and an engineering judgement in such matters is not particularly relevant ;o). Facts are facts, there are records and plenty of video out there. If a student wants to build a hover-craft for rebound rumble, we tell them it is a crazy idea. If a student wants to build a mecanum drive, we tell them it requires special skill sets - that is all I'm saying. A student, to be taken seriously, should endeavor to offer informed opinions in a public forum.

Good luck this year!!

Re: Mecanum on the bridge?!
 

To my knowledge 148 has never put mecanum wheels on their robot. Unless when they were creating prototypes for their nonadrive they experimented with mecanums before they used omnis.

Re: Mecanum on the bridge?!
 

Pretty sure 148 had them in 2006.

Re: Mecanum on the bridge?!
 

When 488 posted pictures of their octocanum, JVN mentioned that 148 had tried it in the off-season.

See this thread

Re: Mecanum on the bridge?!
 

Probably, the only picture that I could see of 148 in 2006 didn't clearly show the drivetrain.