Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

This entirely depends on your CG. If your CG is nice and low, the downforce on the front wheels won't change much on an incline so you'll retain manuverability. If your CG is high, the slight incline will shift more of your weight to your back wheels.

Reason number 450,000 to build with a low CG.

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

I think that particular driver would be able to look better regardless of which robot he was driving.

What's the fastest mecanum drive anyone has seen? They all tend to be pretty slow. WPI's 2005 drive seemed faster than anything I see now.

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

I am a bit confused. Chris is me what are you trying to prove? That mecanum is ineffective or not as effective as people think they may be?

I really believe it depends on the team and what they are comfortable with. 25 and 103 have used the same drive system for years 6 and 4 wheels both and every year are a force to be reckoned with. My team 272 has used mecanum now since 2007 minus 09 obviously. We absolutly love them. In reality do we use the crab function that much. No actually almost never but we have that capability and at times it has proven useful....
Our programers love it because in their minds it simplifies their code in autonomous. Whether or not that is even true if in your mind you believe it so isnt it true to you.

As many have pointed out it really comes down to the drivers and the software controlling the commands. If you are fortunate enough to have a combination of both I dont care if its 4 6 8 wheels mecanum or not you can be very dangerous.

I like mecanum well because I do. Others like 6 and 4 wheel tank drive because well they do.

I know pushing power I will give that up any day of the week for a little of the crap. I love seeing that happen. :yikes:

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

I think what he is trying to announce to the public is to back up all statements. He is trying to illustrate that an idea that may seem logical in someone's mind is not always fact. Never make dogmatic statements without solid proof, such as a video.

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

Not sure where you're getting this - Our mecanum drive had no problem last year on either the bumps or the slight rise before the bumps. It drove beautifully.

As for "running circles" around other robots - that's not why we build mecanum drives. We build mecanum drives because they're a fairly large gain in maneuverability (extra axis of motion opens up a lot of extra possiblities when driving, *especially* in anything involving lining up) for a fairly negligible increase in complexity and a small decrease in maximum pushing force. Not every benefit in maneuverability comes directly from robot-on-robot situations, and even in those, while you might not be "running circles" around a 6wd, you certainly will have an advantage if your goal is to get past the other robot rather than push it out of the way (and even with a traction drive, pushing another robot out of the way is far from trivial and often not the best course of action).

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

Until and unless the normal force on any wheel becomes small enough to cause that wheel to slip, the force reduction has no significant effect on the kinematics of the mec drive.

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

Which is unfortunate, because I don't think people were actually paying attention.

http://www.youtube.com/watch?v=7mBxVPvyYwQ

There's the link again, and watch the one robot with mecanum wheels play to its strengths.

Does this one video mean mecanums are definitively better or worse? No, but this mecanum drivetrain did its job in this particular match.

Count the balls scored for the winning alliance - 3 in autonomous, and 3 in teleop. I would challenge a LOT of teams to hold an alliance of 1114 and 2056 to 3 balls scored in teleop, and the little blue mecanum bot was a big reason why that happend.

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

I believe 1305 and 1310 had wonderful robots last year and actually used their mecanum drive to their advantage. Seriously.

However - it doesn't meet the strict definition of this thread - I don't think they proved to be better offensive robots adept at evading defenders with their mecanum drive.

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

I am, by no means, a fan of mecanum. I have, however, subsided with using it once in the 1 year it has been allowed during my tenure as a Team 2337 member ('09 and '10).

That said, maybe 2010 isn't a good year at which to look. Take teams that didn't have steel-solid ball control (let's face it, like 90% of teams). These teams cannot hold a ball going directly backwards (totally us in early (like until mid-April). Because most ball control mechanisms provided totally backwards force, and little side-to-side control besides friction, a strafe would be even harder than backwards movement for ball control.

This means that most teams couldn't strafe while holding a ball. Thus, they probably didn't strafe! This limited them to essentially a 4 omni wheel drive, on offense anyway, and not exactly like omni, and ability to strafe to get balls, just not while possessing, and multiple other exceptions.

I'm not saying every game won't have similar situations. I don't know.
But let the record show that I am not a fan of using mecanums.

In 2337's defense (most members would go the "it's more maneuverable route"), we used our strafing to hang. Strafe into tower, line up with forwards/backwards motion. We also used it while getting shoved backwards, to turn and strafe, at the same time, getting out of the essential pin. We were pushed both because we were geared for speed, not only due to the mecanums.

As has been mentioned, in 2007 getting pushed at all (especially from the side) was a huge deal, and in 2008 there wasn't a large advantage except not having to turn if you're just doing laps. We did mecanums in 2008. I don't know the reason, but we did okay I guess. Second divisional seed at the CMP...

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

Last year we wanted the pushing power of 6WD but the maneuverability of mecannum so we came up with this.

The middle wheels in the video are white wheels that can slide. This was before we had out middle wheel s manufactured.
The actual wheel were 8inch diameter by 2 inch wide CNCed aluminum wheels with roughtop threads.
To be able to travel sideways the middle wheels were lifted off the ground 1/4 of an inch.

http://www.youtube.com/watch?v=s5vBpImX8Ds

and also this:

http://www.youtube.com/watch?v=LVtHI...eature=related

Meccanum is great in my opinion but it needs some semi-intelligent programming.
in 2010 we had a gyro on the robot that did 2 things:
1, to stop the robot from spinning when it was not desired. (robot kept its direction even if pushed by other robots)
2, pushing the joystick forward in mecannum mode always meant the robot travels away from the driver no matter what orientation it was in.

We also had the vision system that on demand, kept the robot pointed at the target and the driver could translate freely.

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

Here is video of us from the final match of the Boilermaker regional.
We used a gyro for field centric mecanum drive, watch how the robot looks like its moving with purpose, effortlessly doing what the drivers want it to do.
You can't get that kind of motion with a 6 wheel drive.

http://www.youtube.com/watch?v=v2jZz0r0wbk

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

The robot in the video is completely undefended...

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

When one of four wheels is lifted a half inch, one of the other three wheels is extremely likely to have its normal force reduced by a significant amount.

Re: Video of Mecanum Drive Running Circles Around 6 Wheel Drives
 

16 FPS? That's a bit quick for an FRC field don't you think?