Video of Mecanum Drive Running Circles Around 6 Wheel Drives

[Chris is me]

Originally Posted by PayneTrain

Our build lead and I ran some simple vector addition, and realized that any mecanum wheel on a slight incline like the steel plates under the towers can and likely will cause 20% of the force lost on one wheel diagonally opposite to one on the incline, and transferred to the wheel on the incline. This will cause you to lose significant control of the robot, and in this case, a trip to your scoring lane can likely end up as a trip to the opponent's zone. It is very hard to right the bot after that, and can cause the rollers on the mecanum wheel to lock up.

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.

[Tom Bottiglieri]

Originally Posted by EugeneF

Hmmm. Not exactly what you wanted, but to show the other side, here's a video of an 8wd running circles around mecanum drive.

2010 SVR, 971 vs 675:
http://www.youtube.com/watch?v=0X27bojZ26k

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.

[liam.larkin]

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.

[davidthefat]

Originally Posted by liam.larkin

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 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.

[Oblarg]

Originally Posted by PayneTrain

A MASSIVE problem with mecanum drive this year, just as you could have had the issue in Breakaway last year with our mecanum bot, is the steel plates under the carpet.

Our build lead and I ran some simple vector addition, and realized that any mecanum wheel on a slight incline like the steel plates under the towers can and likely will cause 20% of the force lost on one wheel diagonally opposite to one on the incline, and transferred to the wheel on the incline. This will cause you to lose significant control of the robot, and in this case, a trip to your scoring lane can likely end up as a trip to the opponent's zone. It is very hard to right the bot after that, and can cause the rollers on the mecanum wheel to lock up.

Be wary of this.

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).

[Ether]

Originally Posted by PayneTrain

A MASSIVE problem with mecanum drive this year, just as you could have had the issue in Breakaway last year with our mecanum bot, is the steel plates under the carpet.

Our build lead and I ran some simple vector addition, and realized that any mecanum wheel on a slight incline like the steel plates under the towers can and likely will cause 20% of the force lost on one wheel diagonally opposite to one on the incline, and transferred to the wheel on the incline. This will cause you to lose significant control of the robot

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.

[Mr. Lim]

Originally Posted by Kevin Sevcik

*polite cough* I think he was pointing our the quick maneuvering of the blue robot with the mecanum wheels. Not 1114 with their 8-wheel drive.

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.

[Chris is me]

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.

[Basel A]

Originally Posted by Chris is me

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.

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...

[BornaE]

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.

[FlyingHedgeHog]

Originally Posted by maverickfan138

This isn't 100% what you want, Chris, but I think it's pretty close:

http://www.youtube.com/watch?v=QwlHlx-QAIQ

Watch 2337 and 2619 duke it out. 2337 had 8" mecanums and custom gear boxes. 2619 had 4 wheel tank drive with a wide bot. 2619 was the red alliance's main scoring robot and 2337 shut them down until the end game.

The thing I would say about that video is that if you notice, the mecanum bot really didn't use it's crab capabilities. It more game down to the the sheer pushing power and speed it had over the other robot as oppose to sheer out maneuvering. It didn't exactly "run circles" around the other bot; it slammed into it.

[efoote868]

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

[Chris is me]

The robot in the video is completely undefended...

[Alan Anderson]

Originally Posted by Ether

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...

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.

[wilsonmw04]

Originally Posted by Cory

The 4WD bot they're defending is way too slow. Like 8 FPS max. If you can find a mechanum driving circles around a 16 FPS 6WD with competent drivers I'd be impressed.

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