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View Poll Results: Mecanum or 6WD
Mecanum 90 40.36%
6WD 133 59.64%
Voters: 223. You may not vote on this poll

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Unread 09-01-2011, 20:32
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Re: Mecanum or 6WD

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Originally Posted by ThaineP View Post
How about Mechanum6? It could be like this:

\\\ ||| ///

\\\ ||| ///

So that there are six wheels, where the front and back pairs are Mechanum, and the center pair is straight Omnis. It seems like it could be possible, so it may not work.

Just an idea.


Thaine
like this?

I assume it would allow you enough traction to effectively push other mecanum bots, but thats about it.
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Unread 09-01-2011, 20:35
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Re: Mecanum or 6WD

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Originally Posted by Jeffy View Post
like this?

I assume it would allow you enough traction to effectively push other mecanum bots, but thats about it.
Maybe they needed the omni's to assist rotation since the mecanums are mounted incorrectly.


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Unread 09-01-2011, 20:59
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Re: Mecanum or 6WD

A. Yes, like that.

B. I haven't build a Mechanum drive before, so humor me.

I was thinking you'd get the strafing ability as well as extra power and speed from six wheels.
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Unread 09-01-2011, 21:09
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Re: Mecanum or 6WD

Is there any method way to increase traction of a mecanum drive system?
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Unread 09-01-2011, 21:18
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Re: Mecanum or 6WD

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Originally Posted by Charmander View Post
Is there any method way to increase traction of a mecanum drive system?
Last year i think team 190 had a method in which they locked the rollers of their mecanum wheels effectively turning them into regular wheels. Can anyone from team 190 double check me on this?

I have also seen some examples of rovers which had the ability to switch from mecanum to regular wheels. They looked like an 8 wheeled robot that could lift its outer wheels.

Last edited by Mark Sheridan : 09-01-2011 at 21:19. Reason: clarify
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Unread 09-01-2011, 22:09
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Re: Mecanum or 6WD ...we're leaving something out

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Originally Posted by Charmander View Post
Is there any method way to increase traction of a mecanum drive system?

In the Andy Mark type you can tighten the roller bolts to put friction on the roller so you can have a bit more "traction" but you'll sacrifice ...probably a bit of speed in other directions. I also depends on the co-efficient of friction of the rollers.


OKAY... A PROBLEM WITH THIS DISCUSSION. Mechanum are NOT that easy to push around. If you mean a 6WD trying to push a mechanum bot.... it's a TIE... DEPENDING ON... something people have not mentioned. Do you mean a 2 motor 6WD or a 4 motor 6WD... A European Swallow or an African Swallow?
Mechanums are all about understanding the vectors of the wheels and without needing to put numbers in... in any given direction, mechanums are the equivalent of the torque of TWO motors driving TWO wheels with the rollers locked. (Remember all mechanum drives are 4 motors unless you have a REALLY elaborate nightmarish power distribution system!)
When you push a regular robot sideways, you are trying to overcome the sideways wheel contact with the floor so co-efficient of friction is the major factor. Anytime you contact a mechanum, you are contacting it "head on". The driver can elect to drive into you and push back until the wheels slip... co-efficient of friction again. I think the real issue is the number of motors you have to burn up with mechanums. You need 4 for a mechanum while you can have a nice 6wd for only 2.

In the end, either is a good choice.


Steve
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Unread 10-01-2011, 00:13
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Re: Mecanum or 6WD ...we're leaving something out

Quote:
Originally Posted by Steve_Alaniz View Post
In the Andy Mark type you can tighten the roller bolts to put friction on the roller so you can have a bit more "traction" but you'll sacrifice ...probably a bit of speed in other directions. I also depends on the co-efficient of friction of the rollers.


OKAY... A PROBLEM WITH THIS DISCUSSION. Mechanum are NOT that easy to push around. If you mean a 6WD trying to push a mechanum bot.... it's a TIE... DEPENDING ON... something people have not mentioned. Do you mean a 2 motor 6WD or a 4 motor 6WD... A European Swallow or an African Swallow?
Mechanums are all about understanding the vectors of the wheels and without needing to put numbers in... in any given direction, mechanums are the equivalent of the torque of TWO motors driving TWO wheels with the rollers locked. (Remember all mechanum drives are 4 motors unless you have a REALLY elaborate nightmarish power distribution system!)
When you push a regular robot sideways, you are trying to overcome the sideways wheel contact with the floor so co-efficient of friction is the major factor. Anytime you contact a mechanum, you are contacting it "head on". The driver can elect to drive into you and push back until the wheels slip... co-efficient of friction again. I think the real issue is the number of motors you have to burn up with mechanums. You need 4 for a mechanum while you can have a nice 6wd for only 2.

In the end, either is a good choice.


Steve
I think the argument is a 4 CIM 6WD versus a 4 CIM mecanum drive. The 4 CIM wins every time. I don't think I've ever seen anyone build a 6WD with less than 4 CIMs (on a winning robot and occasionally I see 2 CIMs and 2 FP) last time I saw 2 CIMs on a 6WD was 254 in 2006 but they had shifters.
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Unread 10-01-2011, 00:36
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Re: Mecanum or 6WD ...we're leaving something out

Quote:
Originally Posted by James Tonthat View Post
I think the argument is a 4 CIM 6WD versus a 4 CIM mecanum drive. The 4 CIM wins every time. I don't think I've ever seen anyone build a 6WD with less than 4 CIMs (on a winning robot and occasionally I see 2 CIMs and 2 FP) last time I saw 2 CIMs on a 6WD was 254 in 2006 but they had shifters.
OK I just never saw anyone specify. As with your experience, I have seen two motor 6WD and I think there needs to be clarity on that point.

Steve
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Unread 10-01-2011, 01:06
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Re: Mecanum or 6WD

From what I have seen with the 2007 challenge, 6WD really doesn't suffer from as large of a disadvantage as some people state. As said above you have a large margin of error when placing the tube just because of the width of the rack. Also, most of the maneuverability issues can be minimized with a well designed arm and a proficient driver.
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Unread 10-01-2011, 01:14
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Re: Mecanum or 6WD ...we're leaving something out

my vote is for mecanum. here's why:

the pushing arugement is valid but overplayed. you can push but mecanum can just slide sideways out of the way.

mecanum would make hanging tubes so much better as all you have to do is get to the grid and slide into position.

lining up for minibot release is another spot where mecanum would pwn. getting lined up is critical and mecanum would allow one to back up and slide into position. with 6wd, one would have to either get it right the first time or pull forward and try again.

not to mention the tube loading areas are narrow. once again, being able to slide makes lining up w/o getting stuck a lot easier and quicker.

anybody who has parallel parked will know how being able to slide would be helpful...

i see it as this:

if you want to be a defensive dozer go ahead and use 6wd

if you want to score and do it well, mecanum or crab (if you know what you are doing).

my $0.02
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Unread 10-01-2011, 01:35
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Re: Mecanum or 6WD

our team talked about this for about 2 hours on Saturday. both are great choices for this game. as a former driver, including '07, i preferred meccanums. i like the overall driving capabilities along with the option for precise strafing movements when going to hang a tube. it doesn't fair too well with defensive play but it can hold its own.
6WD is also great with the traction and pushing power it delivers. it does lack the unique abilities for precise movement that meccanums have. but seeing that a huge number of successful teams used 6WD in '07 i'm sure they'll work great as well.
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Unread 10-01-2011, 02:57
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Re: Mecanum or 6WD ...we're leaving something out

Quote:
Originally Posted by ratdude747 View Post
if you want to be a defensive dozer go ahead and use 6wd

if you want to score and do it well, mecanum or crab (if you know what you are doing).

my $0.02
Mecanum has never been vital for FRC. What makes this year different?

Honest question.
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Unread 10-01-2011, 07:52
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Re: Mecanum or 6WD

All,

All of the drive systems mentioned have been successfully implemented by a wide range of FRC teams, but the only thing that matters is what your team can implement given all of your specific team constraints and talents.

We had a pretty decent debate between traditional swerve (think 111 or 71), mecanum, Nonadrive (148 & 217), Octocanum (I know someone will do it this year), and 6WD skid. To understand our final decision, here is some history of team 217:

2000 - 2WD using 2 drill motors no shifting
2001 - Started as 6WD using drill motors ended up 4WD no shifting
2002 - 4WD swerve with a CVT we called the Crazy Chicken Transmission using 2 CIMS, 2 drill motors, and 2 FP motors.
2003 - 4WD Forklift drive (2 rear wheels were swerve) pneumatic shifter with 2 CIMS and 2 drill motors
2004 - 6WD skid steer with shifting using 2 CIMs and 2 Drill motors
2005 - 6WD skid steer no shifting using 4 CIMs* and 2 FP.
*NOTE: 2005 was the first year of the kitbot as we know it and the first year of 4 CIMs in the kit. The drill motors were retired from the kit.
2006 - 6WD skid no shifting using 4 CIM motors
2007 - 6WD skid no shifting using 4 CIM motors
2008 - 6WD skid using 4 CIM motors with shifting
2009 - 6WD skid using 2 CIM motors no shifting
2010 - Nonadrive using 5 CIM motors no shifting

This year we have decided to use 6WD skid once again. Given all of our constraints we want to put our innovation into other parts of the robot(s). I can see arguments for the other drive systems, but for us we are going with 6WD this year.

Paul
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Unread 10-01-2011, 09:15
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Re: Mecanum or 6WD

6WD, mecanum, swerve, and whatever can all be viable winning drives for this game.

The best drive will be the one that your team can build in time to give your programmers time to program and your drivers plenty of time to practice.

You could build the slickest unobtainium drive in the world but if your drivers can't practice with it you won't be a winner.

Like JVN said, "KNOW THYSELF!"
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Unread 10-01-2011, 09:27
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Re: Mecanum or 6WD

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Originally Posted by IndySam View Post
6WD, mecanum, swerve, and whatever can all be viable winning drives for this game.

The best drive will be the one that your team can build in time to give your programmers time to program and your drivers plenty of time to practice.

You could build the slickest unobtainium drive in the world but if your drivers can't practice with it you won't be a winner.

Like JVN said, "KNOW THYSELF!"
That's extremely true, and it's why we're leaning toward 6WD or mecanum.

If our main driver hadn't graduated last year, we'd do mecanum, no contest -- he was an absolute wizard with that thing!

...but now I'm not so sure. This will take some serious team discussions, and as usual the final decision will be up to the team, not the mentors.
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