Your thoughts on Mecanum wheels....

[Maggie27]

What are your thoughts/tips on mecanum wheels?

I believe my team has already decided to use these this year, but if you have any good reasons as to why not, or even as to why we should use them, please post.

I've seen other threads on mecanum wheels, and they've helped a little, but all I really got out of them was that we lose about 45% "push". Is that all?

http://andymark.biz/am-0083.html

http://www.araa.asn.au/acra/acra2002...eter-Tlale.pdf

[JamesBrown]

Mecanum wheels are pretty cool, just a couple of things to keep in mind are some sort of suspension to ensure all wheels are always in contact with the floor. Also I would reccommend using the gyro to make sure the robot tracks straight, otherwise if the mechanical compenents of the robot are not perfect then it will drift.

[Tytus Gerrish]

more moving parts. more things that can break

[BigJ]

also, your programmers will need a lot of time to develop and test (also trig skills)

1675 used mecanum fro the first time last year, and although it was hard, I had fun learning all the vector theory to program it.

[Maggie27]

Originally Posted by Tytus Gerrish

more moving parts. more things that can break

That's what I'm most worried about. My team has a tendency of having things break when we MOST need it!

Originally Posted by BigJ

also, your programmers will need a lot of time to develop and test (also trig skills)

1675 used mecanum fro the first time last year, and although it was hard, I had fun learning all the vector theory to program it.

Also with the programming, we have almost no knowledge on, so I'm definately worried about this as well. We do have some people learning it though as we speak.

[T3_1565]

Originally Posted by JamesBrown

Mecanum wheels are pretty cool, just a couple of things to keep in mind are some sort of suspension to ensure all wheels are always in contact with the floor. Also I would reccommend using the gyro to make sure the robot tracks straight, otherwise if the mechanical compenents of the robot are not perfect then it will drift.

amen to that, thats the biggest flaw in mecanums, they drift... sometimes alot!!

[whytheheckme]

We used the AndyMark mecanum wheels last year.... with some problems.

The first set of wheels that we received, the tabs on each side of all the wheels weren't bent to the proper angle (or even evenly!)

We received new plates from AndyMark, that were bent properly (we still needed to do some minor adjustments, but it was much better.) The biggest problem after that was how freely the rollers spun. Some rollers on the same wheel would spin freely, while others were completely bound up.

This was just our experience though, because I know that The Enforcers (Farmington, CT) used mecanum wheels last year, with very very minimal problems (as I recall, they opened the box and assembled the wheels with no modifications.) They also somehow got away with going through all of their regionals using the original carrier plates in the BaneBots transmissions.... (lucky!)

So all in all, the mecanum can provide some good features that can't be seen in other drive trains, but the assembly is very heavy (4 motors and 4 gear boxes), and can require A LOT of fiddling with.

From the coding aspect (my specialty), it didn't take long to come up with code to drive the system. We actually have the BaneBots encoders installed on all four wheels from last years bot, which we implemented into a PID loop...... but the BaneBots encoders are constructed poorly, and after a few matches, the superglue (Yes, Superglue) thats holding the encoder wheel to the shaft starts to heat, and allows the wheel to move around, and eventually grind up against the encoder, rendering them useless. I would not recommend the BaneBots encoders.

Jacob

[kSniper]

Yea my team is debating between several drive trains as well, but we are stuck on the comparisons between holonomic and mecanum....i have made another thread for this so if anyone could help me out i have a few questions posted on it.....thanks

[Kyle Love]

Mecanum wheels take immense amounts of tweaking of the rollers, just a half turn of the bolt too much can make it not spin freely. There also needs to be some kind of suspension, spring steel makes a really good suspension for mecanums.

From the construction stand point. If you haven't built a mecanum in the fall, it may be a little too labor/software/testing intensive to be successfully done in the build season.

[DB_UPS]

Originally Posted by BigJ

also, your programmers will need a lot of time to develop and test (also trig skills)

1675 used mecanum fro the first time last year, and although it was hard, I had fun learning all the vector theory to program it.

Like josh said, Our progrem team did have fun programing it. Its wasn't really hard to build, we had a rolling chassic by week two last year (it wouldn't been soon by due to the shortage of AM mecanum we get done a little later) it was on the KOP chassic with the wonderful BaneBots transmissions.

The only problem we truely had was it wasn't encoded. It was open loop.

Would i do it again, sure if we make a custom chassic so the wheel are perfectly squared and encoded, i would do it in a heart beat.

[yoshibrock]

Some cons to Mecanum wheels are fragility (they break rather often) and drift (which can also be a pro). With any wheels that are omnidirectional you get pushed around a lot easier (which isn't too much of a problem this year, but still something to consider). Also, if you don't use a suspension, they're very bumpy. Some pros are mobility and a unique experience for your drivers.

[Jared Russell]

One unavoidable problem with both Mecanum and Kiwi-style omni drives are that you are essentially throwing away 30% of your speed. For every rotation of the Mecanum wheel, the robot only translates 1/sqrt(2) = 70.7% of the wheel's circumference when driving straight. Driving diagonally (with two wheels driving and the other two fixed) alleviates this problem.

This is why 341 changed our 2007 kiwi drive from this:

/ \

\ /

to this:

| --

-- |

last year.

[GMKlenklen]

what would be a good encoder choice? banebots is our first choice because we are considering using the banebots 56mm tannie... (worked great last year... already have all the parts). we'll probably be using the kitbot chassis, so as to aliviate as much cost from the drivetrain as possible.

[GUI]

Originally Posted by Abwehr

One unavoidable problem with both Mecanum and Kiwi-style omni drives are that you are essentially throwing away 30% of your speed. For every rotation of the Mecanum wheel, the robot only translates 1/sqrt(2) = 70.7% of the wheel's circumference when driving straight. Driving diagonally (with two wheels driving and the other two fixed) alleviates this problem.

This is why 341 changed our 2007 kiwi drive from this:

/ \

\ /

to this:

| --

-- |

last year.

This is not a- much of a problem with mecanum, because the rollers don't spin when driving forward or backward you only lose speed going sideways/diagonally.

[Zyik]

From what I've seen the benefits of having Mechanum wheels are:

• Allows for good freedom of movement
• Amazingly agile
• They look cool

I don't know how they are for speed or if having them effects that at all. However I have seen my teams robot push mechanum wheeled robots almost anywhere. There doesn't seem to be anything you can do once we come up behind you, if we wanted you to go away from the rack then thats exactly where you were going.